MECHANICAL PROPERTIES:

The mechanical properties of a material describe how it will react to physical forces.

Mechanical properties occur as a result of the physical properties inherent to each material,

and are determined through a series of standardized mechanical tests.

Strength :

Strength has several definitions depending on the material type and application. Before

choosing a material based on its published or measured strength it is important to understand

the manner in which strength is defined and how it is measured. When designing for strength,

material class and mode of loading are important considerations.

For metals the most common measure of strength is the yield strength. For most polymers it is

more convenient to measure the failure strength, the stress at the point where the stress strain

curve becomes obviously non-linear. Strength, for ceramics however, is more difficult to define.

Failure in ceramics is highly dependent on the mode of loading. The typical failure strength in

compression is fifteen times the failure strength in tension. The more common reported value

is the compressive failure strength.

Elastic limit :

The elastic limit is the highest stress at which all deformation strains are fully recoverable. For

most materials and applications this can be considered the practical limit to the maximum

stress a component can withstand and still function as designed. Beyond the elastic limit

permanent strains are likely to deform the material to the point where its function is impaired.

Proportional limit :

The proportional limit is the highest stress at which stress is linearly proportional to strain. This

is the same as the elastic limit for most materials. Some materials may show a slight deviation

from proportionality while still under recoverable strain. In these cases the proportional limit is

preferred as a maximum stress level because deformation becomes less predictable above it.

 

1

Yield Strength :

The yield strength is the minimum stress which produces permanent plastic deformation. This

is perhaps the most common material property reported for structural materials because of the

ease and relative accuracy of its measurement. The yield strength is usually defined at a

specific amount of plastic strain, or offset, which may vary by material and or specification. The

offset is the amount that the stress-strain curve deviates from the linear elastic line. The most

common offset for structural metals is 0.2%.

Ultimate Tensile Strength :

The ultimate tensile strength is an engineering value calculated by dividing the maximum load

on a material experienced during a tensile test by the initial cross section of the test sample.

When viewed in light of the other tensile test data the ultimate tensile strength helps to provide

a good indication of a material's toughness but is not by itself a useful design limit. Conversely

this can be construed as the minimum stress that is necessary to ensure the failure of a

material.

True Fracture Strength :

The true fracture strength is the load at fracture divided by the cross sectional area of the

sample. Like the ultimate tensile strength the true fracture strength can help an engineer to

predict the behavior of the material but is not itself a practical strength limit. Because the

tensile test seeks to standardize variables such as specimen geometry, strain rate and

uniformity of stress it can be considered a kind of best case scenario of failure.

Ductility :

Ductility is a measure of how much deformation or strain a material can withstand before

breaking. The most common measure of ductility is the percentage of change in length of a

tensile sample after breaking. This is generally reported as % El or percent elongation. The

R.A. or reduction of area of the sample also gives some indication of ductility.

 

2

Toughness :

Toughness describes a material's resistance to fracture. It is often expressed in terms of the

amount of energy a material can absorb before fracture. Tough materials can absorb a

considerable amount of energy before fracture while brittle materials absorb very little. Neither

strong materials such as glass or very ductile materials such as taffy can absorb large

amounts of energy before failure. Toughness is not a single property but rather a combination

of strength and ductility.

The toughness of a material can be related to the total area under its stress-strain curve. A

comparison of the relative magnitudes of the yield strength, ultimate tensile strength and

percent elongation of different material will give a good indication of their relative toughness.

Materials with high yield strength and high ductility have high toughness. Integrated stress-

strain data is not readily available for most materials so other test methods have been devised

to help quantify toughness. The most common test for toughness is the Charpy impact test.

In crystalline materials the toughness is strongly dependent on crystal structure. Face centered

cubic materials are typically ductile while hexagonal close packed materials tend to be brittle.

Body centered cubic materials often display dramatic variation in the mode of failure with

temperature. In many materials the toughness is temperature dependent. Generally materials

are more brittle at lower temperatures and more ductile at higher temperatures. The

temperature at which the transition takes place is known as the DBTT, or ductile to brittle

transition temperature. The DBTT is measured by performing a series of Charpy impact tests

at various temperatures to determine the ranges of brittle and ductile behavior. Use of alloys

below their transition temperature is avoided due to the risk of catastrophic failure.

Fatigue ratio :

The dimensionless fatigue ratio f is the ratio of the stress required to cause failure after a

specific number of cycles to the yield stress of a material. Fatigue tests are generally run

through 107 or 108 cycles. A high fatigue ratio indicates materials which are more susceptible to

crack growth during cyclic loading.

3

Loss coefficient :

The loss coefficient is an other important material parameter in cyclic loading. It is the fraction

of mechanical energy lost in a stress strain cycle. The loss coefficient for each material is a

function of the frequency of the cycle. A high loss coefficient can be desirable for damping

vibrations while a low loss coefficient transmits energy more efficiently. The loss coefficient is

also an important factor in resisting fatigue failure. If the loss coefficient is too high, cyclic

loading will dissipate energy into the material leading to fatigue failure.

GENERAL PHYSICAL PROPERTIES :

Density :

Density is one of the most fundamental physical properties of any material. It is defined as the

ratio of an objects mass to its volume. Because most designs are limited by either size and or

weight density is an important consideration in many calculations.

Density is a function of the mass of the atoms making up the materials and the distance

between them. Massive, closely packed atoms characterize high density materials such as

Tungsten or Neptunium. In contrast light, relatively distant atoms compose low density

materials such as Beryllium or Aluminum. Density on a macroscopic level is also a function of

the microscopic structure of a material. A relatively dense material may be capable of forming

a cellular structure such as a foam which can be nearly as strong and much less dense than

the bulk material. Composites including natural constituents such as wood and bone, for

example, generally rely on microscopic structure to achieve densities far lower than common

monolithic materials.

Availability/Manufacturability :

Availability and manufacturability requirements are often unseen limiting factors in materials

selection. The importance of a material being available is obvious. Materials which are not

available cannot be used. The importance of processibility is not always so obvious.

Any other desirable qualities are useless if a material cannot be processed into the shape

required to perform its function. Most engineering materials in use today have well known

4

substitutes which would perform better and often at lower cost but processes for forming,

cutting, machining, joining, etc. are not available or commercially viable. There is often a

period of time after a new material is introduced during which its application is severely limited

while processing techniques are developed which facilitate its use.

Cost :

A materials cost is also generally a limiting factor. While cost is universally recognized and

perhaps the easiest of all properties to understand there are specific cost considerations for

materials selection. Just as materials and their processing go hand in hand so do material

costs and processing costs. Understanding the entire processing sequence is critical to

accurately evaluating the true cost of a material.

Appearance :

Because the appearance of many mechanical components seems fairly trivial it is also easy to

overlook its importance in the marketing and commercial success of a product.

THERMAL PROPERTIES :

Thermal conductivity :

The thermal conductivity is the rate of heat transfer through a material in steady state. It is not

easily measured, especially for materials with low conductivity but reliable data is readily

available for most common materials.

Thermal diffusivity :

The thermal diffusivity is a measure of the transient heat flow through a material.

Specific heat :

The specific heat is a measure of the amount of energy required to change the temperature of

a given mass of material. Specific heat is measured by calorimetry techniques and is usually

reported both as CV, the specific heat measured at constant pressure, or CP, the specific heat

measured at constant pressure.

5

Melting point :

The melting point is the temperature at which a material goes from the solid to the liquid state

at one atmosphere. The melting temperature is not usually a design criteria but it offers

important clues to other material properties.

Glass transition temp :

The glass transition temperature, or Tg is an important property of polymers. The glass

transition temperature is a temperature range which marks a change in mechanical behavior.

Above the glass transition temperature a polymer will behave like a ductile solid or highly

viscous liquid. Below Tg the material will behave as a brittle solid. Depending on the desired

properties materials may be used both above and below their glass transition temperature.

Thermal expansion coefficient :

The thermal expansion coefficient is the amount a material will change in dimension with a

change in temperature. It is the amount of strain due to thermal expansion per degree Kelvin

expressed in units of K-1. For isotropic materials " is the same in all directions, anisotropic

materials have separate "s reported for each direction which is different.

Thermal shock resistance :

Thermal shock resistance is a measure of how large a change in temperature a material can

withstand without damage. Thermal shock resistance is very important to most high

temperature designs. Measurements of thermal shock resistance are highly subjective

because if is extremely process dependent. Thermal shock resistance is a complicated

function of heat transfer, geometry and material properties. The temperature range and the

shape of the part play a key role in the material's ability to withstand thermal shock. Tests must

be carefully designed to mimic anticipated service conditions to accurately asses the thermal

shock resistance of a material.

Creep resistance :

Creep is slow, temperature aided, time dependent deformation. Creep is typically a factor in

materials above one third of their absolute melting temperature or two thirds of their glass

transition temperature. Creep resistance is an important material property in high temperature

6

design, but it is difficult to quantify with a single value. Creep response is a function of many

material and external variables, including stress and temperature. Often other environmental

factors such as oxidation or corrosion play a role in the fracture process.

Creep is plotted as strain vs. time. A typical creep curve shows three basic regimes. During

stage I, the primary or transient stage, the curve begins at the initial strain, with a relatively

high slope or strain rate which decreased throughout stage I until a steady state is reached.

Stage II, the steady state stage, is generally the longest stage and represents most of the

response. The strain rate again begins to increase in stage III and rupture at tR generally

follows quickly.

Different applications call for different creep responses. In situations where long life is desired

minimum creep rate is the most important material consideration. Testing through stage II

should be sufficient for determining minimum creep rate. Is not necessary to proceed all the

way to rupture. For this type of test the longer the test the more accurate the creep rate will be.

Unfortunately practicality limits most creep tests to times shorter than would be desirable for

high accuracy.

For short lived applications such as rocket nozzles the time to failure may be the only

consideration. The main issue is whether or not the component fails, not the amount of

deformation it may undergo. For this application creep tests may be run to completion but

without recording any data but the time to rupture. In this case temperatures may be elevated

above expected conditions to provide a margin of safety.

The main objective of a creep test is to study the effects of temperature and stress on the

minimum creep rate and the time to rupture. Creep testing is usually run by placing a sample

under a constant load at a fixed temperature. The data provided from a complete creep test at

a specific temperature, T, and stress includes three creep constants: the dimensionless creep

exponent, n, the activation energy Q, and A, a kinetic factor.

7

FERROUS METALS :

As the most abundant of all commercial metals, alloys of iron and steel continue to cover a

broad range of structural applications. Iron ore is readily available, constituting about 5% of the

earth's crust, and is easy to convert to a useful form. Iron is obtained by fusing the ore to drive

off oxygen, sulfur, and other impurities. The ore is melted in a furnace in direct contact with the

fuel using limestone as a flux. The limestone combines with impurities and forms a slag, which

is easily removed.

Cast Iron :

Cast iron is defined as an iron alloy with more than 2% carbon as the main alloying element. In

addition to carbon, cast irons must also contain from 1 to 3% silicon which combined with the

carbon give them excellent castability. Cast iron has a much lower melting temperature than

steel and is more fluid and less reactive with molding materials. However, they do not have

enough ductility to be rolled or forged.

The precipitation of carbon (as graphite) during solidification is the key to cast iron's distinctive

properties. The graphite provides excellent machinability (even at wear-resisting hardness

levels), damps vibration, and aids lubrication on wearing surfaces (even under borderline

lubrication conditions).

Steels and cast irons are both primarily iron with carbon (C) as the main alloying element.

Steels contain less than 2% and usually less than 1% C, while all cast irons contain more than

2% C. About 2% is the maximum C content at which iron can solidify as a single phase alloy

with all of the C in solution in austenite. Thus, the cast irons by definition solidify as

heterogeneous alloys and always have more than one constituent in their microstructure.

In addition to C, cast irons also must contain appreciable silicon (Si), usually from 1–3%, and

thus they are actually iron-carbon-silicon alloys. The high C content and the Si in cast irons

make them excellent casting alloys.

Carbon Steel :

Carbon steel is a malleable, iron-based metal containing less than 2% carbon (usually less

than 1%), small amounts of manganese, and other trace elements. Steels can either be cast to

shape or wrought into various mill forms from which finished parts are formed, machined, 8

forged, stamped, or otherwise shaped. Carbon steels are specified by chemical composition,

mechanical properties, method of deoxidation, or thermal treatment.

Alloy Steel :

Steels that contain specified amounts of alloying elements -- other than carbon and the

commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus -- are

known as alloy steels. Alloying elements are added to change mechanical or physical

properties. A steel is considered to be an alloy when the maximum of the range given for the

content of alloying elements exceeds one or more of these limits: 1.65% Mn, 0.60% Si, or

0.60% Cu; or when a definite range or minimum amount of any of the following elements is

specified or required within the limits recognized for constructional alloy steels: aluminum,

chromium (to 3.99%), cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium,

zirconium or other element added to obtain an alloying effect. Technically, then, tool and

stainless steels are alloy steels.

Tool Steels :

Tool Steels' defining properties include resistance to wear, stability during heat treatment,

strength at high temperatures, and toughness. To develop these properties, tool steels are

always heat treated. Because the parts may distort during heat treatment, precision parts

should be semifinished, heat treated, then finished. Tool steels are classified into several

broad groups, some of which are further divided into subgroups according to alloy composition,

hardenability, or mechanical similarities.

Type W - Water-hardening, or carbon, tool steels rely on carbon content for their useful

properties.

Type S - Shock-resisting tool steels are strong and tough, but not as wear resistant as

many other tool steels.

Types O, A, and D Cold-work tool steels include oil and air-hardened types are often

more costly but can be quenched less drastically than water-hardening types. Type O

steels are oil hardening; Type A and D steels are air hardening (the least severe

quench), and are best suited for applications such as machine ways, brick mold liners,

and fuel-injector nozzles. The air-hardening types are specified for thin parts or parts

with severe changes in cross section -- parts that are prone to crack or distort during

9

hardening. Hardened parts from these steels have a high surface hardness; however,

these steels should not be specified for service at elevated temperatures.

Type H - Hot-work steels serve well at elevated temperatures.

Types T (tungsten alloy) and M (molybdenum alloy) - High-speed tool steels make

good cutting tools because they resist softening and maintain a sharp cutting edge at

high service temperatures.

Type L - A special-purpose, low-cost, low-alloy, tool steel often specified for machine

parts when wear resistance combined with toughness is important.

Type F - Carbon-tungsten alloys (Type F) are shallow hardening and wear resistant, but

are not suited for high temperatures or for shock service.

Type P - A mold steel are designed specifically for plastic-molding and zinc die-casting

dies.

HSLA Steel :

High-Strength Low-Alloy (HSLA) steels have a higher strength-to-weight ratio than

conventional low-carbon steels for only a modest price premium. Because HSLA alloys are

stronger, they can be used in thinner sections, making them particularly attractive for

transportation-equipment components where weight reduction is important. HSLA steels are

usually low-carbon steels with up to 1.5% manganese, strengthened by small additions of

elements, such as columbium, copper, vanadium or titanium and sometimes by special rolling

and cooling techniques.

NON-FERROUS METALS :

Non-ferrous metals are metals that do not contain iron. There are two groups of metals; ferrous

and non-ferrous. Ferrous metals contain iron, for example carbon steel, stainless steel (both

alloys; mixtures of metals) and wrought iron. Non-ferrous metals don't contain iron, for example

aluminium, brass, copper (which can be remembered as ABC) and titanium. You can also get

non-ferrous metals as alloys eg, brass is an alloy of copper and zinc.

Nonferrous metals are specified for structural applications requiring reduced weight, higher

strength, nonmagnetic properties, higher melting points, or resistance to chemical and

atmospheric corrosion. They are also specified for electrical and electronic applications.

10

Aluminum :

Pure aluminum is a silvery-white metal with many desirable characteristics. It is light, nontoxic

(as the metal), nonmagnetic and nonsparking. It is easily formed, machined, and cast. Pure

aluminum is soft and lacks strength, but alloys with small amounts of copper, magnesium,

silicon, manganese, and other elements have very useful properties. Aluminum is an abundant

element in the earth's crust, but it is not found free in nature. The Bayer process is used to

refine aluminum from bauxite, an aluminum ore. Because of aluminum's mechanical and

physical properties, it is an extremely convenient and widely used metal.

Some Common Uses :

Building & Construction Industry:

door and window frames

wall cladding, roofing, awnings

Manufacture of Electrical Products:

high tension power lines, wires, cables, busbars

components for television, radios, refrigerators and air-conditioners

Packaging & Containers:

beverage cans, bottle tops

foil wrap, foil semi-rigid containers

Cooking Utensils:

kettles and saucepans

Aeronautical, Aviation & Automotive Industries:

propellers

airplane and vehicle body sheet

gearboxes, motor parts

11

Leisure Goods:

tennis racquets, softball bats

indoor and outdoor furniture

Properties :

very lightweight (about 1/3 the mass of an equivalent volume of steel or copper) but with

alloying can become very strong.

excellent thermal conductor

excellent electrical conductor (on a weight-for-mass basis, aluminium will conduct more

than twice as much electricity as copper)

highly reflective to radiant energy in the electromagnetic spectrum

highly corrosion resistant in air and water (including sea water)

highly workable and can be formed into almost any structural shape

non-magnetic

non-toxic

Beryllium :

Beryllium has one of the highest melting points of the light metals. The modulus of elasticity of

beryllium is approximately 1/3 greater than that of steel. It has excellent thermal conductivity, is

nonmagnetic and resists attack by concentrated nitric acid. It is highly permeable to X-rays,

and neutrons are liberated when it is hit by alpha particles, as from radium or polonium (about

30 neutrons/million alpha particles). At standard temperature and pressures beryllium resists

oxidation when exposed to air (although its ability to scratch glass is probably due to the

formation of a thin layer of the oxide). Beryllium is a very light weight metal with a high

modulus of elasticity (five times that of ultrahigh-strength steels), high specific heat, and high

specific strength (strength to weight ratio).

Uses :

Beryllium is used as an alloying agent in the production of beryllium-copper because of its

ability to absorb large amounts of heat. Beryllium-copper alloys are used in a wide variety of

applications because of their electrical and thermal conductivity, high strength and hardness,

nonmagnetic properties, along with good corrosion and fatigue resistance. These applications

12

include the making of spot-welding electrodes, springs, non-sparking tools and electrical

contacts.

Due to their stiffness, light weight, and dimensional stability over a wide temperature range,

beryllium-copper alloys are also used in the defense and aerospace industries as light-weight

structural materials in high-speed aircraft, missiles, space vehicles and communication

satellites.

Thin sheets of beryllium foil are used with X-ray detection diagnostics to filter out visible light

and allow only X-rays to be detected.

In the field of X-ray lithography beryllium is used for the reproduction of microscopic integrated

circuits.

Because it has a low thermal neutron absorption cross section, the nuclear power industry

uses this metal in nuclear reactors as a neutron reflector and moderator.

Beryllium is used in nuclear weapons for similar reasons. For example, the critical mass of a

plutonium sphere is significantly reduced if the plutonium is surrounded by a beryllium shell.

It is, however, brittle, chemically reactive, expensive to refine and form, and its impact strength

is low compared to values for most other metals.

Copper :

Copper provides a diverse range of properties: good thermal and electrical conductivity,

corrosion resistance, ease of forming, ease of joining, and color. However, copper and its

alloys have relatively low strength-to-weight ratios and low strengths at elevated temperatures.

Some copper alloys are also susceptible to stress-corrosion cracking unless they are stress

relieved. Next to silver, copper is the next best electrical conductor. It is a yellowish red metal

that polishes to a bright metallic luster. It is tough, ductile and malleable. Copper has a

disagreeable taste and a peculiar smell. Copper is resistant to corrosion in most atmospheres

including marine and industrial environments. It is corroded by oxidizing acids, halogens,

sulphides and ammonia based solutions.

13

Copper and its alloys -- the brasses and bronzes -- are available in rod, plate, strip, sheet, tube

shapes, forgings, wire, and castings.

Lead :

Lead is the most impervious of all common metals to X-rays and gamma radiation and it

resists attack by many corrosive chemicals, most types of soil, and marine and industrial

environments. Main reasons for using lead often include low melting temperature, ease of

casting and forming, high density, good sound and vibration absorption, and ease of salvaging

from scrap. Sheet lead, lead-loaded vinyls, lead composites, and lead-containing laminates are

used to reduce machinery noise. The natural lubricity and wear resistance of lead make the

metal suitable, in alloys, for heavy-duty bearing applications such as railroad-car journal

bearings and piston-engine crank bearings.

Magnesium :

As the lightest structural metal available, magnesium has a high strength-to-weight ratio. With

its low modulus of elasticity combined with moderate strength, magnesium alloys can absorb

energy elastically, providing excellent dent resistance and high damping capacity. Magnesium

has good fatigue resistance and performs particularly well in applications involving a large

number of cycles at relatively low stress. The metal is sensitive to stress concentration,

however, so notches, sharp corners, and abrupt section changes should be avoided.

Magnesium alloys are the easiest of the structural metals to machine and they can be shaped

and fabricated by most metalworking processes, including welding.

Nickel :

Nickel fits many applications that require specific corrosion resistance or elevated temperature

strength. Some nickel alloys are among the toughest structural materials known. When

compared to steel, other nickel alloys have ultrahigh strength, high proportional limits, and high

moduli of elasticity. Commercially pure nickel has good electrical, magnetic, and

magnetostrictive properties.

14

PRECIOUS METALS :

Gold is an extremely inert, soft, ductile metal, that undergoes very little work hardening.

A gram of pure gold can be worked into leaf covering 6 ft^2 and only 0.0000033 in.

thick. It is used chiefly for linings or electrodeposits and is often alloyed with other

metals such as copper or nickel to increase strength or hardness.

Silver is a very malleable, ductile, and corrosion resistant metal that has the highest

thermal and electrical conductivity of all metals and is the least costly of all the precious

metals. Alloyed with copper, and sometimes with zinc, silver is also used in high-melting

temperature solders.

Platinum is an extremely malleable, ductile, and corrosion resistant silver-white metal.

When heated to redness, it softens and is easily worked. It is nearly nonoxidizable and

is soluble only in liquids that generate free chlorine such as aqua regia. Because

platinum is inert and stable, even at high temperatures, the metal is used for high-

temperature handling of high-purity chemicals and laboratory materials. Other

applications include electrical contacts, resistance wire, thermocouples, and standard

weights.

REFRACTORY METALS :

Refractory metals are characterized by their extremely high melting points, which range well

above those of iron, cobalt, and nickel. They are used in demanding applications requiring

high-temperature strength and corrosion resistance. The most extensively used of these

metals are tungsten, tantalum, molybdenum, and columbium (niobium).

Tin :

Tin is characterized by a low-melting point (450°F), fluidity when molten, readiness to form

alloys with other metals, relative softness, and good formability. The metal is nontoxic,

solderable, and has a high boiling point. The temperature range between melting and boiling

points exceeds that for nearly all other metals (which facilitates casting). Upon severe

deformation, tin and tin-rich alloys work soften. Principal uses for tin are as a constituent of

solder and as a coating for steel (tinplate, or terneplate). Tin is also used in bronze, pewter,

and bearing alloys.

15

Titanium :

There are three structural types of titanium alloys:

Alpha Alloys are non-heat treatable and are generally very weld- able. They have low to

medium strength, good notch toughness, reasonably good ductility and possess

excellent mechanical properties at cryogenic temperatures. The more highly alloyed

alpha and near-alpha alloys offer optimum high temperature creep strength and

oxidation resistance as well.

Alpha-Beta Alloys are heat treatable and most are weldable. Their strength levels are

medium to high. Their hot-forming qualities are good, but the high temperature creep

strength is not as good as in most alpha alloys.

Beta or near-beta alloys are readily heat treatable, generally weldable, capable of high

strengths and good creep resistance to intermediate temperatures. Excellent formability

can be expected of the beta alloys in the solution treated condition. Beta-type alloys

have good combinations of properties in sheet, heavy sections, fasteners and spring

applications.

Zinc :

Zinc, a crystalline metal with moderate strength and ductility, is seldom used alone except as a

coating. In addition to its metal and alloy forms, zinc also extends the life of other materials

such as steel (by hot dipping or electrogalvanizing), rubber and plastics (as an aging inhibitor),

and wood (in paints). Zinc is also used to make brass, bronze, and die-casting alloys in plate,

strip, and coil; foundry alloys; superplastic zinc; and activators and stabilizers for plastics.

Zirconium :

Relatively few metals besides zirconium can be used in chemical processes requiring alternate

contact with strong acids and alkalis. Major uses for zirconium and its alloys are as a

construction material in the chemical-processing industry.

Zinc :

16

Zinc is a silvery blue-grey metal with a relatively low melting point (419.5°C) and boiling point

(907°C). When unalloyed, its strength and hardness is greater than that of tin or lead, but

appreciably less than that of aluminium or copper. The pure metal cannot be used in stressed

applications due to low creep-resistance. For these reasons most uses of zinc are after

alloying with small amounts of other metals or as a protective coating for steel.

Uses :

One of the most useful characteristics of zinc is its resistance to atmospheric corrosion, and

just over half of its use is for the protection of steelwork. In addition to its metal and alloy forms,

zinc also extends the life of other materials such as steel (by hot dipping or electrogalvanizing),

rubber and plastics (as an aging inhibitor), and wood (in paints). Zinc is also used to make

brass, bronze, and die-casting alloys in plate, strip, and coil; foundry alloys; superplastic zinc;

and activators and stabilizers for plastics.

Zirconium :

Relatively few metals besides zirconium can be used in chemical processes requiring alternate

contact with strong acids and alkalis. Major uses for zirconium and its alloys are as a

construction material in the chemical-processing industry.

17

PLASTIC MATERIALS:

INTRODUCTION :

Humans have taken advantage of the versatility of polymers for centuries in the form of oils,

tars, resins, and gums. However, it was not until the industrial revolution that the modern

polymer industry began to develop. In the late 1830s, Charles Goodyear succeeded in

producing a useful form of natural rubber through a process known as "vulcanization." Some

40 years later, Celluloid (a hard plastic formed from nitrocellulose) was successfully

commercialized. Despite these advances, progress in polymer science was slow until the

1930s, when materials such as vinyl, neoprene, polystyrene, and nylon were developed. The

introduction of these revolutionary materials began an explosion in polymer research that is

still going on today.

Some degree of compromise is almost always necessary in designing plastic parts. Arriving at

the best compromise usually requires satisfying the mechanical, thermal, and electrical

requirements of the part, utilizing the most economical resin or compound that will perform

satisfactorily and be attractive, and choosing a manufacturing process compatible with the part

design and material choice.

Probably no plastic will provide 100% of the requirements for the desired performance,

appearance, processibility, and price. Selecting the best qualified material is not based simply

on comparing numbers on published data sheets; such values can be grossly misleading. For

example, choosing the most economical material for a part by comparing the cost per pound of

various plastics is a mistake. Some plastics weigh twice as much per cubic inch as others and

so would require twice as much to fill a given cavity and cost twice as much to ship.

Polymers have a wide range of mechanical properties. Network polymers are often quite

strong and stiff (high yield strength and modulus of elasticity), although they have poor

ductility. Linear polymers have much lower strength but quite high ductility, and elastomers

have very large values of ductility and a variable modulus of elasticity. Polymers are generally

classified according to their structure, properties and use as:

Thermoplastic

Thermosetting

Elastomers

18

Thermoplastics :

Thermoplastic materials are melt processable, that is they are formed when the are in a melted

or viscous phase. This generally means they are heated, formed, then cooled in their final

shape. Depending upon their chemistry, thermoplastics can be very much like rubber, or as

strong as aluminum. Some high temperature thermoplastic materials can withstand

temperature extremes of up to 600 F, while others retain their properties at -100 F.

Thermoplastics do not oxidize and some materials have no known solvents at room

temperature. Most thermoplastic materials are excellent electrical and thermal insulators. On

the other hand thermoplastic composites can be made to be electrically conductive with the

addition of carbonor metal fibers.

In general the combination of light weight , high strength, and low processing costs make

thermoplastics well suited to many applications. The most common methods of processing

thermoplastics are injection molding, extrusion , and thermoforming.

Thermoplastics include:

ABS (Acrylanitrile Butadiene Styrene)

ABS Polycarbonate Alloy

Acetal

Acrylic

ASA (acrylic-styrene-acrylonitrile) Alloys

Cellulose Butyrate

ETFE (Tefzel)

EVA Ethylene Vinyl Acetate

LCP (Polyester Liquid Crystal Polymer)

Nylon 6

Nylon 4-6

Nylon 6-6

Nylon 11

Nylon 12

Nylon amorphous

Nylon impact modified

Polyallomer

19

PBT Polyester (Polybutylene Terepthalate)

Polycarbonate

PEEK Polyetheretherkeytone

PEI Polyetherimid (Ultem)

Polyethersulfone

Polyethylene High Density

Polyethylene Low Density

Polyethylene Medium Density

PET Polyester (Polyethylene Terepthalate)

Polyimide Thermoplastic (Aurum)

Polypropylene

PPA Polyphthalamide (Amodel)

PPO Modified Polyphenylene Oxide (Noryl)

PPS Polyphenylene Sulfide

Polystyrene Crystal

Polystyrene High Impact HIPS

Polystyrene Medium Impact MIPS

Polysulfone

Polyurethane

PVC Polyvinyl Chloride Rigid

PVC Flexible

PVDF Polyvinylidene Fluoride (Kynar)

SAN Styrene Acrylonitrile

TPE Thermoplastic Elastomers

TPR Thermoplastic Rubbers

Thermoset Plastics :

Thermoset plastics such as amino, epoxy, phenolic, and unsaturated polyesters, are so named

because they experience a chemical change during processing and become "set", hard solids.

