KARPAGAM UNIVERSITY Coimbatore-641021 FACULTY OF ENGINEERING

DEPARTMENT OF AERONAUTICAL ENGINEERING

13BEAR302 - AIRACRAFT MATERIALS AND MANUFACTURING PROCESSES

Compiled by

R.PandyRajan,Lecturer,

Department of Aeronautical Engineering.Karpagam University.

UNIT -1

AIRCRAFT STEELS

CLASSIFICATIONS OF ALLOY STEELS

Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low-alloy steels and high-alloy steels.

Advantages: Greater harden ability Less distortion and cracking Greater ductility at high strength Greater high temperature strength Greater stress relief at given hardness Better mach inability at high hardness High elastic ratio and endurance strength.

Disadvantages: Tendency toward austenite retention Cost Special handling Temper brittleness in certain grades.

Purpose of alloying:  Strengthening of the ferrite  Improved corrosion resistance  Better harden ability  Grain size control  Greater strength  Improved mach inability  Improved ductility  Improved toughness  Better wear resistance  Improved cutting ability  Improved case hardening properties etc.  Improved high or low temperature stability.

Classification of alloy steels according to chemical composition:

Alloys steels are divided into three-component steels, containing one alloying element in addition to iron and carbon: four component steels, containing two alloying elements, etc

Classification of alloy steels according to structural class:

Alloys steels may be classified on the basis of the structure that is obtained when specimens of small cross section are cooled in air.

They are classified as:

1.  Pearlitic2.  Martensitic3.  Austentic4.  Ferritic5.  Carbidic

Classification of alloy steels according to purpose:

Alloys steels are further classified according to their use.  Structural Steels  Tools Steels  Steels with special physical properties

Quenched and Tempered Steels

Corrosion resistant steels

Stainless steels Ultra-High Strength Steels Heat Resisting Steels Shock resisting Steels Magnet Steels

EFFECTS OF ALLOYING ELEMENTSAlloying elements are added to effect changes in the properties of steels. The basis of this section is to cover some of the different alloying elements added to the basic system of iron and carbon, and what they do to change the properties or effectiveness of steel.

Carbon : The presence of carbon in iron is necessary to make steel. Carbon is essential to the formation of cementite (as well as other carbides), and to the formation of pearlite, spheroidite, bainite, and iron-carbon martensite, with martensite being the hardest of the micro-structures, and the structure sought after by knife makers.

The hardness of steel (or more accurately, the hardenability) is increased by the addition of more carbon, up to about 0.65 percent. Wear resistance can be increased in amounts up to about 1.5 percent. Beyond this amount, increases of carbon reduce toughness and increase brittleness.

The steels of interest to knife makers generally contain between 0.5 and 1.5 percent carbon. They are described as follows:

• Low Carbon: Under 0.4 percent • Medium Carbon: 0.4 - 0.6 percent • High Carbon: 0.7 - 1.5 percent Carbon is the single most important alloying element in steel.

Manganese Manganese slightly increases the strength of ferrite, and also increases the hardness penetration of steel in the quench by decreasing the critical quenching speed. This also makes the steel more stable in the quench. Steels with manganese can be quenched in oil rather than water, and therefore are less susceptible to cracking because of a reduction in the shock of quenching. Manganese is present in most commercially made steels.

Chromium As with manganese, chromium has a tendency to increase hardness penetration. This element has many interesting effects on steel. When 5 percent chromium or more is used in conjunction with manganese. The critical quenching speed is reduced to the point that the steel becomes air hardening. Chromium can also increase the toughness of steel, as well as the wear resistance. Probably one of the most well known effects of chromium on steel is the tendency to resist staining and corrosion. Steels with 14 percent or more chromium are referred to as stainless steels. A more accurate term would be stain.

Silicon : Silicon is used as a deoxidizer in the manufacture of steel. It slightly increases the strength of ferrite, and when used in conjunction with other alloys can help increase the toughness and hardness penetration of steel.

Nickel : Nickel increases the strength of ferrite, therefore increasing the strength of the steel. It is used in low alloy steels to increase toughness and hardenability. Nickel also tends to help reduce distortion and cracking during the quenching phase of heat treatment

Molybdenum :

Molybdenum increases the hardness penetration of steel, slows the critical quenching speed, and increases high temperature tensile strength. Vanadium

Vanadium helps control grain growth during heat treatment. By inhibiting grain growth it helps increase the toughness and strength of the steel.

Tungsten:

Used in small amounts, tungsten combines with the free carbides in steel during heat treatment, to produce high wear resistance with little or no loss of toughness.

High amounts combined with chromium gives steel a property known as red hardness. This means that the steel will not lose its working hardness at high temperatures.

An example of this would be tools designed to cut hard materials at high speeds, where the friction between the tool and the material would generate high temperatures.

Copper : The addition of copper in amounts of 0.2 to 0.5 percent primarily improves steels resistance to atmospheric corrosion. It should be noted that with respect to knife steels, copper has a detrimental effect to surface quality and to hot-working behavior due to migration into the grain boundaries of the steel.

Niobium : In low carbon alloy steels Niobium lowers the transition temperature and aids in a fine grain structure. Niobium retards tempering and can decrease the hardenability of steel because it forms very stable carbides. This can mean a reduction in the amount of carbon dissolved into the austenite during heat treating.

Boron : Boron can significantly increase the hardenability of steel without loss of ductility. Its effectiveness is most noticeable at lower carbon levels. The addition of boron is usually in very small amounts ranging from 0.0005 to 0.003 percent.

Titanium :

This element, when used in conjunction with Boron, increases the effectiveness of the Boron in the hardenability of steel

Carbon steel v/s Alloys Steels:

Carbon steel Alloys Steels

Carbon steel is also known as plain steel It is an alloy of steel where carbon is the

main constituent and no minimum percentage of other alloying elements is mentioned.

Carbon steel is not stainless steel as it is classified under alloy steels.

As the name implies, carbon content is increased in the steel making it harder and stronger through application of heat treatments. 

addition of carbon makes the steel less ductile. 

The weldability of carbon steel is low and higher carbon content also lowers the melting point of the alloy.

Alloy steel is a type of steel that has presence of certain other elements apart from iron and carbon

Commonly added elements in alloy steel are manganese, silicon, boron, chromium, vanadium and nickel.

The quantity of these metals in alloy steel is primarily dependent upon the use of such steel

Alloy steels are divided into low alloy steels and high alloy steels

When the percentage of added elements goes past 8 (in terms of weight), the steel is referred to as high alloy steel.

In cases where added elements remain below 8% by weight of the steel, it is a low alloy steel.

To keep the alloy steel wieldable, carbon content needs to be reduced.

Heat Treatment of Steels:

Steels can be heat treated to produce a great variety of microstructures and properties. Generally, heat treatment uses phase transformation during heating and cooling to change a microstructure in a solid state.

In heat treatment, the processing is most often entirely thermal and modifies only structure.

Thermo mechanical treatments, which modify component shape and structure, Thermo chemical treatments which modify surface chemistry and structure are also

important processing approaches which fall into the domain of heat treatment. According to cooling rate we can distinguish two main heat treatment operations: annealing - upon slow cooling rate (in air or with a furnace)

- produces equilibrium structures according to the Fe-Fe3C diagram

Quenching - upon fast cooling (in oil or in water) - gives non-equilibrium structures

Among annealing there are some important heat treatments processes like:• normalising • Spheroid sing • stress relieving

Normalising The soaking temperature is 30-50°C above A3 or A cm in austenite field range.

The temperature depends on carbon content. After soaking the alloy is cooled in still air. This cooling rate and applied temperature produces small grain size. The small grain structure improve both toughness and strength (especially yield strength). During normalising we use grain refinement which is associated with allotropic

transformation upon heating .Spheroidising:

The process is limited to steels in excess of 0.5% carbon and consists of heating the steel to temperature about A1 (727°C). At this temperature any cold worked ferrite will recrystallise and the iron carbide present in pearlite will form as spheroids or “ball up”. As a result of change of carbides shape the strength and hardness are reduced

Quenching : Soaking temperature 30-50°C above A3 or A1, then fast cooling (in water or oil) with cooling rate exceeding a critical value. The critical cooling rate is required to obtain non-equilibrium structure called marten site During fast cooling austenite cannot transform to ferrite and pearlite by atomic

Diffusion. Martensite is supersaturated solid solution of carbon in α-iron (greatly supersaturated ferrite) with tetragonal body centered structure. Martensite is very hard and brittle. Martensite has a “needle-like” structure.

Tempering: This process is carried out on hardened steels to remove the internal stresses and brittleness created by the severe rate of cooling. The treatment requires heating the steel to a temperature range of between 200 and 600°C depending upon the final properties desired. This heat energy allows carbon atoms to diffuse out of the distorted lattice Structure associated with martensite, and thus relieves some of the internal stresses. As a result the hardness is reduced and the ductility (which was negligible before tempering treatment) is increased slightly. The combined effect is to “toughen” the material which is now capable of resisting certain degree of shock loading. The higher the tempering temperature the greater the capacity for absorbing shock.

Corrosion prevention techniques: They are classified into following points-

1. Environmental Modifications2. Metal Selection and Surface Conditions

3. Cathodic Protection4. Corrosion Inhibitors5. Coating6. Plating

Environmental Modification:

Corrosion is caused through chemical interactions between metal and gases in the surrounding environment. By removing the metal from, or changing, the type of environment, metal deterioration can be immediately reduced.

This may be as simple as limiting contact with rain or seawater by storing metal materials indoors, or could be in the form of direct manipulation of the environmental affecting the metal.

Methods to reduce the sulfur, chloride or oxygen content in the surrounding environment can limit the speed of metal corrosion.

For example, feed water for water boilers can be treated with softeners or other chemical media to adjust the hardness, alkalinity or oxygen content in order to reduce corrosion on the interior of the unit.

Metal Selection and Surface Conditions:

No metal is immune to corrosion in all environments, but through monitoring and understanding the environmental conditions that are the cause of corrosion, changes to the type of metal being used can also lead to significant reductions in corrosion.

Metal corrosion resistance data can be used in combination with information on the environmental conditions to make decisions regarding the suitability of each metal.

The development of new alloys, designed to protect against corrosion in specific environments are constantly under production. Hastelloy® nickel alloys, Nirosta® steels and Timetal®titanium alloys are all examples of alloys designed for corrosion prevention.

Monitoring of surface conditions is also critical in protecting against metal deterioration from corrosion. Cracks, crevices or asperous surfaces, whether a result of operational requirements, wear and tear or manufacturing flaws, all can result in greater rates of corrosion.

Proper monitoring and the elimination of unnecessarily vulnerable surface conditions, along with taking steps to ensure that systems are designed to avoid reactive metal combinations and that corrosive agents are not used in the cleaning or maintenance of metal parts are all also part of effective corrosion reduction program.

Cathodic Protection: Galvanic corrosion occurs when two different metals are situated together in a

corrosive electrolyte.

This common problem for metals submerged together in seawater, but can also occur when two dissimilar metals are immersed in close proximity in moist soils. For these reasons, galvanic corrosion often attacks ship hulls, offshore rigs and oil and gas pipelines.

Cathodic protection works by converting unwanted anodic (active) sites on a metal's surface to cathodic (passive) sites through the application of an opposing current.

This opposing current supplies free electrons and forces local anodes to be polarized to the potential of the local cathodes.

Cathodic protection can take two forms. The first is the introduction of galvanic anodes. This method, known as a sacrificial system, uses metal anodes, introduced to the electrolytic environment, to sacrifice themselves (corrode) in order to protect the cathode.

