U3PEA01: PRODUCTION TECHNOLOGY

PREPARED BY

G.JEYAKUMAR

AUTOMOBILE ENGG DEPT

UNIT I

Casting Process

Casting

Refractory mold pour liquid metal solidify, remove finish

• VERSATILE: complex geometry, internal cavities, hollow sections

• VERSATILE: small (~10 grams) very large parts (~1000 Kg)

• ECONOMICAL: little wastage (extra metal is re-used)

• ISOTROPIC: cast parts have same properties along all directions

• Casting Process;

• Casting is the process of pouring molten metal into the previously made cavity to the desired

shape and allow it to solidify.

• The following are the basic operations of casting process – Pattern making– Melting the metal– Pouring it into a previously made mould which

confirms to the shape of desired component.

• Pattern

• A pattern is an element used for making cavities in the mould, into which molten

• metal is poured to produce a casting.

• Requirements of a good pattern, and pattern allowances. – Secure the desired shape and size of the casting– Simple in design, for ease of manufacture– Cheap and readily availableLight in mass and

convenient to handle– Have high strength

• Pattern materials– Wood– Common metals such as Brass, cast Iron,

Aluminium and white metal etc.– Plastic– Gypsum– Pattern allowances– Shrinkage allowance– Machining allowance– Draft allowance– Shake allowance

• Distortion allowance

• Different types of patterns

• Split or Parted Pattern

• Loose Piece Pattern

• Draw backs

• Gated Patterns.

• Match Plate pattern

• Cope and Drag Pattern

• Sweep Patterns.

• MOULD PREPARATION

•  Green sand mould :

•   A green sand mould is composed of mixture of sand, clay and water.

•   Dry sand mould :

•   Dry sand moulds are basically green sand moulds with 1 to 2% cereal flour and 1 to 2% pitch.

• Materials used in mould preparation

• Silica sand, Binder, Additives and water

• .

• Various properties of moulding sand .

•  Permeability

• Strength or CohesivenessRefractoriness.

• Plasticity or flowability

• Collapsibility

• Adhesiveness.

• Co-efficient of Expansion

• Different moulding sand test procedures.

• The following tests have been recommended by B.I.S.

• 1. Moisture content test

• 2. Clay content test

• 3. Permeability test

• 4. Fineness test or Sand grain size test (Sieve analysis)

• 5. Strength test

• 6. Mould hardness test.

• CORE MAKING

• Core

• is a body made of refractory material (sand or metal, metal cores being less frequently used), which is set into the prepared mould before closing and pouring it, for forming through holes, recesses, projections, undercuts and internal cavities.

• Core Prints. Core prints are the projections on a pattern and are used to make recesses (core seats) in the mould to locate the core

• Casting

• Factors to be considered for selecting a furnace for a job

• Capacity of molten metal

• Melting rate and temp armature control desired, Quality of melt required

• Method of pouring and types of product contemplated.

•  

• Cupola Furnace operation

•  The cupola is the most widely used furnace in the foundry for melting ferrous and non-ferrous metals and alloys. A cross-section of a cupola is shown. A cupola is a shaft furnace of cylindrical shape erected on legs or columns. The cupola shell is made of steel plate 8 or 10 mm thick. The interior is lined with refractory bricks to protect the shell from getting over-heated. The charge for the cupola consists of metallic materials, fuel and fluxes.

Different Casting Processes

Process Advantages Disadvantages Examples

Sand many metals, sizes, shapes, cheap poor finish & tolerance engine blocks, cylinder heads

Shell mold better accuracy, finish, higher production rate

limited part size connecting rods, gear housings

Expendablepattern

Wide range of metals, sizes, shapes

patterns have low strength

cylinder heads, brake components

Plaster mold complex shapes, good surface finish

non-ferrous metals, low production rate

prototypes of mechanical parts

Ceramic mold complex shapes, high accuracy, good finish

small sizes impellers, injection mold tooling

Investment complex shapes, excellent finish small parts, expensive jewellery

Permanent mold

good finish, low porosity, high production rate

Costly mold, simpler shapes only

gears, gear housings

Die Excellent dimensional accuracy, high production rate

costly dies, small parts,non-ferrous metals

gears, camera bodies, car wheels

Centrifugal Large cylindrical parts, good quality

Expensive, few shapes pipes, boilers, flywheels

Sand Casting

Sand Casting

cope: top half

drag: bottom half

core: for internal cavities

pattern: positive

funnel sprue runners gate cavity {risers, vents}

Sand Casting Considerations..

(d) taper

- do we need it ?

Mold cavity

chaplet

Mold cavity

chaplet

(e) core prints, chaplets

- hold the core in position - chaplet is metal (why?)