Thermosets are highly cross-linked polymers that have a molecular mesh or network of

polymer chains like a three-dimensional version of a net. Thermosets undergo a chemical as

well as a phase change when they are heated. Once cured they cannot be melted or remolded

and are resistant to solvents - that is once they are formed they are 'set' (hence the name).

20

Thermoset plastics, because of their tightly crosslinked structure, resist higher temperatures

and provide greater dimensional stability than do most thermoplastics. Thermosets are tough,

durable with high temperature performance, and have found applications in a wide variety of

fields including electronic chips, fibre-reinforced composites, polymeric coatings, spectacle

lenses and dental fillings.

Elastomers :

Elastomers and rubber are differentiated from polymers by the mechanical property of

returning to their original shape after being stretched to several times their length. The rubber

industry differentiates between the terms "elastomer" and "rubber" on the bases of how long a

deformed material sample requires to return to its approximate original size after a deforming

force is removed, and of its extent of recovery. Synthetic materials such as neoprene, nitrile,

styrene butadiene (SBR), and butadiene rubber are now grouped with natural rubber. These

materials serve engineering needs in fields dealing with shock absorption, noise and vibration

control, sealing, corrosion protection, abrasion protection, friction production, electrical and

thermal insulation, waterproofing, confining other materials, and load bearing.

As with almost any material, selecting a rubber for an application requires consideration of

many factors, including mechanical or physical service requirements, operating environment, a

reasonable life cycle, manufacturability of the part, and cost.

Manufacturing rubber parts is accomplished in one of three ways: transfer molding,

compression molding, or injection molding. The choice of process depends on a number of

factors, including the size, shape, and function of the part, as well as anticipated quantity, type,

and cost of the raw material.

Elastomers are classified as follows:

Nonoil-resistant rubbers

Oil-resistant rubbers

Thermoplastic elastomers

21

INTRODUCTION TO CERAMICS :

Ceramics are inorganic non-metallic materials. Metal oxides (Al2O3, FeO, etc.) are common

examples of ceramics, but other compounds such as carbides and nitrides are also included.

Porcelain, glass, bricks and refractory materials are some examples of traditional ceramics. In

the last 30 years, advances in material science have transformed formerly brittle ceramics into

materials tough enough to withstand engine environments. Ceramics are used in a variety of

applications including window glass, implantable teeth, brick, ceramic bones, nuclear fuel,

tennis racquets, solid-state electronic devices, engine components, cutting tools, valves,

bearings, and chemical-processing equipment.

The properties for which ceramics are most often selected include:

High-temperature resistance (High melting temperatures.)

High electrical resistivity (Although some ceramics are superconductors.)

Broad range of thermal conductivity (Some ceramics are excellent insulators)

High hardness (Many ceramics are brittle.)

Good chemical and corrosion resistance.

Low cost of raw materials and fabrication for some ceramics.

Good appearance control through surface treatments, colorization, etc.

Ceramics are generally more brittle than metals and can have similar stiffness (modulus of

elasticity) and similar strength, particularly in compression. But in a tensile test they are likely

to fail at a much lower applied stress. This is because the surfaces of ceramics nearly always

contain minute cracks ("Griffith cracks"), which magnify the applied stress.

Since ceramics often have very high wear-resistance and hardness, most ceramic parts are

formed as near net shape as possible. Ceramics are most often produced by compacting

powders into a body which is then sintered at high temperatures. During sintering the body

shrinks, the grains bond together and a solid material is produced. Other ceramic forming

processes include: Dry Pressing, Isostatic Pressing, Roll Compaction, Continuous Tape

Casting, Slip Casting, Extrusion, Injection Molding, Pre-Sinter Machining, Hot-Pressing, Hot

Isostatic Pressing, Grinding, Lapping and Polishing.

22

Ceramics are generally separated into the following categories.

1. Metallic Oxides

2. Glass Ceramics

3. Nitrides and Carbides

4. Glass

5. Carbon and Graphite

6. Porcelain

7. Ceramic Fibers

Metallic Oxides Alumina

Abundant and easily fabricated.

Good strength and hardness.

Wear and Temperature Resistant.

Good electrical insulators.

Low dielectric loss.

Beryllium Oxides

Exceptionally high thermal conductivities (for ceramics) at low to moderate

temperatures.

Zirconia

Extreme inertness to most metals.

Good toughness and strength.

Glass Ceramics Glass-Ceramics

Low, medium or high thermal expansion depending on composition type.

Good electrical insulators.

Transparent

One can be machined with steel tools.

Nitrides and Carbides Silicon Nitrides

Resistant to high temperatures, to thermal stress and shock.

High strength and oxidation resistant.

Good electrical insulators. 23

Boron Carbide

High hardness and low density.

Best abrasion resistance of any ceramic.

Low strength at high temperatures.

Silicon Carbides

Low electrical resistivity.

High strength and resistance to chemical attack, high temperature and thermal stress.

Tungsten Carbides

Used for tool tips.

Excellent hardness and mechanical strength.

Good thermal conductivity.

Good wear and abrasion resistance.

Glass Glasses

Oxide (silica)

Silicates

Phosphates

Borosilicates

Good resistance to thermal shock.

Large range of special optical characteristics.

Transperent.

Low thermal expansion and high dielectric strength.

Good chemical resistance.

Carbon and Graphite Carbons and Graphites

Poor strength except when produced as fibre.

Good electrical and thermal conductivity

Creep resistant at high temperatures in non-oxidizing conditions.

Self-lubricating.

Good refractoriness and thermal shock resistance.

Low density and chemically inert.

24

Carbon/Carbon Composites

High strength and low coefficient of thermal expansion at temperatures above 2000C.

Excellent thermal shock resistance.

Superior toughness, excellent thermal and electrical conductivity

Resistance to corrosion and abrasion.

High cost.

Porcelain Porcelain

Good chemical and thermal resistance.

High density, strength, resistivity and dielectric strength

Good thermal shock, wear and hot strength.

Chemically inert.

Ceramic Fibers Ceramic Fibers

Oxides spun to fiber and bulked to felt.

Used for high temperature insulation including former applications of asbestos.

25

INTRODUCTION TO COMPOSITES :

Composites are materials formed from a mixture of two or more components to produce a

material with properties or characteristics superior to those of the individual materials. Most

composites are formed of two phases: Matrix and Reinforcement. The matrix is a continuous

phase material which is usually less stiff and weaker than the reinforcement. It is used to hold

the reinforcement together and distribute the load among the reinforcements. Reinforcements

in the form of fibers, fabric, whiskers, or particulates are embedded in the matrix to produce the

composite. They are discontinuous, usually stronger and stiffer than the matrix and provide the

primary load-carrying capability of the composite.

The shape of the finished part is dependent on a mold, die or other tooling that controls the

geometry of the composite during processing. Composites may be thought of as advanced

materials, but they mimic the features of living organisms that have existed for millions of years

such as the microstructures of wood and bioceramics like mollusk shells.

The fibers and matrix of advanced composites may be combined using a variety of fabrication

processes, with the choice depending on the desired alignment of fibers, the number of parts

to be produced, the size and complexity of the parts, and so on. Perhaps best known for their

use in aerospace applications, advanced composites are also used by the automotive,

biomedical, and sporting goods markets.

All of these developments mean a larger and more complicated materials-choice menu. This

diversity has made plastics applicable to a broad range of consumer, industrial, automotive,

and aerospace products. It has also made the job of selecting the best materials from such a

huge array of candidates quite challenging.

Composites fall into the general categories:

1. Polymer-Matrix Composites

o Thermoplastic Composites

o Thermoset Composites

o Laminated Plastics

2. Ceramic-matrix Composites

o Carbon-matrix Composites

3. Metal-matrix Composites

26

MANUFACTURING: INTRODUCTION

The word manufacturing is derived from the Latin manu factus, meaning made by hand.

Manufacturing involves making products from raw materials by various processes or

operations.

Manufacturing is generally a complex activity, involving people who have a broad range of

disciplines and skills and a wide variety of machinery, equipment, and tooling with various

levels of automation, including computers, robots, and material-handling equipment.

Manufacturing activities must be responsive to several demands and trends:

  A product must fully meet design requirements and specifications.

A product must be manufactured by the most economical methods in order to minimize

costs.

Quality must be built into the product at each stage, from design to assembly, rather

than relying on quality testing after the product is made.

In a highly competitive environment, production methods must be sufficiently flexible so

as to respond to changing market demands, types of products, production rates,

production quantities, and on-time delivery to the customer.

New developments in materials, production methods, and computer integration of both

technological and managerial activities in a manufacturing organization must constantly

be evaluated with a view to their timely and economic implementation.

Manufacturing activities must be viewed as a large system, each part of which is

interrelated to others. Such systems can be modelled in order to study the effect of

factors such as changes in market demands, product design, material and various other

costs, and production methods on product quality and cost.

The manufacturing organization must constantly strive for higher productivity, defined as

the optimum use of all its resources: materials, machines, energy, capital, labour and

technology. Output per employee per hour in all phases must be maximized.

Many processes are used to produce parts and shapes. There is usually more than one

method of manufacturing a part from a given material. The broad categories of processing

methods for materials are:

27

 

Metal Casting Expendable mold and permanent mold .

Metal Forming

& shaping

Rolling, forging, extrusion, drawing, sheet forming, powder metallurgy, and

molding .

Plastics

Molding

& Forming

Blow Molding, CNC Machining, Centrifugal Casting, Continuous Strip

Molding, Compression Molding, Profile Extrusion, Continuous Lamination,

Injection Molding, Filament Winding, Thermoforming,Vacuum Forming,

Pressure Bag Molding, Pressure Forming, Pulshaping, Twin Sheet

Forming, Pultrusion, Liquid Resin Molding, Reaction Injection Molding

(RIM), Rotational Molding, Resin transfer molding (RTM)

Rapid

Prototyping

Stereolithography - SLA or SL, 3D Printing - 3DP, Selective Laser

Sintering - SLS, Fused-Deposition Modeling - FDM, Solid-Ground Curing -

SGC, Laminated Object Manufacturing - LOM, Multi-Jet Modeling - MJM,

Direct Shell Production Casting - DSPC, Polyjet Technology, Laser

Engineered Net Shaping - LENS

Joining Welding, brazing, soldering, diffusion bonding, adhesive bonding, and

mechanical joining .

Machining

Turning, boring, drilling, milling, planing, shaping, broaching, grinding,

ultrasonic machining, chemical, electrical, and electrochemical machining

and high-energy beam machining .

Finishing

Operations

Honing, lapping, polishing, burnishing, deburring, surface treating, coating

and plating processes.

Casting is a manufacturing process where a solid is melted, heated to proper temperature

(sometimes treated to modify its chemical composition), and is then poured into a cavity or

mold, which contains it in the proper shape during solidification. Thus, in a single step, simple

or complex shapes can be made from any metal that can be melted. The resulting product can

have virtually any configuration the designer desires.

28

In addition, the resistance to working stresses can be optimized, directional properties can be

controlled, and a pleasing appearance can be produced.

Cast parts range in size from a fraction of an inch and a fraction of an ounce (such as the

individual teeth on a zipper), to over 30 feet and many tons (such as the huge propellers and

stern frames of ocean liners). Casting has marked advantages in the production of complex

shapes, parts having hollow sections or internal cavities, parts that contain irregular curved

surfaces (except those made from thin sheet metal), very large parts and parts made from

metals that are difficult to machine. Because of these obvious advantages, casting is one of

the most important of the manufacturing processes.

Today, it is nearly impossible to design anything that cannot be cast by one or more of the

available casting processes. However, as in all manufacturing techniques, the best results and

economy are achieved if the designer understands the various options and tailors the design to

use the most appropriate process in the most efficient manner. The various processes differ

primarily in the mold material (whether sand, metal, or other material) and the pouring method

(gravity, vacuum, low pressure, or high pressure). All of the processes share the requirement

that the materials solidify in a manner that would maximize the properties, while

simultaneously preventing potential defects, such as shrinkage voids, gas porosity, and

trapped inclusions.

Conventional Molding Processes :

These are the conventional molding processes which are the most widely used in the foundry

industry today.

Green Sand Molding :

Green sand is by far the most diversified molding method used in current metalcasting

operations. The green sand process utilizes a mold made of compressed or compacted moist

sand packed around a wood or metal pattern. The term "green" denotes the presence of

moisture in the molding sand, and indicates that the mold is not baked or dried.

Process :

The mold material consists of silica sand mixed with a suitable bonding agent (usually clay)

and moisture. To produce the mold a flask, usually a metal frame, (although wood may be 29

used for some processes and types of castings), is placed over the pattern to produce a cavity

representing one half of the casting. Compaction is achieved by either jolting or squeezing the

mold. The other half of the mold is produced in like manner and the two flasks are positioned

together to form the complete mold.

If the casting has hollow sections, a core consisting of hardened sand (baked or chemically

hardened) is used. Cores are located in pockets formed by projections on the pattern

equipment to produce coreprints. Should extra support for the core be required, chaplets or

spacers are properly positioned to maintain the required dimension. These will fuse with the

molten metal when the casting is poured.

Green sand is the best known of all the sandcasting methods, as the molds may be poured

without further conditioning. This type of molding is most adaptable to light, bench molding for

medium-sized castings or for use with production molding machines.

VARIATION OF GREEN SAND MOLDING :

High-Density Molding (High Squeeze Pressure / Impact) :

In recent years, the introduction of high-pressure molding techniques has greatly improved the

standards of accuracy and finish which can be achieved with certain types of castings.

Dramatic changes have occurred in the foundry molding system by increasing the capacity and

ability of the molding machines to produce molds. This has been accomplished by more

effective use of large air cylinders, application of electronics, use of hydraulics, and the

innovative use of an explosive-type method of compacting the sand around the pattern,

referred to as impact molding.

In recent years high-pressure or high-density molding has been widely adapted for the casting

of most metals. High -pressure (high-density) molding has virtually eliminated the past

problems of mold-wall movement. Mold-wall movement has been markedly aggravated by the

moisture content of the molding sand, the density of the molds, and the mold surface

hardness.

High-pressure molding practices have allowed lower moisture contents in the molding sand, so

that higher mold densities can be achieved. Thus, castings having considerably better

30

dimensional accuracy are produced, surface finish of the casting is improved, and the castings

more accurately reflect pattern accuracy.

Advantages :

Most metals can be cast by this process.

Castings produced with this method also demonstrate closer dimensional tolerances,

consistently uniform casting weight, better surface finish, increased productivity, and

lower cost.

Reduced feed metal

Improved casting soundness

Reduced cleaning costs

Minimum setup for machining because of casting dimensional accuracy.

Disadvantages :

Tighter quality controls are required with this type of molding. As a result, the foundry

using high-pressure (high-density) molding is generally accustomed to more

sophisticated equipment, maintenance, and operating procedures.

VARIATION OF GREEN SAND MOLDING :

Flaskless Molding :

One recent innovation in green sand molding has been the introduction of flaskless molding-

with both vertical as well as horizontal partings.

Contrary to any misconceptions, a flask must be used on all green sand molding primarily for

containment of sand while it is compacted about the pattern. In flaskless molding (whether

vertical or horizontal) instead of using "tight" individual flasks for each mold produced, the

master flask is contained as an integral unit of the totally mechanized mold producing system.

Once the mold has been stripped from the integral mold producing unit, it is held against the

other half of the mold with enough pressure to allow pouring of the metal.

31

Through advanced engineering techniques as well as continuous modification and

improvements, vertical flaskless molding has achieved notable production and casting quality

levels and has attained new heights of casting dimensional tolerance and accuracy. The

vertical flaskless systems are suited to gray, malleable and ductile iron as well as steel,

aluminum and brass castings.

In the vertical flaskless systems, the completely contained molding unit blows and squeezes a

mold against a pattern (or multiple patterns) which has been designed for a vertical gating

system. Molds of this type can be produced in very high quantities per hour, and of high

density (mold hardness ranging from 85-95 B scale) with excellent dimensional reproducibility.

Advantages:

No expenditure is required for flasks nor is there any cleaning or maintenance of flasks.

Working conditions are improved and there is no handling, storing or shakeout of flasks.

Disadvantages :

Restrictions apply to size of casting, use of complicated cores and core assemblies, and

number of castings per mold. Mold handling may be more difficult.

VARIATION OF GREEN SAND MOLDING :

Tight Flask Molding :

The tight flask molding process uses a flask (made of metal or wood) to contain the sand

during the mold producing operation. The flask remains around the sand during the core

setting, dosing of the mold, pouring and cooling of the casting. After cooling, castings and sand

are separated from the flasks, which are then reused to produce more molds.

Advantages :

This method offers more flexibility in type and number of castings poured per mold.

Increased use of the total flask surface when compared to flaskless molding.

Increases the size and weight of a casting which may be poured.

32

Use of complicated cores or core assemblies is not a problem compared to flaskless

molding.

Disadvantages :

Flask handling systems require capital investment and a good maintenance program.

The variety and size of castings produced in a tight flask molding line may require

changing the flask for a larger size casting.

VARIATION OF GREEN SAND MOLDING :

Skin Dried Molding :

Skin-dried or air-dried molds are sometimes preferred to green sand molds where assurance is

desired that the surface moisture and other gas-forming materials are lowered. By skin drying

the face of the mold after special bonding materials have been added to the sand molding

mixture, a firm mold face is produced similar to that obtained in dry sand practice. Shakeout of

the mold is almost as good as that obtained with green sand molding. Skin-dried molds are

commonly employed in making medium-heavy and heavy castings.

Generally, the surface of the mold is washed or sprayed with a refractory mold coating. The

most common method of drying the refractory mold coating uses hot air, gas or oil flame. Skin

drying of the mold can be accomplished with the aid of torches, a bank of radiant heating

lamps or electrical heating elements directed at the mold surface.

Advantages :

This process reduces surface moisture and other gas-forming materials from mold. It

can commonly be used in the production of medium-heavy to heavy castings.

Disadvantages :

These molds are more expensive to produce. Mold sections must be completely dry and

cool prior to assembly.

33

VARIATION OF GREEN SAND MOLDING :

Dry Sand Molding :

Dry sand molding is the green sand practice modified by baking the mold at 400-600F (204-

316C). Some foundries use dry sand molds to produce intricate parts which are difficult to cast

to exact size and dimensions. Molds are generally dried (or baked) in large mold drying or with

large mold heaters.

Castings of large or medium size and of complex configuration such as frames, engine

cylinders, rolls, large gears and housings are often made using the dry sand technique. Both

ferrous and nonferrous metals are cast in this type of mold.

Advantages :

Dry sand molds are generally stronger than green sand molds and therefore can

withstand much additional handling.

Better dimension control than if they were molded in green sand.

The improved quality of the sand mixture due to the removal of moisture can result in a

much smoother finish on the castings than if made in green sand molds. Where molds

are properly washed and sprayed with refractory coatings, the casting finish is further

improved.

Disadvantages

This type of molding is much more expensive than green sand molding and is not a

high-production process. Correct baking (drying) times are essential.

PRECISION MOLDING AND CASTING PROCESSES :

These are molding processes that produce castings with an improved surface finish, while

providing excellent detail, with a higher degree of dimensional accuracy.

Die Casting

Squeeze casting or Squeeze Forming

Investment Casting (Lost Wax) 34

The "V" Process

Shaw Process - ceramic molding

Hitchiner Process (CLA, CLAS, CLAV)

Metal Casting Techniques - Die Casting :

This process is used for producing large volumes of zinc, aluminum and magnesium castings

of intricate shapes. The essential feature of diecasting is the use of permanent metal dies into

which the molten metal is injected under high pressure (normally 5000 psi or more).

The rate of production of diecasting depends largely on the complexity of design, the section

thickness of the casting, and the properties of the cast metal. Great care must be taken with

the design and gating of the mold to avoid high-pressure porosity to which this process is

prone.

Advantages :

Cost of castings is relatively low with high volumes.

High degree of design complexity and accuracy.

Excellent smooth surface finish.

Suitable for relatively low melting point metals (1600F/871C) like lead, zinc, aluminum,

magnesium and some copper alloys.

High production rates.

Disadvantages :

Limits on the size of castings - most suitable for small castings up to about 75 lb.

Equipment and die costs are high.

Metal Casting Techniques - Squeeze Casting :

Squeeze Casting combines the processes and advantages of Gravity Casting and Forging.

Squeeze Casting uses metal permanent molds and it has a material tank. The pouring process

uses a cylinder at the bottom of the material tank to push the material into molds. This pouring

process is similar as Gravity Casting, but Gravity Casting uses gravity instead of a cylinder to

load the mold.

35

After material goes into the mold, the cylinder of the material tank continues loading pressure,

about 300 tons, until the end of the casting cycle. When the material in the mold starts to cool

down, it will begin to shrink. The cylinder will continue the loading pressure to push more metal

into the mold, making the casting more solid and with greater detail. This makes the process

similar to Forging. The casting quality of Squeeze Casting is close to Forging.

Process :

Liquid metal is introduced into an open die, just as in a closed die forging process. The dies

are then closed. During the final stages of closure, the liquid is displaced into the further parts

of the die. No great fluidity requirements are demanded of the liquid, since the displacements

are small. Thus forging alloys, which generally have poor fluidities which normally precludes

the casting route, can be cast by this process

Metal Casting Techniques - Investment Casting or Lost Wax :

Investment Casting is the process of completely investing a three-dimensional pattern in all of

its dimensions to produce a one-piece destructible mold into which molten metal will be

poured. A refractory slurry flows around the wax pattern, providing excellent detail.

The wax patterns are assembled on a "tree" and invested with a ceramic slurry. The tree is

then immersed into a fluidized bed of refractory particles to form the first layer of the ceramic

shell. The mold is allowed to dry and the process repeated with coarser material until sufficient

thickness has been built up to withstand the impact of hot metal.

When the slurry hardens, the wax pattern is melted out and recovered and the mold or ceramic

shell is oven cured prior to casting.

Most materials can be cast by this process but the economics indicate that fairly high volume is

necessary and the shape and complexity of the castings should be such that savings are made

by eliminating machining.

Advantages :

Excellent accuracy and flexibility of design.

Useful for casting alloys that are difficult to machine.

Exceptionally fine finish.

36

Suitable for large or small quantities of parts.

Almost unlimited intricacy.

Suitable for most ferrous / non-ferrous metals.

No flash to be removed or parting line tolerances.

Disadvantages :

Limitations on size of casting.

Higher casting costs make it important to take full advantage of the process to eliminate

all machining operations.

Metal Casting Techniques - Vacuum ("V") Process Molding :

This adaptation of vacuum forming permits molds to be made out of free-flowing, dry,

unbonded sand without using high-pressure squeezing, jolting, slinging or blowing as a means

of compaction. The V-process is dimensionally consistent, economical, environmentally and

ecologically acceptable, energy thrifty, versatile and clean.

Because the V-Process uses clean, dry unbonded sand, you can forget about mullers and

mixers, and costly sand reclamation and reconditioning equipment. Most V-Process users

require only sand cooling and transportation, dust collection and simple screening to remove

tramp metals.

Molding equipment is simple too. It can be limited to as few as five items (a vacuum system,

Film heater, vibrating table, pattern carrier and flasks) or automated for higher production.

There is no need for heavy, noisy jolt squeeze equipment, ramming of slingers.

The molding media is clean and dry therefore shakeout equipment is usually nothing more

than a grate to allow the sand to flow away from the casting and back into the sand system.

Fume and odor control is unnecessary in most applications.

Process :

The molding medium is clean, dry, unbonded silica sand, which is consolidated through

application of a vacuum or negative pressure to the body of the sand. The patterns must be

mounted on plates or boards and each board is perforated with vent holes connected to a

vacuum chamber behind the board. A preheated sheet of highly flexible plastic material is

37

draped over the pattern and board. When the vacuum is applied, the sheet clings closely to the

pattern contours. Each part of the molding box is furnished with its own vacuum chamber

connected to a series of hollow perforated flask bars. The pattern is stripped from the mold and

the two halves assembled and cast with the vacuum on.

Advantages :

Superb finishes.

Good dimensional accuracy.

No defects from gas holes.

All sizes and shapes of castings are possible from thin walls to thick sections, or from

castings weighing ounces to several tons. Sand thermal conductivity is lower and metal

fluidity is improved. Solidification time is slower. In addition, zero draft designs are

common, and can reduce clean up and rough machining operations.

Most ferrous / non-ferrous metals can be used.

Low operating cost - You not only save on the cost of sand binders but all of the cost of

sand mixing, testing and disposal/ reclamation. Even pattern life is extended because

the sand never touches the pattern and it is never subjected to the rigors of a

conventional molding machine. Finally, V-Process produces castings with fewer

imperfections and less scrap.

Disadvantages :

The V-process requires plated pattern equipment.

Metal Casting Techniques - Ceramic Molding (Shaw Process)

Ceramic molding can be accomplished through two diverse techniques:

1. True ceramic molding.

2. Ethyl silicate slurry molding (also known as the Shaw process, Avnet-Shaw, Osborn-

Shaw and the Dean process ).

Ceramics are materials which are made from a clay base and contain various oxides and

ingredients other than sand. The raw clays are calcined or fired at high temperatures and are

then blended, mixed with water, formed into mold components, and then fired.

38

In true ceramic molding, the refractory grain can be bonded with calcium or ammonium

phosphates. The preferred methods for producing ceramic molds is the dry pressing method in

which molds are made by pressing the clay mixture containing 4-9% moisture in dies under a

pressure of 1-10 ton/sq in. After pressing, molds are stripped from the dies and then fired at

temperatures between 1650-2400F (899C and 1316C).

The ethyl silicate variation is accomplished in the following manner: a mixture of a graded

refractory filler, hydrolyzed ethyl silicate, and a liquid catalyst are blended together to form a

slurry consistency. The slurry is then poured over a pattern and allowed to jell. After gelation,

the mold is stripped and torched with a high pressure gas torch. The mold can then be cooled,

assembled and fired prior to pouring.

The best known of these process variations is a development from the United Kingdom called

the Shaw process. The chief difference between the Shaw and other investment molding

processes is that a jelling agent is added to the refractory slurry-like mixture before it is poured

over the pattern. When this mixture forms a somewhat flexible gel, the mold can be stripped off

the pattern.

Patterns can be made of various materials such as plaster, wood or metal and can be reused.

In this manner, this process differs from the expendable (wax or plastic) process. Molds are

torched, then brought to a red heat in a furnace. The molds are allowed to cool prior to

assembly for pouring. Occasionally the Shaw process and the lost wax process are combined

to gain the advantages of each. The complex pattern configurations which are difficult or

impossible to remove from the mold can be made of wax and placed into the regular pattern.

This provides for the regular pattern to be stripped off and the wax to be melted and burned

out later.

Metal Casting Techniques - Hitchiner Process (CLA, CLAS, CLAV) :

The Hitchiner casting process utilizes a counter gravity (vacuum) system to fill the mold cavity

with molten metal. The molds are usually produced using a resin-bonded shell and/or a

chemically bonded sand molding process. The design of the mold provides small diameter

feeders through the drag half of the mold to pull the metal up into the mold cavity.

39

The mold is partially submerged into the metal bath and the metal is drawn into the mold

cavities. The vacuum system draws the decomposition gases out of the mold cavity as they

are generated during the pouring of the mold.

Process capabilities include the ability to produce light section castings in a variety of alloys

normally not castable by other processes. The Hitchiner process also offer the capability of

making castings with good dimensional accuracy and casting finish normally only obtainable in

the lost wax/investment casting process. Casting integrity is excellent in alloy steels and nickel

alloys with designs not normally castable by other processes. Castings of up to 100 lb in steel

and high alloys including iron, nickel and cobalt-base metals.

Advantages :

High casting yield

Good casting definition

Less casting cleaning is required compared to green sand, low sand and gas inclusions

Low scrap.

Disadvantages :

The process only offers low- to medium-volume production capabilities.

Chemically Bonded Sand Molding Processes :

This section describes the molding processes that use chemical binders mixed with sand to

produce a mold. Since their introduction to the foundry, they have gained wide acceptance for

the production of molds.

Some chemical binder systems will bond or cure the mold through a chemical reaction

established during the sand and binder mixing cycle, while other chemically bonded molding

processes may require gassing of the sand mixture, or heat applied to the sand mixture to

complete the cure. The simplicity of the chemical system usually makes quality control less

complex and results more consistent.

40

Shell Molding (Organic)

Sodium Silicate CO2 Bonded Molding (Inorganic)

Nobake Molding (Chemically Bonded Self-setting Sand Mixtures/Organic)

Metal Casting Techniques - Organic Shell Molding :

Shell Molding is probably the earliest, most automated and most rapid of mold (and

coremaking) processes.

Resin-bonded silica sand is placed onto a heated pattern, for a predetermined time. Ejector

pins enable the mold to be released from the pattern and the entire cycle is completed in

seconds depending upon the shell thickness desired. The two halves of the mold, suitably

cored, are glued and clamped together prior to the pouring of the metal. Shell molds may be

stored for long periods if desired.

Because of pattern costs, this method is best suited to higher volume production. Designers

should seek the advice of the foundry to ensure that all the benefits of the process are

achieved.

Advantages :

Shell molds may be stored for extended periods of time.