While the metal needing protection can vary, sacrificial anodes are generally made of zinc, aluminum or magnesium, metals that have the most negative electro-potential.

The galvanic series provides a comparison of the different electro-potential - or nobility - of metals and alloys.

In a sacrificial system, metallic ions move from the anode to the cathode, which leads the anode to corrode more quickly than it otherwise would. As a result, the anode must regularly be replaced.

A second method of cathodic protection is referred to as impressed current protection. This method, which is often used to protect buried pipelines and ship hulls, requires an alternative source of direct electrical current to be supplied to the electrolyte.

The negative terminal of the current source is connected to the metal, while the positive terminal is attached to an auxiliary anode, which is added to complete the electrical circuit. Unlike a galvanic (sacrificial) anode system, in an impressed current protection system, the auxiliary anode is not sacrificed.

Corrosion Inhibitors: 

Corrosion inhibitors are chemicals that react with the metal's surface or the environmental gases causing corrosion, thereby, interrupting the chemical reaction that causes corrosion.

Inhibitors can work by adsorbing themselves on the metal's surface and forming a protective film. These chemicals can be applied as a solution or as a protective coating via dispersion techniques. The inhibitors process of slowing corrosion depends upon: Changing the anodic or cathodic polarization behavior Decreasing the diffusion of ions to the metal's surface Increasing the electrical resistance of the metal's surface

Major end-use industries for corrosion inhibitors are petroleum refining, oil and gas exploration, chemical production and water treatment facilities. The benefit of corrosion inhibitors is that they can be applied in-situ to metals as a corrective action to counter unexpected corrosion.

Coatings:

Paints and other organic coatings are used to protect metals from the degradative effect of environmental gases.

Coatings are grouped by the type of polymer employed. Common organic coatings include: Alykd and epoxy ester coatings that, when air dried, promote cross-link oxidation Two-part urethane coatings Both acrylic and epoxy polymer radiation curable coatings Vinyl, acrylic or styrene polymer combination latex coatings Water soluble coatings High-solid coatings Powder coatings

Plating:Metallic coatings, or plating, can be applied to inhibit corrosion as well as provide aesthetic, decorative finishes.There are four common types of metallic coatings: Electroplating: A thin layer of metal - often nickel, tin or chromium - is deposited on

the substrate metal (generally steel) in an electrolytic bath. The electrolyte usually consists of a water solution containing salts of the metal to be deposited.

Mechanical plating: Metal powder can be cold welded to a substrate metal by tumbling the part, along with the powder and glass beads, in a treated aqueous solution. Mechanical plating is often used to apply zinc or cadmium to small metal parts

Electroless: A coating metal, such as cobalt or nickel, is deposited on the substrate metal using a chemical reaction in this non-electric plating method.

Hot dipping: When immersed in a molten bath of the protective, coating metal a thin layer adheres to the substrate metal.

Aircraft Alloy Steels Selection &Applications:

Steel is considered to be an alloy if the maximum alloying element content within the steel surpasses at least one of the following limits:

1.65% Manganese 0.6% Copper 0.6% Silicon

It may also be considered an alloy steel if there is a prescribed minimum quantity of the following elements added to produce a specific alloying effect:

Up to 3.99% Chromium

Up to 3.99% Aluminum Up to 3.99% Boron

and a definite minimum quantity of cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium, and etc.

American Iron and Steel Institute Designations The first two digits of the AISI number series indicates the primary alloying element in the alloy steel as follows:

13xx

Manganese 1.75%

40xx

Molybdenum 0.25%

41xx

Chromium 0.5%, 0.8%, 0.95%, Molybdenum 0.12%, 0.2%, 0.3%

43xx

Chromium 0.5%, 0.8%, Molybdenum .25%, Nickel 1.83%

44xx

Molybdenum 0.53%

46xx

Molybdenum 0.2%, 0.25%, Nickel 0.85%, 1.83%

47xx

Chromium 0.45%, Molybdenum 0.2%, 0.35%, Nickel 1.05%

48xx

Molybdenum 0.25%, Nickel 3.50%

50xx

Chromium 0.4%

51xx

Chromium 0.8%, 0.88%, 0.93%,0.95%, 1.00%

51xxx

Chromium 1.03%, 1.45%, Carbon 1.04%

61xx

Chromium 0.6%, 0.95%, Vanadium 0.13%, 0.15%

86xx

Chromium 0.5%, Molybdenum 0.2%, Nickel .55%

87xx

Chromium 0.5%, Molybdenum 0.25%, Nickel 0.55%

88xx

Chromium 0.5%, Molybdenum 0.35%, Nickel 0.55%

92xx

Silicon 2.0%

9 Chromium 1.2%, Molybdenum 0.12%, Nickel 3.25%

3xx 

The letter "E" prefixed before the number indicates that the alloy was electric' furnace pro-cessed. All other alloys were either open hearth processed, or processed by the basic oxygen method, or it may be electric furnace processed with no adjustments made in the phosphorus and sulfur limits. The last two digits indicate the mid-carbon range contained within the alloy. Example: 4140 indicates the mid-carbon range of this alloy is .40%.  If there is a five number series, the last three digits indicate the mid-carbon range     Example: 52100 indicate the mid-carbon range of this alloy is 1.00%. 

E4130 Aircraft Quality Sheet and Plate  

Type 4130 is an electric-furnace processed, chromium-molybdenum aircraft quality alloy used primarily for welding or where moderate tensile strength is a requirement. The careful processing it undergoes completely eliminates the possibility of seams, grooves, pitting or blistering. It also undergoes diligent inspection and rolling to insure its freedom from lamination and tears. It is available in the normalized or annealed condition, and maybe pickled and oiled.

ApplicationsType 4130 finals its primary use in the aircraft industry where moderate tensile strength in combination with good weldability is required.

  E4130 Aircraft Quality Bars

4130 is an electric-furnace, through-hardening, chromium-molybdenum alloy processed to meet the rigid standards of the aircraft industry and vacuum degassed to conform to the magnetic particle inspection standards of AMS-2301.

Its excellent weldability, formability and temperate hardenability predispose this alloy to a wide range of applications.

Normalizing without liquid quenching increases its strength sufficiently for most uses; however, it may be heat treated for greater strength.

It may be nitrited for maximum wear and abrasion resistance. Applications

Type 4130 finds exceptional use where extremely high strength and hardness are required from relatively thin sections.

It finds major use in applications requiring welding. It is extensively used in the aircraft industry for parts and components.

E4140 Aircraft Quality Bars  

4140 is an electric furnace processed, through-hardening alloy processed to meet the rigid standards of the aircraft industry and vacuum degassed to conform to the magnetic particle inspection standards of AMS-2301.

It contains .95% chromium and approximately .20% molybdenum. It has good fatigue, impact and abrasion resistance, and an extremely wide range of strength and toughness, obtainable by variations in heat treatments.

In the fully hardened condition, it has outstanding tensile strength. It has a high fatigue and tensile ratio. 4140 may be successfully nitrited for maximum wear and abrasion

resistance. It is remarkably well suited for use in extremely elevated temperatures.

Applications4140 is generally used for applications of parts ½” or less necessitating a through hardening steel with strength as high as Rockwell "C" 50. Frequently used for fittings and forgings in the aircraft industry. E4340 Aircraft Quality Bars

E4340 is a highly alloyed, electric-furnace processed; vacuum degassed grade, which conforms to the rigid aircraft standards of AMS-2301.

It contains approximately 0.8% chromium, 1.8% nickel, and 25% molybdenum. The combination of these elements assures deep and uniform hardness when heat-treated, particularly when oil quenched.

It possesses exceptional ductility and toughness and remarkably high fatigue strength, snaking E4340 the steel to use for highly stressed parts operating under heavy-duty conditions.

It also maintains its excellent strength and hardness while functioning under extremely elevated temperatures.

ApplicationsE4340 finds its most typical use in highly stressed parts that must operate under severe conditions. It is commonly used in the aircraft and missile industries.

E8740 Aircraft Quality Bars

8740 is an electric-furnace processed, chromium-nickel alloy containing approximately .25% molybdenum.

It is primarily an oil hardening steel designed to provide excellent shock resistance and outstanding hardenability.

It is a very tough alloy, especially free from temper brittleness.

Applications8740 finds extensive use in the aircraft industry for parts and components. It is primarily used where high strength, hardness, and good shock resistance are required.

  E9310 Aircraft Quality Bars

  Type 9310 is a vacuum degassed, carburizing steel containing approximately 1.25% chromium, 3.25% nickel, and .12% molybdenum. This alloy is suitable for heavy sectioned components because of its high hardenability and fatigue resistance, and because of its high core strength and hardness offering a narrow hardness range between light and heavy sections. It offers excellent ductility and toughness, and may be used without carburizing. Most applications of 9310 do call for use in the carburized state, which increases its wear and abrasion resistance to a high degree. It passes the most rigid magnetic particle inspections.

ApplicationsUsed principally in the carburized state where extreme core hardness is required in combination with a minimal hardness range.

  E52100 Bearing Quality Bars

  552100 is an electric-furnace processed, vacuum degassed alloy containing approximately 1.5% chromium and 1.0% carbon. In order to maximize machinability and because of the high carbon content, 552100 may be spheroidize annealed. It is primarily a bearing steel possessing excellent resistance to wear and abrasion, medium toughness, and high strength in compression. It is a moderately deep hardening alloy with low softening resistance to elevated temperatures.

 Applications52100 finds its primary use in roller or ball bearing applications.

 

UNIT-I

PART-A (Important Questions and Answers)

1. What are the advantages and disadvantages of alloys?

Advantages:

Greater harden ability

Less distortion and cracking

Greater ductility at high strength

Greater high temperature strength

Greater stress relief at given hardness

Better mach inability at high hardness

Disadvantages:

Tendency toward austenite retention

Cost

Special handling

Temper brittleness in certain grades.

2. Effect of manganese alloying elements?

Manganese slightly increases the strength of ferrite, and also increases the hardness

penetration of steel in the quench by decreasing the critical quenching speed.

This also makes the steel more stable in the quench.

Steels with manganese can be quenched in oil rather than water, and therefore are less

susceptible to cracking because of a reduction in the shock of quenching.

Manganese is present in most commercially made steels.

3. Define annealing and Quenching.

annealing - upon slow cooling rate (in air or with a furnace)

- produces equilibrium structures according to the Fe-Fe3C diagram

Quenching - upon fast cooling (in oil or in water)

- gives non-equilibrium structures

4. Differenciate carbon steels v/s Alloys Steels.

5. Define Corrosion inhibitors. Corrosion inhibitors are chemicals that react with the metal's surface or the environmental gases causing corrosion, thereby, interrupting the chemical reaction that causes corrosion

6. Write down the types of prevention methods of corrosion Environmental Modifications Metal Selection and Surface Conditions Cathodic Protection Corrosion Inhibitors Coating Plating

7. Write own the selection criteria for steel alloys.

No metal is immune to corrosion in all environments. Metal should be corrosion resistance. Alloy must be able to protecting against metal deterioration from corrosion. Cracks, crevices or asperous surfaces,. vulnerable surface conditions,

8. Define Hot dipping.When immersed in a molten bath of the protective, coating metal a thin layer adheres to the substrate metal

9. What do you mean by Tempering?This process is carried out on hardened steels to remove the internal stresses and brittleness created by the severe rate of cooling

10. Write down the application of steel alloys. Aircraft structures parts Automotive spars and parts Tools manufacturing Aerospace vehicles nose and skin parts

PART B- Important Questions

1. Write down the effects of alloying elements briefly.

2. Explain heat treatment of steel alloys in detail.

3. Write down the selection and application of steel alloys in brief.

4. Explain in brief corrosion prevention methods.

5. Write down in detail the classification of alloy steels

6. Explain in detail about carbon steel and alloys of steels.

UNIT IILIGHT METAL ALLOYS

Aluminum alloys: Aluminum alloys (or aluminum alloys; see spelling differences) are alloys in

which aluminum (Al) is the predominant metal. The typical alloying elements are

copper, magnesium, manganese, silicon and zinc  There are two principal classifications, namely casting alloys and wrought alloys,

both of which are further subdivided into the categories heat-treatable and non-heat-treatable.