(f) cut-off, finishing

Shell mold casting - metal, 2-piece pattern, 175C-370C- coated with a lubricant (silicone)- mixture of sand, thermoset resin/epoxy- cure (baking) - remove patterns, join half-shells mold- pour metal- solidify (cooling)- break shell part

Expendable Mold Casting

- Styrofoam pattern- dipped in refractory slurry dried- sand (support)- pour liquid metal- foam evaporates, metal fills the shell- cool, solidify- break shell part

polystyrenepattern

patternsupport

sand

moltenmetal

polystyreneburns;gas escapespolystyrene

pattern

patternsupport

sand

moltenmetal

polystyreneburns;gas escapes

Plaster-mold, Ceramic-mold casting

Plaster-mold slurry: plaster of paris (CaSO4), talc, silica flour

Ceramic-mold slurry: silica, powdered Zircon (ZrSiO4)

- The slurry forms a shell over the pattern- Dried in a low temperature oven- Remove pattern- Backed by clay (strength), baked (burn-off volatiles)- cast the metal- break mold part

Plaster-mold: good finish (Why ?) plaster: low conductivity => low warpage, residual stresslow mp metal (Zn, Al, Cu, Mg)

Ceramic-mold: good finishhigh mp metals (steel, …) => impeller blades, turbines, …

Investment casting (lost wax casting)

(a) Wax pattern (injection molding)

(b) Multiple patterns assembled to wax sprue

(c) Shell built immerse into ceramic slurry immerse into fine sand (few layers)

(d) dry ceramic melt out the wax fire ceramic (burn wax)

(e) Pour molten metal (gravity) cool, solidify [Hollow casting: pouring excess metal before solidification

(f) Break ceramic shell (vibration or water blasting)

(g) Cut off parts (high-speed friction saw) finishing (polish)

Die casting

- a type of permanent mold casting- common uses: components for rice cookers, stoves, fans, washing-, drying machines, fridges, motors, toys, hand-tools, car wheels, …

HOT CHAMBER: (low mp e.g. Zn, Pb; non-alloying)(i) die is closed, gooseneck cylinder is filled with molten metal(ii) plunger pushes molten metal through gooseneck into cavity(iii) metal is held under pressure until it solidifies(iv) die opens, cores retracted; plunger returns(v) ejector pins push casting out of ejector die

COLD CHAMBER: (high mp e.g. Cu, Al)(i) die closed, molten metal is ladled into cylinder(ii) plunger pushes molten metal into die cavity(iii) metal is held under high pressure until it solidifies(iv) die opens, plunger pushes solidified slug from the cylinder(v) cores retracted(iv) ejector pins push casting off ejector die

Centrifugal casting

- permanent mold- rotated about its axis at 300 ~ 3000 rpm- molten metal is poured

- Surface finish: better along outer diameter than inner,- Impurities, inclusions, closer to the inner diameter (why ?)

Typical casting defects

UNIT II

WELDING PROCESS

Welding ProcessesFusion Welding Processes

GMAW – Gas Metal Arc Welding

SMAW – Shielded Metal Arc Welding

Non-Consumable Electrode

GTAW – Gas Tungsten Arc Welding

Electron Beam Welding

SAW – Submerged Arc Welding

Consumable Electrode

PAW – Plasma Arc Welding

High Energy Beam

Laser Beam Welding

Welding 

Welding is defined as an localized coalescence of metals, where in coalescence is obtained by heating to suitable temperature, with or without the application of pressure and with or without the use of filler metal.

Different welding processes. • Fusion Welding, Brazing & Soldering

• Solid State Welding

• Chemical, welding

• Electrical Resistance

• Diffusion, Explosion

• Mechanical

• Cold Friction Ultrasonic

• Oxyfuel gas, hermit welding

• Electron Beam, Laser Beam,Plasma arc welding

Gaswelding. 

Gas welding is a group of welding processes where in coalescence is produced by heating with a flame or flames with or without the application of pressure and with or without the use of filler material.

Welding ProcessesSMAW – Shielded Metal Arc Welding

• Slag keeps oxygen off weld bead during cooling

• Consumable electrode

• Flux produces protective gas around weld pool

• Flux coated rod

Power = VI 10 kW

Power... Current I (50 - 300 amps)Voltage V (15 - 45 volts)

• General purpose welding—widely used

• Thicknesses 1/8” – 3/4”

• Portable

Welding ProcessesElectric Arc Welding -- Polarity

SMAW - DC Polarity

Straight Polarity

Shallow penetration Deeper weld penetration

(thin metal)

Reverse Polarity

(+)(+)

(–)(–)

(–)(–)

(+)(+)

AC - Gives pulsing arc

- used for welding thick sections

Welding ProcessesGMAW – Gas Metal Arc Welding (MIG)

• DC reverse polarity - hottest arc

• MIG - Metal Inert Gas

• Consumable wire electrode

• AC - unstable arc

Groover, M., Fundamentals of Modern Manufacturing,, p. 734, 1996

Gas Metal Arc Welding (GMAW) Torch

• Shielding provided by gas

• Double productivity of SMAW

• Easily automated

GMAW

• An arc welding process that uses an arc between a continuous filler metal electrode and the weld pool to produce a fusion (melting) together of the base metal

• The process is used with a shielding gas supplied from an external source without pressure.

Welding ProcessesGMAW – Gas Metal Arc Welding (MIG)

• DC reverse polarity - hottest arc

• MIG - Metal Inert Gas

• Consumable wire electrode

• AC - unstable arc

Groover, M., Fundamentals of Modern Manufacturing,, p. 734, 1996

Gas Metal Arc Welding (GMAW) Torch

• Shielding provided by gas

• Double productivity of SMAW

• Easily automated

Welding ProcessesSAW – Submerged Arc Welding

• 300 – 2000 amps (440 V)

• Consumable wire electrodeGas Metal Arc Welding (GMAW) Torch

• Shielding provided by flux granules

• Automated process (limited to flats)

• Low UV radiation & fumes

• Flux acts as thermal insulator

• High speed & quality (4 – 10x SMAW)

• Suitable for thick plates http://www.twi.co.uk

Welding ProcessesGTAW – Gas Tungsten Arc Welding (TIG)

• Non-consumable electrode

• a.k.a. TIG - Tungsten Inert Gas

• Shield gas usually argon

• Used for thin sections of Al, Mg, Ti.