Good casting detail

Good dimensional accuracy

Molds are lightweight.

Disadvantages :

Because the tooling require heat to cure the mold, pattern costs and pattern wear can

be higher.

Energy costs also tend to be higher.

Material costs tend to be higher than those for green sand molding.

Metal Casting Techniques - Sodium Silicate CO2 InOrganic Shell Molding :

Instead of using an oil or resin that requires heat for bonding or curing, this process uses a

sand which has been mixed with sodium silicate (NA2SiO3).

41

In this process, the CO2 gas forms a weak acid which hydrolyzes the sodium silicate, thus

forming an amorphous silica that becomes the bond. There is also a bonding action from the

sodium silicate itself. The use of CO2 gives an almost instantaneous set. The mold is fully

hardened before the pattern is drawn from the mold sections.

Advantages :

Materials for the sodium silicate process tend to be low cost.

All sands can be used as the base aggregate for the silicate sand mixture. These

include silica sands, bank sands, lake sands as well as zircon, chromite and olivine

sands.

Disadvantages :

The more alkaline the binder, the longer it takes to gas and the greater the tendency for

the core to remain rubbery instead of firm.

Metal Casting Techniques - No-bake Molding :

Since their introduction, furan and urethane nobake binders have gained wide acceptance for

the production of molds and cores for producing metal castings.

The advantages, regardless of which resins are used, are based upon control of the setting

times by means of the addition of specific amounts of catalyst. This feature, combined with

high strength and a desirable range of hot properties for use with various alloys, presents the

opportunity for great flexibility in mold making.

To produce a mold using nobake binders, the pattern is covered to a depth of 4-5 in. with the

nobake sand mixture. The sand is allowed to set completely and the flask is then filled with

conventional backup sand or, as the sand becomes tacky during its setting up period, the

backup sand may be added with a sand slinger. If ramming energy is applied before the sand

sets, the density of the sand mass at the pattern surface is increased. This is reflected in a

better casting finish.

42

Advantages :

Most ferrous / non-ferrous metals can be used.

Adaptable to large or small quantities

High strength mold

Better as-cast surfaces.

Improved dimensional repeatability

Less skill and labor required then in conventional sand molding.

Better dimensional control.

Disadvantages :

Sand temperatures critical.

Patterns require additional maintenance

The bench life of the sand mixture is limited.

SPECIAL AND INNOVATIVE MOLDING AND CASTING PROCESSES :

Expendable Pattern Casting (EPC/lost foam)

Vacuum ("V") Process Molding

Centrifugal Casting

"H" Process Molding

Metal Injection Molding

Metal Casting Techniques - Expandable Pattern Casting (Lost Foam) :

Also known as Expanded Polystyrene Molding or Full Mold Process, the EPC or Lost Foam

process is an economical method for producing complex, close-tolerance castings using an

expandable polystyrene pattern and unbonded sand.

The EPC process involves attaching expandable polystyrene patterns to an expandable

polystyrene gating system and applying a refractory coating to the entire assembly. After the

coating has dried, the foam pattern assembly is positioned on several inches of loose dry sand

43

in a vented flask. Additional sand is then added while the flask is vibrated until the pattern

assembly is completely embedded in sand.

A suitable downsprue is located above the gating system and sand is again added until it is

level to the top of the sprue. Molten metal is poured into the sprue, vaporizing the foam

polystyrene, perfectly reproducing the pattern. Gases formed from the vaporized pattern

permeate through the coating on the pattern, the sand and finally through the flask vents.

In this process, a pattern refers to the expandable polystyrene or foamed polystyrene part that

is vaporized by the molten metal. A pattern is required for each casting.

Advantages :

No cores are required.

Reduction in capital investment and operating costs.

Closer tolerances and walls as thin as 0.120 in.

No binders or other additives are required for the sand, which is reusable.

Flasks for containing the mold assembly are inexpensive, and shakeout of the castings

in unbonded sand is simplified and do not require the heavy shakeout machinery

required for other sand casting methods.

Need for skilled labor is greatly reduced.

Casting cleaning is minimized since there are no parting lines or core fins.

Disadvantages :

The pattern coating process is time-consuming, and pattern handling requires great

care.

Good process control is required as a scrapped casting means replacement not only of

the mold but the pattern as well.

Centrifugal Casting :

The Centrifugal Casting process consists of a metal or graphite mold that is rotated in the

horizonal or vertical plane during solidification of the casting. Centrifugal force shapes and

feeds the molten metal into the designed crevices and details of the mold. The centrifugal force

improves both homogeneity and accuracy of the casting.

44

This method is ideally suited to the casting of cylindrical shapes, but the outer shape may be

modified with the use of special techniques.

Advantages :

Rapid production rate.

Suitable for Ferrous / Non-ferrous parts.

Good soundness and cleanliness of castings.

Ability to produce extremely large cylindrical parts.

Disadvantages :

Limitations on shape of castings. Normally restricted to the production of cylindrical

geometric shapes.

Metal Casting Techniques - "H" Process Molding :

This process utilizes a horizontal, controlled pouring process for the repetitious production of

castings. It makes use of rigid, double-sided molds produced by coreblowing machines. Each

mold carries a half casting impression on each side, complete with runner bar, feeder head

and ingates.

Molds, when clamped together horizontally, form a pouring system of a top continuous runner

and feeder bar. This runner/feeder bar is opened up at one end to form a pouring basin. Each

mold is designed so that when the string of molds is poured, control of the metal flow is

obtained.

The first mold is poured and is full before the metal proceeds to fill the second mold. This

procedure of mold filling ensures a "flow feed" of each casting as all metal must pass through

the feeder heads of the preceding castings. Maximum yield of metal is obtained.

The horizontal clamping arrangement of the molds in the "H" process achieves the lowest

possible ferrostatic casting pressure. This reduces the strain on mold parting joints, resulting in

close control of casting dimensions and a minimum of casting cleaning. Presently the process

has been applied to most cast metals.

45

Advantages :

Close control of casting dimensions.

Reduction in casting cleaning costs.

The molds can be produced on core machines and from any of the known core or mold

binder technologies in use today.

Disadvantages :

Mold size with this process is limited to available equipment.

Productivity is controlled by existing production of molds, molding handling systems,

and the pouring of mold assemblies.

MANUFACTURING: METAL FORMING :

Roll Forming :

Rolling is a forming process which reduces the cross-sectional area of the incoming metal

stock or produces a new cross-section of the material at the exit while improving its

mechanical properties through the use of rotating rolls.

The process can be carried out hot, warm, or cold, depending on the application and the

material involved. Rolling of blooms, slabs, billets, plates is usually done at temperatures

above the recrystallization temperature (hot rolling). Sheet and strip often are rolled cold in

order to maintain close thickness tolerances.

Specific Processes :

1. Flat Rolling

2. Thread Rolling

3. Seamless Tubing

4. Continuous Casting and Rolling

46

Forging :

Forging is controlled, plastic deformation or working of metals into predetermined shapes by

means of pressure or impact blows, or a combination of both. Forging improves the quality of

the metal, refines the grain structure and increases strength and toughness. Forgings can offer

decisive cost advantages, especially in high-volume production runs. Forged parts are

generally near-net shapes, making better use of material, generating little scrap, and requiring

less machining and labor time. Properly designed, a forging can replace an entire

multicomponent assembly.

Specific Processes :

1. Cold Forging

2. Impression Die Forging

3. Open Die Forging

4. Closed Die Forging

5. Seamless Rolled Ring Forging

Extrusion and Drawing :

Extrusion is a plastic deformation process in which material is forced under pressure to flow

through one or more die orifices to produce products of the desired configuration. This process

provides a practical forming method for producing a limitless variety of parallel-surfaced

shapes to meet almost any design requirement. Other advantages include improving the

microstructure and physical properties of the material, maintaining close tolerances, material

conservation, economical production, and increased design flexibility.

Drawing is a process of cold forming a flat precut metal blank into a hollow vessel without

excessive wrinkling, thinning, or fracturing. The various forms produced may be cylindrical or

box shaped, with straight or tapered sides or a combination of straight, tapered, and curved

sides. The parts may vary from 1/4" (6mm) diam parts or smaller to aircraft or automotive parts

large enough to require mechanical handling equipment.

 

47

Specific Processes-

1. Aluminum Extrusions

2. Cold extrusion

3. Drawing

4. Hydrostatic extrusion

5. Impact extrusion

Sheetmetal Forming :

The stamping of parts from sheet metal is a straightforward operation in which the metal is

shaped or cut through deformation by shearing, punching, drawing, stretching, bending,

coining, etc. Production rates are high and secondary machining is generally not required to

produce finished parts within tolerances. This versatile process lends itself to low costs, since

complex parts can be made in a few operations at high production rates. Sheet metal has a

high strength-to-weight factor, enabling production of parts that are lightweight and strong.

Specific Sheetmetal Forming Processes :

Sheet Metal Forming Processes

Deep

Drawing

Electro-

hydraulic

Forming

Electro-

magnetic

Forming

Explosive

Forming

Fine

Blanking

Hydro-

forming

Magnetic

Pulse

Forming

Metal

Spinning

Peen

Forming

Press Brake

Forming Shearing

Stretch

Forming

Superplastic

Forming

Tube

Bending

Sheetmetal Forming - Deep Drawing :48

Drawing is a process of cold forming a flat precut metal blank into a hollow vessel without

excessive wrinkling, thinning, or fracturing. The various forms produced may be cylindrical or

box shaped, with straight or tapered sides or a combination of straight, tapered, and curved

sides. The parts may vary from 1/4" (6mm) diam parts or smaller to aircraft or automotive parts

large enough to require mechanical handling equipment.

The deep drawing process is simply defined as the stretching of sheet metal stock,

commonly referred to as a blank, around a plug. The edges of the metal blank are restrained

by rings and the plug is deep drawn into a top die cavity to achieve the end shape that is

desired. There are many shapes that can be made through deep drawing and stamping

including --

1. cups

2. cans

3. pans

4. cylinders

5. domes

6. hemispheres

7. tubes

8. hoppers

9. irregular shaped products.

When necessary, deep drawing can be complemented with the metal spinning process to

ensure the highest quality, most affordable method of production is utilized to fit your

production and cost needs.

Sheetmetal Forming - Electrohydraulic Sheetmetal Forming :

In electrohydraulic forming, an electric arc discharge is used to convert electrical energy to

mechanical energy. A capacitor bank delivers a pulse of high current across two electrodes,

which are positioned a short distance apart while submerged in a fluid (water or oil). The

electric arc discharge rapidly vaporizes the surrounding fluid creating a shock wave. The

workpiece, which is kept in contact with the fluid, is deformed into an evacuated die.

The potential forming capabilities of submerged arc discharge processes were recognized as

early as the mid 1940s. During the 1950s and early 1960s, the basic process was developed

49

into production systems. This work principally was by and for the aerospace industries. By

1970, forming machines based on submerged arc discharge, were available from machine tool

builders. A few of the larger aerospace fabricators built machines of their own design to meet

specific part fabrication requirements.

Electrohydraulic forming is a variation of the older, more general, explosive forming method.

The only fundamental difference between these two techniques is the energy source, and

subsequently, the practical size of the forming event.

Very large capacitor banks are needed to produce the same amount of energy as a modest

mass of high explosives. This makes electrohydraulic forming very capital intensive for large

parts. On the other hand, the electrohydraulic method was seen as better suited to automation

because of the fine control of multiple, sequential energy discharges and the relative

compactness of the electrode-media containment system.

Sheetmetal Forming - Electromagnetic forming :

Electromagnetic forming (EM forming or Magneforming) is a high energy rate metal forming

process that uses pulsed power techniques to create ultrastrong pulsed magnetic fields to

rapidly reshape metal parts.

In practice the metal "work piece" to be fabricated is placed in close proximity to a heavily

constructed coil of wire (called the work coil). A huge pulse of current is forced through the

work coil by rapidly discharging a high voltage capacitor bank using an ignitron or a spark gap

as a switch. This creates a rapidly oscillating, ultrastrong electromagnetic field around the work

coil.

The rapidly changing magnetic field induces a circulating electrical current within the work

piece through electromagnetic induction, and the induced current creates a corresponding

magnetic field around the metal work piece. Because of Lenz's Law, the magnetic fields

created within the metal work piece and work coil strongly repel each another. The high work

coil current (typically tens or hundreds of thousands of amperes) creates ultrastrong magnetic

forces that easily overcome the yield strength of the metal work piece, causing permanent

deformation. The metal forming process occurs extremely quickly (typically tens of

microseconds). The forming process is most often used to shrink or expand cylindrical tubing,

but it can also form sheet metal by repelling the work piece onto a shaped die at a high

50

velocity. Since the forming operation involves high acceleration and decelleration, inertia of the

work piece plays a critical role during the forming process. The process works best with good

electrical conductors such as copper or aluminum, but it can be adapted to work with poorer

conductors such as steel.

Other high energy rate metal forming techniques include electrohydraulic forming and

explosive forming. Instead of using powerful magnetic fields, these forming processes use a

powerful shock wave created within a fluid, usually water, to perform the operation. The

underwater shock wave is generated by either triggering a powerful spark discharge (using a

high voltage capacitor bank) or by detonating a high explosive.

Sheetmetal Forming - Explosive Forming :

Explosive forming has evolved as one of the most dramatic of the new metalworking

techniques. Explosive forming is employed in aerospace and aircraft industries and has been

successfully employed in the production of automotive-related components. Explosive Forming

or HERF (High Energy Rate Forming) can be utilized to form a wide variety of metals, from

aluminum to high strength alloys. In this process the punch is replaced by an explosive charge.

The process derives its name from the fact that the energy liberated due to the detonation of

an explosive is used to form the desired configuration. The charge used is very small, but is

capable of exerting tremendous forces on the workpiece. In Explosive Forming chemical

energy from the explosives is used to generate shock waves through a medium (mostly water),

which are directed to deform the workpiece at very high velocities.

Methods of Explosive Forming :

Explosive Forming Operations can be divided into two groups, depending on the position of the

explosive charge relative to the workpiece.

Standoff Method :

In this method, the explosive charge is located at some predetermined distance from the

workpiece and the energy is transmitted through an intervening medium like air, oil, or water.

Peak pressure at the workpiece may range from a few thousand psi to several hundred

thousand psi depending on the parameters of the operation.

Contact Method : 51

In this method, the explosive charge is held in direct contact with the workpiece while the

detonation is initiated. The detonation produces interface pressures on the surface of the metal

up to several million psi (35000 MPa).

The system used for Standoff Method consists of following parts: -

1) An explosive charge

2) An energy transmitted medium

3) A die assembly

4) The workpiece The system used for Standoff Method consists of following parts: -

The die assembly is put together on the bottom of a tank. Workpiece is placed on the die and

blankholder placed above. A vacuum is then created in the die cavity. The explosive charge is

placed in position over the centre of the workpiece. The explosive charge is suspended over

the blank at a predetermined distance. The complete assembly is immersed in a tank of water.

After the detonation of explosive, a pressure pulse of high intensity is produced. A gas bubble

is also produced which expands spherically and then collapses until it vents at the surface of

the water. When the pressure pulse impinges against the workpiece, the metal is displaced

into the die cavity.

Explosives :

Explosives are substances that undergo rapid chemical reaction during which heat and large

quantities of gaseous products are evolved. Explosives can be solid (TNT-trinitro toluene),

liquid (Nitroglycerine), or Gaseous (oxygen and acetylene mixtures). Explosives are divide into

two classes; Low Explosives in which the ammunition burns rapidly rather than exploding,

hence pressure build up is not large, and High Explosive which have a high rate of reaction

with a large pressure build up. Low explosives are generally used as propellants in guns and in

rockets for the propelling of missiles.

Advantages of Explosion Forming :

1. Maintains precise tolerances

2. Eliminates costly welds.

3. Controls smoothness of contours. 52

4. Reduces tooling costs.

5. Less expensive alternative to super-plastic forming.

Die Materials :

Different materials are used for the manufacture of dies for explosive working, for instance high strength

tool steels, plastics, concrete. Relatively low strength dies are used for short run items and for parts

where close tolerances are not critical, while for longer runs higher strength die materials are required.

Kirksite and plastic faced dies are employed for light forming operations; tool steels, cast steels, and

ductile iron for medium requirements.

Material of Die Application Area

Kirksite Low pressure and few parts

Fiberglass and Kirksite Low pressure and few parts

Fiberglass and

ConcreteLow pressure and large parts

Epoxy and Concrete Low pressure and large parts

Ductile Iron High pressure and many parts

ConcreteMedium pressure and large

parts

Characteristics of Explosive Forming Process :

Very large sheets with relatively complex shapes, although usually axisymmetric.

Low tooling costs, but high labor cost.

Suitable for low-quantity production.

Long cycle times.

Transmission Medium :

Energy released by the explosive is transmitted through medium like air, water, oil, gelatin,

liquid salts. Water is one of the best media for explosive forming since it is available readily,

inexpensive and produces excellent results. The transmission medium is important regarding 53

pressure magnitude at the workpiece. Water is more desirable medium than air for producing

high peak pressures to the workpiece.

Sheetmetal Forming - Fine Blanking :

Fine blanking produces complex 'net shape' finished parts in just one or two operations. It can

replace castings, forgings, fabrication and all subsequent machining operations. Consequently,

it can be very cost-effective. Fine blanking is used primarily in the automotive components

industry where quality is paramount, and the volumes can justify the cost of the press and

tools.

The process, which is essentially a hybrid between stamping and cold extrusion, was

developed in Switzerland in the 1920s for the watch and clock industry.

Advantages :

1. Repeatability - the closely toleranced design of the tool, and the fact that all operations

are contained within the tool, so that special features are created as the basic

component is produced, which lead to inherent quality and reliability

2. Cleanly sheared edges - with little or no edge break, eliminating the need for shaving,

broaching, or profile grinding.

3. Tolerance on holes and profiles - infinitely better than conventional pressing because

of the inherent characteristics of the process and the tooling

4. Flatness and surface finish - the fact that both sides of the component are supported

at all times ensures a flatness standard which cannot be matched by conventional

pressing, thus avoiding the need for planishing and other flattening processes.

5. Additionally, many advanced features such as gear teeth, ratchets and splines can all

be formed without the need for hobbing, broaching etc.

6. Counter sinks, half shears, coined sections, self rivets or location point welding

projections and many other shapes can all be made at the same time as the part is

blanked, thus maintaining uniformity of position, component to component, and batch to

batch.

The cost of fine blank tooling is, size for size, a little higher than conventional press tooling, but

less than powder metal sintering tooling. All competent fine blanking companies have their own

54

tool design and manufacturing facilities. The normal practice is for customers to own the

tooling, which they pay for on satisfactory completion of a sample inspection.

A fine blank press does not run as fast as a conventional press and consequently for simple

components such as brackets, where tolerances are not that tight and edge finish and

cosmetic appearance not so important, conventional pressing or stamping has the economic

advantage. When tight tolerances have to be held and where edge finish or flatness is

important, or special features such as small holes, countersinks or half shears have to be

added, fine blanking comes into its own. Basically, if a conventional high-volume pressing

requires a secondary operation such as flattening, drilling, broaching, welding or hand

finishing, it is likely that a fine blanked component will be better value.

By virtue of being able to produce a 'net shape' to drawing without any further machining, fine

blanking is almost always less expensive than forging or casting and subsequent machining.

Clearly there are many complex three-dimensional shapes where fine blanking is not

appropriate, but with some forethought and creative design, a product can be designed that

takes advantage of the economic benefits of fine blanking.

Sheetmetal Forming - Hydroforming :

Hydroforming, sometimes referred to as fluid forming or rubber diaphragm forming, was

developed during the late 1940's and early 1950's in response to a need for a lower cost

method of producing relatively small quantities of deep drawn parts.

Hydroforming, in simple terms, replaces the punch in traditional stamping with liquid--usually

water--to provide shaping force. Hydroforming refers to the manufacture, via fluid pressure, of

hollow parts with complex geometries. Hydroforming can be used to shape tubes or extrusions

—where it finds its greatest use--or to shape sheet blanks.

In tube and extrusion hydroforming, the workpiece is inflated by introducing fluid into the cavity

while the tube undergoes axial or radial compression. The tube then expands where permitted

by the tooling to the die wall. Such hydroforming in many cases is preceded by forming steps

such as bending the tube to distribute where it’s needed—corner radii, usually--for final

hydroforming, or bent in order to fit into the die. Hydroforming dies used for tubes or extrusions

55

consist of upper and lower blocks and plates as well as axial units used for sealing and end-

feeding of the part.

A sheet blank can be formed via fluid applied directly or through a bladder system to force the

sheet to assume the shape of the die wall or punch end. Here, the punch may provide

additional pressure to assist in the process.

The hydroforming process requires specialized presses—or specially fitted hydraulic presses--

and tooling as well as fluid delivery, storage, disposal and reclamation capability. Fluid

pressure can range from the about 3,000 to nearly 100,000 psi.

Competitive processes :

Deep-draw stamping, tube bending, fabrication.

Applications :

In automotive, the process delivers hollow parts such as radiator frames, engine cradles,

exhaust manifolds, roof and frame rails and instrument-panel supports. Various rails, manifolds

and supports find use in aircraft and appliance applications. Parts made through sheet

hydroforming, currently a low-volume specialty process, include automotive deep-drawn fuel-

tank trays and body panels as well as appliance parts such as panels and sink basins. The

process also works well with smaller parts such as fittings and fuel filler necks

Benefits :

Hydroforming results in lighterweight parts in applications where it has replaced traditional

stamping, fabrication and assembly methods. In many cases, one-piece hydroformed parts

can replace assemblies, thus increasing structural integrity while saving on material costs and

reducing scrap. Hydroforming is better suited in producing parts from high-strength steel and

aluminum than competing processes. Recently, technology has allowed inclusion of operations

such as piercing during hydroforming.

Capacities:

Part size is dependent on press size. Currently, the largest hydroforming press available can

churn out parts to nearly 20 ft. long, but typical parts are less than half that size, and can be

56

produced in sizes down to a few inches. Cycle times are slower than traditional stamping

methods.

Materials:

High-strength steel and aluminum are the materials of choice in hydroforming parts for

automotive use. But any sheet material that can be cold formed is a candidate for

hydroforming.

Sheetmetal Forming - Magnetic Pulse Forming :

The magnetic pulse forming process which uses opposing magnetic fields to force a sheet of

metal onto a mandrel or other form. First, an extremely large current discharge is directed

through a coil which creates a magnetic field. Capacitor banks are used to store charge for

larger discharges. In the nearby sheet of metal, an opposing magnetic field is induced which

causes the metal sheet to be pushed into a form of some shape. The method generates

pressures up to 50 Kpsi creating velocities up to 900 fps. The process production rate can

climb to 3 parts a second.

Applications :

1. fittings for ends of tubes

2. embossing

3. forming

Three methods of magnetic pulse forming :

1. Swaging - An external coil forces a metal tube down onto a base shape (tubular coil).

2. Expanding - an inner tube is expanded outwards to take the shape of an outer collar

(tubular coil).

3. Embossing and Blanking - A part is forced into a mold or over another part (a flat coil)

- This could be used to apply thin metal sheets to plastic parts.

Sheetmetal Forming - Metal Spinning : 

The metal spinning process starts with special machinery that produces rotationally

symmetrical (i.e. cone-shaped) hollow parts; usually from circular blanks. Shear forming, a

57

related process where parts are formed over a rotating conical mandrel, can be used to

produce not only cone-shaped parts but also elliptical or other concave or convex parts. Often,

shear forming is used in conjunction with metal spinning. Metal spinning is used as a

replacement for the stamping and deep drawing processes.

The metal spinning process starts with a sheet metal blank which rotates on a lathe. The metal

disc is pressed against a tool (called a mandrel or a chuck) with a tailstock. The metal disc,

tailstock and tool rotate in a circular motion and a roller presses against the metal to form the

metal over the tool through a series of passes by the roller. The resulting part is a piece that

duplicates the exterior portion of the tool it was formed on. The basic shapes in metal spinning

are cones, flanged covers, hemispheres, cylindrical shells, venturis and parabolic nose

shapes.

Metal spinning yields pots and pans, vases, lamp shades, musical-instrument parts and

trophies. Automotive parts include wheel discs, rims, hubcaps and clutch drums. Other

examples include radar reflectors, parabolic dishes, hoppers, concrete-mixer bodies, drums,

pressure bottles, tank ends, compensator and centrifuge parts, pulleys, hydraulic cylinders,

engine inlet rings and a variety of jet-engine and missile parts.

Some of the advantages of metal spinning include :

1. Low capital-investment

2. Low tooling and energy costs

3. Short setup times

4. Quick and inexpensive adaptation of tooling and methods to accommodate design

changes

5. Ability to carry out other operations such as beading, profiling, trimming and turning in

the same production cycle with one setup.

6. Forming forces are appreciably lower than competing processes due to localized

working.

7. Economical for one-off parts; prototypes; and small, medium and high volumes.

8. Any sheet material that can be cold formed is a candidate for metal spinning including -

cold rolled steel, hot rolled steel, aluminum, stainless steel, brass, copper and exotic

metals such as titanium, inconel, and hastealloy.

58

Tooling for spinning is relatively inexpensive and simple to employ, translating to a short lead

time for parts. Tight tolerancing requirements may require secondary operations, but the

advent of automated spinning machines allows more precise forming than with manual

spinning machines, with less reliance on operator skill.

Sheetmetal Forming - Peen Forming :

Shot peen forming is a dieless process performed at room temperature, whereby small round

steel shot impact the surface of the work piece. Every piece of shot acts as a tiny peening

hammer, producing elastic stretching of the upper surface and local plastic deformation that

manifests itself as a residual compressive stress. The combination of elastic stretching and

compressive stress generation causes the material to develop a compound, convex curvature

on the peened side.

The shot peen forming process is ideal for forming large panel shapes where the bend radii

are reasonably large and without abrupt changes in contour. Shot peen forming is best suited

for forming curvatures where radii are within the metal's elastic range. Although no dies are

required for shot peen forming, for severe forming applications, stress peen fixtures are

sometimes used. Shot peen forming is effective on all metals, even honeycomb skins and ISO

grid panels.

Shot peen forming is often more effective in developing curvatures than rolling, stretching or

twisting of metal. Saddle-back shapes also are achievable. Because it is a dieless process,

shot peen forming reduces material allowance from trimming and eliminates costly

development and manufacturing time to fabricate hard dies. The shot peen forming process

also is flexible to design changes, which may occur after initial design. Metal Improvement

Company can make curvature changes by adjusting the shot peen forming process.

Parts formed by shot peen forming exhibit increased resistance to flexural bending fatigue.

Unlike most other forming methods, all surface stresses generated by shot peen forming are of

a compressive nature. Although shot peen formed pieces usually require shot peening on one

side only, the result causes both sides to have compressive stress. These compressive

stresses serve to inhibit stress corrosion cracking and to improve fatigue resistance. Some

work pieces should be shot peened all over prior to or after shot peen forming to further

improve fatigue and stress corrosion cracking resistance.

59

Shot peening of parts that have been cold formed by other processes overcomes the harmful

surface tensile stresses set up by these other forming processes.

Sheetmetal Forming - Press braking / Brake forming :

Brake forming is one of the oldest mechanical metal deformation process. During the process,

a piece of sheet metal is formed along a straight axis. This may be accomplished by a "V"-

shaped, "U"-shaped, or channel-shaped punch and die set.

Although press braking appears a simple concept, maintaining accuracy can often be quite

difficult. Precision bending is a function of both the press, the tooling, and the work-piece

material. Material properties such as yield strength, ductility, hardness, and the condition of the

material, all affect the amount of spring back of the material.

The most common industrial press braking process is called air bending. Air bending relies

upon three point bending. The angle of the bend is dictated by how far the punch tip

penetrates the "V" cavity. The greater the penetration of the punch tip the greater the angle

achieved.

The main benefit of air bending is that it uses much less force than other methods to achieve a

90° bend due to the leverage effect.

Characteristic of the metal brake forming process include:

Its ability to form ductile materials

Its use in both low and medium production run applications,

The need for minimal tooling,

Its suitability to produce smaller parts,

Its output of long workpieces using a "V", "U", channel, or other special punch and dies.

Brake forming can commonly form metals up to 10" thick and some machinery will form pieces

as long as 20 feet. Materials commonly used in the brake forming process include:

Aluminum

Brass

60

Cold rolled carbon steel

Hot rolled carbon steel

Stainless steel

Tool materials for brake forming :

1. Low-carbon steel is used for low production runs, die and punch base material, and soft

to medium hardness materials.

2. Tool steel is used for medium to high production, for medium to server bending, and for

medium to strong materials.

3. Carbide tools are used for high production runs on materials that required severe

bending, and are usually designed as tool inserts.

4. Hardwood tools are used for very low production runs, for very simple bending

applications, and are normally used on very soft materials.

Sheetmetal Forming - Shearing :

Shearing is a metal fabricating process used to cut straight lines on flat metal stock. During

the shearing process, an upper blade and a lower blade are forced past each other with the

space between them determined by a required offset. Normally, one of the blades remains

stationary.

Characteristics of the shearing process include:

Its ability to make straight-line cuts on flat sheet stock

Metal placement between an upper and lower shear blades

Its trademark production of burred and slightly deformed metal edges

Its ability to cut relatively small lengths of material at any time since the shearing blades

can be mounted at an angle to reduce the necessary shearing force required.