About 85% of aluminium is used for wrought products, for example rolled plate, foils and extrusions.

Cast aluminium alloys yield cost-effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys

The most important cast aluminium alloy system is Al–Si, where the high levels of silicon (4.0–13%) contribute to give good casting characteristics.

Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required

Alloys composed mostly of aluminium have been very important in aerospace manufacturing since the introduction of metal skinned aircraft.

Aluminium-magnesium alloys are both lighter than other aluminium alloys and much less flammable than alloys that contain a very high percentage of magnesium.

Aluminium alloy surfaces will formulate a white, protective layer of corrosion aluminium oxide if left unprotected by anodizing and/or correct painting procedures.

Heat Treatment of Aluminum and Aluminum Alloys:

The application of the term heat treatable to aluminum alloys, both wrought and cast, is restricted to the specific operations employed to increase strength and hardness by precipitation hardening thus the term heat treatable serves to distinguish the heat treatable alloys from those alloys in which no significant strength improvement can be achieved by heating and cooling.

The non-heat treatable alloys depend primarily on cold work to increase strengthAnnealing

Annealing is applied to both grades to promote softening. Complete and partial annealing heat treatments are the only ones used for the non-heat treatable alloys. The exception is the 5000 series alloys which are sometimes given low temperature stabilisation treatment and this is carried out by the producer. Annealing is carried out in the range 300-410°C depending on the alloy. Heating times at temperature vary from 0.5 to 3 hours, conditional on the size of the load and the alloy type. Generally, the time need not be longer than that required to stabilise the load at temperature. Rate of cooling after annealing is not critical.

Where parts have been solution heat-treated a maximum cooling rate of 20°C per hour must be maintained until the temperature is reduced to 290°C.

Below this temperature, the rate of cooling is not important.Solution Heat Treatment :

This is applicable to the heat treatable alloys and involves a heat treatment process whereby the alloying constituents are taken into solution and retained by rapid quenching. Subsequent heat treatment at tower temperatures i.e. ageing or natural ageing at room temperature allows for a controlled precipitation of the constituents thereby achieving increased hardness and strength. Time at temperature for solution treatment depends on the type of alloy and the furnace load. Sufficient time must be allowed to take the alloys into solution if optimum properties are to be obtained. The solution treatment temperature is critical to the success of the procedure. It is desirable that the solution heat treatment is carried out as close as possible to the liquidus temperature in order to obtain maximum solution of the constituents. Accurate furnace temperature and special temperature variation must be controlled to within a range of ±5°C for most alloys. Overheating must be avoided i.e. exceeding initial eutectic melting temperatures. Often the early stages of overheating are not apparent but will result in a deterioration of mechanical properties. Proper solution heat treatment of the aluminium alloys requires an expert knowledge of the alloy being treated plus the correct heat treatment plant.

Quenching This is a critical operation and must be carried out to precise limits if optimum results are to be obtained. The objective of the quench is to ensure that the dissolved constituents remain in solution down to room temperature. The speed of quenching is important and the result can be affected by excessive delay in transferring the work to the quench. The latitude for the delay is dependant on section and varies from 5 to 15 seconds for items of thickness varying from 0.4mm to 12.7mm. Generally, very rapid precipitation of constituents commences at around 450°C for most alloys and the work must not be allowed to fall below this temperature prior to quenching. Another factor to be considered in quenching is the work load and the ability of the quenchant to extract the heat at sufficient rate to achieve the desired results. The usual quenching medium is water at room temperature. In some circumstances slow quenching is desirable as this improves the resistance to stress corrosion cracking of certain copper-free Al-Zn-Mg alloys. Parts of complex shapes such as forgings, castings, impact extrusions and components produced from sheet metal may be quenched at slower quenching rates to improve distortion characteristics.

Thus a compromise must be considered to achieve a balance of properties in some instances. Quenchants used in slower quenching applications include water heated to 65-80°C, boiling water, aqueous solutions of polyalkalene glycol or forced air blast.

Age Hardening After solution treatment and quenching, hardening is achieved either at room temperature (natural ageing) or with a precipitation heat treatment (artificial ageing).

In some alloys sufficient precipitation occurs in a few days at room temperature to yield stable products with properties that are adequate for many applications.

These alloys sometimes are precipitation heat treated to provide increased strength and hardness in wrought and cast alloys.

Other alloys with slow precipitation reactions at room temperature are always precipitation heat treated before being used.

In some alloys, notably those of the 2xxx series, cold working of freshly quenched materials greatly increases its response to later precipitation treatment.

Mills take advantage of this phenomenon by applying a controlled amount of rolling (sheet and plate) or stretching (extrusion, bar and plate) to produce higher mechanical properties.

However, if the higher properties are used in design, reheat treatment must be avoided.

Where natural ageing is carried out the time may vary from around 5 days for the 2xxx series alloys to around 30 days for other alloys.

The 6xxx and 7xxx series alloys are considerably less stable at room temperature and continue to exhibit changes in mechanical properties for many years.

With some alloys, natural ageing may be suppressed or delayed for several days by refrigeration at -18°C or lower.

It is common practice to complete forming, straightening and coining before ageing changes material properties appreciably.

Conventional practice allows for refrigeration of alloys 2014 - T4 rivets to maintain good driving characteristics.

The artificial ageing or precipitation heat treatments are low temperature long time processes. Temperatures range from 115-200°C and times from 5-48 hours.

As with solution treatment accurate temperature control and spatial variation temperatures are critical to the process and generally temperatures should be held to a range of ±7°C.

The change of time-temperature parameters for precipitation treatment should receive careful consideration.

Larger particles or precipitates result from longer times and higher temperatures. The objective is to select the cycle that produces the optimum precipitate size and distribution pattern.

Unfortunately, the cycle required to maximise one property, such as tensile strength, is usually different from that required to maximise others such as yield strength and corrosion resistance.

Consequently, the cycles used represent compromises that provide the best combination of properties.

Magnesium Alloys:

Magnesium alloy developments have traditionally been driven by aerospace industry requirements for lightweight materials to operate under increasingly demanding conditions. Magnesium alloys have always been attractive to designers due to their low density, only two thirds that of aluminium. This has been a major factor in the widespread use of magnesium alloy castings and wrought products. A further requirement in recent years has been for superior corrosion performance and dramatic improvements have been demonstrated for new magnesium alloys. Improvements in mechanical properties and corrosion resistance have led to greater interest in  magnesium alloys for aerospace and speciality applications, and alloys are now being specified on programmes such as the McDonnell Douglas MD 500 helicopter.

Properties:•         Light weight•         Low density (two thirds that of aluminum)•         Good high temperature mechanical properties•         Good to excellent corrosion resistance

Applications:Aerospace :

For many years, RZ5 alloy has been the preferred material for helicopter transmission casings due to the combination of low density and good mechanical properties. More recently, however, the requirement for longer intervals between overhauls and hence improved corrosion properties has caused manufacturers to reconsider material choice. In the past, RZ5 was generally used for gearbox casings but many new programmes will use WE43 instead including the main rotor gearbox castings. For this application, an aluminium transmission would have been used but for the exceptional corrosion resistance of WE43. The Eurocopter EC 120 and NH90 helicopters have also flown with WE43 transmission casings and WE43 is specified for the Sikorsky S92. Further applications for WE43 will go ahead in the future both on new programmes and also to replace RZ5 on older helicopters. RZ5, ZRE1, MSR and EQ21 alloys are widely used for aircraft engine and gearbox casings. This will continue although it is likely that WE43 will be used increasingly for its corrosion and high temperature properties. Very large magnesium castings can be made, such as intermediate compressor casings for turbine engines.

These include the Rolls Royce Tay casing in MSR, which weighs 130kg and the BMW Rolls Royce BR710 casing in RZ5. Other aerospace applications include auxiliary gearboxes (F16, Eurofighter 2000, Tornado) in MSR or RZ5, generator housings (A320 Airbus, Tornado and Concorde in MSR or EQ21) and canopies, generally in RZ5. Magnesium alloy forgings are also used in aerospace applications including critical gearbox parts for the Westland Sea King helicopter and aircraft wheels, both in ZW3. Forged magnesium parts are also used in aero engine applications. In the future, magnesium forgings are most likely to be used in higher temperature applications

Automotive – motor racing : In motor racing, RZ5 is generally used for gearbox casings although MSR/EQ21

alloys are also being used increasingly due to their superior ambient temperature properties or because of increased operating temperatures.

RZ5 wheels have been shown to have significantly better performance than Mg-Al-Zn alloy wheels under arduous racing conditions.

Due to the high operating temperature of racing engines, WE54 castings have been used for a variety of Formula 1 engine parts and are used for engine components for a limited edition road car.

Forged WE54 pistons offer great future potential for motor racing and other applications will exist for other wrought products.

Magnesium alloys are also used in many other engineering applications where having light weight is a significant advantage.

Magnesium-zirconium alloys tend to be used in relatively low volume applications where they are processed by sand or investment casting, or wrought products by extrusion or forging.

Zirconium-free alloys, principally AZ91 but also other alloys, are used in automotive and various other high volume applications.

Bicycles : As mentioned above Melram 072, the metal matrix composite is used in the bicycle industry due to its excellent stiffness and reduced weight compared to aluminium.

Other Applications : Other applications include electronics, sporting goods, nuclear applications, office equipment, flares, sacrificial anodes for the protection of other metals, flash photography and tools

UNIT-II

PART-A (Important Questions and Answers)

1. What are light metal alloys?Light alloys and light metals have low density and high strength-to-weight ratios. They are generally characterized by low toxicity in comparison to heavy metals, although beryllium is an exception.

2. Write down Types of light metal alloys.

Light weight metals include aluminum, magnesium, titanium, beryllium alloys.

3. Write down the application of light metal alloys.Light metals are utilized most readily for operations and materials that require both good performance properties and lighter materials. Common uses include aerospace, marine, chemical process, and medical applications.

4. What is Aluminum alloy? Aluminum alloys are lightweight, non-ferrous metals with good corrosion resistance, ductility, and strength. Aluminum is relatively easy to fabricate by forming, machining, or welding. This metal is a good electrical and thermal conductor. Aluminum is also useful as an alloying element in steel and titanium alloys. Aluminum alloys are versatile metals with applications in almost every industrial and commercial segment.

5. Write down the properties of Aluminum alloy. aluminum alloys are lightweight, Non-ferrous metals with good corrosion resistance, ductility, and strength. Aluminum is relatively easy to fabricate by forming, machining, or

welding. This metal is a good electrical and thermal conductor. Aluminum is also useful as an alloying element in steel and titanium

alloys.  Aluminum alloys are versatile metals with applications in almost every

industrial and commercial segment.6. Define Quenching.

The soaking of a metal at a high temperature above the recystallization phase, followed by a rapid cooling process. The quenching of steel creates martensite.