• With or without filler metal

Power 8-20 kW

Current I (200 A DC) (500 A AC)

• Most expensive, highest quality

Welding ProcessesFriction Welding (Inertia Welding)

• One part rotated, one stationary

• Stationary part forced against rotating part

• Friction converts kinetic energy to thermal energy

• Metal at interface melts and is joined

• When sufficiently hot, rotation is stopped & axial force increased

Welding ProcessesResistance Welding

Resistance Welding is the coordinated application of electric current and mechanical pressure in the proper magnitudes and for a precise period of time to create a coalescent bond between two base metals.

• Heat provided by resistance to electrical current (Q=I2Rt)

• Force applied by pneumatic cylinder

• Typical 0.5 – 10 V but up to 100,000 amps!

• Often fully or partially automated

- Spot welding

- Seam welding

Welding ProcessesResistance Welding

• Heat provided by resistance to electrical current (Q=I2Rt)

• Force applied by pneumatic cylinder

• Typical 0.5 – 10 V but up to 100,000 amps!

• Often fully or partially automated

- Spot welding

- Seam welding

Welding ProcessesDiffusion Welding

• Parts forced together at high temperature (< 0.5Tm absolute) and pressure

Kalpakjian, S., Manufacturing Engineering & Technology, p. 889, 1992

• Atoms diffuse across interface

• After sufficient time the interface disappears

• Good for dissimilar metals

• Heated in furnace or by resistance heating

• Bond can be weakened by surface impurities

Soldering & Brazing Metal Joining Processes

Soldering & Brazing

• Filler metal distributed by capillary action

• Only filler metal is melted, not base metal

• Strength of joint typically

– Can join dissimilar metals

– Less heat - can join thinner sections (relative to welding)

– stronger than filler metal itself

– weaker than base metal

– Excessive heat during service can weaken joint

• Pros & Cons

• Lower temperatures than welding

– gap at joint important (0.001 – 0.010”)

• Metallurgical bond formed between filler & base metals

LASER BEAM WELDING

Laser Beam Welding (LBW)

Keyhole welding

Laser beam

Plasma plume

Moltenmaterial

shieldinggas nozzle(optional)

workpiece motion

Plasmakeyhole

High Energy Density Processes

Focusing the Beam

Heat Surface Welding Cuttingtreatment modification

High Energy Density Processes

Advantages• Single pass weld

penetration up to 3/4” in steel

• High Travel speed• Materials need not be

conductive• No filler metal required• Low heat input

produces low distortion

• Does not require a vacuum

0.1.1.2.1.T4.95.12

0

2

4

6

8

10

12

1 3 5 7Welding speed, m/min

Wel

d p

enet

rati

on

, m

m

6 kW CO2

2 kW Nd:YAG

Soldering

Solder = Filler metal

Metal Joining Processes

Soldering

Applications:

• Printed Circuit Board (PCB) manufacture

• Pipe joining (copper pipe)

• Jewelry manufacture

Easy to solder: copper, silver, gold

Difficult to solder: aluminum, stainless steels

(can pre-plate difficult to solder metals to aid process)

• Alloys of Tin (silver, bismuth, lead)

• Melt point typically below 840 F

Flux used to clean joint & prevent oxidation

• Typically non-load bearing

Tinning = pre-coating with thin layer of solder

• separate or in core of wire (rosin-core)

PCB Soldering

• Soldering Iron & Solder Wire

Metal Joining Processes

Manual PCB Soldering

• Heating lead & placing solder

• Trim excess lead

• Heat for 2-3 sec. & place wire opposite iron

PCB Reflow Soldering Metal Joining Processes

Automated Reflow Soldering SMT = Surface Mount Technology

Printed solder paste on a printed circuit board (PCB)

• Solder Paste serves the following functions:– supply solder material to the soldering spot, – hold the components in place prior to soldering, – clean the solder lands and component leads – prevent further oxidation of the solder lands.

• Solder/Flux paste mixture applied to PCB using screen print or similar transfer method

• PCB assembly then heated in “Reflow” oven to melt solder and secure connection

Brazing

Use of low melt point filler metal to fill thin gap between mating surfaces to be joined utilizing capillary action

Metal Joining Processes

Brazing

Applications:

• Pipe/Tubing joining (HVAC)

• Filler metals include Al, Mg & Cu alloys (melt point typically above 840 F)

• Automotive - joining tubes

• Electrical equipment - joining wires

• Jewelry Making

• Flux also used

• Types of brazing classified by heating method:

– Torch, Furnace, Resistance

• Joint can possess significant strength

Brazing

Use of low melt point filler metal to fill thin gap between mating surfaces to be joined utilizing capillary action

Metal Joining Processes

Brazing

Applications:

• Pipe/Tubing joining (HVAC)

• Filler metals include Al, Mg & Cu alloys (melt point typically above 840 F)