Limitations :

The use of shears in sheet metal production has diminished through the use of cut-off tooling

in CNC punching and the use of shake-out technology to separate parts from the sheet

61

skeleton. Shears are used mainly for rough shearing sub-sizes of sheets for CNC presses or

strips for stamping press dies.

In those cases where finished dimensions are sheared, the thickness of the material and the

X-Y dimension of the part dictate the degree of precision which is feasible economically.

Thicker material and greater X-Y dimensions require greater tolerances.

Process :

Typically, the upper shear blade is mounted at an angle to the lower blade that is normally

mounted horizontally. The shearing process performs only fundamental straight-line cutting but

any geometrical shape with a straight line cut can usually be produced on a shear.

Metal shearing can be performed on sheet, strip, bar, plate, and even angle stock. Bar and

angle materials can only be cut to length. However, many shapes can be produced by

shearing sheet and plate.

Materials that are commonly sheared include:

1. Aluminum

2. Brass

3. Bronze

4. Mild steel

5. Stainless steel

Sheetmetal Forming - Stretch Forming :

Stretch forming is a very accurate and precise method for forming metal shapes, economically.

The level of precision is so high that even intricate multi-components and snap-together

curtainwall components can be formed without loss of section properties or original design

function. Stretch forming capabilities include portions of circles, ellipses, parabolas and arched

shapes. These shapes can be formed with straight leg sections at one or both ends of the

curve. This eliminates several conventional fabrication steps and welding.

The stretch forming process involves stretch forming a metal piece over a male stretch form

block (STFB) using a pneumatic and hydraulic stretch press. Stretch forming is widely used in

producing automotive body panels. Unlike deep drawing, the sheet is gripped by a blank

62

holder to prevent it from being drawn into the die. It is important that the sheet can deform by

elongation and uniform thinning.

The variety of shapes and cross sections that can be stretch formed is almost unlimited.

Window systems, skylights, store fronts, signs, flashings, curtainwalls, walkway enclosures,

and hand railings can be accurately and precisely formed to the desired profiles. Close and

consistent tolerances, no surface marring, no distortion or ripples, and no surface

misalignment of complex profiles are important benefits inherent in stretch forming. A smooth

and even surface results from the stretch forming process.

This process is ideally suited for the manufacture of large parts made from aluminum, but does

just as well with stainless steel and commercially pure titanium. It is quick, efficient, and has a

high degree of repeatability.

Sheetmetal Forming - Superplastic Forming :

The superplastic forming (SPF) operation is based on the fact that some alloys can be slowly

stretched well beyond their normal limitations at elevated temperatures. The higher

temperatures mean the flow stress of the sheet material is much lower than at normal temps.

This characteristic allows very deep forming methods to be used that would normally rupture

parts. Superplastic alloys can be stretched at higher temperatures by several times of their

initial length without breaking. Superplastic forming can produce complex shapes with

stiffening rims and other structural features as well.

The process begins by placing the sheet to be formed in an appropriate SPF die, which can

have a simple to complex geometry, representative of the final part to be produced. The sheet

and tooling are heated and then a gas pressure is applied, which plastically deforms the sheet

into the shape of the die cavity.

Process Advantages :

63

Reduced weight for high fuel efficiency

Improved structural performance

Increased metal formability and part complexity

Near net shape forming of complex shapes reduces part count

Cost/weight savings

Low-cost tooling

Low environmental impacts - non-lead die lubes, low noise

Materials used :

1. Titanium alloys

2. Aluminum alloys

3. Bismuth-tin alloys

4. Zinc-aluminum alloys

5. Stainless steel

6. Aluminum-lithium alloys

Sheetmetal Forming - Tube Bending :

Methods of Bending :

1.Mandrel Bending :

There are various methods available to bend tubing. One method is Mandrel Bending (Rotary

Draw where a mandrel supports the inside of the tube to avoid collapsing). This produces

round, smooth, and wrinkle free bends with centerline radius between 1 and 5 times the

outside diameter.

2. CNC Mandrel Bending :

Computer Numeric Controlled (CNC) Mandrel benders give the capabilities to bend high

volume multiple bend parts in much less time than it would take for a skilled operator to bend

the part on a manual hydraulic bender. The speed of these machines makes them very

valuable assets.

3. Roll Bending :

64

We can roll bend tubing in sizes up to 2 1/2" in diameter. Roll bending allows us to form any

radius larger than 4 times the diameter. Roll bending differs from Mandrel Bending in that the

bend is not supported by an inside mandrel. The process is simple to set up, and allows for an

infinite amount of bend radii, without re-tooling.

POWDER METALLURGY :

Powder metallurgy, or P/M, is a highly developed method of manufacturing reliable ferrous and

nonferrous parts. Made by mixing elemental or alloy powders and compacting the mixture in a

die, the resultant shapes are then sintered or heated in a controlled-atmosphere furnace to

metallurgically bond the particles. Basically a 'chipless' metalworking process, P/M typically

uses more than 97% of the starting raw material in the finished part. Because of this, P/M is an

energy and materials conserving process.

The P/M process is cost effective in producing simple or complex parts at or very close to final

dimensions at production rates that can range from a few hundred to several thousand parts

per hour. As a result, only minor, if any, machining is required. P/M parts also can be sized for

closer dimensional control that essentially eliminates secondary fabrication steps and/or

coined for both higher density and strength.

Manufacturing: Machining :

Machine Tools are stationary power-driven machines used to shape or form solid materials,

especially metals. The shaping is accomplished by removing material from a workpiece or by

pressing it into the desired shape. Machine tools form the basis of modern industry and are

used either directly or indirectly in the manufacture of machine and tool parts.

  Machine tools may be classified under three main categories:

1. Conventional chip-making machine tools.

2. Presses.

3. Unconventional machine tools.

Conventional chip-making tools shape the workpiece by cutting away the unwanted portion in

the form of chips. Presses employ a number of different shaping processes, including

65

shearing, pressing, or drawing (elongating). Unconventional machine tools employ light,

electrical, chemical, and sonic energy; superheated gases; and high-energy particle beams to

shape the exotic materials and alloys that have been developed to meet the needs of modern

technology.

Conventional Machine Tools :

Lathe

Shaper

Planer

Milling Machine

Drilling & Boring

Grinder

Saw

Press

Cutting Tools

Lathe :

A lathe, the oldest and most common type of turning machine, holds and rotates metal or wood

while a cutting tool shapes the material. The tool may be moved parallel to or across the

direction of rotation to form parts that have a cylindrical or conical shape or to cut threads. With

special attachments, a lathe may also be used to produce flat surfaces, as a milling machine

does, or it may drill or bore holes in the workpiece.

Shaper :

The shaper is used primarily to produce flat surfaces. The tool slides against the stationary

workpiece and cuts on one stroke, returns to its starting position, and then cuts on the next

stroke after a slight lateral displacement. In general, the shaper can produce almost any

surface composed of straight-line elements. It uses a single-point tool and is relatively slow,

because it depends on reciprocating (alternating forward and return) strokes. For this reason,

the shaper is seldom found on a production line. It is, however, valuable for tool and die rooms

and for job shops where flexibility is essential and relative slowness is unimportant because

few identical pieces are being made.

Planer :66

The planer is the largest of the reciprocating machine tools. Unlike the shaper,

which moves a tool past a fixed workpiece, the planer moves the workpiece past

a fixed tool. After each reciprocating cycle, the workpiece is advanced laterally to

expose a new section to the tool. Like the shaper, the planer is intended to

produce vertical, horizontal, or diagonal cuts. It is also possible to mount several

tools at one time in any or all tool holders of a planer to execute multiple

simultaneous cuts.

Milling Machines - Machining Centers :

In a milling machine, a workpiece is fed against a circular device with a series of cutting edges

on its circumference. The workpiece is held on a table that controls the feed against the cutter.

The table conventionally had three possible movements: longitudinal, horizontal, and vertical.

Modern milling machines, such as routers, use robotic arms and can be up to 9 - axis.

Milling machines are the most versatile of all machine tools. Flat or contoured surfaces may be

machined with excellent finish and accuracy. Angles, slots, gear teeth, and recess cuts can be

made by using various cutters.

Types of CNC Machining Centers :

1. Vertical

2. Horizontal

3. Bed

4. Knee Mills

Drilling and Boring Machines :

Hole-making machine tools are used to drill a hole where none previously existed; to alter a

hole in accordance with some specification (by boring or reaming to enlarge it, or by tapping to

cut threads for a screw); or to lap or hone a hole to create an accurate size or a smooth finish.

Drilling machines vary in size and function, ranging from portable drills to radial drilling

machines, multispindle units, automatic production machines, and deep-hole-drilling machines.

67

Boring is a process that enlarges holes previously drilled, usually with a rotating single-point

cutter held on a boring bar and fed against a stationary workpiece. Boring machines include jig

borers and vertical and horizontal boring mills.

Grinder :

Grinding is the removal of metal by a rotating abrasive wheel; the action is similar to that of a

milling cutter. The wheel is composed of many small grains of abrasive, bonded together, with

each grain acting as a miniature cutting tool.

The process produces extremely smooth and accurate finishes. Because only a small amount

of material is removed at each pass of the wheel, grinding machines require fine wheel

regulation. The pressure of the wheel against the workpiece can be made very slight, so that

grinding can be carried out on fragile materials that cannot be machined by other conventional

devices.

Saws :

Commonly used power-driven saws are classified into three general types, according to the

kind of motion used in the cutting action: reciprocating, circular, and band-sawing machines.

They generally consist of a bed or frame, a vise for clamping the workpiece, a feed

mechanism, and the saw blade.

Press :

Presses shape workpieces without cutting away material, that is, without making chips. A

press consists of a frame supporting a stationary bed, a ram, a power source, and a

mechanism that moves the ram in line with or at right angles to the bed. Presses are equipped

with dies and punches designed for such operations as forming, punching, and shearing.

Presses are capable of rapid production because the operation time is that needed for only

one stroke of the ram.

Cutting Tools :

Because cutting processes involve high local stresses, frictions, and considerable heat

generation, cutting-tool material must combine strength, toughness, hardness, and wear

resistance at elevated temperatures. These requirements are met in varying degrees by such

68

cutting-tool materials as carbon steels (steel containing 1 to 1.2 percent carbon), high-speed

steels (iron alloys containing tungsten, chromium, vanadium, and carbon), tungsten carbide,

and diamonds and by such recently developed materials as ceramic, carbide ceramic, and

aluminum oxide.

In many cutting operations fluids are used to cool and lubricate. Cooling increases tool life and

helps to stabilize the size of the finished part. Lubrication reduces friction, thus decreasing the

heat generated and the power required for a given cut. Cutting fluids include water-based

solutions, chemically inactive oils, and synthetic fluids.

MANUFACTURING: NON-TRADITIONAL MACHINING :

Introduction :

When people hear the word "machining" they generally think of machines that utilize

mechanical energy to remove material from the work piece. Milling machines, saws and lathes

are some of the most common machines using mechanical energy to remove material. The

tool makes contact with the work piece and the resulting shear causes the material to flow over

the tool. All traditional forms of metal cutting use shear as the primary method of material

removal. However, there are other sources of energy at work.

Chemical energy has a significant effect on every turning operation. Think of the effect that

different kinds of coolants have on the cutting action of a tool. Some amount of chemical

energy is being used in most metal cutting operations. All forms of manufacturing use more

than one type of energy.

The category of nontraditional machining covers a broad range of technologies, including

some that are used on a large scale, and others that are only used in unique or proprietary

applications. These machining methods generally have higher energy requirements and slower

throughputs than traditional machining, but have been developed for applications where

traditional machining methods were impractical, incapable, or uneconomical.

69

Nontraditional machining can be thought of as operations that do not use shear as their

primary source of energy. For example, abrasive water jet operations use mechanical energy,

but material is removed by erosion.

Non traditional machining methods are typically divided into the following categories:

1. Mechanical - Ultrasonic Machining, Rotary Ultrasonic Machining, Ultrasonically

Assisted Machining

2. Electrical - Electrochemical Discharge Grinding, Electrochemical Grinding,

Electrochemical Honing,Hone-Forming, Electrochemical Machining, Electrochemical

Turning, Shaped Tube Electrolytic Machining, Electro-Stream

3. Thermal - Electron Beam Machining, Electrical Discharge Machining, Electrical

Discharge Wire Cutting, Electrical Discharge Grinding, Laser Beam Machining.

4. Chemical - Chemical Milling, Photochemical Machining

These machine tools were developed primarily to shape the ultrahard alloys used in heavy

industry and in aerospace applications and to shape and etch the ultrathin materials used in

such electronic devices as microprocessors.

Abrasive Flow Machining (AFM) :

Abrasive Flow Machine (AFM) is a nontraditional machining process that is used to deburr,

polish, radius, and remove recast layers of critical components in aerospace, automotive,

electronic and die-making industries. Extrude Hone patented the Abrasive Flow Machining

(AFM) process in the 1960's as a method to deburr, polish and radius difficult-to-reach

surfaces. AFM operates by flowing an abrasive laden viscoelastic compound through a

restrictive passage formed by a workpart/tooling combination. Inaccessible areas and complex

contours both internal and external can be finished economically and productively.

The workpiece is hydraulically clamped between two vertically opposing media cylinders. The

AFM process starts with the lower cylinder filled with the proper volume of the abrasive laden

media. The media is then extruded through the work-piece and into the upper media cylinder.

The procedure is reversed as the media is fed back through the part and into the lower

cylinder. This combination of one upstroke and one downstroke constitutes a complete AFM

cycle.

70

AFM can work within areas that are inaccessible to conventional manual finishing methods.

Unlike conventional processes, AFM can be fully automated to provide a much more cost-

effective method of finishing extrusion dies and aircraft and aerospace components.

AFM is used in a wide range of finishing operations. It can simultaneously process multiple

parts or many areas of a single workpiece. Inaccessible areas and complex internal passages

can be finished economically and effectively. Automatic AFM systems are capable of handling

thousands of parts per day, greatly reducing labor costs by eliminating tedious handwork. By

understanding and controlling the process parameters, AFM can be applied to an impressive

range of finishing operations that provide uniform, repeatable, predictable results. Anywhere

that the media can be forced to flow represents a practical application.

Chemical Machining :

Chemical Machining aides in the manufacture of light gauge metal parts. The photo etching

process (also called chemical etching and chemical milling) allows people to produce intricate

metal components with close tolerances that are impossible to duplicate by other production

methods. It is also known as chemical milling.

  Applications :

Chemical Machining is utilized in the manufacturing of encoders, masks, filters, lead frames,

flat springs, strain gauges, laminations, chip carriers, step covers, fuel cell plates, heat sinks,

shutter blades, electron grids, fluidic circuit plates, reticles, drive bands, haptics, and shims.

Chemical Milling :

Chemical Milling aides in the manufacture of light gauge metal parts. The photo etching

process (also called chemical etching and chemical milling) allows people to produce intricate

metal components with close tolerances that are impossible to duplicate by other production

methods. It is also known as chemical machining.

  Applications :

Chemical Milling is utilized in the manufacturing of encoders, masks, filters, lead frames, flat

springs, strain gauges, laminations, chip carriers, step covers, fuel cell plates, heat sinks,

shutter blades, electron grids, fluidic circuit plates, reticles, drive bands, haptics, and shims.

71

Electrical Discharge Grinding - EDG :

A process which is basically the same as EDM

Electrical Discharge Machining (EDM) :

Electrical Discharge Machining (EDM), also known as spark erosion, employs electrical energy

to remove metal from the workpiece without touching it. A pulsating high- frequency electric

current is applied between the tool point and the workpiece, causing sparks to jump the gap

and vaporize small areas of the workpiece. Because no cutting forces are involved, light,

delicate operations can be performed on thin workpieces. EDM can produce shapes

unobtainable by any conventional machining process.

RAM EDM :

A process using a shaped electrode made from graphite or copper. The electrode is separated

by a nonconductive liquid and maintained at a close distance (about 0.001"). A high DC

voltage is pulsed to the electrode and jumps to the conductive workpiece. The resulting sparks

erode the workpiece and generate a cavity in the reverse shape of the electrode, or a through

hole in the case of a plain electrode. Permits machining shapes to tight accuracies without the

internal stresses conventional machining often generates. Also known as “die-sinker” or

“sinker”electrical-dischargemachining.

WireEDM :

A process similar to sinker electrical-discharge machining except a small-diameter copper or

brass wire is used as a traveling electrode. The process is usually used in conjunction with a

CNC and will only work when a part is to be cut completely through. A common analogy is to

describe wire electrical-discharge machining as an ultraprecise, electrical, contour-sawing

operation.

Applications:

EDM permits machining shapes to tight accuracies without the internal stresses conventional

machining often generates. Useful in diemaking.

Electrochemical Discharge Grinding (ECDG) :72

Electrochemical-discharge grinding is a combination of electrochemical grinding and electrical-

discharge machining. The process is very similar to conventional EDM except a grinding-wheel

type of electrode is used. Material is removed by both processes. Like any EDM process, the

workpiece and the grinding wheel never come into contact.

Electrochemical Grinding (ECG) :

Electrochemical grinding combines electrical and chemical energy for metal removal with an

EDM finish. It is a non-abrasive process and, therefore, produces precise cuts that are free of

heat, stress, burrs and mechanical distortions. It is avariation on electrochemical machining

that uses a conductive, rotating abrasive wheel. The chemical solution is forced between the

wheel and the workpiece. The shape of the wheel determines the final shape.

Electrochemical Honing - ECH :

A process similar to electrochemical grinding involving the use of honing stones rather than a

grinding wheel.

Electrochemical machining (ECM) :

Electrochemical machining (ECM) also uses electrical energy to remove material. An

electrolytic cell is created in an electrolyte medium, with the tool as the cathode and the

workpiece as the anode. A high-amperage, low-voltage current is used to dissolve the metal

and to remove it from the workpiece, which must be electrically conductive. ECM is essentially

a deplating process that utilizes the principles of electrolysis. The ECM tool is positioned very

close to the workpiece and a low voltage, high amperage DC current is passed between the

two via an electrolyte. Material is removed from the workpiece and the flowing electrolyte

solution washes the ions away. These ions form metal hydroxides which are removed from the

electrolyte solution by centrifugal separation. Both the electrolyte and the metal sludge are

then recycled.

Unlike traditional cutting methods, workpiece hardness is not a factor, making ECM suitable for

difficult-to-machine materials. Takes such forms as electrochemical grinding, electrochemical

honing and electrochemical turning.

Electrochemical deburring is another variation on electrochemical machining designed to

remove burrs and impart small radii to corners. The process normally uses a specially shaped 73

electrode to carefully control the process to a specific area. The process will work on material

regardless of hardness.

 Advantages of Electrochemical Machining (ECM) :

1. The components are not subject to either thermal or mechanical stress.

2. There is no tool wear during Electrochemical machining.

3. Non-rigid and open work pieces can be machined easily as there is no contact between

the tool and workpiece.

4. Complex geometrical shapes can be machined repeatedly and accurately

5. Electrochemical machining is a time saving process when compared with conventional

machining

6. During drilling, deep holes can be made or several holes at once.

7. ECM deburring can debur difficult to access areas of parts.

8. Fragile parts which cannot take more loads and also brittle material which tend to

develop cracks during machining can be machined easily through Electrochemical

machining

9. Surface finishes of 25 µ in. can be achieved during Electrochemical machining

Electrochemical Turning (ECT) :

A variation of Electrochemical Machining.

Electron-beam Machining – EBM :

In electron-beam machining (EBM), electrons are accelerated to a velocity nearly three-fourths

that of light (~200,000 km/sec). The process is performed in a vacuum chamber to reduce the

scattering of electrons by gas molecules in the atmosphere. The electron beam is aimed using

magnets to deflect the stream of electrons and is focused using an electromagnetic lens. The

stream of electrons is directed against a precisely limited area of the workpiece; on impact, the

kinetic energy of the electrons is converted into thermal energy that melts and vaporizes the

material to be removed, forming holes or cuts.

Typical applications are annealing, welding, and metal removal. A hole in a sheet 1.25 mm

thick up to 125 micro m diameter can be cut almost instantly with a taper of 2 to 4 degrees.

74

EBM equipment is commonly used by the electronics industry to aid in the etching of circuits in

microprocessors.

Ion Beam Milling - (IBM) :

In simple terms ion beam milling can be viewed as an atomic sand blaster. The grains of sand

are actually submicron ion particles accelerated to bombard the surface of the work mounted

on a rotating table inside a vacuum chamber. The work is typically a wafer, substrate or

element that requires material removal by atomic sandblasting or dry etching.

A selectively applied protectant, photo sensitive resist, is applied to the work element prior to

introduction into the ion miller. The resist protects the underlying material during the etching

process which may be up to eight hours or longer, depending upon the amount to be removed

and the etch rate of the materials. Everything that is exposed to the collimated ion beam (may

be 15" in diameter in some equipment) etches during the process cycle, even the resist.

In most micromachining applications the desired material to be removed etches at a rate 3 to

10 times faster than the resist protectant thus preserving the material and features underneath

the resist.

Applications:

Ion Beam Milling is used in fabricating electronic and mechanical elements for a wide variety of

commercial, industrial, military and satellite applications including custom film circuits for RF

and Microwave circuits.

Laser-beam machining -- LBM :

Laser-beam machining (LBM) is accomplished by precisely manipulating a beam of coherent

light to vaporize unwanted material. LBM is particularly suited to making accurately placed

holes. It can be used to perform precision micromachining on all microelectronic substrates

such as ceramic, silicon, diamond, and graphite. Examples of microelectronic micromachining

75

include cutting, scribing & drilling all substrates, trimming any hybrid resistors, patterning

displays of glass or plastic and trace cutting on semiconductor wafers and chips.

Applications:

The LBM process can make holes in refractory metals and ceramics and in very thin materials

without warping the workpiece. The laser can scribe, drill, mark, and cut thin metals and

ceramics, trim resistors, and process plastics, silicon, diamond, and graphite with tolerances to

one micron.

Laser Cutting:

Laser cutting is the process of vaporizing material in a very small, well-defined area. The laser

itself is a single point cutting source with a very small point, (0.001" to 0.020" / 0.025mm to

0.5mm) allowing for very small cut widths.

The advantages of cutting with a laser make it a preferred choice over conventional cutting

methods.

Laser Cutting Advantages

1. There is almost no limit to the cutting path; the point can move in any direction unlike

other processes that use knives or saws.

2. The process is forceless allowing very fragile or flimsy parts to be laser cut with no

support.

3. Since the laser beam exerts no force on the part and is a very small spot, the

technology is well suited to fabricating high accuracy parts, especially flexible materials.

The part keeps its original shape from start to finish.

4. The laser beam is always sharp and can cut very hard or abrasive materials.

5. Sticky materials that would otherwise gum up a blade are not an obstacle for a laser.

6. Lasers cut at high speeds. The speed at which the material can be processed is limited

only by the power available from the laser.

7. Cutting with lasers is a very cost effective process with low operating and maintenance

costs and maximum flexibility.

76

Laser Drilling :

Laser drilling is the process of repeatedly pulsing focused laser energy at a specific material.

The laser beam consistently drills holes down to 0.004" with little or no debris. Holes with

length-to-diameter ratios of up to 50 can be drilled with reliable, high quality results.

With lasers it is possible to drill in very difficult locations using mirrors to bend the beam. Laser

drilling at very high rates, 1000 pulses per second or greater, is also possible.

Laser Drilling Advantages --

1. Using laser system software, the operator instantly can control hole shape and size to

produce round, oval or rectangular holes, or any shape imaginable. This eliminates

downtime due to tool changes.

2. Very small holes can be laser drilled in production. A focused spot can be as small as

0.1mm (0.004") in diameter.

3. Since the tool is a beam of light, the tool never needs to be replaced eliminating

downtime because of punch breakage.

Photo Chemical Machining - (PCM) :

Photochemical Machining - (PCM) components are produced by the photo-etching technique

using a wide array of metal and alloys. This technique avoids burrs, no mechanical stresses

are built into the parts and the properties of the metal worked are not affected. Hardened and

tempered metals are machined as easily as regular metals. The technique is ideal for

machining thin metals and foils. Parts with very precise and intricate designs can be produced

without difficulty. The photo chemical machining/milling processes can precisely etch lines and

spaces on all types of metals (alloys: kovar, nickel, brass, beryllium, copper, stainless steel,

aluminum, and others) with detailed accuracies. This is used for creating specialty flex circuits,

plus in engineering of other rigid technologies. This results in a burr free part with very close

tolerances.

Applications:

77

The technique is ideal for machining thin metals and foils. Parts with very precise and intricate

designs can be produced without difficulty.

 

Plasma Arc Machining :

Plasma-arc machining (PAM) employs a high-velocity jet of high-temperature gas to melt and

displace material in its path. Called PAM, this is a method of cutting metal with a plasma-arc,

or tungsten inert-gas-arc, torch. The torch produces a high velocity jet of high-temperature

ionized gas called plasma that cuts by melting and removing material from the workpiece.

Temperatures in the plasma zone range from 20,000° to 50,000° F (11,000° to 28,000° C).

It is used as an alternative to oxyfuel-gas cutting, employing an electric arc at very high

temperatures to melt and vaporize the metal.

Applications:The materials cut by PAM are generally those that are difficult to cut by any

other means, such as stainless steels and aluminum alloys. It has an accuracy of about 0.008".

Ultrasonic Machining :

Ultrasonic machining (USM) is a mechanical material removal process used to erode holes

and cavities in hard or brittle workpieces by using shaped tools, high frequency mechanical

motion, and an abrasive slurry. . A relatively soft tool is shaped as desired and vibrated against

the workpiece while a mixture of fine abrasive and water flows between them. The friction of

the abrasive particles gradually cuts the workpiece.

Materials such as hardened steel, carbides, rubies, quartz, diamonds, and glass can easily be

machined by USM. Ultrasonic machining is able to effectively machine all materials harder

than HRc 40, whether or not the material is an electrical conductor or an insulator

Waterjet Machining :

78

A water jet cutter is a tool capable of slicing into metal or other materials using a jet of water at

high velocity and pressure. It is often used during fabrication or manufacture of parts for

machinery and other devices. It has found applications in a diverse number of industries from

mining to aerospace where it is used for operations such as cutting, shaping, carving, reaming.

The cutter is commonly connected to a high-pressure water pump (a local water main does not

supply sufficient pressure) where the water is then ejected out of the nozzle, cutting through

the material by bombarding it with the stream of high-speed water. Additives in the form of

suspended grit or other abrasives, such as sand and silicon carbide, can assist in this process.

Because the nature of the cutting stream can be easily modified, water jets can be used to cut

materials as diverse as fish sticks and titanium.

Beyond cost cutting, the waterjet process is recognized as the most versatile and fastest

growing process in the world (per Frost & Sullivan and the Market Intelligence Research

Corporation) . Waterjets are used in high production applications across the globe. They

compliment other technologies such as milling, laser, EDM, plasma and routers. No noxious

gases or liquids are used in waterjet cutting, and waterjets do not create hazardous materials

or vapors. No heat effected zones or mechanical stresses are left on a waterjet cut surface. It

is truly a versatile, productive, cold cutting process.

The most important benefit of the water jet cutter is its ability to cut material without interfering

with the materials inherent structure as there is no "heat affected zone" or HAZ. This allows

metals to be cut without harming their intrinsic properties.

The waterjet has shown that it can do things that other technologies simply cannot. From

cutting whisper thin details in stone, glass and metals; to rapid hole drilling of titanium; to

cutting of food, to the killing of pathogens in beverages and dips, the waterjet has proven itself

unique

History of Waterjets :

WaterJet Cutting is a technology that has mainly evolved in the past two decades and it has

created ripples within the manufacturing industry during this time, due to its versatility and

flexibility in usage. Many types of water jets exist today, including plain water jets, abrasive

water jets, percussive water jets, cavitation jets and hybrid jets.

79

Dr. Norman Franz is regarded as the father of the waterjet. He was the first person who

studied the use of ultrahigh-pressure (UHP) water as a cutting tool. The term UHP is defined

as more than 30,000 pounds per square inch (psi). Dr. Franz, a forestry engineer, wanted to

find new ways to slice thick trees into lumber. In the 1950's, Franz first dropped heavy weights

onto columns of water, forcing that water through a tiny orifice. He obtained short bursts of

very high pressures (often many times higher than are currently in use), and was able to cut

wood and other materials. His later studies involved more continuous streams of water, but he

found it difficult to obtain high pressures continually. Also, component life was measured in

minutes, not weeks or months as it is today.

Dr. Franz never made a production lumber cutter. Ironically, today wood cutting is a very minor

application for UHP technology. But Franz proved that a focused beam of water at very high

velocity had enormous cutting power — a power that could be utilized in applications beyond

Dr. Franz's wildest dreams.

Only in the 1970s did the usage of water for cutting start advancing noticably. Today the water

jet is unparalelled in many aspects of cutting and has changed the way products are

manufactured.

AbrasiveJet Machining :

Abrasive waterjet cutting systems (abrasivejet) use a combination of water and garnet to cut

through materials considered "unmachineable" by conventional cutting methods. Using small

amounts of water while eliminating the friction caused by tool-to-part contact, abrasivejet

cutting avoids thermal damage or heat affected zones (HAZ) which can adversely affect

metallurgic properties in materials being cut. The ability to pierce through material also

eliminates the need and cost of drilling starter holes. Because abrasivejet cuts with a narrow

kerf, parts can be tightly nested thus maximizing material usage.