7. What is magnesium alloy?Magnesium alloys are mixtures of magnesium with other metals (called an alloy), often aluminium, zinc, manganese, silicon, copper and zirconium. Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice structure, which affects the fundamental properties of these alloys.

8. List out the properties of magnesium alloys. The strength-to-weight ratio of the precipitation-hardened magnesium alloys is comparable with that of the strong alloys of aluminium or with the alloy steels. have a lower density and stand greater column loading per unit weight have good resistance to corrosion

9. Define cast alloys.

Magnesium casting proof stress is typically 75-200 MPa, tensile strength 135-285 MPa and elongation 2-10%. Typical density is 1.8 g/cm3 and Young's modulus is 42 GPa

10. Define wrought alloy.Wrought magnesium alloys have a special feature. Their compressive proof strength is smaller than tensile proof strength. After forming, wrought magnesium alloys have a stringy texture in the deformation direction, which increases the tensile proof strength. In compression the proof strength is smaller because of twinning, which happens more easily in compression than in tension in magnesium alloys because of the hexagonal lattice structure

PART B (Important Questions)

1. Explain in detail light weight materials and its alloys.

2. Write down the properties and application of magnesium alloys.

3. What is the factors affection in choosing materials for airplane parts?

4. Explain in detail about the heat treatment of aluminum alloys.

5. Write down the application of aluminum and magnesium alloys.

6. Explain magnesium alloys.

UNIT III

HIGH STRENGTH AND HEAT RESISTANT ALLOYS

Refractory metals:

Are classes of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: two of the fifth period (niobium and molybdenum) and three of the sixth period (tantalum, tungsten, and rhenium). They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder metallurgy the method of choice for fabricating components from these metals. Some of their applications include tools to work metals at high temperatures, wire filaments, casting molds, and chemical reaction vessels in corrosive environments. Partly due to the high melting point, refractory metals are stable against creep deformation to very high temperatures. Most definitions of the term 'refractory metals' list the extraordinarly high melting point as a key requirement for inclusion By one definition, a melting point above 4,000 °F (2,200 °C) is necessary to qualify the five elements niobium, molybdenum, tantalum, tungsten and rhenium are included in all definitions.

Molybdenum alloys: Molybdenum based alloys are widely used, because they are cheaper than superior tungsten alloys. The most widely used alloy of molybdenum is the Titanium-Zirconium- Molybdenum alloy TZM, composed of 0.5% titanium and 0.08% of zirconium (with molybdenum being the rest).  The alloy exhibits a higher creep resistance and strength at high temperatures, making service temperatures of above 1060°C possible for the material. The alloy exhibits a higher creep resistance and strength at high temperatures, making service temperatures of above 1060°C possible for the material.  The high resistivity of Mo-30W an alloy of 70% molybdenum and 30 tungsten against the attack of molten zinc makes it the ideal material for casting zinc. It is also used to construct valves for molten zinc

Molybdenum is used in mercury wetted reed relays, because molybdenum does not form amalgams and is therefore resistant to corrosion by liquid mercury Molybdenum is the most commonly used of the refractory metals. Its most important use is as a strengthening alloy of steel.Structural tubing and piping often contains molybdenum, as do many stainless steels. Its strength at high temperatures, resistance to wear and low coefficient of friction are all properties which make it invaluable as an alloying compound

Its excellent anti-friction properties lead to its in greases and oils where reliability and performance are critical

Tungsten and its alloys

Up to 22% rhenium is alloyed with tungsten to improve its high temperature strength and corrosion resistance. Thorium as an alloying compound is used when electric arcs have to be established. The ignition is easier and the arc burns more stable than without the addition of thorium. For powder metallurgy applications binders have to be used for the sintering process.  For the production of the tungsten heavy alloy a binder mixtures of nickel and iron or nickel and copper are widely used. the tungsten content of the alloy is normally above 90%. The diffusion of the binder elements into the tungsten grains is low even at the sintering temperatures and therefore the interior of the grains is pure tungsten. Tungsten and its alloys are often used in applications where high temperatures are present but still a high strength is necessary and the high density is not troublesome Tungsten's high density and strength is also a key property for its use in weapon projectiles, for example as an alternative to depleted Uranium for tank guns. Its high melting point makes tungsten a good material for applications like rocket nozzles, for example in the UGM-27 Polaris.

Niobium alloys Niobium is nearly always found together with tantalum, and was named after Niobe, the daughter of the mythical Greek king Tantalus for whom tantalum was named.  Niobium has many uses, some of which it shares with other refractory metals. It is unique in that it can be worked through annealing to achieve a wide range of strength and elasticity, and is the least dense of the refractory metals.  It can also be found in electrolytic capacitors and in the most practical  superconducting  alloys.  Niobium can be found in aircraft gas turbines, vacuum tubes and nuclear reactors An alloy used for liquid rocket thruster nozzles, such as in the main engine of theApollo Lunar Modules, is C103, which consists of 89% niobium, 10% hafnium and 1% titanium. Another niobium alloy was used for the nozzle of the Apollo Service Module. As niobium is oxidized at temperatures above 400 °C, a protective coating is necessary for these applications to prevent the alloy from becoming brittle

Tantalum and its alloys Tantalum is one of the most corrosion resistant substances available. Many important uses have been found for tantalum owing to this property,

particularly in the medical and surgical fields, and also in harsh acidic environments.

It is also used to make superior electrolytic capacitors Tantalum films provide the second most capacitance per volume of any substance

after Aerogel and allow miniaturization of electronic components and circuitry Many cellular phones and computers contain tantalum capacitors.

Rhenium alloys Rhenium is the most recently discovered refractory metal It is found in low concentrations with many other metals, in the ores of other refractory metals, platinum or copper ores. it is useful as an alloy to other refractory metals, where it adds ductility and tensile strength. Rhenium alloys are being used in electronic components, gyroscopes and nuclear reactors.  Rhenium finds its most important use as a catalyst. It is used as a catalyst in reactions such as alkylation, dealkylation,hydrogenation and oxidation.  However its rarity makes it the most expensive of the refractory metals.

Inconel alloys:

Inconel is a family of austenitic nickel-chromium-based super alloys Inconel alloys are typically used in high temperature applications. It is sometimes referred to in English as "Inco" (or occasionally "Inconel"). Common trade names for Inconel Alloy 625 include: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 and Nicrofer 6020

Properties: Inconel alloys are oxidation- and corrosion-resistant materials well suited for service in extreme environments subjected to high pressure and kinetic energy.  When heated, Inconel forms a thick and stable passivating oxide layer protecting the surface from further attack.  Inconel retains strength over a wide temperature range, attractive for high-temperature applications where aluminum and steel would succumb to creep as a result of thermally-induced crystal vacancies (see Arrhenius). Inconel's high temperature strength is developed by solid solution strengthening or precipitation strengthening, depending on the alloy. In age-hardening or precipitation-strengthening varieties, small amounts of niobium combine with nickel to form the intermetallic compound Ni3Nb or

gamma prime (γ'). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures. The formation of gamma-prime crystals increases over time, especially after three hours of a heat exposure of 850 °C, and continues to grow after 72 hours of exposure.

Monel alloys: Monel is a series of nickel alloys, primarily composed of nickel (up to 67%) and copper, with some iron and other trace elements. Monel alloy 400 is binary alloy of the same proportions of nickel and copper as is found naturally in the nickel ore from the Sudbury (Ontario) mines and is therefore considered a puritan alloy

Properties: Compared to steel, Monel is very difficult to machine as it work-hardens very quickly. It needs to be turned and worked at slow speeds and low feed rates. It is resistant to corrosion and acids, and some alloys can withstand a fire in pure oxygen It is commonly used in applications with highly corrosive conditions. Small additions of aluminum and titanium form an alloy (K-500) with the same corrosion resistance but with much greater strength due to gamma prime formation on aging.  Monel is typically much more expensive than stainless steel. Monel alloy 400 has a specific gravity of 8.83, an electrical conductivity of approximately 34% IACS, and (in the annealed state) a hardness of 65 Rockwell

K Monel: It Is a nickel-copper alloy which combines the excellent corrosion resistance of MONEL alloy 400 with the added advantages of greater strength and hardness The increased properties are obtained by adding aluminum and titanium to the nickel-copper base, and by heating under controlled conditions so that submicroscopic Particles of Ni3 (Ti, Al) are precipitated throughout the matrix. The thermal processing used to effect precipitation is commonly called age hardening or aging.

Nimonic: is a registered trademark of Special Metals Corporation that refers to a family of nickel-based high-temperature low creep superalloys. Nimonic alloys typically consist of more than 50% nickel and 20% chromium with additives such astitanium and aluminium The main use is in gas turbine components and extremely high performance reciprocating internal combustion engines. 

Properties: Due to its ability to withstand very high temperatures, Nimonic is ideal for use in aircraft parts and gas turbine components such as turbine blades and exhaust nozzles on jet engines, for instance, where the pressure and heat are extreme.

It is available in different grades, including Nimonic 75, Nimonic 80A, and Nimonic 90. Nimonic 80a was used for the turbine blades on the Rolls-Royce Nene, Nimonic 90 on the Bristol Proteus, and Nimonic 105 on the Rolls-Royce Spey aviation gas turbines Nimonic 263 was used in the combustion chambers of the Rolls-Royce/Bristol Olympus used on the Concorde supersonic airliner.

Super alloy: A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and resistance to creep (tendency for solids to slowly move or deform under stress) at high temperatures; good surface stability; and corrosion and oxidation resistance. Superalloys typically have a matrix with an austenitic face-centered cubic crystal structure. A superalloy's base alloying element is usually nickel, cobalt, or nickel-iron.  Superalloy development has relied heavily on both chemical and process innovations and has been driven primarily by the aerospace and power industries. Typical applications are in the aerospace, industrial gas turbine and marine turbine industries, e.g. for turbine blades for hot sections of jet engines, and bi-metallic engine valves for use in diesel and automotive applications. Examples of superalloys are Hastelloy, Inconel (e.g. IN100, IN600,

IN713), Waspaloy, Rene alloys (e.g. Rene 41, Rene 80, Rene 95, Rene N5), Haynes alloys, Incoloy, MP98T, TMS alloys, and CMSX (e.g. CMSX-4) single crystal alloys.

Superalloys are commonly used in parts of gas turbine engines that are subject to high temperatures and require high strength, excellent high temperature creep resistance, fatigue life, phase stability, and oxidation and corrosion resistance

Superalloys develop high temperature strength through solid solution strengthening. The most important strengthening mechanism is through the formation of secondary phase precipitates such as gamma prime and carbides through precipitation.

Superalloys (such as Nimonic 80A) are also used in the poppet valves of piston engines, both for diesel and gasoline engines.

UNIT III

PART-A (Important Questions and Answers)

1. Define heat resistant materialsMaterial is one that is designed to resist burning and withstand heat. It is used in the bunker gear worn by firefighters to protect them from the flames of a burning building.

2. Define refractory materials.

A refractory material is one that retains its strength at high temperatures. ASTMC71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures or as components of systems, that are exposed to environments above 1,000 °F (811 K; 538 °C)

3. Write down the Titanium alloys.Titanium alloys are metals which contain a mixture of titanium and the chemical elements. Such alloys have very high tensile strength and toughness (even at extreme temperatures). They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures.

4. What is Cobalt based alloys?Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt in the Earth's crust is found only in chemically combined form, save for small deposits found in alloys of natural meteoric iron.