• Automotive - joining tubes

• Electrical equipment - joining wires

• Jewelry Making

• Flux also used

• Types of brazing classified by heating method:

– Torch, Furnace, Resistance

• Joint can possess significant strength

Welding defects• Inclusions

– Slag

– Wagontracks

– Tungsten

• Spatter

• Arc Craters

• Cracks– Longitudinal

– Transverse

– Crater

– Throat

– Toe

– Root

– Underbead and Heat-affected zone

– Hot

– Cold or delayed

• Misalignment (hi-lo)

• Undercut

• Underfill

• Concavity or Convexity

• Excessive reinforcement

• Improper reinforcement

• Overlap

• Burn-through

• Incomplete or Insufficient Penetration

• Incomplete Fusion

• Surface irregularity– Overlap

• Arc Strikes

• Base Metal Discontinuities– Lamellar tearing

– Laminations and Delaminations

– Laps and Seams

• Porosity– Uniformly Scattered

– Cluster

– Linear

– Piping

• Heat-affected zone microstructure alteration

• Base Plate laminations

• Size or dimensions

UNIT III

MACHINING PROCESS

Machine Tool 

• Lathe

• Lathe is one of the oldest and perhaps most important machine ever developed.The job to be machined is rotated and the cutting tool is moved relative to the job. This is also called as turning machines.

Types of lathe

• Limited or low-production Machines. The lathes included in this category are: engine lathe (centre lathe), bench lathe, tool room lathe and speed lathe.

• Medium-production Machines. Turret lathes and duplicating (or tracer controlled) lathes.

• High-production Machines. Semiconductor automatic and automatic lathes.

Lathe

• Main parts of a lathe.

• Bed, Head stock, tail stock & carriage., saddle, apron,cross

slide, compound rest ,spindle lead screw,• Size /capacity of lathe

• Lathe size is specified by length of the bed and swing dia

• Swing =2xHeight of centres from the bed slide way.

• The size can also be specified by which max dia of the component turned over the bed, and max length of the

component that can be held between centres.

Lathe operations

• Lathe is versatile machine

• Lathe is called as versatile machine because of the following many operations unlike in other machines where the operations are limited.

• Turning, Facing, Step turning, Boring, Thread cutting, Uunder cutting,chamferring,counter boring,internal threading boring.parting off,knurling,drilling,reaming

Turret and capstan lathe

• Turret lathe

• It is medium production lathe and semi automatic lathe to make parts in great quantities to close tolerances and faster. In which tail sock is replaced with a turret slide hexagonal shape in which six tools can be mounted in six faces of the turret, tool post is replaced by a square cross slide which can hold four tools,two more tools can be mounted on the rear cross slide.Operations like turning, drilling, boring, reaming, threading cutoff etc can be formed in this machine by proper tool setup.

• The work is held in the chuck or by collet. All centre lathe operations camn be performed in this lathe

• Capstan lathe

• In this machine the turret is carried on a ram which moves longitudinally on a saddle positioned and clamped on the ways of the bed at any desired position. The lathe which is used for small

• and medium component. All the operation performed in turret lathe can be performed in this machine.

Shaper,planer and slotter

The main function of shapers, planers and slotters is the

machining of flat surfaces by means of straight line reciprocating single point cutting tools similar to

those used in lathe operations.

HORIZONTAL SHAPER

• Advantages of a shaper. • The shapers have got the following advantages. • The single point cutting tools used in shapers are

inexpensive, these tools can be easily grounded to any desired shape.

• The simplicity and ease of holding work, its easy adjustment, and the simple tool give the shaper its great flexibility.

• Shaper set up is very quick and easy and can be readily changed from one job to another.

• Thin or fragile jobs can be conveniently machined on shapers because of lower cutting forces.

• Ram drive mechanisms of a Slotters.

•  Hydraulic Drive, Variable Speed Reversible Motor drive, Slotted disc mechanism

• Uses of Vertical Shaper / Slotter

• Internal machining of blind holes.

• Work requiring machining on internal sections such as splines, keyways, various slots and grooves and teeth.

• Cutting of teeth on ratchet or gear rings which require primarily rotary feed.

• Machining of die, punchet, straight and curved slots.

Drilling Process

• The drilling process is an extensively used machining operation by which through or blind holes are cut or originated in a workpiece. The drilling tool is called a “drill” which is a multi-point ctting tool. The hole is produced by axially feeding the rotating drill into the workpiece which is held on the table of the drilling machine.

Milling Process

• Milling is the process of removing excess material from a work piece by rotating cutting tool called milling cutteris a multi pint cutting tool having the shape of teeth arranged on the periphery or on end face or on both.

• Types of milling process

• Up & down milling operation

• Up milling process

• Cutter is rotating in opposite direction of feed

• Down milling process

• Cutter is rotating in the same direction of feed

• Advantages of Planers.

• Larger work can be handled as compared to shapers and millers.

• Capable of taking much heavier cuts as compared to shapers and millers.

• There are no overhanging parts such as a ram. So there is no work or tool deflection or distortion.

• The work is mounted on a table which is supported throughout its entire movement. So, a maximum support is obtained.