Abrasive waterjet can cut through materials ranging from 1/16 inch (1.6 mm) to 12 inches (305

mm) thick with an accuracy of ± 0.005 inch (0.13 mm). The typical orifice diameter for an

abrasivejet nozzle is 0.010" to 0.014" (0.25 mm to 0.35 mm). The orifice jewel may be ruby,

sapphire or diamond, with sapphire being the most common. Diamond is recognized to last

longer than the other two, but most operators find that it is not worth the additional cost. A

typical high-quality jewel assembly consisting of a sapphire orifice and a precision stainless

steel mount with integral abrasive feed chamber costs about $50. A similar assembly using a 80

diamond orifice would cost several hundred dollars and does not provide a reasonable

payback.

Ruby and sapphire are very similar in their life expectancy, neither having a distinct advantage

over the other. In theory, a jewel orifice should operate reliably until dissolved solids and

minerals in the water build up next to the water passage. The jewel does not really fail, but it

no longer produces a straight, smooth stream of water because of scale build-up.

In reality, however, many jewels fail when struck by dirt or abrasive particles that have

managed to get upstream of the jet during nozzle changes or overhauls. This causes the jewel

to crack or pit, substantially altering water flow through the jewel. Once water flow through the

jewel is disturbed, the cut quality will be poor and the mixing tube life will be shortened

dramatically. A cracked $50 jewel assembly can quickly ruin a $150 ceramic mixing tube.

Many operators change the jewel orifice as a matter of course whenever they overhaul a

nozzle.

Abrasive waterjet is excellent for the cutting of complex shapes, and in fragile materials such

as glass, the high failure rate due to breakage and chipping of corners during conventional

processing is virtually eliminated. Whatever your industrial need, abrasivejet is an accurate,

flexible, and efficient cutting system.

Materials :

Abrasivejet cutting is used in the cutting of materials as diverse as:

Titanium

Brass

Aluminum

Stone

Inconel

AnySteel

Glass

Composites

History :

81

In 1979, Dr. Mohamed Hashish working at Flow Research, began researching methods to

increase the cutting power of the waterjet so it could cut metals, and other hard materials. Dr.

Hashish, regarded as the father of the abrasive-waterjet, invented the process of adding

abrasives to the plain waterjet. He used garnet abrasives, a material commonly used on

sandpaper. With this method, the waterjet (containing abrasives) could cut virtually any

material.

In 1980, abrasive-waterjets were used for the first time to cut steel, glass, and concrete. In

1983, the world's first commercial abrasive waterjet cutting system was sold for cutting

automotive glass. The first adopters of the technology were primarily in the aviation and space

industries which found the waterjet a perfect tool for cutting high strength materials such as

Inconel, stainless steel, and titanium as well as high strength light-weight composites such as

carbon fiber composites used on military aircraft and now used on commercial airplanes. Since

then, abrasive waterjets have been introduced into many other industries such as job-shop,

stone, tile, glass, jet engine, construction, nuclear, and shipyard, to name a few.

MANUFACTURING: PLASTIC MOLDING & FORMING:

Blow Molding :

82

Blow Molding is a highly developed molding technology developed back in the late 1800's to

produce celluloid baby rattles. It is best suited for basically hollow parts (such as plastic

bottles) with uniform wall thicknesses, where the outside shape is a major consideration.

The first polyethylene bottle was manufactured using the blow molding process in December of

1942. This was the real beginning of a huge industry which currently produces 30 to 40 billion

plastic bottles per year in the U.S. alone.

The Basic Process :

1. A thermoplastic resin is heated to a molten state

2. It is then extruded through a die head to form a hollow tube called a parison.

3. The parison is dropped between two mold halves, which close around it.

4. The parison is inflated.

5. The plastic solidifies as it is cooled inside the mold.

6. The mold opens and the finished component is removed.

Variations :

There are basically four types of blow molding used in the production of plastic bottles, jugs

and jars. These four types are:

83

1. Extrusion blow molding

2. Injection blow molding

3. Stretch blow molding

4. Reheat and blow molding.

Extrusion blow molding is perhaps the simplest type of blow molding. A hot tube of plastic

material is dropped from an extruder and captured in a water cooled mold. Once the molds are

closed, air is injected through the top or the neck of the container; just as if one were blowing

up a balloon. When the hot plastic material is blown up and touches the walls of the mold the

material "freezes" and the container now maintains its rigid shape.

Injection blow molding is part injection molding and part blow molding. With injection blow

molding, the hot plastic material is first injected into a cavity where it encircles the blow stem,

which is used to create the neck and establish the gram weight. The injected material is then

carried to the next station on the machine, where it is blown up into the finished container as in

the extrusion blow molding process above. Injection blow molding is generally suitable for

smaller containers and absolutely no handleware.

Extrusion blow molding allows for a wide variety of container shapes, sizes and neck openings,

as well as the production of handleware. Extrusion blown containers can also have their gram

weights adjusted through an extremely wide range, whereas injection blown containers usually

have a set gram weight which cannot be changed unless a whole new set of blow stems are

built. Extrusion blow molds are generally much less expensive than injection blow molds and

can be produced in a much shorter period of time.

Stretch blow molding is perhaps best known for producing P.E.T. bottles commonly used for

water, juice and a variety of other products. There are two processes for stretch blow molded

P.E.T. containers. In one process, the machinery involved injection molds a preform, which is

then transferred within the machine to another station where it is blown and then ejected from

the machine. This type of machinery is generally called injection stretch blow molding (ISBM)

and usually requires large runs to justify the very large expense for the injection molds to

create the preform and then the blow molds to finish the blowing of the container. This process

is used for extremely high volume (multi-million) runs of items such as wide mouth peanut

butter jars, narrow mouth water bottles, liquor bottles etc.

84

The reheat and blow molding process (RHB) is a type of stretch blow process. In this

process, a preform is injection molded by an outside vendor. There are a number of

companies who produce these "stock" preforms on a commercial basis. Factories buy the

preforms and put them into a relatively simple machine which reheats it so that it can be blown.

The value of this process is primarily that the blowing company does not have to purchase the

injection molding equipment to blow a particular container, so long as a preform is available

from a stock preform manufacturer. This process also allows access to a large catalog of

existing preforms. Therefore, the major expense is now for the blow molds, which are much

less expensive than the injection molds required for preforms.

There are, however, some drawbacks to this process. If you are unable to find a stock preform

which will blow the container you want, you must either purchase injection molds and have

your own private mold preforms injection molded, or you will have to forego this process. For

either type of stretch blow molding, handleware is not a possibility at this stage of

development. The stretch blow molding process does offer the ability to produce fairly

lightweight containers with very high impact resistance and, in some cases, superior chemical

resistance.

Whether using the injection stretch blow molding process or the reheat and blow process, an

important part of the process is the mechanical stretching of the preform during the molding

process. The preform is stretched with a "stretch rod." This stretching helps to increase the

impact resistance of the container and also helps to produce a very thin walled container.

Materials :

The extrusion blow molding process allows for the production of bottles in a wide variety of

materials, including but not limited to: HDPE, LDPE, PP, PVC, BAREX®, P.E.T., K Resin,

P.E.T.G., and Polycarbonate. As noted above, a wide variety of shapes (including

handleware), sizes and necks are available. Injection blow molding allows for the production of

bottles in a variety of materials, including but not limited to: HDPE, LDPE, PP, PVC, BAREX®,

P.E.T., and Polycarbonate.

Besides the P.E.T. noted above for stretch blow molding, a number of other materials have

been stretch blown, including polypropylene. As time goes on and technology moves forward,

more materials will lend themselves to stretch blow molding as their molecular structures are

altered to suit this process.85

Blow Molding Machine Manufacturers :

For shuttle extrusion type machines Bekum, Battenfeld/Fischer, and Hayssen are probably the

best known in the United States. For injection blow molding machines JOMAR is a well known

brand. For stretch blow and reheat and blow type machines there are Sidel, Nissei and other

machines produced by Johnson Controls and others. For wheel machines you might wish to

contact Johnson Controls or Wilmington Machinery.

Injection Molding :

Injection molding is a versatile process for forming thermoplastic and thermoset materials into

molded products of intricate shapes, at high production rates and with good dimensional

accuracy. The process involves the injection, under high pressure, of a metered quantity of

heated and plasticized material into a relatively cool mold--in which the plastic material

solidifies. Resin pellets are fed through a heated screw and barrel under high pressure. The

liquefied material moves through a runner system and into the mold. The cavity of the mold

determines the external shape of the product while the core shapes the interior. When the

material enters the chilled cavities, it starts to re-plasticize and return to a solid state and the

configuration of the finished part. The machine then ejects the finished parts or products.

Specific Injection Molding Processes

o Air Injection Molding

o Insert Injection Molding

o Outsert Injection Molding

o Push-Pull Injection Molding

o Sandwich Injection Molding

86

Continuous Strip Molding :

Continuous strip molding (or reel-to-reel molding) is used to efficiently manufacture and

assemble small electronic components and other parts that combine tiny metal and plastic

components. The process uses a feed reel and a take-up reel: a continuous metal "carrier"

strip is precisely indexed off the feed reel, passes through an injection mold and onto the take-

up reel. The molded parts are delivered to customers still on the take-up reel, and placed

directly in automated production equipment for hands-off operations that add more

components, install covers, or form electrical leads, etc.

Liquid Resin Molding :

Like metal casting, liquid resin casting usually starts with a male pattern, often produced from

aluminum, which is fastened to a flask. A liquid mold material, such as epoxy, urethane or MY

silicone is poured in. One pattern can make an unlimited number of molds. Liquid resin is then

poured into the mold to produce a part. Unlike metal casting, liquid resin casting captures

significantly more details, particularly when silicone is used as a mold material. Details such as

threads, and surface finishes such as textures or high-gloss can be achieved straight from the

mold, without secondary operations. The process is most economical in cases where the part

design is very complex and where the quantity required is in the range that is not well-suited

for either machining or other kinds of molding processes (generally from 25 to 50 on the low

end to 3000 on the high end).

 

Rotational Molding :

Rotational Molding begins with the melting of a plastic resin in a closed mold. Unlike most

other plastic processes, no pressure is involved. The three-stage process includes loading the

resin in the mold, heating and fusion of the resin and cooling and unloading the mold. After the

charged mold is moved into an oven, the mold is rotated on two axes at low speed. As heat

penetrates the mold, the resin adheres to the mold's inner surface until it is completely fused.

The mold is then cooled by air or water spray or a combination of both while still rotating,

lowering the temperature in a gradual manner. The mold is opened, finished part removed and

mold recharged for the next cycle. Cycle times vary from 7 to 60 minutes, depending on part

size, material and wall thickness.

87

Thermoforming :

Thermoforming involves the controlled heating of a thermoplastic material to a temperature

where its shape may be altered to the shape of the mold. The physical change to the

preheated thermoplastic is accomplished by vacuum, air, pressure or direct mechanical force.

Once the sheet assumes the desired shape of the mold design, it is allowed to cool on the

mold.

Vacuum Forming :

Vacuum forming simply requires the heating of a sheet of plastic until it reaches a forming

temperature then utilizing a vacuum to form it into or around a mold. It has been used widely

for products from camper shells to cold drink cups.

Pressure Forming :

Pressure Forming is a sophisticated version of the vacuum forming process utilizing air

pressure as a forming aid to increase the detail on the mold side. Features that could not be

achieved by vacuum alone can be molded with pressure forming. The result is a product with

the look and feel of an injection or structural foam molded part at a price close to a vacuum-

formed one.

The mold makers start by creating a pattern based upon drawings and specifications of the

custom part. From the pattern, these craftsmen produce either a hardwood or aluminum mold.

A wooden mold is used mainly for a customer required prototype or a very low volume

production run. The aluminum mold is used for a full production run and when the pressure

forming process is necessary.

The pressure forming technique provides for forming heavier sheet from 0.093" thick up to

0.375" thick. The technique is accomplished by forcing a hot sheet against a mold, usually

female, by introducing compressed air to the back side of the heated sheet. This method will

provide as much as 75 psi working on the sheet surface as compared to the 14 psi in vacuum

forming.

Twin Sheet Forming :

88

Twin Sheet Forming utilizes top and bottom molds into which two heated sheets are formed

and then welded together under pressure to form a hollow part.

Profile Extrusion :

Thermoplastic profile extrusions are made by heating a thermoplastic resin in the barrel of an

extruder and forcing it through a die that shapes it into a continuous two-dimensional profile.

Extrusions can be made from a single thermoplastic, from two or three compatible

thermoplastics, or with a continuous embedded reinforcement of metal or other material.

CNC Machining :

There are important differences between machining metal and plastic. An initial step is

recognizing that plastic parts do not have to be molded. Tolerance levels in machining plastic

are ±0.001". CNC turning and milling are the primary operations. Sawing, drilling, routing,

stamping, welding, bonding, polishing, screening and assembly are also essential to the

production of machined plastic parts.

MANUFACTURING: SURFACE FINISHING:

89

Introduction :

Improving the appearance of a finished product for purely aesthetic reasons can be important

because it often increases the salability of the product. The increased product performance

and safety provided by proper edge and surface finishing is also important. The removal of

burrs and sharp edges improves safety for both the worker and product user by eliminating the

possibility of cuts and making parts easier to handle. For critical components, the surface

condition and edge geometry can be a major influence on component performance and

durability.

From strictly an engineering point-of-view, surface finishing is primarily good for one thing:

preventing corrosion. Historically, man has employed three different mechanisms to stop

corrosion: (1) barrier coatings, (2) inhibitive primers and (3) the use of zinc anodes.

Barrier coatings are simply paints applied to the surface of metal to create a "Barrier" or "Wall"

between the metal and the corrosion-initiating exterior atmosphere. To protect yourself on a

rainy day, you put on a raincoat to keep you dry. The paint of a barrier coating acts as a

raincoat for the steel. This method is only partially effective since barrier coats are not

completely impermeable to moisture and will eventually breakdown, allowing the corrosion

process to begin, and will only protect as long as the coating is intact. If a barrier coating is

scratched or damaged in some way exposing the underlying metal, corrosion begins.

Corrosion-inhibitive primers employ special pigments which provide corrosion protection

through their ability to release inhibitive ions which are carried to the metal surface as water

penetrates the coating. At the metal surface, these ions modify anode and/or cathode

reactions, and force the steel's potential to corrode into a passive mode. These coatings are

somewhat effective but give limited service life and will allow corrosion to occur at damaged

areas, like barrier coatings.

Back in the 1700's a man named Luigi Galvani discovered that if you place two dissimilar

metals in direct, electrical contact with each other and subject them to an electrolytic solution,

ions from the least noble metal go into solution, liberating electrons and causing a current flow

into the more noble metal preventing it's ions from going into solution. The process described,

which became known as "Galvanizing" (aptly named for Mr. Galvani), employs the use of zinc

as the anode, or least noble metal. The zinc slowly releases it's ions causing the current to flow

into the metal it's applied to. The "hot-dip" galvanizing process, where iron or steel is dipped 90

into molten zinc at 850 degrees F, was born by a French chemist named Melovin in 1742.

Since then, hot-dip galvanizing has been considered by many to be the epitome of corrosion

protection.

Finish Machining Processes :

1. Honing

2. Lapping

3. Polishing

4. Burnishing

5. Deburring

Honing :

The honing process is used to obtain precise dimensions and surfaces in cylindrical shapes

with a wide range of diameters. This applies to parts such as Hydraulic Cylinders, Pistons,

Bearing Bores, Pin Holes and to some external cylindrical surfaces. The honing process offers

advantages of low capital equipment cost, high metal removal rates, and extreme accuracy of

0.001mm (0.00004´´) in a wide variety of materials.

Other advantages include the ability to create round and straight bores in relatively long

workpieces. Workpiece bore length-to-diameter ratios of 1.5:1 and longer are ideal for the

process. Shorter bore lengths can be accommodated by stacking workpieces in special

fixturing.

Honing can correct parts that are not square, within limits. Understanding the abilities of honing

to correct out-of-squareness requires an explanation of the principles of honing.

How honing works:

The abrasive action of the honing tool removes material from the workpiece's inside diameter.

The tool rotates and expands while the workpiece reciprocates (stroking) back and forth. For

example, tolerances of 0.003mm (0.0001´´) round and straight can be achieved in production

using special fixturing. To achieve such close tolerances, the workpiece must be allowed to

"float" or move in three axes. This movement is the single most important point in achieving

the closer tolerances required in industry today.

91

To correct out-of-squareness, the workpiece must be positioned against a flat face plate that is

perpendicular to the machine spindle axis. This, of course, reduces one of the three axes of

movement, thus reducing the amount of movement or "float."

Lapping :

Lapping is an abrasive machining operation which utilizes a rough chemical-mechanical-

polishing (CMP) process, where a sample (such as a metal, ceramic, plastic, glass, or silicon

substrate) is machined, smoothed, and planarized to a high degree of refinement or accuracy

using a rotating, serrated, cast-iron-alloy circular plate and an abrasive slurry grit in water

suspension applied to the plate in a controlled fashion.. Typically, a soft material - called a lap -

is charged with an abrasive. The lap is then used to cut a harder material - the workpiece. The

abrasive embeds within the softer material which then acts as a holder for the abrasive and

permits it to score across and cut the harder material.

Accuracy and Surface Roughness :

Lapping can be used to obtain a specific surface roughness; it is also used to obtain very

accurate surfaces, usually very flat surfaces. Surface roughness and surface flatness are two

quite different concepts. Unfortunately, they are concepts that are often confused by the

novice.

A typical range of surface roughness that can be obtained without resort to special equipment

would fall in the range of 1 to 30 Ra.

Surface accuracy or flatness is usually measured in Helium Light Bands, one HLB measuring

about 0.000011 inches (11 millionths of an inch). Again, without resort to special equipment

accuracies of 1 to 3 HLB are typical. Though flatness is the most common goal of lapping, the

process is also used to obtain other configurations such as a concave or convex surface.

High Speed Lapping :

92

High-speed lapping, also known as fine grinding or flat honing, was actually introduced to the

United States in the 1990s, awareness of the process remains surprisingly low and is mostly

limited to large manufacturers with in-house component production.

Traditional lapping is a painstaking process using a wet abrasive slurry to slowly finish parts to

precise flatness, parallelism and surface finish. The abrasive slurry requires extensive, time-

consuming cleaning of both parts and equipment. Even with the cleaning, abrasive particle are

often ground into the part itself causing "grit impregnation" that can hurt the part's

performance-particularly in fluid sealing applications.

In contrast, high-speed lapping uses a fixed abrasive wheel in place of the wet slurry. This

dramatically reduces the lengthy cleaning process and eliminates grit impregnation. Advanced

machine controls combine the rapid stock removal rate of traditional grinding with the precision

finishing of traditional flat lapping. Automated systems to load and unload part further speed up

the process.

The results are impressive. High-speed lapping can finish parts up to 20 times faster than

traditional flat lapping. This yields significant cost savings, often up to 40 percent versus

traditional lapping. In fact, high-speed lapping can even cost less than traditionally low-cost

grinding methods, since simple inexpensive parts carriers replace costly fixtures.

High-speed lapping is ideal for all types of metals, including steel, brass, aluminum,

phosphorus bronze, tungsten carbide, cast iron, and powder metals. The process is also used

for plastic, ceramic, glass, carbon, and other materials.

The high-speed lapping process is well-suited for parts with either a regular or irregular shape

and a wide range of sizes. Some very thin parts may be difficult to finish due to limitations of

the carriers that hold the parts in place during the process. Flatness and parallelism can be

maintained within single digit micron tolerances. Surface finishes of 1 Ra micrometers can be

routinely achieved.

A key commercial consideration is the number of parts to be finished. The process is generally

used for parts with annual volumes of one million or more. Companies with sufficient demand

can purchase the equipment or contract with outside companies that specialize in high speed

lapping.

93

Polishing :

A chemical-mechanical-polishing CMP process, where a sample is smoothed or burnished to a

glossy, finished surface using cerium oxide powder mixed with water or colloidal silica.

Polished surfaces are denser, harder, and have more intrinsic stresses than lapped surfaces.

Polishing creates more friction, more drag, and higher substrate/sample temperatures than

lapping processes. Polishing to a glossy surface usually starts around the outside edges of a

specimen/sample and works its way inward over time.

Either of two possible common schools-of-thought may be used to determine how much

material you should seek to remove during polishing:

1. Remove a depth of material on your specimen/sample equal to at least one-half the

abrasive-slurry grit-particle size (e.g. if 12 µm calcined alumina powder was used during

lapping, remove at least 6 µm of material during polishing).

2. Remove a depth of material on your specimen/sample equal to at least three times the

abrasive-slurry grit-particle size (e.g. if 9 µm calcined alumina powder was used during

lapping, remove at least 27 µm of material during polishing). This depth of polishing is

especially used to remove all material that may be within cracked valleys or cracked

grooves caused by the abrasive slurry grit particles.

Deburring :

One of the more difficult aspects of dealing with machined parts is the task of deburring or

removing the burrs left by the machining processes. Burrs are simply small pieces of material,

still clinging to the edges of a newly machined part. They are often very sharp and can cause

problems with handling and finishing the part so they must be removed.

There are literally thousands of methods of deburring since there are so many different

variations of machining processes, part size, and part geometry. Most deburring includes

somes sort of abrasive process - brushes, tumbling etc. - to remove the burrs. One of the most

common methods for small parts is barrel tumbling.

Deburring is often accomplished tumbling parts in a barrel or a vibratory bowl, along with

finishing media. Ceramic media is often used for steels. For softer materials, plastic media,

94

walnut shells and other materials can be used. This type of deburring is usually confined to

unfinished materials.

For materials that are already finished, such as pre-plated or pre-painted materials bulk

deburring operations are not suitable, because the deburring will remove the finish along with

the burrs. For these materials, other forms of deburring such as belt sanding or hand filing will

have to be done with the associated higher costs.

Burnishing :

Burnishing is a cold forming process, without actual removal of metal, where a tool is rubbed

on the metal surface of the part with sufficient force to cause plastic flowing of the metal. This

allows the high spots to be flattened out and the valleys filled in. It is a new concept in finishing

Components.This process eliminates Grinding and honing which are costlier processes while

improving the surface finish, surface hardness, wear-resistance, fatigue resistance and

corrosion resistance of a part.

Roller Burnishing :

The surface of metal parts worked through turning, reaming or boring operations is a

succession of peaks and valleys when microscopically examined. The Roller burnishing

operation compresses the Projections (Peaks) into the Indentation (Valleys) thus forming a

smooth mirror finished surface. Any material not exceeding 40 Rockwell Hardness "C" can be

roller burnished.

One or several rollers are pressed against the workpiece with the nearly perpendicular force

(burnishing force). This generates a high compressive stress in the piece of the surface profile,

which plastically forms the top layer. The material volume of the peaks is displaced into the

zones of lower compressive stress (the valleys).

 

Surface Treatments :

95

1. Anodizing

2. Hardening

3. Heat Treating

Annealing

Carbonitriding

Carburizing

Nitriding

Normalizing

Quenching

Stress Relieving

Tempering

Anodizing Process :

Why do you anodize aluminum?

Exposed to the earth's atmosphere, aluminum combines with oxygen to form a protective

surface film which inhibits further oxidation of the aluminum. Unlike steel or iron alloys,

aluminum will not continue to oxidize (rust) once this protective layer is formed. This natural

oxide is extremely thin and loosely adhered to the aluminum surface, however, and is easily

removed by handling. Anodizing is a process which thickens the natural oxide film resulting in

a heavy aluminum oxide film of controlled thickness having the hardness similar to that of a

ruby or sapphire.

Aluminum anodizing is the electrochemical process by which aluminum is converted into

aluminum oxide on the surface of a part. This coating is desirable in specific applications due

to the following properties:

Increased corrosion resistance

Increased durability / wear resistance

Ability to be colored through dying

Electrical insulation

Excellent base or primer for secondary coatings

96

During the anodizing process, several controls are critical to assure the specified film

thickness, its abrasion resistance and density. These controls include a precise combination of

chemical concentration, temperature and current density. In the production of quality anodized

products, there is no alternative to having sophisticated monitoring equipment and highly-

trained, experienced personnel. The company you choose for your anodizing projects must be

able to demonstrate these qualities.

The Process:

When aluminum is anodized conventionally, direct electrical current (DC) is passed through a

bath of sulfuric acid -- the electrolyte -- while the aluminum being treated serves as the anode.

This produces a clear film of aluminum oxide on the aluminum's surface. Electron microscopy

indicates that this layer is mostly porous with a very thin barrier layer at the base. This

structure lends itself very well to electrolytic coloring or absorptive dying.

1. Pre-Treatment: Cleaning is done in a non-etching, alkaline detergent heated to

approximately 145 degrees Fahrenheit. This process removes accumulated

contaminants and light oils.

2. Rinsing: Multiple rinses, some using strictly de-ionized water, follow each process step.

3. Etching (Chemical Milling): Etching in caustic soda (sodium hydroxide) prepares the

aluminum for anodizing by chemically removing a thin layer of aluminum. This alkaline

bath gives the aluminum surface a matte appearance.

4. Desmutting: Rinsing in an acidic solution removes unwanted surface alloy constituent

particles not removed by the etching process.

5. Anodizing: Aluminum is immersed in a tank containing an electrolyte having a 15%

sulfuric acid concentration. Electric current is passed through the electrolyte and the

aluminum is made the anode in this electrolytic cell; the tank is the cathode. Voltage

applied across the anode and cathode causes negatively charged anions to migrate to

the anode where the oxygen in the anions combines with the aluminum to form

aluminum oxide (Al2O3). View our anodizing video.

6. Coloring: Anodic films are well suited to a variety of coloring methods including

absorptive dyeing, both organic and inorganic dyestuffs, and electrolytic coloring, both

the Sandocolor® and Anolok® processes.

97

7. Sealing: In all the anodizing process, the proper sealing of the porous oxide coating is

absolutely essential to the satisfactory performance of the coating. The pores must be

rendered nonabsorbent to provide maximum resistance to corrosion and stains. This is

accomplished through a hydrothermal treatment in proprietary chemical baths or by

capping the pores via the precipitation of metal salts in the pore openings.

Heat Treatment - Case hardening :

Case hardening or Surface hardening is the process of hardening the surface of steel while

leaving the interior unchanged. The idea behind case hardening is to have two different types

of steel in the same item. This allows a relatively soft, tough core of a component to be

combined with a hard (but potentially brittle) surface. Case hardening improves the wear

resistance of machine parts without affecting the tough interior of the parts. Many processes

are available for surface hardening.

Both carbon and alloy steels are suitable for case-hardening providing their carbon content is

low, usually less than 0.2%. Case hardened steel is usually formed by diffusing carbon and/or

nitrogen into the outer layer of the steel at high temperature.

The term case hardening is derived from the practicalities of the process itself. The steel work

piece (e.g. a firing pin, the head of a rifle bolt, or an engine cam shaft) is placed inside a case

packed tight with a carbon-based case hardening compound. This is also known as a

carburizing pack. The pack is put inside a hot furnace for a variable length of time. Time and

temperature determines how deep into the surface the hardening extends. However, the depth

of hardening is ultimately limited by the inability of carbon to diffuse deeply into solid steel and

a typical depth of surface hardening with this method is up to 1.5mm.

Another common application of Case hardening is on screws, particularly Self-Drilling Screws.

In order for the screws to be able to drill, cut and tap into other materials like steel, the drill

point and the forming threads must be harder than the material(s) that it is drilling into.

However if the whole screw is uniformly hard, it will become very brittle and it will break easily.

This is overcomed by ensuring that only the case is hardened and the core remains relatively

soft. For screws and fasteners, case hardening is less complicated as it is achieved by heating

and quenching in the form of heat treatment.

98

Heat Treatment :

Heat Treating is controlled heating and cooling of a solid metal or alloy by methods designed

to obtain specific properties by changing the microstructure. Heat Treating takes place below

the melting point of the metal and changes in microstructure take place within the solid metal.

Changes in microstructure are due to the movement of atoms within crystal lattices in

response to heating or cooling over a period of time.

The ability to tailor properties by heat treating has contributed greatly to the usefulness of

metals and their alloys in an assortment of applications such as sheet metal for cars and

aircraft.

Heat treating processes include annealing, normalizing, tempering, stress relieving, solution

treating, age hardening, and bright hardening. Quenching, or cooling from a higher

temperature, is an integral part of many heat treating processes when hardening is involved.

Regardless of the reason for the heat treating, the basic process is the same and has three

steps.

1. Heat the metal to a specific temperature

2. Hold the metal at that temperature for a specific amount of time

3. Cool the metal in a specific manner

Basic Processes :

The following heat treatment processes are the most commonly used:

1. Annealing

2. Normalizing

3. Stress Relieving

4. Tempering

5. Quenching

6. Hardening

Heat Treatment - Annealing :

99

Annealing is the process for softening materials or to bring about required changes in

properties, such as machinability, mechanical or electrical properties, or dimensional stability.

The annealing process consists of heating the steel to or near the critical temperature

(temperature at which crystalline phase change occurs) to make it suitable for fabrication.

Annealing is performed to soften steel after cold rolling, before surface coating and rolling,

after drawing wired rod or cold drawing seamless tube. Stainless steels and high alloy steels

generally require annealing because these steels are more resistant to rolling.A material can

be annealed by heating it to a specific temperature and then letting the material slowly cool to

room temperature in an oven. This process is expensive because the oven is unusable during

the cool down process.