5. Write down the properties of Inconel alloy. Inconel alloys are oxidation- and corrosion-resistant materials well suited for service in extreme environments subjected to high pressure and kinetic energy.  When heated, Inconel forms a thick and stable passivating oxide layer protecting the surface from further attack.  Inconel retains strength over a wide temperature range, attractive for high-temperature applications where aluminum and steel would succumb to creep as a result of thermally-induced crystal vacancies.

6. What is Monel alloy?Monel is a series of nickel alloys, primarily composed of nickel (up to 67%) and copper, with some iron and other trace elements.

7. List out the properties of Nimonic alloys. Due to its ability to withstand very high temperatures, Nimonic is ideal for use in aircraft parts and gas turbine components such as turbine blades and exhaust nozzles on jet engines, for instance, where the pressure and heat are extreme. It is available in different grades, including Nimonic 75, Nimonic 80A, and Nimonic 90. Nimonic 80a was used for the turbine blades on the Rolls-Royce Nene, Nimonic 90 on the Bristol Proteus, and Nimonic 105 on the Rolls-Royce Spey aviation gas turbines Nimonic 263 was used in the combustion chambers of the Rolls-Royce/Bristol Olympus used on the Concorde supersonic airliner.

8. Define ceramic materials.Ceramic materials are inorganic, non-metallic materials made from compounds of a metal and a non metal. Ceramic materials may be crystalline or partly crystalline.

9. Define properties of crystalline materials.

Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with them tend to fall into one of two categories - either make the ceramic in the desired shape, by reaction in situ, or by "forming" powders into the desired shape, and then sintering to form a solid body

PART B (Important Questions)

1. Explain in detail heat resistant materials.

2. Write down the properties and application of inconel alloys.

3. Explain in detail Titanium alloy and its types?

4. Write down the properties and application of ceramic material.

5. Write down the application of Inconel and Monel alloys.

6. Explain Cobalt based alloys.

UNIT IV

CASTING AND WELDING

Manufacturing • Manufacturing in its broadest sense is the process of converting raw materials into useful products. • It includes

i) Design of the product

ii) Selection of raw materials and iii) The sequence of processes through which the product will be manufactured.

Classification of Manufacturing Processes: For producing of products materials are needed. It is therefore important to know the characteristics of the available engineering materials. Raw materials used manufacturing of products, tools, machines and equipments in factories or industries are extracted from ores. The ores are suitably converted the metal into a molten form by reducing or refining processes in foundries. This molten metal is poured into moulds for providing commercial castings, called ingots. Such ingots are then processed in rolling mills to obtain market form of material supply in form of bloom, billets, slabs and rods. These forms of material supply are further subjected to various manufacturing processes for getting usable metal products of different shapes and sizes in various manufacturing shops. All these processes used in manufacturing concern for changing the ingots into usable products may be classified into six major groups as primary shaping processes, secondary machining processes, metal forming processes, joining processes, surface finishing processes and processes effecting change in properties.

Primary Shaping Processes: Primary shaping processes are manufacturing of a product from an amorphous material. Some processes produces finish products or articles into its usual form whereas others do not, and require further working to finish component to the desired shape and size. Castings need re-melting of scrap and defective ingots in cupola or in some other melting furnace and then pouring of the molten metal into sand or metallic moulds to obtain the castings. Thus the intricate shapes can be manufactured. Typical examples of the products that are produced by casting process are machine beds, automobile engines, carburetors, flywheels etc. The parts produced through these processes may or may not require to under go further operations. Some of the important primary shaping processes is:

(1)Casting, (2) Powder metallurgy, (3) Plastic technology, (4) Gas cutting, (5) Bending and (6) Forging.

Secondary or Machining Processes: As large number of components require further processing after the primary processes.

These components are subjected to one or more number of machining operations in machine shops, to obtain the desired shape and dimensional accuracy on flat and cylindrical jobs. Thus, the jobs undergoing these operations are the roughly finished products received through primary shaping processes. The process of removing the undesired or unwanted material from the work piece or job or component to produce a required shape using a cutting tool is known as machining. This can be done by a manual process or by using a machine called machine tool (traditional machines namely lathe, milling machine, drilling, shaper, planner, slotter). In many cases these operations are performed on rods, bars and flat surfaces in machine shops. These secondary processes are mainly required for achieving dimensional accuracy and a very high degree of surface finish. The secondary processes require the use of one or more machine tools, various single or multi-point cutting tools (cutters), job holding devices, marking and measuring instruments, testing devices and gauges etc. for getting desired dimensional control and required degree of surface finish on the work pieces. The example of parts produced by machining processes includes hand tools machine tools instruments, automobile parts, nuts, bolts and gears etc. Lot of material is wasted as scrap in the secondary or machining process. Some of the common secondary or machining processes are -

(1) Turning, (2) Threading, (3) Knurling, (4) Milling, (5) Drilling, (6) Boring, (7) Planning, (8) Shaping, (9) Slotting, (10) Sawing, (11) Broaching, (12) Hobbing, (13) Grinding, (14) Gear cutting, (15) Thread cutting and (16) Unconventional machining processes namely machining with Numerical Control (NC) machines tools or Computer Numerical Control (CNC) machines tools using ECM, LBM, AJM, USM setups etc.

Metal Forming Processes Forming processes encompasses a wide variety of techniques, which make use of suitable Force, pressure or stresses, like compression, tension and shear or their combination to cause a permanent deformation of the raw material to impart required shape. These processes are also known as mechanical working processes and are mainly classified into two major categories i.e., hot working processes and cold working processes. In these processes, no material is removed; however it is deformed and displaced using suitable stresses like compression, tension, and shear or combined stresses to cause plastic deformation of the materials to produce required shapes. Such processes lead to production of directly usable articles which include kitchen utensils, rods, wires, rails, cold drink bottle caps, collapsible tubes etc. Some of the important metal forming processes are:

Hot working Processes(1) Forging, (2) Rolling, (3) Hot spinning, (4) Extrusion, (5) Hot drawing and (6) Hot

spinning. Cold working processes(1) Cold forging, (2) Cold rolling, (3) Cold heading, (4) Cold drawing, (5) Wire

drawing,(6) Stretch forming, (7) Sheet metal working processes such as piercing, punching,

lancing,Notching, coining, squeezing, deep drawing, bending etc.

Joining Processes: The process of putting the parts together to form the product, which performs the desired function, is called assembly. An assemblage of parts may require some parts to be joined together using various joining processes. But assembly should not be confused with the joining process. Most of the products cannot be manufactured as single unit they are manufactured as different components using one or more of the above manufacturing processes, and these components are assembled to get the desired product. Joining processes are widely used in fabrication and assembly work. In these process two or more pieces of metal parts are joined together to produce desired shape and size of the product. The joining processes are carried out by fusing, pressing, rubbing, riveting, screwing or any other means of assembling. These processes are used for assembling metal parts and in general fabrication work. Such requirements usually occur when several pieces are to be joined together to fabricate a desired structure of products. These processes are used developing steam or water-tight joints. Temporary, semi-permanent or permanent type of fastening to make a good joint is generally created by these processes. Temporary joining of components can be achieved by use of nuts, screws and bolts. Adhesives are also used to make temporary joints. Some of the important and common joining processes are:

(1) Welding (plastic or fusion), (2) Brazing, (3) Soldering, (4) Riveting, (5) Screwing, (6) Press fitting, (7) Sintering, (8) Adhesive bonding, (9) Shrink fitting, (10) Explosive welding, (11) Diffusion welding, (12) Keys and cotters joints, (13) Coupling and (14) Nut and bolt joints.

Surface Finishing Processes Surface finishing processes are utilized for imparting intended surface finish on the surface of a job.

By imparting a surface finishing process, dimension of part is not changed functionally either a very negligible amount of material is removed from the certain material is added to the surface of the job. These processes should not be misunderstood as metal removing processes in any case as they are primarily intended to provide a good surface finish or a decorative or protective coating on to the metal surface. Surface cleaning process also called As a surface finishing process. Some of the commonly used surface finishing processes are:

Honing, (2) Lapping, (3) Super finishing, (4) Belt grinding, (5) Polishing, (6) Tumbling, (7) Organic finishes, (8) Sanding, (9) deburring, (10) Electroplating, (11) Buffing, (12) Metal spraying, (13) Painting, (14) Inorganic coating, (15) Anodizing, (16) Sheradising, (17) Parkerizing, (18) Galvanizing, (19) Plastic coating, (20) Metallic coating, (21) Anodizing and (22) Sand blasting.

Casting Processes: The casting process involves pouring of liquid metal in to a mold cavity and allowing it to solidify to obtain the final casting. The flow of molten metal into the mold cavity depends on several factors like minimum section thickness of the part, presence of corners, non-uniform cross-section of the cast, and so on. The casting processes can be broadly classified into expendable mold casting and permanent mold casting processes

Expendable Mold Casting:

Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) molds. All these methods use temporary, non-reusable molds. After the molten metal in the mold cavity solidifies, the mold is broken to take out the solidified cast. Expendable mold casting processes are suitable for very complex shaped parts and materials with high melting point temperature. However, the rate of production is often limited by the time to make mold rather than the casting itself. Following are a few examples of expendable mold casting processes.

Sand Casting: Sand casting is widely used for centuries because of the simplicity of the process. The sand casting process involves the following basic steps: (a) place a wooden or metallic pattern in sand to create a mold, (b) fit in the pattern and sand in a gating system, (c) remove the pattern, (d) fill the mold cavity with molten metal, (e) allow the metal to cool, and (f) break the sand mold and remove the casting. The sand casting process is usually economical for small batch size production.

The quality of the sand casting depends on the quality and uniformity of green sand material that is used for making the mold. a two-part sand mold, also referred to as a cope-and-drag sand mold. The molten metal is poured through the pouring cup and it fills the mold cavity after passing through down sprue, runner and gate. The core refers to loose pieces which are placed inside the mold cavity to create internal holes or open section. The riser serves as a reservoir of excess molten metal that facilitates additional filling of mold cavity to compensate for volumetric shrinkage during solidification. Sand castings process provides several advantages. It can be employed for all types of metal. The tooling cost is low and can be used to cast very complex shapes. However sand castings offer poor dimensional accuracy and surface finish.

Shell molding

Shell molding: It is similar to sand casting. Normally a machined pattern of grey iron or aluminum is used in this process. The pattern is heated to 2500 C to 2600 C and the sand resin mixture is poured over its surface. The heated pattern melts the resin creating bonds between the sand grains. After a dwell period the pattern and sand inverted and extra sand is cleaned off. The mold cavity is now formed by a hardened shell of sand. The mold is then heated in an oven for further curing. The shell thus formed constitutes one half of the mold. Two such halves are placed over one another to make the complete mold. The sands used in shell molding process are usually finer than the same used in sand casting. This process is ideal for complex shaped medium sized parts. This method can be employed for making an integrate shapes, thin and sharp corners small projection which are not possible in green sand mold.

Subsequent machining operations are also reduced due to more dimensional accuracy.

Investment casting: Investment casting is also referred to as lost-wax casting since the pattern is

made of wax. The wax patterns are first dipped into a slurry of refractory material and

subsequently, heated so that the wax melts away keeping a refractory mold.

The mold is then further cured to achieve proper strength. Very high melting temperature material can be cast in investment casting process because of the refractory mold.

The molten metal is poured into the mold and is taken out after solidification by breaking the mold.

Very high dimensional accuracy and surface finish can be achieved in investment casting process. However, the tooling cast is usually high and hence, investment casting process is primarily used for large size batch production or for specific requirements of complex shape or casting of very high melting temperature material.

Vacuum Casting: In this process, a mixture of fine sand and urethane is molded over metal dies and cured with amino vapor. The molted metal is drawn into the mold cavity through a gating system from the bottom of the mold.