Cylindrical Grinding Machine

• The cylindrical grinder is a type of grinding machine used to shape the outside of an object. The cylindrical grinder can work on a variety of shapes, however the object must have a central axis of rotation. This includes but is not limited to such shapes as a cylinders an ellipse a cam, or a crankshaft

Rolling

Important Applications:

Steel Plants,Raw stock production (sheets, tubes, Rods, etc.)Screw manufacture

• Cylindrical grinding is defined as having four essential actions

• The work (object) must be constantly rotating

• The grinding wheel must be constantly rotating

• The grinding wheel is fed towards and away from the work

• Either the work or the grinding wheel is traversed with the respect to the other.

• While the majority of cylindrical grinders employ all four movements, there are grinders that only employ three of the four actions.

• Grinding operations

• Outside diameter grinding

• ID grinding• Plunge grinding

Abrassive Jet Machining (AJM)

 • In abrasive et machining method, the material is removed form the surface or a Workpiece, by impinging a focused jet of fine abrasive particles carried by a compressed gas which imparts kinetic energy to the stream of fine abrasives. The stream leaves through a nozzle at a velocity of the order of 300 m/s and strikes the surface of the Workpiece, producing impact loading on it. plastic deformation or micro-cracks occur is the vicinity of the impact. Due to repeated impacts, small chips of material get loosened and fresh surface gets exposed to the jet.

Ultrasonic Machining (USM)

• Ultrasonic machining is a kind of grinding method. An abrasive slurry is pumped between tool and work, and the tool is given a high frequency, low amplitude oscillation which, in turn, transmits a high velocity to fine abrasive particles which are driven against the work piece. At each stroke, minute chips of material are removed by fracture or erosion.

Electrical Discharge Machining

• It has long been recognized that a powerful spark, such as at the terminals of an automobile battery, will cause pitting or erosion of the metal at both the anode and cathode. This principle is utilized in Electric Discharge Machining (EDM), also called spark erosion. If anode and cathode are of the same material, it has been found that greater erosion takes place at anode (positive electrode). Therefore, in EDM process, work is made the anode and the tool is the cathode (negative electrode).

Electro Chemical Machining

• In ECM, the principle of electrolysis is used to remove metal from the workpiece. The principle of electrolysis is based on Faraday’s laws of electrolysis which may be stated as: “The weight of substance produced during electrolysis is directly proportional to the current which passes, the length of time of the electrolysis process and the equivalent weight of the materials which is deposited”. ECM is just the reverse of electroplating (which also uses the principle

Plasma Arc machining or Plasma Jet Machining (PAM or PJM

• We know that all gases burning at high temperatures are ionized gases. In plasma arc machining, the gases are isonized by placing an arc across the path of gas flow. The gas molecules get dissociated causing large amounts of thermal energy to be liberated. This generates temperatures of the order of 16500C, which are than utilized in removing metal by melting and vapourization. Figure shows a schematic view of PAM.

Electron Beam Machining• In electron beam machining (EBM), electrons emitted by a hot

surface and accelerated by a voltage of 10 to 50 kV are focused to a very small areas on the workpiece. This stream of high energy electrons possess a very high energy density (of the order of 104 kW/mm2) and when this narrow stream strikes the work piece (by impact), the kinetic energy of the electrons is converted to powerful heat energy which is quite sufficient to melt and vaporize any material. Even though, it can

penetrate metals to a depth of only a few atomic layers the electron beam can melt metal to a depth of 25 mm or more. The electron beam which travels at about half to three- fourth the velocity of sound is focused on the workpiece by electro-static or electro-magnetic lenses.

•  

• EBM is done in a high vacuum chamber to eliminate the scattering of the electron beam as it contacts the gas molecules on the work piece. Figure shows schematic view of EBM.

• Since a continuous beam loses considerable heat by conduction through the work piece, a pulsed beam at a frequency of less than 100 cps is used in electron beam machining. This consists of repeatedly striking the electron beam on the work piece for a few milli-seconds and then turning it off for a certain period of time.

Laser Beam Machining• A Laser (Light Amplification by Stimulated

Emission of Radiation) is a device which produces a beam of light Laser light can be a very powerful source of power. In LBM, exceedingly high electromagnetic energy densities (of the order of 105 kW/mm2) are focused on the surface of the work piece (in air or vacuum) to remove metal by melting and evaporation.

Rolling Basics

Sheets are rolled in multiple stages (why ?)

Vo

Vfto tfVo

Vfto tfVo

Vfto tfVo

Vfto tf

thread rolling machine

stationary die

rolling diethread rolling machine

stationary die

rolling die

Reciprocating flat thread-rolling diesReciprocating flat thread-rolling dies

Screw manufacture:

UNIT IVFORMING PROCESS

Forming process

• Hot working :

•  The Metal working process which is done above recrystallaisation temperature is known as hot working.

• Cold working:

•  The metal working process which is done below recrystallaisation temperature is known as cold working.

• Hot working :

• The Metal working process which is done above recrystallaisation temperature is known as hot working.

•  Cold working:

•  The metal working process which is done below recrystallaisation temperature is known as cold working.

• Recrystallaisation temperature.

• When a metal is heated and deformed under mechanical force, an energy level will be reached when the old grain structure starts disintegrating, and entirely new grain structure (equip axed, stress free) with reduced grain size starts forming simultaneously. This phenomenon is known as recrystallaisation, and the temperature at which this phenomenon starts called recrystallaisation temperature.