Heat Treatment - Normalizing :

Normalizing is a heat treatment process for making material softer but does not produce the

uniform material properties of annealing.. A material can be normalized by heating it to a

specific temperature and then letting the material cool to room temperature outside of the

oven. This treatment refines the grain size and improves the uniformity of microstructure and

properties of hot rolled steel.

Normalizing is used in some plate mills, in the production of large forgings such as railroad

wheels and axles, some bar products. This process is less expensive than annealing.

HeatTreatmentStressRelieving:

Stress Relieving consists of heating the steel to a temperature below the critical range to

relieve the stresses resulting from cold working, shearing, or gas cutting. It is not intended to

alter the microstructure or mechanical properties significantly.also a process for making

material softer. However stress relieving does not change the material properties as does

annealing and normalizing. A material can be stress relieved by heating it to a specific

temperature that is lower than that of annealing or normalizing and letting it cool to room

temperature inside or outside of the oven. This heat treatment is typically used on parts that

have been severely stressed during fabrication.

It is worth noting that many heat treatments and welding processes cause stresses in the

material that can lead to warpage either after the heat treating process or during subsequent

100

machining operations. Of specific concern is the stress induced by welding. If a weldment is to

be machined it should almost always be stress relieved or normalized before the machining

process. This is because machining chunks of material from a stressed weldment redistributes

the internal stresses and can cause the part to warp. If the stresses are first relaxed then

abrupt changes in geometry after machining are reduced.

Heat Treatment - Quenching :

Quenching is the process for making material harder. This method has been known for

hundreds of years but was only perfected in the last century. The metal is heated to a specific

temperature and rapidly cooled (quenched) in a bath of water, brine, oil, or air to increase its

hardness.

One drawback of using this method by itself is that the metal becomes brittle. This treatment is

therefore typically followed by a tempering process which is a heating process at another

lower specific temperature to stress relieve the material and minimize the brittleness problem.

The temperature chosen for the tempering process directly impacts the hardness of the work

piece . The higher the temperature in the tempering process, the lower the hardness.

Heat Treatment - Tempering :

Tempering is carried out by preheating previously quenched or normalized steel to a

temperature below the critical range, holding, and then cooling to obtain the desired

mechanical properties. Tempering is used to reduce the brittleness of quenched steel. Many

products that require hardness and resistance to breakage are quenched and tempered. The

temperature chosen for the tempering process directly impacts the hardness of the work

piece . The higher the temperature in the tempering process, the lower the hardness.

PLATING :

1. Electroplating

o Alloys (Bronze/brass and others)

101

o Chromium

o Dense Chromium

o Copper & Tin

o Gold, silver and other precious metals

o Zinc & Nickel

2. Electroforming

3. Electroless Nickel

4. Hot Dip Galvanizing

5. Selective/Brush Plating

Electroplating: 

The process used in electroplating is called electrodeposition. The item to be coated is placed

into a container containing a solution of one or more metal salts. The item is connected to an

electrical circuit, forming the cathode (negative) of the circuit while an electrode typically of the

same metal to be plated forms the anode (positive). When an electrical current is passed

through the circuit, metal ions in the solution are attracted to the item. The result is a layer of

metal on the item. However, considerable skill and craft-technique is required to assure an

evenly-coated finished product. This process is analogous to a galvanic cell acting in reverse.

A more detailed description of the electrodeposition process follows: The anode and cathode

in the electroplating cell are connected to an external supply of direct current, a battery, or

more commonly a rectifier. The anode is connected to the positive terminal of the supply, and

the cathode (article to be "plated")is connected to the negative terminal. When the external

power supply is switched on, the metal at the anode is oxidized from the 0 valence state to

form cations with a positive charge. These cations associate with the anions in the solution.

The cations are reduced at the cathode to deposit in the metallic, 0 valence state. Example: In

an acid solution Cu is oxidized to Cu++ by losing two electrons. The Cu++ associates with the

anion SO4 2- in the solution to form copper sulfate. At the cathode, the Cu++ is reduced to

metallic Cu by gaining two electrons.The plating is most commonly a single metallic element,

not an alloy. However, some alloys can be electrodeposited, notably brass and solder.

102

Use in manufacturing:

Electroplating is used in many industries for functional and/or decorative purposes. Some well

known examples are chrome-plating of steel parts on automobiles. Steel bumpers become

more corrosion-resistant when they have been electroplated with first nickel and then

chromium.

Steel camshafts resist wear better when they have been electroplated with chromium.

Plain steel or aluminum parts in light fixtures become beautiful when they are

electroplated with nickel and then decorative chromium or brass.

Steel bolts last much longer because they are sold with a coating of zinc that has been

applied by electroplating. Zinc electroplating and passivation provides a double

protection system for steel components. Virtually all types of steel can be protected

including castings.

Newly developed electrolytes and process methods are able to provide greatly increased

corrosion prevention.

In addition to the well known yellow full passivation, there are blue, olive and black variants

available to meet modern requirements. Modern electrolytes can produce brilliant chrome like

finishes. Specially developed processes produce improved metal distribution over complex

shapes. Alloy zinc deposits offer extra performance.

Passivation processes (also known as conversion coatings) are usually applied to zinc

deposits to improve component life. These coatings used to be based on hexavalent chromium

chemistry providing unique surface corrosion resistance which will withstand even the most

extreme conditions over prolonged periods but have recently been superseded by trivalent

chromium chemistry on both health and environmental grounds.

Electroplating can be used to silver plate copper or brass electrical connectors, since silver

tarnishes much more slowly and has a higher conductivity than those metals. The benefit of

the silver is lower surface electrical resistance resulting in a more efficient electrical

connection. Silver plating is also popular for RF connectors because radio frequency current

flows primarily on the surface of its conductor; the connector will thus have the strength of

brass and the conductivity of silver.

103

Low force/low voltage separable connectors used in telecommunications switchgear,

computers, and other electronic devices are typically plated with gold or palladium over a

barrier layer of nickel. The tail ends of these connectors, which are usually joined to the device

by soldering, are plated with a tin/lead alloy, or pure tin.

History:

Modern electroplating was invented by Italian chemist Luigi V. Brugnatelli in 1805. Brugnatelli

used his colleague Alessandro Volta's invention of five years earlier, the voltaic pile, to

facilitate the first electrodeposition. Unfortunately, Brugnatelli's inventions were repressed by

the French Academy of Sciences and did not become used in general industry for the following

thirty years.

By 1839, scientists in Britain and Russia had independently devised metal deposition

processes similar to Brugnatelli's for the copper electroplating of printing press plates. Soon

after, John Wright of Birmingham, England discovered that potassium cyanide was a suitable

electrolyte for gold and silver electroplating. Wright's associates, George Elkington and Henry

Elkington were awarded the first patents for electroplating in 1840. These two then founded the

electroplating industry in Birmingham England from where it spread around the world.

One of American physicist Richard Feynman's first projects was to develop technology for

electroplating metal onto plastic. Feynman successfully developed this technology, allowing his

employer to keep commercial promises he had made but could not have fulfilled otherwise.

On June 28, 1988, four workers at an electroplating plant in Auburn, Indiana were asphyxiated

by hydrogen cyanide gas produced when muriatic acid was mixed with zinc cyanide in a

cleaning operation. A fifth victim died two days later.

Surface Finishing Coatings :

1. Air Spray Painting

2. Chemical Vapor Deposition - (CVD)

3. Conversion Coating

4. Diamond Coating (CVD)

5. Diffusion Coating

104

6. Electrocoating

7. Low Temperature Arc Vapor Deposition (LTAVD)

8. Pad Printing

9. Physical Vapor Deposition - (PVD)

10.Polyurethane Coatings

11.Porcelain Enameling

12.Powder Coating

13.Silk screen printing

14.Thermal Spraying

MANUFACTURING PROCESSES - FASTENING & JOINING PROCESSES:

Introduction :

Every joining technique has particular design requirements, while certain joint requirements

may suggest a particular joining technique. Design for assembly, automation, and fastener

selection impose their own requirements.

105

Bolting is a common fastening method, for example, but welding may reduce the weight of an

assembly. Naturally, joints designed for the two techniques would differ greatly. However, all

joint designs must consider characteristics such as load conditions, assembly efficiency,

operating environment, overhaul and maintenance, and the materials used.

Welding is often a cost-effective way to fabricate. It does not require overlapping materials, so

it eliminates excess weight caused by other fastening means. Fasteners do not have to be

bought and kept in inventory. Welding also can reduce costs associated with extra elements,

such as angles fastened between parts.

Welded joints distribute operating stresses evenly. However, design of a welded joint

significantly affects the welding processes that are used. Many design options permit excellent

welding performance. Nevertheless, designers who are unaware of the range of technology

and methods available may fail to realize welding's potential.

There are a variety of joining methods that do no use fasteners. Alternative methods are

especially important for some materials.

Methods to join materials without the use of fasteners include adhesives, welding, brazing,

soldering, clinching, and injected-metal assembly. In addition, materials such as plastics,

composites, and metal-ceramic combinations may indicate the use of certain joining methods.

Fusion Welding Processes

Arc-weldingOxyacetylene Gas Welding

(OFW)

Shielded-metal Arc Welding

(SMAW) Laser-beam Welding (LBW)

Gas-metal Arc Welding (GMAW) Electroslag Welding (ESW)

106

or (MIG)

Fluxed-core Arc Welding (FCAW) Electron-beam Welding (EBW)

Gas-tungsten Arc Welding

(GTAW) or (TIG) Percussive Arc Welding

Submerged Arc Welding (SAW) Resistance Spot Welding

(RSW)

Plasma Arc Welding (PAW)  

 

Arc Welding :

Arc welding processes use a welding power supply to create and maintain an electric arc

between an electrode and the base material to melt metals at the welding point. They can use

either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes.

The welding region is sometimes protected by some type of inert or semi-inert gas, known as a

shielding gas, and filler material is sometimes used as well.

Arc welding is one of several fusion processes for joining metals. By applying intense heat,

metal at the joint between two parts is melted and caused to intermix - directly, or more

commonly, with an intermediate molten filler metal. Upon cooling and solidification, a

metallurgical bond is created. Since the joining is an intermixture of metals, the final weldment

potentially has the same strength properties as the metal of the parts. This is in sharp contrast

to non-fusion processes of joining (i.e. soldering, brazing etc.) in which the mechanical and

physical properties of the base materials cannot be duplicated at the joint.

In arc welding, the intense heat needed to melt metal is produced by an electric arc. The arc is

formed between the actual work and an electrode (stick or wire) that is manually or

mechanically guided along the joint. The electrode can either be a rod with the purpose of

simply carrying the current between the tip and the work. Or, it may be a specially prepared

107

rod or wire that not only conducts the current but also melts and supplies filler metal to the

joint. Most welding in the manufacture of steel products uses the second type of electrode.

Shielded-metal Arc Welding (SMAW) :

Shielded Metal Arc Welding (SMAW) or Stick welding is a process which melts and joins

metals by heating them with an arc between a coated metal electrode and the workpiece. The

stick electrode has an outer coating, called flux, that assists in creating the arc and provides

the shielding gas and slag covering to protect the weld from contamination. The electrode core

provides most of the weld filler metal.

When the electrode is moved along the workpiece at the correct speed the metal deposits in a

uniform layer called a bead.The Stick Welding power source provides constant current (CC)

and may be either alternating current (AC) or direct current (DC), depending on the electrode

being used. The best welding characteristics are usually obtained using DC power sources.

The power in a welding circuit is measured in voltage and current. The voltage (Volts) is

governed by the arc length between the electrode and the workpiece and is influenced by

electrode diameter. Current is a more practical measureof the power in a weld circuit and is

measured in amperes (Amps). The amperage needed to weld depends on electrode diameter,

the size and thickness of the pieces to be welded,and the position of the welding. Generally, a

smaller electrode and lower amperage is needed to weld a small piece than a large piece of

the same thickness. Thin metals require less current than thick metals, and a small electrode

requires less amperage than a large one.

It is preferable to weld on work in the flat or horizontal position. However, when forced to weld

in vertical or overheadpositions it is helpful to reduce the amperage from that used when

welding horizontally. Best welding results areachieved by maintaining a short arc, moving the

electrode at a uniform speed, and feeding the electrode downward at a constant speed as it

melts.

Gas-metal Arc Welding (GMAW) or (MIG) :

In Gas Metal Arc Welding (GMAW), more commonly known as Metal Inert Gas (MIG) welding,

an electric arc is established between the workpiece and a consumable bare wire electrode.

108

The arc continuously melts the wire as it is fed to the weld puddle. The weld metal is shielded

from the atmosphere by a flow of an inert gas, or gas mixture.

The mig welding process operates on D.C. (direct current) usually with the wire electrode

positive. This is known as ”reverse” polarity. ”Straight” polarity, is seldom used because of poor

transfer of molten metal from the wire electrode to the workpiece. Welding currents of from 50

amperes up to more than 600 amperes are commonly used at welding voltages of 15V to 32V.

A stable, self correcting arc is obtained by using the constant potential (voltage) power system

and a constant wire feed speed.

Continuing developments have made the mig process applicable to the welding of all

commercially important metals such as steel, aluminum, stainless steel, copper and several

others. Materials above .030 in. (.76 mm) thick can be welded in all positions, including flat,

vertical and overhead. It is simple to choose the equipment, wire electrode, shielding gas, and

welding conditions capable of producing high-quality welds at a low cost.

Fluxed-cored Arc Welding (FCAW) :

The Fluxed Cored Arc Welding (FCAW) process is also referred to as “fluxed cored”. In FCAW,

a continuous solid wire is fed through the welding gun from a wire feeder. The wire consists of

a metal sheath filled with a flux. The flux helps to establish the arc, provides additives to the

weld, and produces a slag.

In gas-shielded FCAW, the shield gas (mix of carbon dioxide & inert gas) is used to protect the

arc. In self-shielded FCAW, the flux decomposes to produce the shielding gas and slag. FCAW

is used to weld mild and alloy steel and generates large amounts of fumes.

Gas-tungsten Arc Welding (GTAW) or (TIG) :

Tungsten Arc Welding (GTAW) is also referred to as Tungsten Inert Gas (TIG) Welding. In

GTAW, an electric arc is established between the work piece and the tungsten electrode. In

contrast to SMAW, this is a non-consumable electrode process. The arc is protected by a flow

of a shielding gas, commonly argon (also helium or mixtures of these two gases), which

displace atmospheric gases from the weld zone. The arc can fuse two metals together without

the use of a filler metal. A hand-held filler rod can be placed near the arc and melted to fill any

gaps.

109

GTAW is commonly used to weld aluminum. It also is utilized in mild and stainless steel

applications. Ultraviolet (UV) light from the electric arc is intense and ozone gas is produced

during the process. . GTAW produces no slag and produces small amounts of fume. The

tungsten electrodes contain small amounts of thorium (<4%), readily burning in air to thorium

oxide. Thorium is a radioactive metal and poses an inhalation and ingestion hazard.

Submerged Arc Welding (SAW) :

Similar to MIG welding, SAW involves formation of an arc between a continuously-fed bare

wire electrode and the workpiece. The process uses a flux to generate protective gases and

slag, and to add alloying elements to the weld pool. A shielding gas is not required.

Prior to welding, a thin layer of flux powder is placed on the workpiece surface. The arc moves

along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused

slag layers can be easily removed after welding. As the arc is completely covered by the flux

layer, heat loss is extremely low. This produces a thermal efficiency as high as 60%

(compared with 25% for manual metal arc). There is no visible arc light, welding is spatter-free

and there is no need for fume extraction.

Plasma Arc Welding (PAW) :

In the Plasma Arc Welding (PAW) process, a non-consumable tungsten electrode and a

shielding gas is used in a way similar to TIG welding. The plasma torch uses a constriction

cup, which forces the arc out into a narrow jet. When the diameter of the constriction cup is

reduced, a finer arc jet is produced which can be used for cutting or gouging applications. Arc

cutting is the general process in which the cutting or removal of metals is completed by melting

with the heat of an arc between the base metal and the electrode.

Oxyfuel gas welding (OFW) :

Oxyfuel gas welding (OFW) is a group of welding processes which join metals by heating with

a fuel gas flame or flares with or without the application of pressure and with or without the use

of filler metal. OFW includes any welding operation that makes use of a fuel gas combined with

oxygen as a heating medium. The process involves the melting of the base metal and a filler

metal, if used, by means of the flame produced at the tip of a welding torch. Fuel gas and

oxygen are mixed in the proper proportions in a mixing chamber which may be part of the

110

welding tip assembly. Molten metal from the plate edges and filler metal, if used, intermix in a

common molten pool. Upon cooling, they coalesce to form a continuous piece.

There are three major processes within this group:

1. oxyacetylene welding

2. oxyhydrogen welding

3. pressure gas welding.

There is one process of minor industrial significance, known as air acetylene welding, in which

heat is obtained from the combustion of acetylene with air. Welding with methylacetone-

propadiene gas (MAPP gas) is also an oxyfuel procedure.

Process Advantages :

(1) One advantage of this welding process is the control a welder can exercise over the rate of

heat input, the temperature of the weld zone, and the oxidizing or reducing potential of the

welding atmosphere.

(2) Weld bead size and shape and weld puddle viscosity are also controlled in the

welding :rocess because the filler metal is added independently of the welding heat source.

(3) OFW is ideally suited to the welding of thin sheet, tubes, and small diameter pipe. It is also

used for repair welding. Thick section welds, except for repair work, are not economical.

Laser-beam Welding (LBW) :

Laser Beam Welding (LBW) produces a coalescence of metals by the radiation emitted from a

concentrated beam of coherent light. A shielding gas is used to protect the molten pool. Welds

may be fabricated with or without filler metal. LBW is used to weld all the commercially

important metals, including steel, stainless steel, aluminum, titanium, nickel, copper and

certain dissimilar metal combinations.

111

Advantages :

1. high travel speeds

2. minimal heat affected zones

3. high mechanical properties

4. low distortion

5. no slag or spatter

6. automated process

Thick (>1 inch) single pass welds can be achieved with high powered CO2 systems. Nd:YAG

lasers can be delivered via fiber optics and thus can be manipulated by robotics and can weld

complex structures.

Electroslag Welding (ESW) :

Electroslag welding (ESW) is a process joining metals with heat generated by passage of

electric current through molten conductive slag which melts the filler and base metals. Due to

practically unlimited deposition rates ESW is considered the most productive of any welding

processes in joining very thick components.

The (ESW) process was developed at the Institute of Electric Welding named after E.O. Paton

(former USSR) in the late 40's. In the U.S., ESW came into practice in the late 60's. In the mid

70's, ESW became a well established fabrication process for joining thick wall components in

bridge, building, shipbuilding, pressure vessel, machine building and other industries.

Electron-beam Welding (EBW) :

Electron beam welding (EBW) is a welding process which produces coalescence of metals

with the heat obtained from a concentrated beam composed primarily of high-velocity electrons

impinging upon the surfaces to be joined. The workpieces melt as the kinetic energy of the

electrons is transformed into heat upon impact, and the filler metal, if used, also melts to form

part of the weld. Pressure is not applied, and a shielding gas is not used, though the welding is

often done in conditions of a vacuum to prevent dispersion of the electron beam.

As the electrons strike the workpiece, their energy is converted into heat, instantly vaporizing

the metal under temperatures near 25,000 °C. The heat penetrates deeply, making it possible

to weld much thicker workpieces than is possible with most other welding processes. However, 112

because the electron beam is tightly focused, the total heat input is actually much lower than

that of any arc welding process. As a result, the effect of welding on the surrounding material is

minimal, and the heat-affected zone is small. Distortion is slight, and the workpiece cools

rapidly, and while normally an advantage, this can lead to cracking in high-carbon steel.

Almost all metals can be welded by the process, but the most commonly welded are stainless

steels, superalloys, and reactive and refractory metals. The process is also widely used to

perform welds of a variety of dissimilar metals combinations. The process was developed in

France and released on November 23, 1957 in Paris by J. A. Stohr.

Arc-Percussive Welding :

Arc-Percussive technology is a method by which similar and dissimilar metals are easily and

consistently joined. This process is used in various industries for applications such as lead

attachment, cable termination, and small parts welding.

Arc percussive welding is best applied to butt welding of two wires or a wire “end-on” to a

plate. Arc percussive welding uses a high voltage generator to provide an arc between the two

materials to be joined. This arc ionizes the air and provides a locally shielded atmosphere.

Following the arc initiation, one of the materials is thrust against the other and a capacitor is

discharged into the resulting electric circuit. Due to the ionization and high voltage, materials

with inherent oxide layers can be welded due to the cleaning provided by the ionized atmo-

sphere. Also, due to the higher voltage, contact resistance is not an issue as it can be with

resistance welding. With proper fixturing, wires down to 0.005” can be butt welded. Smaller

wires can be welded to a plate.

Since there are no consumables, electrodes, solder, or flux, the Arc-Percussive welding

process is easier to use and more cost effective than resistance welding, soldering, brazing, or

crimping.

Resistance spot welding (RSW) :

Resistance spot welding (RSW) is a resistance welding process which produces coalescence

at the faying surfaces in one spot by the heat obtained from resistance to electric current

through the work parts held together under pressure by electrodes.

113

The size and shape of the individually formed welds are limited primarily by the size and

contour of the electrodes. The equipment for resistance spot welding can be relatively simple

and inexpensive up through extremely large multiple spot welding machines. The stationary

single spot welding machines are of two general types: the horn or rocker arm type and the

press type.

The horn type machines have a pivoted or rocking upper electrode arm, which is actuated by

pneumatic power or by the operator`s physical power. They can be used for a wide range of

work but are restricted to 50 kVA and are used for thinner gauges. For larger machines

normally over 50 kVA, the press type machine is used. In these machines, the upper electrode

moves in a slide. The pressure and motion are provided on the upper electrode by hydraulic or

pneumatic pressure, or are motor operated.

For high-volume production work, such as in the automotive industry, multiple spot welding

machines are used. These are in the form of a press on which individual guns carrying

electrode tips are mounted. Welds are made in a sequential order so that all electrodes are not

carrying current at the same time.

Solid State Welding :

1. Diffusion Bonding

2. Explosive Welding

3. Friction Welding

4. Friction Stir Welding

5. Inertia Welding

6. Magnetic Pulse Welding (MPW)

7. Ultrasonic Welding (USW)

Plastics Joining :

Processes Involving External Heating

1. Hot Plate Welding

2. Infrared Heating

3. Hot Gas and Extrusion Welding

114

4. RF or Dielectric Welding

5. Microwave Welding

6. Implant Welding

7. Induction Welding

8. Resistive Implant Welding

 

Processes Involving Frictional and Hysteresis Heating

1. Spin Welding

2. Vibration Welding

3. Stir Welding

4. Ultrasonic Welding

INDUSTRIAL ADHESIVES:

A huge variety of adhesives used for manufacturing purposes are currently available from

manufacturers. Adhesives are classified by either the way they are used or by their chemical

type. The strongest adhesives solidify by a chemical reaction while weaker varieties harden by

some physical change.

The major classifications are described in the following sections:

 

Industrial Adhesives

AcrylicsAnaerobic

s

Cyanoacrylate

s

(Super Glues)

Epoxies Hot Melts Phenolic

s

Plastisol Polyimides Polyurethanes Pressure- Polyvinyl Silicones

115

ssensitive

Adhesives

Acetate

(PVAs)

  Selection of Adhesives Based on Substrate Combinations:

Acrylic Adhesives

Metals

Thermoplastics

SMC/FRP/RTM

Hard wood

Primed glass

Urethane Adhesives

Prepared metals

Thermoplastics

SMC/FRP/RTM

Foam

Wood

Primed glass

Fabric

Prepared rubber

Leather

Epoxy Adhesives

Prepared metals

Thermoplastics

SMC/FRP/RTM

Foam

Wood

Primed glass

Prepared rubber

Cyanoacrylate Adhesives

116

Metals

Thermoplastics

Rubber

RAPID MANUFACTURING -- RAPID PROTOTYPING :

Introduction to RP:

Rapid prototyping (a.k.a. Desktop Manufacturing, Solid Free-form Manufacturing or Solid Free-

form Fabrication) consists of various manufacturing processes by which a solid physical model

of a part is made directly from 3D computer-aided design (CAD) model data. This CAD data

may be generated by 3D CAD Modelers, CT and MRI scan data or model data created by 3D

digitizing systems.

To begin the Rapid Prototyping process, the 3-D data is sliced into thin (~.005 in.) cross-

sectional planes by a computer. The cross-sections are sent from the computer to the rapid

prototyping machine which builds the part layer-by layer. The first layer's geometry is defined

by the shape of the first cross-sectional plane generated by the computer. It is bonded to a

platform or starting base and additional layers are bonded on top of the first, shaped according

to their respective cross-sectional planes. This process is repeated until the prototype part is

complete.

The resulting prototype provides a "conceptual model" for design visualization and review by

the entire design team. It may be used by engineers to check form and fit and perform limited

function tests. It can also be utilzed for soft tooling for prototypes and as a pattern for hard

tooling.

117

The various existing rapid prototyping methods can be categorized by the material they use:

photopolymer, thermoplastic, and adhesives. Photopolymer systems start with a liquid resin,

which is then solidified by discriminating exposure to a specific wavelength of light.

Thermoplastic systems begin with a solid material, which is then melted and fuses upon

cooling. The adhesive systems use a binder to connect the primary construction material.

Commercially Available Rapid Prototyping Processes :

1. 3D Printing - 3DP

2. Direct Shell Production Casting - DSPC

3. Electron Beam Melting - EB

4. Fused-Deposition Modeling - FDM

5. Laminated Object Manufacturing - LOM

6. Laser Engineered Net Shaping - LENS

7. Multi-Jet Modeling - MJM

8. Polyjet Technology

9. Selective Laser Sintering - SLS

10.Solid-Ground Curing - SGC

11.Stereolithography - SLA or SL

Rapid Prototyping -- 3D Printing (3DP) :

3D Printing, a patented MIT process, refers to the process of using an ink-jet print head to lay

down a liquid adhesive on a layer of powder, binding the powder particles together. First, a thin

distribution of powder is spread over the surface of a powder bed. From a computer model of

the desired part, a slicing algorithm computes information for the layer. Using a technology

similar to ink-jet printing, a binder material joins particles where the object is to be formed.

A piston then lowers so that the next powder layer can be spread and selectively joined. This

layer-by-layer process repeats until the part is completed. Following a heat treatment, the

loose powder is removed, leaving the fabricated part.

  Some of the applications of this process include --

1. Soligen is using ceramic powders to directly produce investment castings.

2. Extrude Hone uses it for direct metal tooling.

118

3. Z Corporation uses the process to create conceptual models out of cellulose,

engineered plaster and other types of powders. The company also has machines

capable of producing color models.

Rapid Prototyping -- Direct Shell Production Casting:

DSPC (Direct Shell Production Casting) produces the actual ceramic molds for investment

casting molds for metal parts directly from 3-D CAD designs. No tooling or patterns are

required. DSPC is a unique application of the Three Dimensional Printing technology to

produce the ceramic casting molds using a layer-by-layer process. It is used exclusively by the

Soligen Corp.

Rapid Prototyping -- Electron Beam Melting - EBM :

With Arcam's Electron Beam Melting method a 100% solid metallic object is produced directly

from metal powder. The part, which is to be produced, is designed in a three-dimensional CAD

program. The model is sliced into thin layers, approximately a tenth of a millimeter thick. From

a magazine of powder, an equally thin layer of powder is scraped onto a vertically adjustable

surface. The first layer’s geometry is then created through the layer of powder melting together

at those points directed from the CAD file, with a computer controlled electron beam.

Thereafter, the building surface is lowered just as much as the layer of powder is thick, and the

next layer of powder is placed on top of the previous. The procedure is then repeated so that

the object from the CAD model is shaped, layer by layer by layer, until a finished metal part is

complete.

The usage of a highly efficient computer controlled electron beam in vacuum provides high

precision and quality. EBM makes possible the fabrication of homogeneous metal components

such as complex tooling for spray-forming and injection molding tools and functional

prototypes in a very short time. The production process is fast in comparison with conventional

manufacturing methods. The highly efficient system produces parts from titanium powder and

does so between three and five times faster than other additive fabrication methods. One other

advantage is that reworking of the part is minimized. In contrast to laser sintering (SLS), the

electron beam fully melts the metal particles to produce a void-free part. The process occurs in

119

a high vacuum, which ensures the part is completely solid, without imperfections caused by

oxidation.

The EBM process is ideal for applications where high strength or high temperatures are

required. The machine creates parts comparable to wrought titanium and better than cast

titanium, with a 95 percent powder recovery yield. Medical product manufacturers can benefit

from the parts' high flexural strength for bone implants requiring cycle life exceeding 10 million

cycles (or movements). Automobile makers can build strong parts for high temperature testing,

including under-the-hood applications. Aerospace engineers will be interested in the

combination of a high strength yet light weight titanium part. And because the EBM process

produces a homogenous solid, parts can be flight-certified.

The process uses a high power electron beam that is 95 percent efficient -- 5 to 10 times more

so than a laser beam. This efficiency results in the creation of parts 3 to 5 times faster than

other metal additive-fabrication methods, and it uses only seven kW of average power. With

laser-based systems, like sintering, 95 percent of the light energy is reflected by the powder

rather than absorbed, significantly reducing efficiency.