The pressure inside the mold is usually one-third of the atmospheric pressure. Because the mold cavity is filled under vacuum, the vacuum casting process is very suitable for thin walled, complex shapes with uniform properties.

Plaster mold casting

Plaster mold casting, also called rubber plaster molding (RPM), is a method of producing aluminum or zinc castings by pouring liquid metal into typical plaster (gypsum) molds.

The plaster molds used as negative molds are created from gypsum and water. After mixing and forming the mold shape, the plaster molds are dried and baked

in an oven to remove any water remaining in the mold. Often, the molds are made in two halves – i.e. cope and drag molds – and the

halves of the plaster molds are clamped together with any required cores positioned appropriately in the mold.

Molten metal is subsequently poured into the negative plaster mold and allowed to dry. The final part is taken out after breaking the mold.

The final cast may require machining operation depending upon the requisite dimensional accuracy.

This process is often used for producing prototypes of final part or component. Ceramic mold casting . The ceramic mold casting is used to produce split molds from a quick-setting

ceramic investment. Blended ceramic particles are mixed rapidly with liquid binder to form free

flowing slurry that is poured quickly over a pattern. The casting does not require wax patterns and there are no limits to size or alloy. Foundry applications are large and complex impellers, valve bodies, and military

hardware. The green strength of ceramic mold casting is high. Ceramic mold casting. method uses a ceramic slurry prepared by mixing fine grained refractory powders

of Zircon (ZrSiO4), Alumina (Al2O3), Fused Silica (SiO2) and a liquid chemical binder (Alcohol based Silicon Ester) for making the mold.

Permanent Mold Casting processes :

Permanent mold casting processes involve the use of metallic dies that are permanent in nature and can be used repeatedly.

The metal molds are also called dies and provide superior surface finish and close tolerance than typical sand molds.

The permanent mold casting processes broadly include pressure die casting, squeeze casting, centrifugal casting, and continuous casting.

Pressures die casting: The pressure die casting process is the most common for Al, Zn and Mg castings

(low melting point). The liquid metal is injected into the mold under high pressure and allowed to

solidify at the high pressure. The solidified cast is then taken out of the mold or the die which is ready for the

next cast. Pressure die casting is suitable for large batch size production. Two types of

pressure die casting are generally common in the industry – (a) high pressure die casting and (b) low pressure die casting.

Very high production rates can be achieved in pressure die casting process with close dimensional control of the casting.

However, the process is not suitable for casting of high melting temperature materials as the die material has to withstand the melting (or superheated) temperature of the casting. Pressure die castings also contain porosity due to the entrapped air. Furthermore, the dies in the pressure die casting process are usually very costly.

In the hot-chamber die casting process, the furnace to melt material is part of the die itself and hence, this process is suitable primarily for low-melting point temperature materials such as aluminum, magnesium etc.

Squeeze casting: Molten metal is poured into a metallic mold or die cavity with one-half of the die squeezing the molten metal to fill in the intended cavity under pressure . Fiber reinforced casting with SiC or Al2O3 fibers mixed in metal matrix have been successfully squeeze cast and commercially used to produce automobile pistons. However, squeeze casting is limited only to shallow part or part with smaller dimensions.

Centrifugal casting: In centrifugal casting process, the molten metal poured at the center of a rotating mold or die. Because of the centrifugal force, the lighter impurities are crowded towards the center of the case. For producing a hollow part, the axis of rotation is placed at the center of the desired casting. The speed of rotation is maintained high so as to produce a centripetal acceleration of the order of 60g to 75g. The centrifuge action segregates the less dense nonmetallic inclusions near to the center of rotation that can be removed by machining a thin layer. No cores are therefore required in casting of hollow parts although solid parts can also be cast by this process. The centrifugal casting is very suitable for axisymmetric parts. Very high strength of the casting can be obtained. Since the molten metal is fed by the centrifugal action, the need for complex metal feeding system is eliminated. Both horizontal and vertical centrifugal castings are widely used in the industry.

Continuous casting Continuous casting process is widely used in the steel industry. In principle, continuous casting is different from the other casting processes in the

fact that there is no enclosed mold cavity. Molten steel coming out from the furnace is accumulated in a ladle. After undergoing requisite ladle treatments, such as alloying and degassing, and

arriving at the correct temperature, the ladle is transported to the top of the continuous casting set-up.

From the ladle, the hot metal is transferred via a refractory shroud (pipe) to a holding bath called a tundish.

The tundish allows a reservoir of metal to feed the casting machine. Metal is then allowed to pass through a open base copper mold. The mold is water-cooled to solidify the hot metal directly in contact with it and

removed from the other side of the mold. The continuous casting process is used for casting metal directly into billets or other

similar shapes that can be used for rolling. The process involves continuously pouring molten metal into a externally chilled

copper mold or die walls and hence, can be easily automated for large size production.

Since the molten metal solidifies from the die wall and in a soft state as it comes out of the die wall such that the same can be directly guided into the rolling mill or can be sheared into a selected size of billets.

Defects in Casting Processes:

There are various defects that are experienced during casting, in particular, sand casting processes. A brief explanation of some of the significant defects and their possible remedial measures are indicated in the text to follow.Shrinkage Shrinkage of molten metal as it solidifies is an important issue in casting. It can reduce the 5-10% volume of the cast. Gray cast iron expands upon solidification due to phase changes. Need to design part and mold to take this amount into consideration. The thickness of the boss or pad should be less than the thickness of the section of the boss adjoins and the transition should be gradual. The radius for good shrinkage control should be from one half to one third of the section thickness. Shrinkage defect can be reduced by decreasing the number of walls and increasing the draft angle.

Porosity:Porosity is a phenomenon that occurs in materials, especially castings, as they change state from liquid to solid during the manufacturing process. Casting porosity has the form of surface and core imperfections which either effects the surface finish or as a leak path for gases and liquids. The poring temperature should be maintained properly to reduce porosity. Adequate fluxing of metal and controlling the amount of gas-producing materials in the molding and core making sand mixes can help in minimizing this defect.

Hot tear Hot tears are internal or external ragged discontinuities or crack on the casting surface, caused by rapid contraction occurring immediately after the metal solidified. They may be produced when the casting is poorly designed and abrupt sectional changes take place; no proper fillets and corner radii are provided, and chills are inappropriately placed. Hot tear may be caused when the mold and core have poor collapsibility or when the mold is too hard causing the casting to undergo severe strain during cooling. Incorrect pouring temperature and improper placement of gates and risers can also create hot tears. Method to prevent hot tears may entail improving the casting design, achieving directional solidification and even rate of cooling all over, selecting proper mold and poured materials to suit the cast metal, and controlling the mold hardness in relation to other ingredients of sand.

Scar:It is usually found on the flat casting surface. It is a shallow blow.

Blowhole:Blowholes are smooth round holes that are clearly perceptible on the surface of the casting. To prevent blowholes, moisture content in sand must be well adjusted, sand of proper grain size should be used, ramming should not be too hard and venting should be adequate.

Blister: This is a scar covered by the thin layers of the metal.

Dross:The lighter impurities are appearing on the top of the cast surface is called the dross. It can be taken care of at the pouring stage by using items such as a strainer and a skim bob.

Dirt Sometimes sand particles dropping out of the cope get embedded on the top surface of a casting. When removed, these leave small angular holes is known as dirts.

Wash It is a low projection on the drag surface of a casting commencing near the gate. It is caused by the erosion of sand due to high velocity liquid metal.

Buckle It refers to a long fairly shallow broad depression at the surface of a casting of a high temperature metal. Due to very high temperature of the molten metal, expansion of the thin layered of the sand at the mold face takes place. As this expansion is obstructed by the flux, the mold tends to bulge out forming a V shape.

Rat tail It is a long shallow angular depression found in a thin casting. The cause is similar to buckle.

Shift A shift results in a mismatch of the sections of a casting usually as a parting line. Misalignment is common cause of shift. This defect can be prevented by ensuring proper alignment of the pattern for die parts, molding boxes, and checking of pattern flux locating pins before use.

Warped casting

Warping is an undesirable deformation in a casting which occurs during or after solidification. Large and flat sections are particularly prone to wrap edge. Wrap edge may also be due to insufficient gating system that may not allow rapid pouring of metal or due to low green strength of the sand mold or inadequate / inappropriate draft allowance in the pattern / mold cavity.

Metal Penetration and Rough Surfaces This defect appears as an uneven and rough external surface of the casting. It may be caused when the sand has too high permeability, large grain size, and low strength. Soft ramming may also cause metal penetration.

Fin A thin projection of metal, not intended as a part of casting, is called a fin. Fins occur at the parting of the mold or core sections. Molds and cores in correctly assembled will cause the fin.High metal pressures due to too large downsprue, insufficient weighing of the molds or improper clamping of flasks may again produce the fin defect.

Cold Shut and Mis-Run A cold shut is a defect in which a discontinuity is formed due to the imperfect fusion of two streams of metal in the mold cavity. The reasons for cold shut or mis-run may be too thin sections and wall thickness, improper gating system, damaged patterns, slow and intermittent pouring , poor fluidity of metal caused by low pouring temperature, improper alloy composition, etc.

Inspections of Casting:

Visual inspection Visible defects that can be detected provide a means for discovering errors in the pattern equipment or in the molding and casting process. Visual inspection may prove inadequate only in the detection of sub surface or internal defects.

Dimensional inspection Dimensional inspection is one of the important inspections for casting. When precision casting is required, we make some samples for inspection the tolerance, shape size and also measure the profile of the cast. This dimensional inspection of casting may be conducted by various methods: • Standard measuring instruments to check the size of the cast. • Contour gauges for the checking of profile, curves and shapes • Coordinate measuring and Marking Machine • Special fixtures

X-Ray Radiography

In all the foundries the flaw detection test are performed in the casting where the defects are not visible. This flaw detection test is usually performed for internal defects, surface defects etc. These tests are valuable not only in detecting but even in locating the casting defects present in the interior of the casting. Radiography is one of the important flaw detection test for casting. The radiation used in radiography testing is a higher energy (shorter wavelength) version of the electromagnetic waves that we see as visible light. The radiation can come from an X-ray generator or a radioactive source.

Magnetic particle inspection This test is used to reveal the location of cracks that extend to the surface of iron or steel castings, which are magnetic nature. The casting is first magnetized and then iron particles are sprinkled all over the path of the magnetic field. The particles align themselves in the direction of the lines of force. A discontinuity in the casting causes the lines of the force to bypass the discontinuity and to concentrate around the extremities of the defect.

Fluorescent dye-penetration test This method is very simple and applied for all cast metals. It entails applying a thin penetration oil-base dye to the surface of the casting and allowing it to stand for some time so that the oil passes into the cracks by means of capillary action. The oil is then thoroughly wiped and cleaned from the surface. To detect the defects, the casting is pained with a coat of whitewash or powdered with tale and then viewed under ultraviolet light. The oil being fluorescent in nature, can be easily detect under this light, and thus the defects are easily revealed.

Ultrasonic Testing Ultrasonic testing used for detecting internal voids in casting is based on the principle of reflection of high frequency sound waves. If the surface under test contains some defect, the high frequency sound waves when emitted through the section of the casting, will be reflected from the surface of defect and return in a shorter period of time. The advantage this method of testing over other methods is that the defect, even if in the interior, is not only detected and located accurately, but its dimension can also be quickly measured without in any damaging or destroying the casting.