• Advantages of hot working:-•  Very large work pieces can be deformed with

equipment of reasonable size • Strength of the metal is low at high temperature.

Hence low tonnage equipments are adequate for hot working.

• Gra in size can be controlled to be minimum.• Advantages of cold working:-•  Surface defects are removed.• High dimensional accuracy.• Cold working is done at room temperature, no

oxidation and scaling of the work material occurs.

Drawing.• Drawing is a cold working process in which the work

piece is pulled through a tapered hole in a die so as to reduce its diameter. The process imparts accurate dimensions, specified cross – section and a clean excellent Quality of surface to the work.

• Degree of drawing (RA).• The degree of drawing is measured in terms of

“reduction of area” which is defined as the ratio of the difference in cross – sectional area before and after drawing to the initial cross sectional area expressed in percent.

•  

Drawing

Commonly used to make wires from round bars

stock (bar)

F (pulling force)

wirediestock (bar)

F (pulling force)

wiredie

Similar to extrusion, except: pulling force is applied

• DRAWING

• Drawing is a cold working process in which the work piece (wire, rod or tube) is pulled through a tapered hole in a die so as to reduce its diameter. The process imparts accurate dimensions, specified cross section and a clean and excellent quality of surface to the work. The process may appreciably increase the strength and hardness of metal.

Rolling.• Rolling is the process in which the metals and alloys

are plastically deformed into semi-finished or finished condition by passing these between circular rolls. The main objective in rolling is to decrease the thickness of metal.

• The faster method is to pass the stock through a series of rolls for successive reduction, but this method requires more investment in equipment.

• Tube drawing

• Tubes which are made by hot metal working, processes are finally cold drawn to obtain better surface finish and dimensional tolerances, to enhance the mechanical properties of the pipe, and to produce tubes of reduced wall thickness.

Types of rolling mills

• Two high rolling mill• Three high rolling mill• Four-high rolling mil• Multiple –roll mills

Forging.

• Forging may be defined as a metal working process by which metals and alloys are plastically deformed to desired shapes by the application of compressive force. Forging may done either hot or cold.

Forging

[Heated] metal is beaten with a heavy hammer to give it the required shape

Hot forging,

open-die

1. Blank (bar) 2. Edging 3.Blocking 4. Finishing 5. Trimming

Flash

(a)

(b)

(c)

1. Blank (bar) 2. Edging 3.Blocking 4. Finishing 5. Trimming1. Blank (bar) 2. Edging 3.Blocking 4. Finishing 5. Trimming

Flash

(a)

(b)

(c)Flash

(a)

(b)

(c)

Stages in Closed-Die Forging

[source:Kalpakjian & Schmid]

Stages in Open-Die Forging

(a) forge hot billet to max diameter

(b) “fuller: tool to mark step-locations

(c) forge right side

(d) reverse part, forge left side

(e) finish (dimension control)

[source:www.scotforge.com]

• Basic Forging Operations• . Upsetting• Heading• Fullering• . Drawing down• Edging• . Bending• Flattening• . Blocking • Cut – off• Piercing• Punching

Quality of forged parts

Stronger/tougher than cast/machined parts of same material

Surface finish/Dimensional control:Better than casting (typically)

[source:www.scotforge.com]

Extrusion.

• Extrusion may be defined as the manufacturing process in which a block of metal enclosed in a container is forced to flow through the opening of a die. The metal is subjected to plastic deformation and it undergoes reduction and elongation during extrusion.

Extrusion

Metal forced/squeezed out through a hole (die)

Typical use: ductile metals (Cu, Steel, Al, Mg), Plastics, Rubbers

Common products:

Al frames of white-boards, doors, windows, …

[source:www.magnode.com]

FORGING HAMMERS

• Pneumatic forging hammer

• Hydraulic presses Direct – drive hydraulic presses

• Accumulator – driven hydraulic presses

Sheet Metal Processes

Raw material: sheets of metal, rectangular, large

Raw material Processing: Rolling (anisotropic properties)

Processes:ShearingPunchingBendingDeep drawing

Shearing

A large scissors action, cutting the sheet along a straight line

Main use: to cut large sheet into smaller sizes for making parts.

Punching

Cutting tool is a round/rectangular punch,that goes through a hole, or die of same shape

F t X edge-length of punch X shear strength

Punch

die

sheet

crack(failure in shear)

clearance

die

piece cut away, or slug

t

F t X edge-length of punch X shear strength

Punch

die

sheet

crack(failure in shear)

clearance

die

piece cut away, or slug

t

Punching

Main uses: cutting holes in sheets; cutting sheet to required shape

typical punched part

nesting of parts

Exercise: how to determine optimal nesting?

Bending

Body of Olympus E-300 camera

component with multiple bending operations

[image source: dpreview.com]

component with punching,bending, drawing operations

Typical bending operations and shapes

(a)

(b)

Sheet metal bending

Planning problem: what is the sequence in which we do the bending operations?

Avoid: part-tool, part-part, part-machine interference

Bending mechanics

R = Bend radius

Neutral axis

L = Bend length

This section isunder extension

This section isin compression

Bend allowance, Lb = (R + kT)

T = Sheet thickness

R = Bend radius

Neutral axis

L = Bend length

This section isunder extension

This section isin compression

Bend allowance, Lb = (R + kT)

T = Sheet thickness

Bending Planning what is the length of blank we must use?