Two variations of titanium "six four" alloy are available for the EBM S400: Ti6AL4V and

Ti6AL4V ELI. Titanium parts created on the system are accurate near-net shape and are HIP

heat treatable. The system builds parts up to approximately 8 x 8 x 7 in. (200 x 200 x 180 mm),

with a layer thickness range of 0.002 to 0.008 in. (0.05 - 0.2 mm).

EBM systems are manufactured by Arcam AB and distributed in North America by Stratasys.

Outside North America, the system is available from Arcam as the EBM S12.

Rapid Prototyping -- Fused Deposition Modeling :

FDM utilizes a thermoplastic filament similar to wire, which is then fed through a heated

extruding head controlled by a 3-axis NC-machine. The material hardens immediately when

exposed the temperature of the environment

Rapid Prototyping -- Laminated Object Manufacturing - LOM :

120

The LOM process builds layered, three-dimensional objects by stacking and fusing thin layers

of paper that are trimmed to shape using a CO2 Laser. Essential to this process are software

algorithms that slice a CAD file into cross sectional layers and coordinate this information with

system hardware. The building sequence begins with the lamination of a fresh layer of

adhesive paper to a solid base. Lamination is accomplished with a heated, stainless steel

roller.

Next, the laser cuts the part boundary contained within the first cross section, cutting only one

layer deep. Second, the laser cuts the excess material in a crosshatch pattern. The excess

material is not removed so as to provide support for subsequent layers. Next, an overall

rectangular outline is cut, freeing the cross section from the paper roll. The platform then

moves down and the feed paper advances. The sequence repeats when the platform returns

to the paper level. The process continues, layer by layer, until all of the cross sections have

been deposited and cut.

The product comes out of the machine as a rectangular block. The excess material

surrounding the part has already been sectioned into crosshatched columns which are

removed manually at the end of the process. The final LOM parts exhibit a wood-like

appearance, are dimensionally stable, and can be finished by sanding or sealing if necessary.

Rapid Prototyping -- Laser Engineered Net Shaping – LENS :

The LENS system uses 4 nozzles to make 3-dimensional, high-density, parts and molds from

the inside out. The nozzles direct a stream of metal powder in argon gas at a moveable central

point while a high-powered laser beam heats the point. Throughout the process, the substrate

continuously moves, guided by data derived from a thin layer of a CAD solid model. Layer-by -

layer the nozzles and laser worked together to gradually build up the model.

The LENS process is unique since it goes from raw material directly to metal parts without any

secondary operations. It can produce parts in a wide range of alloys, including titanium,

stainless steel, aluminum, and inconel. Primary applications for LENS technology include

Repair & Overhaul, Rapid Prototyping, Low-Volume Manufacturing, and Product Development

for Aerospace, Defense, and Medical markets.

This process was developed at Sandia National Laboratories and is being commercialized and

distributed by Optomec.

121

Rapid Prototyping -- MultiJet Modeling :

This process begins with a print head of 96 jets arranged in a linear array. Each individual jet

dispenses thermopolymer material on demand. The print head speeds back in forth like a line

printer, building layer upon layer of material that solidifies into the physical prototype. The part

is built on a moveable platform that lowers after each layer is built.

Rapid Prototyping -- Polyjet Technology :

PolyJet™ technology drives the precision inside the Eden333 from Stratasys (available only in

North America). Instead of the single head in other FDM machines, eight jetting heads

simultaneously deposit identical amounts of photopolymer on the build tray with each pass

along an X-axis. UV bulbs alongside the jets immediately cure and harden each layer –

eliminating the need for any post-modeling curing. The result is a perfectly smooth surface of

super thin layers down to just 16 microns (0.0006") – fully cured, that users can handle

immediately after the process is complete.

Unlike the messy, multi-step baths and post processing typically associated with expensive

laser and SLA machines, PolyJet technology fully cures each layer of super fine UV

photopolymer model and support materials as they are precisely deposited. There are no

special baths or time-consuming post processing needed.

Support material separates easily from the fully-cured model by water jet or hand and brush –

there is no extra finishing treatment required.

Model material readily absorbs paint and can be machined, drilled, chrome-plated or used as a

mold.

Rapid Prototyping -- Selective Laser Sintering – SLS :

The SLS® process creates three dimensional objects, layer by layer, from powdered materials

with heat generated by a CO2 laser. The part is built inside of a cylinder that contains a

moveable platform, and is formed layer-by-layer. A roller deposits a layer of powder across the

top of the cylinder; the laser fuses the powder to create the part geometry and also bonds each

layer to the one beneath it; the platform drops by the height of one layer; the roller deposits

another layer of powder, and the process continues.

122

Some materials being used are polycarbonate, nylon, polyester, Protoform@153

Composite(Nylon & Glass), TrueForm&153 PM Polymer, Rapid Steel Metal(Carbon Steel

particles w/ Polymer coating) and polystyrene.

The SLS process can typically hold tolerances in the range of +.002" to +.010" across the part-

building envelope.

Rapid Prototyping -- Solid Ground Curing :

Solid Ground Curing utilizes the general process of hardening of photopolymers by a complete

lighting and hardening of the entire suface, using specially prepared masks. A photopolymer

liquid in each layer is covered with a photomask and cured for several seconds by a strong

ultraviolet lamp. The exposed liquid polymer is then removed and the voids are filled with wax

to support the next layer.

Solid Ground Curing was originally developed and sold by Cubital Ltd. of Israel. Their system

was very complex and therefore suffered from high initial and operating costs that eventually

caused their downfall. The company no longer exists and its intellectual property has been

acquired by Objet Geometries, Ltd in Israel.

Stereolithography (SLA) Rapid Prototyping Process :

Stereolithography (SLA) is a rapid prototyping process utilizing a 3D CAD model to produce a

physical object which may be used as a conceptual model or a master pattern.

Stereolithography can be described as a process capable of producing copies of solid or

surface models in plastic materials. The process uses a computer controlled ultraviolet Helium-

Cadmium or Argon laser to trace cross-sections of the model onto the surface of a vat of a

photocurable polymer, hardening the material. The hardened layer is lowered leaving a new

layer of the liquid polymer over the cured material equal in thickness to the slice of the CAD

model and the laser traces the next cross-section. This unattended process continues

repeatedly until the part is complete.

The SLA are accurate with tolerances within .004" and speedy with delivery times of 2 to 3

days on average.

Main uses for Stereolithography models include--

123

1. Producing pre-production prototypes of a part for visualization of a product as well as

communication between project team members.

2. Master patterns for castings and secondary processes.

3. Medical models.

RAPID TOOLING - METAL PARTS :

Ferrous/Non-Ferrous Metal Parts :

Patterns for Molds :

Direct Investment Casting

QuickCast

Indirect Investment Casting

Rubber Plaster Mold (RPM)

Rubber Plaster Casting

Direct Sand Casting

 

Direct Construction of Molds

Direct Shell Production Casting (DSPC)

Direct Croning Process (DCP)

Nickel Ceramic Composite

Direct Investment Casting :

124

Utilizing solid and quick cast resin models produced by the following process:

Stereolithography , Selective Laser Sintering , Laminated Object Manufacturing, and 3D

Printing investment casting patterns can be produced. The resin model is used directly as an

expendable pattern and is ultimately burned rather than melted away, as is done with the wax

pattern.

Lead times for prototype investment castings are typically 3-4 weeks after receipt of the resin

model. The process is capable of producing intricate parts ranging in size from 1" to over 36".

 QuickCast :

QuickCast, a 3D Systems proprietary process, replaces traditional wax patterns for investment

casting with stereolithography (SLA) patterns created in a robust, durable material, without

tooling and without delay. The net result is QuickCast patterns in as little as 2 to 4 days and

quality metal castings in 1 to 4 weeks.The QuickCast part resembles a beehive hatch pattern

and ends up being about 80% hollow. It will burn out in the investment casting process with

very little residue.

PROCESS DESCRIPTION :

A Stereolithography QuickCast pattern is created from an STL file.

The pattern is leak tested to make sure it is air tight.

An investment caster is chosen (based on experience & material required).

QuickCast pattern is given to the caster.

Caster puts part through ceramic coating process and performs firing procedure to burn

out SLA pattern.

Metal is poured into the fired ceramic shell.

Ceramic shell is broken off to reveal metal part.

Indirect Investment Casting :

125

The Indirect Investment Casting process involves utilizing an RP process to generate a mold

which in turn is used to generate wax patterns for the Investment Casting process. The mold

may be directly produced by the LOM or ACES SLA process or instead an RTV or composite

mold generated from an SLA, SLS, LOM or any other pattern may be used.

 

Rubber Plaster Mold (RPM) :

Rubber Plaster Molding (RPM), also known as plaster mold casting, offers an alternative to

investment casting, sand casting and prototype die casting. This process is suitable for both

prototype and short run production quantities of aluminum and zinc parts.

The plaster casting process begins with a positive SLA model of the entire assembly being

built, which is used as a master pattern to make a negative silicone rubber mold. Another type

of silicone rubber is poured into the previously prepared negative rubber mold to form a

silicone rubber part of the same positive geometry as the master SLA pattern. A plaster mold is

then created around this silicone pattern. The silicone pattern is removed and metal is cast into

the cavity.

Rubber Plaster Casting :

Rubber plaster casting is used to manufacture highly complex aluminum components that

require a higher surface finish then sand casting can provide. Rubber Plaster casting is perfect

for components which surface finish must closely simulate that of die cast parts. In this

process, LOM parts are used as patterns around which a rubber sheet is pulled. Plaster is

packed into the rubber sheet which is then removed. Next, metal is poured into the plaster

cavity which is later broken away to expose the metal part.

Sand Casting :

Sand casting is used for production of metal components when high surface finish is not

critical. It is a high volume production technology which requires stable foundry patterns, cores

and core boxes. The LOM process is well suited for the creation of the often large, bulky

patterns and cores used in sand casting. When up to 100 components are needed, LOM parts

can be finished, sealed, painted and used directly to create impressions in the sand.

126

SLA, SLS and other RP processes are also used on a smaller scale to generate Sand Casting

patterns.

DSPC (Direct Shell Production Casting) :

DSPC (Direct Shell Production Casting) produces the actual ceramic molds for metal castings

directly from 3-D CAD designs. No tooling or patterns are required. DSPC uses Three

Dimensional Printing technology to produce the ceramic casting molds using a layer-by-layer

process.

PROCESS DESCRIPTION :

The CAD file of the designed part is transferred via modem or magnetic tape to the Shell

Design Unit (SDU) of the DSPC system. The SDU operator then designs the ceramic mold for

casting the metal part by adding the gating system to the part geometry and converting the

updated file into a cavity file in CAD space. This is a one time process after which many

identical ceramic mold could be generated. The cavity file for the ceramic mold is then used to

automatically generate the ceramic casting mold.

The ceramic mold is created in layers. The fabrication process involves three steps per layer.

First, the ceramic shell model is "sliced" to yield a cross-section of the ceramic mold. Second,

a layer of fine powder is spread by a roller mechanism. Third, a multi-jet printhead moves

across the section, depositing binder in regions corresponding to the cross-section of the mold.

The binder penetrates the pores between the powder particles and adheres them together to

form a rigid structure. Once a given layer is completed, the ceramic shell model is sectioned

again, at a slightly higher position, and the process is repeated until all layers of the mold are

concretized. The DSPC mold is then cleaned of excess powder, fired and poured with molten

metal.

A DSPC mold may contain an integral ceramic core, producing a hollow metal part. Virtually

any molten metal can be cast in DSPC molds. Automotive parts have already been

manufactured in aluminum, magnesium, ductile iron, and stainless steel.

127

The DSPC machine is like a three dimensional printer that uses the designer’s Computer

Aided Design to create the actual ceramic casting molds. Consequently, it expedites the

design and the functional testing of new automotive components such as engines,

transmissions and turbochargers. First article parts, made directly from the customer’s CAD,

are delivered in days. Importantly, any design change is easily incorporated in CAD space,

which provides the ultimate configuration control and assures that all design changes are

properly documented.

With DSPC, production tooling (dies, patterns and core boxes) are cast as net shape tools

from the CAD file of the approved part. This tooling is now created only once, guaranteeing a

smooth and cost effective transition from the first article part to production. The need for

temporary (prototyping) tooling is eliminated, and so are the huge monetary outlays associated

with prototype tooling that previously had to be considered. With DSPC, an indefinite number

of design iterations, including testing the design with different alloys, can be created without

the costly and time consuming need to produce tooling with each step.

Direct Croning Process (DCP) - EOSINT S :

EOSINT S is the newest development in laser-sintering. Molds for casting metal can be build

directly in foundry sand in just a few hours from CAD data. No patterns or core boxes are

required, and even extremely complex moulds can be manufactured by this layer

manufacturing technique.

This method opens up new design possibilities which can in themselves often produce great

savings, for example by reducing the number of core-pieces in a mould assembly. The logical

progression from traditional mould-making to faster and more cost efficient modern methods is

here taken a step further.

EOSINT S uses a coated foundry sand similar to widely used production materials, therefore

this technology is also known as the "Direct Croning Process (DCP)". It offers an extremely

fast route to metal prototypes in production materials and can even be used for one-off or

small-series component production.

 Nickel Ceramic Composite :

128

Instead of building the mold through a powder metal process, Cemcom builds it atom by atom

through nickel electroforming.

The process begins with an SL model. This "positive" is suggestive of the molded part, but not

a perfect copy. Instead, it has an extra half-inch or so of thickness between the core and cavity

surfaces—as if the molding press had not quite closed.

The resulting rigidity lets core and cavity shells of electroformed nickel grow simultaneously on

the model's opposite faces. The shells—each only about 0.1 inch thick when finished—are

then backed using a thermally conductive ceramic, which fills in the gap between shell and

mold frame. Thus the two nickel shells become two halves of a finished injection mold.

Surface finish is one area where this process shines with a resolution almost on the molecular

level. The molds have precisely the same surface finish as the SL master.

Another strength of the process is its ability to produce molds larger than 6" X 6" X 6", and do

so economically. While the time to machine a mold grows in proportion to mold volume, the

time to electroform does not. As a result, electroforming's cost and leadtime advantage should

grow as the size of the mold grows.

The process is still under development and currently isn't consistent enough yet for general

use. Tool life ranging from 10,000 to 50,000 parts is a reasonable expectation for the

electroforming process.

RAPID TOOLING - PLASTIC PARTS :

Overview :

Rapid tooling is the term for either indirectly utilizing a rapid prototype as a tooling pattern for

the purposes of molding production materials, or directly producing a tool with a rapid

prototyping system.

Rapid Tooling processes complement the Rapid Prototyping options by being able to provide

higher quantities of parts in a wider variety of materials, even short-run injection molded parts

129

in the intended production material. There are several options to pick from depending on time

available and material requirements.

Plastic/Urethane Parts

RTV Molding/Urethane Casting

Composite Tooling (Epoxy Tooling)

Direct Aim

Spray Metal Tooling

3D Keltool

Fundamental Physical Constants

Engineering, Physics, Astronomy, Chemistry etc.

Constant Value Units Definition

Astronomical Unit AU 1.495 978 7 e11 m Mean Sun-Earth distance

Alpha 7.297 352 81 e-

03

µ0 c e2/h Fine Structure Constant

AMU Chemical 1.660 260 00 e-

27

kg 1/16 of the weighted average mass of

the 3 naturally occuring neutral isotopes

of oxygen.

AMU Physical 1.659 810 00 e-

27

kg 1/16 of the mass of a neutral oxygen 16

atom.

Atomic Mass Unit 1.660 540 2 e-27 kg Atomic mass unit (defined to be 1/12 of

the mass of carbon 12)

Avogadro Number NA 6.022 136 7 e23 particles/

mol

Number of particles in 1 mole of

substance

130

Bohr Radius a0 5.291 772 1 e-11 alpha/pi R

Boltzman Constant k 1.380 658 e-23 J/K Boltzmann constant

Coulomb Constant 6.954 063 e-12 pi epsilon0 Listed as "k" sometimes

Dalton 1.660 540 2 e-27 µ

Electron Rest Mass

me

9.109 389 7 e-31 kg Particle mass

Proton Rest Mass mp 1.672 623 1 e-27 kg Particle mass

Neutron Rest Mass

mn

1.674 928 6 e-27 kg Particle mass

Muon Rest Mass mm 1.883 532 7 e-28 kg Particle mass

DeuteronRest

Massmd

3.343 586 e-27 kg Particle mass

Electron rest energy

mec2

8.187 111 2 e-14 J

Elementary Charge e 1.602 177 3 e-19 C Elementary charge

Electron Charge-

Mass ratio e/me

1.758 819 6 e11 C/kg

Energy 8.987 551 8 e16 c2 Convert mass to energy

Faraday Constant F 9.648 46 e4 NA e

Fine Structure

Constant (alpha)

7.297 352 81 e-3 µ0 c e2/h Fine Structure Constant

Gravitational

Constant

6.687 3 e-11 N m2/kg2 Newtonian gravity constant

Gas Constant R 8.314 51 J/mol K Molar gas constant

Hartree 2.625 501 e6 J/mol Atomic energy unit =  e2/(4 pi epsilon0a0)

Light Speed 2.997 924 58 e8 m/s

Molar Volume 2.241 41 e-2 m3/kmol Volume occupied by one mole of an

ideal gas at standard temperatureand

131

pressure.

Mole 1.0 mol Amount of substance of a system which

contains as many elementary entities as

atoms in 0.012 kg of unbound carbon

12 atoms, at rest and in the ground

state.

PI 3.141 592 7 pi

Permeability of

vacuum µ0

1.256 637 06 e-6 T2 m2/J

Permittivity of

vacuum (epsilon0)

8.854 187 817 e-12

C2/Jm Permittivity of vacuum, epsilon0 =

1/(µ0c2) (exact)

Planck Constant h 6.626 075 5 e-34 J s Action of one joule over one second

Prout 2.972 04 e-14 keV Nuclear binding energy equal to 1/12

binding energy of the deuteron

Rydberg Constant R 1.097 373 2 e7 /m

Speed of Light c 2.997 924 58 e8 m/s Speed of light in a vacuum(exact)

Standard

Temperature

2.731 5 e2 K Standard temperature

Unified Mass Unit 1.660 43 e-27 kg

 

Common Physical Constants

Acceleration of gravity, g 32.17 ft/s2 = 9.807 m/s 2

Speed of Light in a Vacuum 299,792,458 m/sec

Density of water 62.4 lbm/ft3 = 1 g/cm3

1 gal H2 O = 8.345 lbm

Gas Constant, R 1545 ft-lbf/pmole-R = 8.314 J/gmole-K

Gas volume (STP: 68°F, 1 atm) 359 ft 3 /pmole = .02241 m3 /gmole

132

Joule's Constant, J 778 ft-lbf/BTU

Poisson's ratio, µ .3 (for steel)

Modulus of Elasticity (steel) 30 X 10 6 psi

Common Steel Densities:

Carbon & Low-Alloy Steels 0.283 lbm/in 3 = 7.84 g/cm3

304 SS 0.29 lbm/in 3 = 7.88 g/cm3

Tool Steels Carbon Steels X 1.000

Moly High Speed Carbon Steels X 1.035

Multiphase Alloys Carbon Steels X 1.074

Steel Tensile Strength (psi) ~ 500 X Brinell Number

U.S. WEIGHTS & MEASURES TABLES :

Linear Measure

12 inches (in.) = 1 foot (ft.)

1 mil = 0 .001 in.

3 feet = 1 yard (yd)

= 36"

Surveyors' Measurements

1 link = 7.92 in

1 rod (rd)= 5 1/2 yards

= 16.5 ft.

1 chain

= 4 rods

= 22 yds.

= 66 ft

= 100 links

133

40 rods

= 1 furlong (fur)

= 220 yds

= 660 ft.

8 furlongs

= 1 statute mile (mi.)

= 80 chains

= 1,760 yds

= 5,280 ft.

5,280 feet = 1 statute or land mile

Nautical Measurements

1 fathom= 2 yds

= 6 ft.

100 fathoms = 1 cable length

10 cables length = 1 international nautical mile

6,076.11549 feet

= 1 international nautical mile

= length of a minute of longitude at equator

= 1.1508 statute miles

3 nautical miles = 1 league

1 knot= 1 nautical mile per hour

= 1.1508 statute miles per hour

60 nautical miles = 1 degree of a great circle of earth (latitude)

360 degrees= circumference of earth at equator

= 21,600 nautical miles

= 24,856.8 statute miles

 

Area Measure

1 sq ft. = 144 square inches

1 sq yd = 9 sq. ft

134

= 1,296 sq in.

1 sq rod

= 30.25 square yards

= 272.25 sq ft.

= 625 sq. links

1 acre

= 160 square rods

= 4,840 sq yds

= 43,560 sq ft.

1 sq mi.= 640 acres

= 1 section (of land)

1 township

= 6 miles square

= 36 sections

= 36 sq mi.

 

Volumes - Cubic

1,728 cubic inches = 1 cu ft.

27 cubic feet = 1 cu yd

 

Volumes - Liquid Measure

1 pint (pt) = 4 gills (gi)

= 16 fluid ounces (oz)

= 28.875 cu in.

1 quart (qt) = 2 pints

= 57.75 cu in.

1 gallon

(gal)

= 4 quarts

= 231 cu in.

= 8 pts

135

= 32 gills

1 cubic foot = 7.48 gallons

1 barrel = 31.5 gallons

1 hogshead = 2 barrels

 

Apothecaries' Fluid Measure

60 minims (min.) = 1 fluid dram (fl dr)

= 0.2256 cu in.

8 fluid drams

= 1 fluid ounce (fl oz)

= 1.8047 cu in.

16 fluid ounces = 1 pt = 28.875 cu in.

= 128 fl drs

2 pints

= 1 qt

= 57.75 cu in.

= 32 fl oz

= 256 fl drs

4 quarts

= 1 gal

= 231 cu in.

= 128 fl oz

= 1,024 fl drs

 

When necessary to distinguish the avoirdupois dram from the apothecaries' dram, or to distinguish the

avoirdupois dram or ounce from the fluid dram or ounce, or to distinguish the avoirdupois ounce or

pound from the troy or apothecaries' ounce or pound, the word “avoirdupois” or the abbreviation “avdp”

should be used in combination with the name or abbreviation of the avoirdupois unit. (The “grain” is the

same in avoirdupois, troy, and apothecaries' weights.)

136

Avoirdupois Weight

2711/32 grains = 1 dram (dr)

16 drams = 1 oz

= 437 1/2 grains

16 ounces

= 1 lb

= 256 drams

= 7,000 grains

100 pounds = 1 hundredweight (cwt)1

20 hundredweights = 1 ton (tn)

= 2,000 lbs1

In “gross” or “long” measure, the following values are

recognized:

112 pounds = 1 gross or long cwt1

20 gross or long

hundredweights

= 1 gross or long ton

= 2,240 lbs1

1. When the terms “hundredweight” and “ton” are used unmodified, they are commonly

understood to mean the 100-pound hundredweight and the 2,000-pound ton, respectively;

these units may be designated “net” or “short” when necessary to distinguish them from the

corresponding units in gross or long measure.

When necessary to distinguish the dry pint or quart from the liquid pint or quart, the word “dry” should

be used in combination with the name or abbreviation of the dry unit.

Volume - Dry Measure

1 quart = 2 pints

= 67.2006 cu in.

1 peck (pk) = 8 quarts

137

= 537.605 cu in.

= 16 pts

1 bushel (bu)

= 4 pecks

= 2,150.42 cu in.

= 32 qts

 

Apothecaries' Weight

20 grains =1 scruple (s ap)

3 scruples

= 1 dram apothecaries' (dr

ap)

= 60 grains

8 drams apothecaries'

= 1 ounce apothecaries' (oz

ap)

= 24 scruples = 480 grains

12 ounces

apothecaries'

= 1 pound apothecaries' (lb

ap)

= 96 drams apothecaries'

= 288 scruples

= 5,760 grains

 

Units of Circular Measure

Second ('') = —

Minute (') = 60 seconds

Degree (°) = 60 minutes

Right angle = 90 degrees

Straight angle = 180 degrees

Circle = 360 degrees

138

 

Troy Weight

24 grains = 1 pennyweight (dwt)

20 pennyweights = 1 ounce troy (oz t)

= 480 grains

12 ounces troy

= 1 pound troy (lb t)

= 240 pennyweights

= 5,760 grains

 

Gunter's or Surveyor's Chain Measure

7.92 inches =1 link (li)

100 links

= 1 chain (ch)

= 4 rods

= 66 ft.

80 chains

=1 statute mile

= 320 rods

= 5,280 ft.

 

 Definitions of the SI / Metric Base Units

Unit of length Meter

The meter is the length of the

path travelled by light in vacuum

during a time interval of

1/299,792,458 of a second.

Unit of mass kilogram The kilogram is the unit of mass;

139

it is equal to the mass of the

international prototype of the

kilogram.

Unit of time second

The second is the duration of 9

192 631 770 periods of the

radiation corresponding to the

transition between the two

hyperfine levels of the ground

state of the cesium 133 atom.

Unit of electric

current ampere

The ampere is that constant

current which, if maintained in

two straight parallel conductors

of infinite length, of negligible

circular cross-section, and placed

1 meter apart in vacuum, would

produce between these

conductors a force equal to 2 x

10-7 newton per meter of length.

Unit of

thermodynamic

temperature

Kelvin

The kelvin, unit of

thermodynamic temperature, is

the fraction 1/273.16 of the

thermodynamic temperature of

the triple point of water.

Unit of amount

of substance

Mole 1. The mole is the amount of

substance of a system which

contains as many elementary

entities as there are atoms in

0.012 kilogram of carbon 12; its

symbol is "mol."

2. When the mole is used, the

elementary entities must be

specified and may be atoms,

140

molecules, ions, electrons, other

particles, or specified groups of

such particles.

Unit of

luminous

intensity

candela

The candela is the luminous

intensity, in a given direction, of a

source that emits monochromatic

radiation of frequency 540 x 1012

hertz and that has a radiant

intensity in that direction of 1/683

watt per steradian.

 

MetricPrefixes:

To help the SI units apply to a wide range of phenomena, the 19th General Conference on

Weights and Measures in 1991 extended the list of metric prefixes so that it reaches from

yotta- at 1024 (one septillion) to yocto- at 10-24 (one septillionth). Here are the metric prefixes,

with their numerical equivalents stated in the American system for naming large numbers:

 

SI Unit Prefixes

Prefix Symbol Meaning Base Unit Multiplied by Factor

yotta- Y septillion 1,000,000,000,000,000,000,000,000 1024

zetta- Z sextillion 1,000,000,000,000,000,000,000 1021

exa- E quintillion 1,000,000,000,000,000,000 1018

peta- p quadrillion 1,000,000,000,000,000 1015

tera- T trillion 1,000,000,000,000 1012

giga- g billion 1,000,000,000 109

mega- M million 1,000,000 106

141

kilo- k thousand 1,000 103

Hector- h hundred 100 102

deca- da ten 10 101

Base units, no prefix - Ex.- meter, liter, gram 100

deci- d tenth 0.1 10-1

centi- c hundredth 0.01 10-2

milli- m thousandth 0.001 10-3

micro- u millionth 0.000001 10-6

nano- n billionth 0.000000001 10-9

pico- p trillionth 0.000000000001 10-12

femto- f quadrillionth 0.000000000000001 10-15

atto- a quintillionth 0.000000000000000001 10-18

zepto- z sextillionth 0.000000000000000000001 10-21

yocto- y septillionth 0.000000000000000000000001 10-24

What's it all mean? A kilometer is a thousand meters, a kiloliter is a thousand liters, a

kilogram is a thousand grams; a centimeter is a hundredth of a meter, a centiliter is a

hundredth of a liter, a centigram is a hundredth of a gram. The prefixes can be applied to any

kind of SI unit. Only temperature degrees (Celsius or Kelvin in SI) seem to be exempt. Also,

there is no accepted metric time system in use.

Unit Conversions :

If you are given a measurement from the left hand side and want to convert to the units on the

right hand side, just multiply your number by the given conversion factor.

Example - Feet to Meters

(10 ft) X (0.304800 m/ ft) X (1/3 yd/ft) = 54.68066 yd

142

Conversely, you can convert units from the right hand side to those units on the left by dividing

by the conversion factor

Example - Millimeters to Inches

(50 mm) / (25.4 mm/in) = 1.97 in.