Fracture test Fracture test is done by examining a fracture surface of the casting. it is possible to observe coarse graphite or chilled portion and also shrinkage cavity, pin hole etc. The apparent soundness of the casting can thus be judged by seeing the fracture.

Macro-etching test (macroscopic examination) The macroscopic inspection is widely used as a routine control test in steel production because it affords a convenient and effective means of determining internal defects in the metal. Macro-etching may reveal one of the following conditions:

Crystalline heterogeneity, depending on solidification Chemical heterogeneity, depending on the impurities present or localized segregation and Mechanical heterogeneity, depending on strain introduced on the metal, if any.

Sulphur Print test Sulphur may exist in iron or steel in one of two forms; either as iron sulphide or manganese sulphide. The distribution of sulphur inclusions can easily examined by this test.

Microscopic Examination Microscopic examination can enable the study of the microstructure of the metal alloy, elucidating its composition, the type and nature of any treatment given to it, and its mechanical properties. In the case of cast metals, particularly steels, cast iron, malleable iron, and SG iron, microstructure examination is essential for assessing metallurgical structure and composition. Composition analysis can also be done using microscopic inspection. Distribution of phase can be observed by metallographic sample preparation of cast product. Grain size and distribution, grain boundary area can be observed by this procedure. Distribution of nonmetallic inclusion can also be found from this process of inspection.

Chill Test Chill test offers a convenient means for an approximate evaluation of the graphitizing tendency of the iron produced and forms an important and quick shop floor test for ascertaining whether this iron will be of the class desired. In chill test, accelerated cooling rate is introduced to induce the formation of a chilled specimen of appropriate dimension. It is then broken by striking with a hammer in such a manner that the fracture is straight and midway of its length. The depth of chill obtained on the test piece is affected by the carbon and silicon present and it can therefore be related to the carbon equivalent, whose value in turn determines the grade of iron.

Design Recommendations for Casting:1. Compensate the shrinkage of the solidified molten metal by making patterns of slightly oversize.

2. In sand casting, it is more economical and accurate if the parting line is on a flat plane Contoured parting lines are not economical. Further, some degree of taper, or draft is recommended to provide to the pattern for its easy removal. The recommended draft angles for patters under various conditions are given elsewhere.3. In sand casting, it is recommended to attach the raiser near to the heavier section. The thinnest sections are farthest from the raiser and solidify first and then the solidification proceeds toward the direction of raiser i.e. towards the heavier section.4. Sharp corners in a casting design cause uneven cooling and lead to formation of hot spots in the final cast structure. Moreover sharp corner in a casting structure acts as a stress raiser. Rounding the corner decreases the severity of the hot spot and lessens the stress concentration. Abrupt changes in sections should be avoided. Fillets and tapers are preferable to sharp steps.5. The interior walls and sections are recommended to be 20% thinner than the outside members to reduce the thermal and residual stresses, and metallurgical changes .6. The interior walls and sections are recommended to be 20% thinner than the outside members to reduce the thermal and residual stresses, and metallurgical changes.7. When a hole is placed in a highly stressed section, add extra material around the hole as reinforcement.8. To minimize the residual stresses in the gear, pulley or wheel casting, a balance between the section size of the rim, spokes and hub is maintained.9. An odd number of curved wheel spokes reduce cast-in-residual stresses. 10. Similar to sand casting, permanent mold castings also require draft for the easy withdrawal of the casting from the mold. The recommended draft angles are given elsewhere.11. Due to pattern shrinkage, investment shrinkage and metal shrinkage during solidification, there is always a tendency for an investment part to “dish” (develop concave surfaces where flat surfaces are specified). This condition takes place in areas of thick cross section. Dishing is minimized by designing parts with uniformly thin walls.

12. When keys and keyways are required, the recommended ratio of width to depth is 1.0 or more. The minimum castable key width is 2.3 mm for ferrous metals and 1.5 mm for nonferrous metals.

13. Heavy bosses connecting to the surface can cause “sinks” due to the shrinkage of the large mass of the metal in the boss during cooling. This shrinkage problem can be reduced by moving the boss away from the surface and connecting it to the surface with a short rib.

JOINING PROCESSES:

Welding:Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material. Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.Classification of welding processes :

(i) Arc welding

• Carbon arc

• Metal arc

• Metal inert gas

• Tungsten inert gas

• Plasma arc

• Submerged arc

• Electro-slag

(ii) Gas Welding

• Oxy-acetylene

• Air-acetylene

• Oxy-hydrogen

iii) Resistance Welding Butt

Spot

Seam

Projection

Percussion

(iv) Thermit Welding(v) Solid State Welding

Friction Ultrasonic Diffusion Explosive

(vi) Newer Welding Electron-beam Laser

(vii)Related Process Oxy-acetylene cutting Arc cutting Hard facing Brazing Soldering

Welding practice & equipment :

STEPS: • Prepare the edges to be joined and maintain the proper position

• Open the acetylene valve and ignite the gas at tip of the torch

• Hold the torch at about 45deg to the work piece plane

• Inner flame near the work piece and filler rod at about 30 – 40 deg

• Touch filler rod at the joint and control the movement according to the flow of the material

Two Basic Types of AW Electrodes :Consumable – consumed during welding process Source of filler metal in arc welding Nonconsumable – not consumed during welding process Filler metal must be added separately

Consumable Electrodes Forms of consumable electrodes • Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter and must be changed frequently

• Weld wire can be continuously fed from spools with long lengths of wire, avoiding frequent interruptions. In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal.

No consumable Electrodes Made of tungsten which resists melting Gradually depleted during welding (vaporization is principal mechanism) Flux A substance that prevents formation of oxides and other contaminants in welding, or dissolves them and facilitates removal Provides protective atmosphere for welding Stabilizes arc Reduces spattering Arc welding Uses an electric arc to coalesce metals Arc welding is the most common method of welding metals Electricity travels from electrode to base metal to ground

Arc welding Equipments • A welding generator (D.C.) or Transformer (A.C.)

• Two cables- one for work and one for electrode

• Electrode holder

• Electrode

• Protective shield

• Gloves

• Wire brush

• Chipping hammer

• Goggles

Advantages Most efficient way to join metals

Lowest-cost joining method

Affords lighter weight through better utilization of materials

Joins all commercial metals

Provides design flexibility

Disadvantages • Manually applied, therefore high labor cost.

• Need high energy causing danger

• Not convenient for disassembly.

• Defects are hard to detect at joints.

GAS WELDING

Sound weld is obtained by selecting proper size of flame, filler material and method of moving torch The temperature generated during the process is 33000c. When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld Fluxes are added to the welded metal to remove oxides Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid. solid coating or gas.

GAS WELDING EQUIPMENT 1. Gas Cylinders Pressure

Oxygen – 125 kg/cm2 Acetylene – 16 kg/cm2

2. Regulators Working pressure of oxygen 1 kg/cm2 Working pressure of acetylene 0.15 kg/cm2 Working pressure varies depends upon the thickness of the work pieces welded.

3. Pressure Gauges 4. Hoses 5. Welding torch 6. Check valve 7. Non return valve Types of Flames

• Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing flame (30000c)

• Addition of little more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)

• Used for welding steels, aluminium, copper and cast iron.

• If more oxygen is added, the cone becomes darker and more pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame

• Has the highest temperature about 34000c

• Used for welding brass and brazing operation

Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame

Fusion welding processes • Definition : Fusion Welding is defined as melting together and coalescing materials by means of heat

• Energy is supplied by thermal or electrical means

• Fusion welds made without filler metals are known as autogenous welds

Filler Metals: • Additional material to weld the weld zone

• Available as rod or wire

• They can be used bare or coated with flux

• The purpose of the flux is to retard the

Shielded metal arc welding process • An electric arc is generated between a coated electrode and the parent metal

• The coated electrode carries the electric current to form the arc, produces a gas to control the atmosphere and provides filler metal for the weld bead

• Electric current may be AC or DC. If the current is DC, the polarity will affect the weld size and application

Process • Intense heat at the arc melts the tip of the electrode

• Tiny drops of metal enter the arc stream and are deposited on the parent metal

• As molten metal is deposited, a slag forms over the bead which serves as an insulation against air contaminants during cooling

• After a weld „pass‟ is allowed the cool, the oxide layer is removed by a chipping hammer and then cleaned with a wirebrush before the next pass.

Fig: Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.

Fig: Schematic illustration of the shielded metal-arc welding process (also known as stick welding, because the electrode is in the shape of a stick).

Submerged arc welding

• Weld arc is shielded by a granular flux, consisting of silica, lime, manganese oxide, calcium fluoride and other compounds.

• Flux is fed into the weld zone by gravity flow through nozzle.• Thick layer of flux covers molten metal • Flux acts as a thermal insulator, promoting deep penetration of heat into the work piece • Consumable electrode is a coil of bare round wire fed automatically through a tube

• Power is supplied by 3-phase or 2-phase power lines

Fig: Schematic illustration of the submerged-arc welding process and equipment. The unfused flux is recovered and reused

Gas metal arc welding • GMAW is a metal inert gas welding (MIG)

• Weld area shielded by an effectively inert atmosphere of argon,helium,carbon dioxide,various other gas mixtures

• Metal can be transferred by 3 methods :

• Spray transfer

• Globular transfer

• Short circuiting

Process capabilities • GMAV process is suitable for welding a variety of ferrous and non-ferrous metals

• Process is versatile, rapid, economical, welding productivity is double that of SMAW

Flux cored arc welding • Flux cored arc welding is similar to a gas metal arc welding

• Electrode is tubular in shape and is filled with flux

• Cored electrodes produce more stable arc improve weld contour and produce better mechanical properties

• Flux is more flexible than others

Fig: Schematic illustration of the flux-cored arc-welding process. This operation is similar to gas metal-arc welding.

Electro gas Welding • EGW is welding the edges of sections vertically in one pass with the pieces placed edge to edge

• Similar to Electro gas welding

• Weld metal is deposited into weld cavity between the two pieces to be joined

• Difference is Arc is started between electrode tip and bottom part of the part to be welded

• Flux added first and then melted by the heat on the arc

• Molten slag reaches the tip of the electrode and the arc is extinguished

• Heat is then continuously produced by electrical resistance of the molten slag

• Single or multiple solid as well as flux-cored electrodes may be used

Process capabilities • Weld thickness ranges from 12mm to 75mm

• Metals welded are steels, titanium, aluminum alloys

• Applications are construction of bridges, pressure vessels, thick walled and large diameter pipes, storage tanks and ships.

’

Fig : Schematic illustration of the electrogas welding process.

It is a low temperature joining process. It is performed at temperatures above 840º F and it generally affords strengths comparable to those of the metal which it joins. It is low temperature in that it is done below the melting point of the base metal. It is achieved by diffusion without fusion (melting) of the base Brazing can be classified as Torch brazing Dip brazing Furnace brazing Induction brazing

Advantages • Dissimilar metals which canot be welded can be joined by brazing

• Very thin metals can be joined

• Metals with different thickness can be joined easily

• In brazing thermal stresses are not produced in the work piece. Hence there is no distortion

• Using this process, carbides tips are brazed on the steel tool holders

Disadvantages • Brazed joints have lesser strength compared to welding

• Joint preparation cost is more

• Can be used for thin sheet metal sections

Soldering • It is a low temperature joining process. It is performed at temperatures below 840ºF for joining.