Ideal case: k = 0.5 Real cases: k = 0.33 ( R < 2T) ~~ k = 0.5 (R > 2T)

Bending: cracking, anisotropic effects, Poisson effect

Bending plastic deformation

Bending disallow failure (cracking) limits on corner radius: bend radius ≥ 3T

Engineering strain in bending = e = 1/( 1 + 2R/T)

effect of anisotropic stock Poisson effect

Exercise: how does anisotropic behavior affect planning?

Bending: springback

1343

ET

YR

ET

YR

R

R ii

f

i

How to handle springback:

(a) Compensation: the metal is bent by a larger angle

(b) Coining the bend: at end of bend cycle, tool exerts large force, dwells

coining: press down hard, wait, release

Initial

Final Ri

Rf

i

f

f

i

T

Deep Drawing

die die die die die

punch punch punch punchblank

part

blank holder

(a) (b) (c) (d) (e)

Examples of deep drawn parts

die die die die die

punch punch punch punchblank

part

blank holder

(a) (b) (c) (d) (e)

die die die die die

punch punch punch punchblank

part

blank holder

(a) (b) (c) (d) (e)

Examples of deep drawn parts

Tooling: similar to punching operation,Mechanics: similar to bending operation

Common applications: cooking pots, containers, …

Sheet metal parts with combination of operations

Body of Olympus E-300 camera

component with multiple bending operations

[image source: dpreview.com]

component with punching,bending, drawing operations

UNIT-5 Powder Metallurgy

Example Parts

Basic Steps In Powder Metallurgy (P/M)

• Powder Production

• Blending or Mixing

• Compaction

• Sintering

• Finishing

Powder Production

• Atomization the most common

• Others– Chemical reduction of

oxides– Electrolytic deposition

• Different shapes produced– Will affect compaction

process significantly

Blending or Mixing

• Can use master alloys, (most commonly) or elemental powders that are used to build up the alloys– Master alloys are with the normal alloy ingredients

• Elemental or pre-alloyed metal powders are first mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients

• The initial mixing may be done by either the metal powder producer or the P/M parts manufacturer

• When the particles are blended:– Desire to produce a homogenous blend– Over-mixing will work-harden the particles and produce variability in

the sintering process

Compaction

• Usually gravity filled cavity at room temperature

• Pressed at 60-100 ksi• Produces a “Green”

compact– Size and shape of finished

part (almost)– Not as strong as finished part

– handling concern

• Friction between particles is a major factor

Isostatic Pressing

• Because of friction between particles Because of friction between particles

• Apply pressure uniformly from all Apply pressure uniformly from all directions (in theory)directions (in theory)

• Wet bag (left)Wet bag (left)

• Dry bag (right)Dry bag (right)

Sintering

• Parts are heated to ~80% of melting temperature

• Transforms compacted mechanical bonds to much stronger metal bonds

• Many parts are done at this stage. Some will require additional processing

Sintering ctd

• Final part properties drastically affected

• Fully sintered is not always the goal– Ie. Self lubricated bushings

• Dimensions of part are affected

Die Design for P/M

• Thin walls and projections create fragile tooling. • Holes in pressing direction can be round, square, D-shaped,

keyed, splined or any straight-through shape. • Draft is generally not required. • Generous radii and fillets are desirable to extend tool life. • Chamfers, rather the radii, are necessary on part edges to

prevent burring. • Flats are necessary on chamfers to eliminate feather-edges on

tools, which break easily.

Advantages of P/M• Virtually unlimited choice of

alloys, composites, and associated properties – Refractory materials are popular

by this process

• Controlled porosity for self lubrication or filtration uses

• Can be very economical at large run sizes (100,000 parts)

• Long term reliability through close control of dimensions and physical properties

• Wide latitude of shape and design

• Very good material utilization

Disadvantages of P/M

• Limited in size capability due to large forces • Specialty machines• Need to control the environment – corrosion concern• Will not typically produce part as strong as wrought

product. (Can repress items to overcome that)• Cost of die – typical to that of forging, except that

design can be more – specialty• Less well known process

Financial Considerations• Die design – must withstand 100

ksi, requiring specialty designs

• Can be very automated– 1500 parts per hour not uncommon for

average size part

– 60,000 parts per hour achievable for small, low complexity parts in a rolling press

• Typical size part for automation is 1” cube– Larger parts may require special

machines (larger surface area, same pressure equals larger forces involved)

Extrusion

• Raw materials in the form if thermoplastic pallets,granules,or powder, placed into a hopper and fed into extruder barrel.

• The barrel is equipped with a screw that blends the pallets and conveys them down the barrel

• Heaters around the extruder’s barrels heats the pellets and liquefies them

Screw has 3-sections • Feed section• Melt or transition section• Pumping section.

• Complex shapes with constant cross-section

• Solid rods, channels, tubing, pipe, window frames, architectural components can be extruded due to continuous supply and flow.

• Plastic coated electrical wire, cable, and strips are also extruded

Pellets :extruded product is a small-diameter rod which is chopped into small pellets

Sheet and film extrusion :Extruded parts are rolled on water and on the rollers

Extruder

Fig : Schematic illustration of a typical extruder for plastics, elastomers, and composite materials.