Common Engineering Design Conversion Factors 

Given Multiply by To Find

Length [L]

Foot (ft) 0.304800 Meter (m)

Inch (in) 25.4000 Millimeter (mm)

Mile (mi) 1.609344 Kilometer (km)

Area [L]2

ft2 0.092903 m2

in2 645.16 mm2

in2 6.45160 cm2

Volume [L]3 & Capacity

in3 16.3871 cm3

ft3 0.028317 m3

ft3 7.4805 Gallon

ft3 28.3168 Liter (l)

Gallon 3.785412 Liter

Energy, Work or Heat [M] [L]2 [t]-2

Btu 1.05435 kJ

Btu 0.251996 kcal

Calories (cal) 4.184* Joules (J)

143

ft-lbf 1.355818 J

ft-lbf 0.138255 kgf-m

hp-hr 2.6845 MJ

KWH 3.600 MJ

m-kgf 9.80665* J

N-m 1. J

Flow Rate [L]3 [t]-1

Ft3/min 7.4805 gal/min

Ft3/min 0.471934 l/s

gal/min 0.063090 l/s

Force or Weight [M] [L] [t]-2

kgf 9.80665* Newton (N)

lbf 4.44822 N

lbf 0.453592 Kgf

Fracture Toughness

Ksi sqr(in) 1.098800 MPa sqr(m)

Heat Content

Btu/lbm 0.555556 cal/g

Btu/lbm 2.324444 J/g

Btu/ft3 0.037234 MJ/m3

Heat Flux

Btu/hr-ft2 7.5346 E-5 cal/s-cm2

Btu/hr-ft2 3.1525 W/m2

cal/s-cm2 4.184* W/cm2

Mass Density [M] [L]-3

144

lbm/in3 27.68 g/cm3

lbm/ft3 16.0184 kg/m3

Power [M] [L]2 [t]-3

Btu/hr 0.292875 Watt (W)

Ft-lbf/s 1.355818 W

Horsepower (hp) 745.6999 W

Horsepower 550.* ft-lbf/s

Pressure (fluid) [M] [L]-1 [t]-2

Atmosphere

(atm)

14.696 lbf/in2

atm 1.01325

E5*

Pascal (Pa)

lbf/ft2 47.88026 Pa

lbf/in2 27.6807 in. H20 at 39.2°F

Stress [M] [L]-1 [t]-2

kgf/cm2 9.80665 E-

2*

MPa

ksi 6.89476 MPa

N/mm2 1. MPa

kgf/mm2 1.42231 ksi

Specific Heat

Btu/lbm-°F 1. cal/g-°C

Temperature*

Fahrenheit (°F-32) /1.8 Celsius

Fahrenheit °F+459.67 Rankine

145

Celsius °C+273.16 Kelvin

Rankine R/1.8 Kelvin

Thermal Conductivity

Btu-ft/hr-ft2-°F 14.8816 cal-cm/hr-cm2-°C

Basic Fluid Power Formulas / Hydraulics / Pneumatics

Variable Word Formula w/ Units Simplified Formula

Fluid Pressure - P (PSI) = Force (Pounds) / Area

( Sq. In.)

P  =  F / A

Fluid Flow Rate - Q GPM= Flow (Gallons) / Unit

Time (Minutes)

Q = V / T

Fluid Power in

Horsepower - HP

Horsepower = Pressure (PSIG)

× Flow (GPM)/ 1714

HP = PQ / 1714

Actuator Formulas

Variable Word Formula w/ Units Simplified Formula

Cylinder Area - A ( Sq. In.) = π × Radius (inch)2 A  =  π  × R2

(Sq. In.) = π × Diameter (inch)2 /

4

A  = π  × D2 / 4

Cylinder Force - F (Pounds) = Pressure (psi)   ×

Area (sq. in.)

F  =  P × A

Cylinder Speed - v (Feet / sec.) = (231 × Flow Rate

(gpm)) / (12 × 60 × Area)

v   =  (0.3208 × gpm) /

A

Cylinder Volume

Capacity - V

Volume = π × Radius2 × Stroke

(In.) / 231

V = π × R2 × L / 231

(L = length of stroke)

Cylinder Flow Rate -

Q

Volume = 12 × 60 × Velocity

(Ft./Sec.) × Net Area(In.)2 / 231

Q = 3.11688 × v × A

146

Fluid Motor Torque -

T

Torque (in. lbs.) = Pressure (psi)

× disp. (in.3 / rev.) / 6.2822

T  =  P × d / 6.2822

Torque = HP × 63025 / RPM T = HP × 63025 / n

Torque = Flow Rate (GPM) ×

Pressure × 36.77 / RPM

T = 36.77 × Q × P / n

Fluid Motor Speed - n Speed (RPM)  =  (231 × GPM) /

Disp. (in.)3

n  =  (231 × GPM) / d

Fluid Motor

Horsepower - HP

HP = Torque (in. lbs.) × rpm /

63025

HP  =  T × n / 63025

Pump Formulas

Variable Word Formula w/ Units Simplified Formula

Pump Output Flow -

GPM

GPM = (Speed (rpm) × disp.

(cu. in.)) / 231

GPM =  (n ×d) / 231

Pump Input

Horsepower - HP

HP =  GPM × Pressure (psi) /

1714 × Efficiency

HP  =  (Q ×P) / 1714

× E

Pump Efficiency - E Overall Efficiency = Output HP /

Input HP

EOverall = HPOut / HPIn X

100

Overall Efficiency = Volumetric

Eff. × Mechanical Eff.

EOverall = EffVol. × EffMech.

Pump Volumetric

Efficiency - E

Volumetric Efficiency = Actual

Flow Rate Output (GPM) /

Theoretical Flow Rate Output

(GPM) × 100

EffVol. = QAct. / QTheo. X

100

Pump Mechanical

Efficiency - E

Mechanical Efficiency =

Theoretical Torque to Drive /

Actual Torque to Drive × 100

EffMech = TTheo. / TAct. ×

100

Pump Displacement -

CIPR

Displacement (In.3 / rev.) = Flow

Rate (GPM) × 231 / Pump RPM

CIPR = GPM × 231 /

RPM

Pump Torque - T Torque = Horsepower × 63025 / T = 63025 × HP /

147

RPM RPM

Torque = Pressure (PSIG) ×

Pump Displacement (CIPR) / 2π

T = P × CIPR / 6.28

 

General Fluid Power Guidelines:

Horsepower for driving a pump: 

For every 1 hp of drive, the equivalent of 1 gpm @ 1500 psi can be produced.

Horsepower for idling a pump: 

To idle a pump when it is unloaded will require about 5% of it's full rated power

Wattage for heating hydraulic oil: 

Each watt will raise the temperature of 1 gallon of oil by 1° F. per hour.

Flow velocity in hydraulic lines: 

Pump suction lines 2 to 4 feet per second, pressure lines up to 500 psi - 10 to 15 ft./sec.,

pressure lines 500 to 3000 psi - 15 to 20 ft./sec.; all oil lines in air-over-oil systems; 4

ft./sec.

NON-DESTRUCTIVE EVALUATION/TESTING - NDE/NDT :

148

Overview :

The process of nondestructive testing determines the existence of flaws, discontinuities, leaks,

contamination, thermal anomalies, or imperfections in materials, components or assemblies

without impairing the integrity or function of the inspected component. NDE is also utilized for

real-time monitoring during manufacturing, measurement of physical properties such as

hardness and internal stress, inspection of assemblies for tolerances, alignment, and periodic

in-service monitoring of flaw/damage growth in order to determine the maintenance

requirements and to assure the reliability and continued safe operation of the part.

Nondestructive evaluation (NDE) is becoming increasingly important to the design-through-

manufacture process. The cost of parts and components is ever-increasing due to the

corresponding costs of material and labor. Consequently, emphasis is being placed on use of

NDE early in the design and fabrication process. Often components are too costly to permit the

luxury of destructively testing a number of them to demonstrate their design goals.

Environmental and liability concerns are also resulting in increased use of NDE.

NDT is a Quality Assurance management tool which can give impressive results when used

correctly. It requires an understanding of the capabilities and limitations of the various methods

available and knowledge of the relevant standards and specifications for performing the tests.

Materials, products and equipment which fail to achieve their design requirements or projected

life due to undetected defects may require expensive repair or early replacement Such defects

may also be the cause of unsafe conditions or catastrophic failure, as well as loss of revenue

due to unplanned plant shutdown.

NDT technology is constantly being improved and new methods developed, particularly in an

effort to keep pace with the development of new materials (i.e. composites) and applications.

Advances in the use of lasers and imaging technology (including video, holography and

thermography) have made non contact NDT more viable in many situations. Optical fibers and

new piezo-electric materials are allowing the creation of intelligent materials and structures

which can not only monitor themselves but may even respond to their environment. Computer

advances have allowed signal processing techniques and expert systems to be used which

enhances the quality of the information obtained using traditional and new NDT methods.

Basic NDT Methods:

149

1. Visual Testing (VT) - Ultraviolet, Infrared, and Visible Light.

2. Penetrant Testing (PT)

3. Electromagnetic Testing (ET)

4. Magnetic Particle Testing (MT)

5. Acoustic Emissions (AE)

6. Utrasonic Testing (UT)

7. Radiography (RT) - X-Rays, Gamma Rays, Beta Particles, Protons, Neutrons

Visual / Optical Testing - VT

Visual inspection is one NDT method used extensively to evaluate the condition or the quality

of a weld or component. It is easily carried out, inexpensive and usually doesn't require special

equipment. It requires good vision, good lighting and the knowledge of what to look for. Visual

inspection can be enhanced by various methods ranging from low power magnifying glasses

through to boroscopes.

InfraredThermography:

Thermography is the use of an infrared imaging and measurement camera to "see" and

"measure " thermal energy emitted from an object.

Thermal, or infrared energy, is light that is not visible because its wavelength is too long to be

detected by the human eye; it's the part of the electromagnetic spectrum that we perceive as

heat. Unlike visible light, in the infrared world, everything with a temperature above absolute

zero emits heat. Even very cold objects, like ice cubes, emit infrared. The higher the object's

temperature, the greater the IR radiation emitted. Infrared allows us to see what our eyes

cannot.

Infrared thermography cameras produce images of invisible infrared or "heat" radiation and

provide precise non-contact temperature measurement capabilities. Nearly everything gets hot

before it fails, making infrared cameras extremely cost-effective, valuable diagnostic tools in

many diverse applications. And as industry strives to improve manufacturing efficiencies,

manage energy, improve product quality, and enhance worker safety, new applications for

infrared cameras continually emerge.

150

Passive Thermography :

The objective of conventional thermography is the measurement of surface temperatures.

Using passive thermography, one can get contactless information about the surface.

Transient Thermography :

Transient thermography is applicable for the detection of deep-seated defects in materials with

low temperature conductivity. The sample is heated up over a long period of time in a furnace

(non-destructive temperature, e.g. 50°C). After that it is brought into a normal climate and at

the same time the surface temperature is gathered with an infrared camera. Because the

sample is losing heat to the environment due to convection and radiation, the surface is

cooling down. Heat is flowing from the inside to the surface of the sample. A defect, typically a

delamination or a cavity, is a thermal barrier for the heat flow. This leads to an inhomogeneous

temperature distribution on the surface, which is detected from the infrared camera. Only one

way, from the defect to the surface of the sample, is relevant for the measurement: The heat

has to cover only half the distance compared to other thermal methods. This explains, why it is

possible to detect deep-seated defects in short time with this method.

Laser Shearography :

Shearography is a variation of holography specifically designed for NDT applications.

Shearography provides full-field, non-contact nondestructive testing for rapid wide-field

inspection of composites, bonded structures and other advanced materials. Shearography is

an optical video strain gauge and an appropriately applied stress is used to locate strain

concentrations caused by internal defects.

OpticalHolography:

Optical holography is an imaging method, which records the amplitude and phase of light

reflected from an object as an interferometric pattern on film. It thus allows reconstruction of

the full 3-D image of the object. In HNDT, the test sample is interferometrically compared in

two different stressed states. Stressing can be mechanical, thermal, vibration etc. The resulting

interference pattern contours the deformation undergone by the specimen in between the two

recordings. Surface as well as sub-surface defects show distortions in the otherwise uniform

pattern. In addition, the characteristics of the component, such as vibration modes, mechanical

151

properties, residual stress etc. can be identified through holographic inspection. Applications in

fluid mechanics and gas dynamics also abound.

Penetrant Testing - (PT) :

Apart from visual inspection this is probably the oldest and most widely used of all the NDT

methods. It can be used on any non-porous material. Its use is confined to the detection of

surface breking defect. inspection is used to reveal surface breaking flaws by bleedout of a

colored or fluorescent dye from the flaw. Test objects are coated with visible or fluorescent dye

solution. Excess dye is then removed from the surface, and a developer is applied. The

developer acts as blotter, drawing trapped penetrant out of imperfections open to the surface.

With visible dyes, vivid color contrasts between the penetrant and developer make "bleedout"

easy to see. With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce

brightly, thus allowing imperfections to be readily seen.

Penetrant inspection can be used on any material and is most often used on materials clad in

stainless steel, and stainless welded items which cannot be inspected by other methods.

Electromagnetic Testing - (ET) :

Eddy current, penetrating radar and other electromagnetic techniques are used to detect or

measure flaws, bond or weld integrity, thickness, electrical conductivity, detect the presence of

152

rebar or metals. Eddy current is the most widely applied electromagnetic NDT technique. The

eddy current method is also useful in sorting alloys and verifying heat treatment. Eddy current

testing uses an electromagnet to induce an eddy current in a conductive sample. The

response of the material to the induced current is sensed. Since the probe does not have to

contact the work surface, eddy current testing is useful on rough surfaces or surfaces with wet

films or coatings.

Methods include --

Eddy Current Testing :

In standard eddy current testing, a circular coil carrying an AC current is placed in close

proximity to an electrically conductive specimen. The alternating current in the coil generates a

changing magnetic field, which interacts with the test object and induces eddy currents.

Variations in the phase and magnitude of these eddy currents can be monitored using a

second 'search' coil, or by measuring changes to the current flowing in the primary 'excitation'

coil. Variations in the electrical conductivity or magnetic permeability of the test object, or the

presence of any flaws, will cause a change in eddy current flow and a corresponding change in

the phase and amplitude of the measured current. This is the basis of standard (flat coil) eddy

current inspection, the most widely used eddy current technique.

Barkhausen Noise Analysis (BNA) :

Barkhausen Noise Analysis (BNA) method, also referred to as the Magnetoelastic or the

Micromagnetic method is based on a concept of inductive measurement of a noise-like signal,

generated when magnetic field is applied to a ferromagnetic sample. After a German scientist

Professor Heinrich Barkhausen who explained the nature of this phenomenon already in 1919,

this signal is called Barkhausen noise.

Ground Penetrating Radar (GPR) :

153

Ground penetrating radar is a nondestructive geophysical method that produces a continuous

cross-sectional profile or record of subsurface features, without drilling, probing, or digging.

Ground penetrating radar (GPR) profiles are used for evaluating the location and depth of

buried objects and to investigate the presence and continuity of natural subsurface conditions

and features.

Ground penetrating radar operates by transmitting pulses of ultra high frequency radio waves

(microwave electromagnetic energy) down into the ground through a transducer or antenna.

The transmitted energy is reflected from various buried objects or distinct contacts between

different earth materials. The antenna then receives the reflected waves and stores them in the

digital control unit.

Magnetic Resonance Imaging (MRI) :

Magnetic resonance imaging (MRI) is an imaging technique used primarily in medical settings

to produce high quality images of the inside of the human body. MRI is based on the principles

of nuclear magnetic resonance (NMR), a spectroscopic technique used by scientists to obtain

microscopic chemical and physical information about molecules.

Microwave Inspection :

Microwave (or short-pulse radar) inspection techniques involve the transmission and reflection

of relatively low frequency (often around 1 GHz) electromagnetic (EM) waves in various

materials. The term ground penetrating radar (GPR) is often used to describe microwave

inspection systems for locating utility lines below ground and mild steel rebar in concrete

decks/pavements. Microwave inspection exploits the principle that dielectric properties of

various materials affect the transmission and reflection of EM waves in those materials.

Magnetic Particle Testing - (MT) :

154

Magnetic particle inspection (MPI) is used for the detection of surface and near-surface flaws

in ferromagnetic materials. A magnetic field is applied to the specimen, either locally or overall,

using a permanent magnet, electromagnet, flexible cables or hand-held prods. If the material is

sound, most of the magnetic flux is concentrated below the material's surface. However, if a

flaw is present, such that it interacts with the magnetic field, the flux is distorted locally and

'leaks' from the surface of the specimen in the region of the flaw. Fine magnetic particles,

applied to the surface of the specimen, are attracted to the area of flux leakage, creating a

visible indication of the flaw.

The materials commonly used for this purpose are black iron particles and red or yellow iron

oxides. In some cases, the iron particles are coated with a fluorescent material enabling them

to be viewed under a UV lamp in darkened conditions.

Acoustic Emission (AE) :

155

Acoustic emission is the technical term for the noise emitted by materials and structures when

they are subjected to stress. Types of stresses can be mechanical, thermal or chemical. This

emission is caused by the rapid release of energy within a material due to events such as

crack initiation and growth, crack opening and closure, dislocation movement, twinning, and

phase transformation in monolithic materials and fiber breakage and fiber-matrix debonding in

composites.

The subsequent extension occurring under an applied stress generates transient elastic waves

which propagate through the solid to the surface where they can be detected by one or more

sensors. The sensor is a transducer that converts the mechanical wave into an electrical

signal. In this way information about the existence and location of possible sources is obtained.

Acoustic emission may be described as the "sound" emanating from regions of localized

deformation within a material.

Until about 1973, acoustic emission technology was primarily employed in the non-destructive

testing of such structures as pipelines, heat exchangers, storage tanks, pressure vessels, and

coolant circuits of nuclear reactor plants. However, this technique was soon applied to the

detection of defects in rotating equipment bearings.

 

Ultrasonic Testing (UT) :

156

Ultrasonic inspection is a nondestructive method in which beams of high-frequency sound

waves are introduced into materials for the detection of subsurface flaws in the material. The

sound waves travel through the material with some attendant loss of energy (attenuation) and

are reflected at interfaces (cracks or flaws). The reflected beam is displayed and then analyzed

to define the presence and location of flaws or discontinuities.

The most commonly used ultrasonic testing technique is pulse echo, wherein sound is

introduced into a test object and reflections (echoes) are returned to a receiver from internal

imperfections or from the part's geometrical surfaces.

Applications include inspections for voids, cracks, and laminations, inspections of welds and

thickness measurements.

Radiography Testing - (RT) :

This technique involves the use of penetrating gamma or X-radiation

to examine parts and products for imperfections. An X-ray machine or radioactive isotope is

157

used as a source of radiation. Radiation is directed through a part and onto film or other media.

The resulting shadowgraph shows the internal soundness of the part. Possible imperfections

are indicated as density changes in the film in the same manner as an X-ray shows broken

bones.

Radiographic applications fall into two distinct categories evaluation of material properties and

evaluation of manufacturing and assembly properties. Material property evaluation includes the

determination of composition, density, uniformity, and cell or particle size. Manufacturing and

assembly property evaluation is normally concerned with dimensions, flaws (voids, inclusions,

and cracks), bond integrity (welds, brazes, etc.), and verification of proper assembly of

component pieces.

Computed Tomography - (CT):

Computed Tomography (CT) is a powerful nondestructive evaluation (NDE) technique for

producing 2-D and 3-D cross-sectional images of an object from flat X-ray images.

Characteristics of the internal structure of an object such as dimensions, shape, internal

defects, and density are readily available from CT images.

Photon Induced Positron Annihilation (PIPA)

& Distributed Source Positron Annihilation (DSPA) :

Photon Induced Positron Annihilation (PIPA) involves penetrating materials with a photon

beam. This process creates positrons, which are attracted to nano-sized defects in the

material. Eventually, the positrons collide with electrons in the material and are annihilated,

releasing energy in the form of gamma rays. The gamma ray energy spectrum creates a

distinct and readable signature of the size, quantity and type of defects present in the material.

Distributed Source Positron Annihilation (DSPA) uses a positron source emitter to deposit

positrons into the subject material. The process is similar to PIPA after the positrons are

deposited and attracted to nano-sized defects in the material.

PIPA and DSPA technologies detect fatigue, embrittlement, and other forms of structural

damage in materials at the atomic level, before cracks appear. PIPA and DSPA can also

accurately determine the remaining life of various materials and are more precise than any

other existing flaw detection technology on the market.

158

Neutron Radiography :

Neutron Radiography is an imaging technique which provides images similar to X-ray

radiography. The difference between neutron and X-ray interaction mechanisms produce

significantly different and often complementary information. While X-ray attenuation is directly

dependent on atomic number, neutrons are efficiently attenuated by only a few specific

elements. For example, organic materials or water are clearly visible in neutron radiographs

because of their high hydrogen content, while many structural materials such as aluminium or

steel are nearly transparent. At the present time, Neutron Radiography is one of the main NDT

techniques able to satisfy the quality-control requirements of explosive devices used in

aerospace and defense programs.

X-ray Diffraction (XRD) :

X-ray diffraction is a versatile, non-destructive technique that reveals detailed information

about the chemical composition and crystallographic structure of natural and manufactured

materials.

A crystal lattice is a regular three-dimensional distribution (cubic, rhombic, etc.) of atoms in

space. These are arranged so that they form a series of parallel planes separated from one

another by a distance d, which varies according to the nature of the material. For any crystal,

planes exist in a number of different orientations - each with its own specific d-spacing.

When a monochromatic X-ray beam with wavelength lambda is projected onto a crystalline

material at an angle theta, diffraction occurs only when the distance traveled by the rays

reflected from successive planes differs by a complete number n of wavelengths.

By varying the angle theta, the Bragg's Law conditions are satisfied by different d-spacings in

polycrystalline materials. Plotting the angular positions and intensities of the resultant diffracted

peaks of radiation produces a pattern, which is characteristic of the sample. Where a mixture

of different phases is present, the resultant diffractogram is formed by addition of the individual

patterns.

Based on the principle of X-ray diffraction, a wealth of structural, physical and chemical

information about the material investigated can be obtained. A host of application techniques

159

for various material classes is available, each revealing its own specific details of the sample

studied.

X-ray Fluorescence (XRF) :

X-ray fluorescence is a technique of chemical analysis. The technique involves aiming an X-

ray beam at the surface of an object; this beam is about 2 mm in diameter.

The interaction of X-rays with an object causes secondary (fluorescent) X-rays to be

generated. Each element present in the object produces X-rays with different energies. These

X-rays can be detected and displayed as a spectrum of intensity against energy: the positions

of the peaks identify which elements are present and the peak heights identify how much of

each element is present.

This is often used by museum curators to study ancient objects because measurements are

non-destructive and usually the whole object can be analyzed, rather than a sample removed

from one.

160

Surface Roughness Table - Shows the roughness average for different manufacturing

processes in micrometers and microinches. The values are shown with a typical range and a

less frequent range for each manufacturing process.

  Average Range

  Less Frequent Range

Manufacturing

Process

Roughness Average

Top Number - Micrometers

Bottom Number - (Microinches)

 50

(2000)

25

(1000)

12.5

(500)

6.3

(250)

3.2

(125)

1.6

(63)

0.80

(32)

0.40

(16)

0.20

(8)

0.10

(4)

0.05

(2)

0.025

(1)

0.012

(.5)

Flame Cutting                                                    

Snagging                                                    

Sawing                                                    

Planing,

Shaping                                                   

Drilling                                                    

Chemical

Milling                                                   

Elect Discharge

Machining                                                    

Milling                                                    

Broaching                                                    

Reaming                                                    

Electron Beam                                                    

Laser                                                    

161

Electro-

Chemical                                                   

Boring, Turning                                                    

Barrel Finishing                                                    

50

(2000)

25

(1000)

12.5

(500)

6.3

(250)

3.2

(125)

1.6

(63)

0.80

(32)

0.40

(16)

0.20

(8)

0.10

(4)

0.05

(2)

0.025

(1)

0.012

(.5)

Electrolytic

Grinding                                                   

Roller

Burnishing                                                   

Grinding                                                    

Honing                                                    

Electro-Polish                                                    

Polishing                                                    

Lapping                                                    

Super Finishing                                                    

Sand Casting                                                    

Hot Rolling                                                    

Forging                                                    

Permanent

Mold Casting                                                   

Investment

Casting                                                   

Extruding                                                    

Cold Rolling,

Drawing                                                   

Die Casting                                                    

162

50

(2000)

25

(1000)

12.5

(500)

6.3

(250)

3.2

(125)

1.6

(63)

0.80

(32)

0.40

(16)

0.20

(8)

0.10

(4)

0.05

(2)

0.025

(1)

0.012

(.5)

 

Melting Temperatures

of Common Metals

Metal

Melting Point

(oF)

Titanium 3020

Mild Steel 2730

Wrought Iron 2700-2900

Stainless Steel 2600

Hard Steel 2555

Gray Cast Iron 2060-2200

Ductile Iron 2100

Copper 1985

Red Brass 1832

Silver 1763

Yellow Brass 1706

Aluminum Alloy 865-1240

Magnesium Alloy 660-1200

Lead 621

Babbitt

480

163

Physical Properties Of Elements

ElementSymbo

l

Atomic

Weight

Melting Point Boiling

Point oF

Density

g/cm3oF oC

Aluminum Al 26.97 1220 660 3272 2.70

Antimony Sb 121.76 1167 630 2516 6.62

Barium Ba 137.36 1562 850 2084 3.50

Beryllium Be 9.02 2462 1350 2732 1.82

Bismuth Bi 209.00 520 271 2642 9.8

Boron B 10.82 4172 2282 4622 2.30

Cadmium Cd 112.41 610 321 1408 8.65

Calcium Ca 40.08 1564 851 2522 1.55

Carbon C 12.00 - - 6512 2.22

Cerium Ce 140.13 1427 640 2552 6.79

Chromium Cr 52.01 3326 1812 3992 7.14

Cobalt Co 58.94 2696 1480 5252 8.90

Columbium Nb 92.91 3542 1932 5972 8.57

Copper Cu 63.57 1982 1082 4259 8.94

Gold Au 197.20 1945 1062 4712 1930

Iron Fe 55.84 2795 1535 5430 7.87

Lead Pb 207.22 621 327 2948 11.35

Lithium Li 6.94 367 186 2437 0.53

Magnesium Mg 24.32 1204 652 2007 1.74

Manganese Mn 54.94 2273 1245 3452 7.20

164

Mercury Hg 200.61 -38 - 676 13.55

Molybdenum Mo 96.00 4748 2602 6692 10.20

Nickel Ni 58.69 2645 1452 5252 8.85

Palladium Pd 106.70 2831 1555 3992 12.00

Phosphorou

sP 31.02 111 42 536 1.82

Platinum Pt 195.23 3224 1755 7772 21.45

Potassium K 39.09 144 62 1400 0.86

Rhodium Rh 102.91 3551 1882 4532 12.50

Selenium Se 78.96 428 220 1270 4.81

Silicon Si 28.06 2588 1420 4712 2.40

Silver Ag 107.88 1761 961 3542 10.50

Sodium Na 22.99 207 97 1616 0.97

Strontium Sr 87.63 1472 800 2102 2.60

Sulfur S 32.06 235 112 832 2.07

Tantalum Ta 180.88 5162 2832 7412 16.60

Tellurium Te 127.61 846 451 2534 6.24

Thallium Ti 204.39 578 302 3002 11.85

Thorium Th 232.12 3353 1827 5432 11.50

Tin Sn 118.70 450 232 4100 7.30

Titanium Ti 47.90 3272 1782 5432 4.50

Tungsten W 184.00 6098 3334 10526 19.30

Uranium U 238.14 3074 1672 6332 18.70

Vanadium V 50.95 3110 1692 5432 5.68

Zinc Zn 65.38 787 419 1661 7.14

Zirconium Zr 91.22 3092 1682 5252 6.40 

165

 

Hardness Conversion Table

Tensile

Strength

(N/mm2)

Brinell Hardness

(BHN)

Vickers

Hardness

(HV)

Rockwell

Hardness

(HRB)

Rockwell

Hardness

(HRC)

285 86 90    

320 95 100 56.2

350 105 110 62.3  

385 114 120 66.7

415 124 130 71.2  

450 133 140 75.0

480 143 150 78.7  

510 152 160 81.7

545 162 170 85.0  

575 171 180 87.1

610 181 190 89.5  

640 190 200 91.5

675 199 210 93.5  

705 209 220 95.0

740 219 230 96.7  

770 228 240 98.1  

800 238 250 99.5  

820 242 255   23.1

166

850 252 265   24.8

880 261 275   26.4

900 266 280   27.1

930 276 290   28.5

950 280 295   29.2

995 295 310   31.0

1030 304 320   32.2

1060 314 330   33.3

1095 323 340   34.4

1125 333 350   35.5

1155 342 360   36.6

1190 352 370   37.7

1220 361 380   38.8

1255 371 390   39.8

1290 380 400   40.8

1320 390 410   41.8

1350 399 420   42.7

1385 409 430   43.6

1420 418 440   44.5

1455 428 450   45.3

1485 437 460   46.1

1520 447 470   46.9

1555 456 480   47.7

1595 466 490   48.4

1630 475 500   49.1

1665 485 510   49.8

1700 494 520   50.5

167

1740 504 530   51.1

1775 513 540   51.7

1810 523 550   52.3

1845 532 560   53.0

1880 542 570   53.6

1920 551 580   54.1

1955 561 590   54.7

1995 570 600   55.2

2030 580 610   55.7

2070 589 620   56.3

2105 599 630   56.8

2145 608 640   57.3

2180 618 650   57.8

 

Densities of

Common Materials

168

Material Density

(g/cm3)

Liquids

Water at 4 °C1.0000

Water at 20 °C0.998

Gasoline0.70

Mercury13.6

Milk1.03

Material Density

(g/cm3)

Solids

Magnesium1.7

Aluminum2.7

Brass 8.55

Copper8.3-9.0

Gold19.3

Iron7.8

Zinc7.14

Steel8.03

169

.Lead11.3

Platinum21.4

Uranium18.7

Osmium22.5

Ice at 0 C0.92

Wood0.67

Material Density

(g/cm3)

Gases at Standard Temperature and

Pressure

Air0.001293

Carbon dioxide.001977

Carbon monoxide0.00125

Hydrogen0.00009

Helium0.000178

Nitrogen0.001251

 

170