Injection molding

Fig : Injection molding with (a) plunger, (b) reciprocating rotating screw, (c) a typical part made from an injection molding machine cavity, showing a number of parts made from one shot, note also mold features such as sprues, runners and gates.

• Similar to extrusion barrel is heated

• Pellets or granules fed into heated cylinder

• Melt is forced into a split-die chamber

• Molten plastic pushed into mold cavity

• Pressure ranges from 70 Mpa – 200 Mpa

• Typical products : Cups, containers, housings, tool handles, knobs, electrical and communication components, toys etc.

Injection molding

• Injection molds have several components such as runners, cores, cavities, cooling channels, inserts, knock out pins and ejectors

3-basic types of molds• Cold runner two plate mold• Cold runner three plate

mold• Hot runner mold

Fig : Examples of injection molding

Injection Molding Machine

Fig : A 2.2-MN (250-ton) injection molding machine. The tonnage is the force applied to keep the dies closed during injection of molten plastic into the mold cavities.

Process capabilities :

• High production rates

• Good dimensional control

• Cycle time range 5 to 60 sec’s

• Mold materials- tool steels, beryllium - Cu, Al

• Mold life- 2 million cycles (steel molds) 10000 cycles ( Al molds)

Machines :• Horizontal or vertical machines• Clamping – hydraulic or electric

Blow molding

• Modified extrusion and Injection Molding process.

• A tube extruded then clamped to mold with cavity larger than tube diameter.

• Finally blown outward to fill the cavity

• Pressure 350Kpa-700Kpa

Other Blow Molding processes• Injection Blow molding• Multi layer Blow molding

Fig : Schematic illustration of (a) the blow-molding process for making plastic beverage bottles, and (b) a three-station injection blow-molding machine.

Rotational Molding

• Thermo plastics are thermosets can be formed into large parts by rotational molding

• A thin walled metal mold is made of 2 pieces

• Rotated abut two perpendicular axes

• Pre-measured quantity of powdered plastic material is rotated about 2-axes

• Typical parts produced-Trash cans, boat hulls, buckets, housings, toys, carrying cases and foot balls.

Rotational Molding

Fig: The rotational molding (rotomolding or rotocasting) process. Trash cans, buckets, and plastic footballs can be made by this process.

Thermoforming• Series process for forming thermoplastic sheet or film over a mold by applying

heat and pressure.

• Typical parts : advertising signs, refrigerator liner, packaging , appliance housing, and panels for shower stalls .

Fig : Various Thermoforming processes for thermoplastic sheet. These processes are commonly used in making advertising signs, cookie and candy trays, panels for shower stalls, and packaging.

Compression molding• Pre-shaped charge ,pre-measured volume of powder and viscous mixture of liquid

resin and filler material is placed directly into a heated mold cavity.

• Compression mold results in a flash formation which is a n excess material.

• Typical parts made are dishes, handles, container caps fittings, electrical and electronic components and housings

• Materials used in compression molding are thermosetting plastics & elastomers

• Curing times range from 0.5 to 5 mins

3- types of compression molds are

• Flash type• Positive type• Semi-positive

Compression Molding

Fig : Types of compression molding, a process similar to forging; (a) positive, (b) semi positive, (c) flash (d) Die design for making compression-molded part with undercuts.

Transfer molding

• Transfer molding is an improvement if compression molding

• Uncured thermosetting material placed in a heated transfer pot or chamber, which is injected into heated closed molds

• Ram plunger or rotating screw feeder forces material into mold cavity through narrow channels

• This flow generates heat and resin is molten as it enters the mold

Typical parts : Electrical & electronic components, rubber and silicone parts

Transfer molding

Fig : Sequence of operations in transfer molding for thermosetting plastics. This process is particularly suitable for intricate parts with varying wall thickness.

CastingConventional casting of thermo plastics :Conventional casting of thermo plastics :

• Mixture of monomer, catalyst and various additives are heated and poured into the mould

• The desired part is formed after polymerization takes place.

Centrifugal casting :Centrifugal casting :

• Centrifugal force used to stack the material onto the mold

• Reinforced plastics with short fibers are used

Fig : Casting

Cold forming• Processes such as rolling ,deep drawing extrusion closed die forging ,coining and rubber

forming can be used for thermoplastics at room temperatures

• Typical materials used : Poly propylene, poly carbonate, Abs, and rigid PVC

Considerations :

• Sufficiently ductile material at room temperature• Non recoverable material deformation

Solid Phase forming• Temperatures from 10oc to 20oc are maintained, which is below melting point

Advantages :

• Spring-back is lower

• Dimensional accuracy can be maintained

Calendaring and Examples of Reinforced Plastics

Fig : Reinforced-plastic components for a Honda motorcycle. The parts shown are front and rear forks, a rear swing arm, a wheel, and brake disks.

Fig : Schematic illustration of calendaring, Sheets produced by this process are subsequently used in thermoforming.

Sheet Molding

Fig : The manufacturing process for producing reinforced-plastic sheets. The sheet is still viscous at this stage; it can later be shaped into various products.

Examples of Molding processesFig : (a) Vacuum-bag forming.

(b) Pressure-bag forming.

Fig : Manual methods of processing reinforced plastics: (a) hand lay-up and (b) spray-up. These methods are also called open-mold processing.

THE END