• Soldering is used for, • Sealing, as in automotive radiators or tin cans

• Electrical Connections

• Joining thermally sensitive components

• Joining dissimilar metals

Inert Gas Welding For materials such as Al or Ti which quickly form oxide layers, a method to place an inert atmosphere around the weld puddle had to be developed Metal Inert Gas (MIG) • Uses a consumable electrode (filler wire made of the base metal)

• Inert gas is typically Argon

Gas Tungsten Arc Welding (GTAW) Uses a non-consumable tungsten electrode and an inert gas for arc shielding Melting point of tungsten = 3410C (6170F) A.k.a. Tungsten Inert Gas (TIG) welding In Europe, called "WIG welding" Used with or without a filler metal When filler metal used, it is added to weld pool from separate rod or wire Applications: aluminum and stainless steel most common

Advantages High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux

Disadvantages Generally slower and more costly than consumable electrode AW processes Plasma Arc Welding (PAW) Special form of GTAW in which a constricted plasma arc is directed at weld area

Tungsten electrode is contained in a nozzle that focuses a high velocity stream of inert gas (argon) into arc region to form a high velocity, intensely hot plasma arc stream

Temperatures in PAW reach 28,000C (50,000F), due to constriction of arc, producing a plasma jet of small diameter and very high energy density

Resistance Welding (RW) A group of fusion welding processes that use a combination of heat and pressure to accomplish coalescence Heat generated by electrical resistance to current flow at junction to be welded Principal RW process is resistance spot welding (RSW)

Fig: Resistance welding, showing the components in spot welding, the main process in the RW group.Components in Resistance Spot Welding Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze parts between electrodes Power supply from which a controlled current can be applied for a specified time duration

Advantages No filler metal required High production rates possible Lends itself to mechanization and automation Lower operator skill level than for arc welding Good repeatability and reliability Disadvantages High initial equipment cost

Limited to lap joints for most RW processes

Resistance Seam Welding

Electron Beam Welding (EBW) Fusion welding process in which heat for welding is provided by a highly-focused, high-intensity stream of electrons striking work surface Electron beam gun operates at: High voltage (e.g., 10 to 150 kV typical) to accelerate electrons Beam currents are low (measured in milliamps) Power in EBW not exceptional, but power density is

Advantages High-quality welds, deep and narrow profiles Limited heat affected zone, low thermal distortion High welding speeds No flux or shielding gases needed

Disadvantages High equipment cost Precise joint preparation & alignment required Vacuum chamber required Safety concern: EBW generates x-rays

Laser Beam Welding (LBW) Fusion welding process in which coalescence is achieved by energy of a highly concentrated, coherent light beam focused on joint Laser = "light amplification by stimulated emission of radiation" LBW normally performed with shielding gases to prevent oxidation

Filler metal not usually added High power density in small area, so LBW often used for small parts Comparison: LBW vs. EBW No vacuum chamber required for LBW No x-rays emitted in LBW Laser beams can be focused and directed by optical lenses and mirrors LBW not capable of the deep welds and high depth-to-width ratios of EBW

Maximum LBW depth = ~ 19 mm (3/4 in), whereas EBW depths = 50 mm (2 in)

Thermit Welding (TW) FW process in which heat for coalescence is produced by superheated molten metal from the chemical reaction of thermite Thermite = mixture of Al and Fe3O4 fine powders that produce an exothermic reaction when ignited Also used for incendiary bombs Filler metal obtained from liquid metal Process used for joining, but has more in common with casting than welding

Fig: Thermit welding: (1) Thermit ignited; (2) crucible tapped, superheated metal flows into mold; (3) metal solidifies to produce weld joint.

Applications Joining of railroad rails Repair of cracks in large steel castings and forgings Weld surface is often smooth enough that no finishing is required

Diffusion Welding (DFW) SSW process uses heat and pressure, usually in a controlled atmosphere, with sufficient time for diffusion and coalescence to occur Temperatures 0.5 Tm Plastic deformation at surfaces is minimal Primary coalescence mechanism is solid state diffusion Limitation: time required for diffusion can range from seconds to hours Applications Joining of high-strength and refractory metals in aerospace and nuclear industries Can be used to join either similar and dissimilar metals For joining dissimilar metals, a filler layer of different metal is often sandwiched between base metals to promote diffusion

Friction Welding (FRW) SSW process in which coalescence is achieved by frictional heat combined with pressure When properly carried out, no melting occurs at faying surfaces No filler metal, flux, or shielding gases normally used Process yields a narrow HAZ Can be used to join dissimilar metals Widely used commercial process, amenable to automation and mass production

Fig: Friction welding (FRW): (1) rotating part, no contact; (2) parts brought into contact to generate friction heat; (3) rotation stopped and axial pressure applied; and (4) weld created.

Applications Shafts and tubular parts Industries: automotive, aircraft, farm equipment, petroleum and natural gas

Limitations At least one of the parts must be rotational Flash must usually be removed Upsetting reduces the part lengths (which must be taken into consideration in product design)

Weld Defects • Undercuts/Overlaps

• Grain Growth A wide T will exist between base metal and HAZ. Preheating and cooling methods will affect the brittleness of the metal in this region

• Blowholes Are cavities caused by gas entrapment during the solidification of the weld puddle. Prevented by proper weld technique (even temperature and speed) • Inclusions Impurities or foreign substances which are forced into the weld puddle during the welding process. Has the same effect as a crack. Prevented by proper technique/cleanliness. • Segregation Condition where some regions of the metal are enriched with an alloy ingredient and others aren‟t. Can be prevented by proper heat treatment and cooling. • Porosity The formation of tiny pinholes generated by atmospheric contamination. Prevented by keeping a protective shield over the molten weld puddle.

UNIT IV

PART-A (Important Questions and Answers)

1. Name the steps involved in making a casting. Steps involved in making a casting are

1. Pattern making 2. Sand mixing and preparation 3. Core making 4. Melting 5. Pouring 6. Finishing 7. Testing 8. Heat treatment 9. Re-testing

2. List out any four arc welding equipment.The most commonly used equipments for arc welding are as follows: (a) A.C or D.C. machine (b) Wire brush (c) Cables and connectors (d) Ear thing clamps (e) Chipping hammer

3. What are the special features of friction welding Friction welding is a solid state welding process where coalescence is produced by the heat Obtained from mechanically induced sliding motion between rubbing surfaces. The work parts are held together under pressure Its operating is simple. Power required for the operation is low. It is used for joining steels, super alloys, non-ferrous metals and combinations of metals

4. What is the purpose of flux? 1) It acts as shield to weld.

2) To prevent atmospheric reaction of molten metal with atmosphere.5. How is welding classified?

Welding is classified as • Gas welding • Arc welding • Resistance welding • Solid state welding

6. Name the types of flamesThe generated flames are classified into following three types(a) Neutral flame (Acetylene and oxygen in equal proportion) (b) Oxidising flame (Excess of oxygen) (c) Reducing flame or carburising flame (Excess of acetylene)

7. What are the applications of casting?

Transportation vehicles (in automobile engine and tractors) 1. Machine tool structures 2. Turbine vanes and power generators

3. Mill housing 4. Pump filter and valve8. Define pattern.

1. A pattern is defined as a model or replica of the object to be cast. 2. A pattern exactly resembles the casting to be made except for the various allowances.

9. What do you mean by core prints in pattern? To produce seats for the cores in the mould in which cores can be placed, for producing

cavity in the casting. Such seats in the mould are called as core prints.

10. Explain wax moulding. After being molded, the wax pattern is not taken out; rather the mould is inverted and

heated and the molten wax comes out or gets evaporated, hence there is no chance of the mould cavity getting damaged while removing the pattern

PART B (Important Questions)

1. Explain in Gas and arc welding.

2. Write down the types of casting process.

3. Explain in detail selection criteria of manufacturing process.

4. Write down the casting defects and its types.

5. Explain in detail soldering and brazing

6. Explain in detail classification of manufacturing process .

UNIT V

METAL FORMING AND MACHINING PROCESSES

Cold working The process is usually performed at room temperature, but mildly elevated temperatures may be used to provide increased ductility and reduced strength For example: Deforming lead at room temperature is a hot working process because the recrystallization temperature of lead is about room temperature. Effects of Cold Working Deformation using cold working results in · Higher stiffness, and strength, but · Reduced malleability and ductility of the metal. · Anisotropy Advantages No heating is required Strength, fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved, so little, if any, secondary machining is required Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized

Disadvantages Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility that accompanies strain hardening Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free Imparted directional properties may be detrimental Undesirable residual stresses may be produced

Hot working Hot working is the deformation that is carried out above the recrystallization temperature.

Effects of hot working · At high temperature, scaling and oxidation exist. Scaling and oxidation produce undesirable surface finish. Most ferrous metals needs to be cold worked after hot working in order to improve the surface finish. · The amount of force needed to perform hot working is less than that for cold work. · The mechanical properties of the material remain unchanged during hot working.

· The metal usually experiences a decrease in yield strength when hot worked. Therefore, it is possible to hot work the metal without causing any fracture. Quenching is the sudden immersion of a heated metal into cold water or oil. It is used to make the metal very hard. To reverse the effects of quenching, tempering is used (reheated of the metal for a period of time) To reverse the process of quenching, tempering is used, which is the reheat of the metal. Cold-working Processes Squeezing Bending Shearing Drawing Presses

Classifications of Squeezing Processes Rolling Cold Forging Sizing Staking Staking Coining Burnishing Extrusion Peening Hubbing Riveting Thread Rolling

ROLLING Process used in sheets, strips, bars, and rods to obtain products that have smooth surfaces and accurate dimensions; most cold-rolling is performed on four-high or cluster-type rolling mills

A sheet or block or strip stock is introduced between rollers and then compressed and squeezed. Thickness is reduced. The amount of strain (deformation) introduced determines the hardness, strength and other material properties of the finished product.

Used to produce sheet metals predominantly Swaging Process that reduces/increases the diameter, tapers, rods or points round bars or tubes by external hammering.

Cold Forging Process in which slugs of material are squeezed into shaped die cavities to produce finished parts of precise shape and size.

Extrusion Process which is commonly used to make collapsible tubes such as toothpaste tubes, cans usually using soft materials such as aluminum, lead, tin. Usually a small shot of solid material is placed in the die and is impacted by a ram, which causes cold flow in the material.

Sizing

Process of squeezing all or selected areas of forgings, ductile castings, or powder metallurgy products to achieve a desired thickness or precision Riveting Process where a head is formed on the shrank end of a fastener to permanently join sheets or plates of material;

Staking Process of permanently joining parts together when one part protrudes through a hole in the other; a shaped punch is driven into the end of the protruding piece where a deformation is formed causing a radial expansion, mechanically locking the two pieces together.

Coining Process where metal while it is confined in a closed set of dies; used to produce coins, medals, and other products where exact size and fine details are required, and thickness varies about a well-defined average.

Peening Process where the surface of the metal is blasted by shot pellets; the mechanical working of surfaces by repeated blows of impelled shot or a round-nose tool Burnishing Process by which a smooth hard tools is rubbed on the metal surface and flattens the high spots by applying compressive force and plastically flowing the material

Hubbing Process is used to form recessed cavities in various types of female tooling dies. This is often used to make plastic extrusion dies in an economical mannerThread Rolling Process is used for making external threads; in this process, a die, which is a hardened tool with the thread profile, is pressed on to a rotating workpiece

The Presses There are many kinds of machines • Hydraulic presses

• Mechanical presses – C frame

– Straight sided • Others

C-frame mechanical press

Types of Forging Presses

Impression Die Forging

Forging operations Forging is a process in which the workpiece is shaped by compressive forces applied through various dies and tools. It is one of the oldest metalworking operations. Most forgings require a set of dies and a press or a forging hammer. A Forged metal can result in the following: - Decrease in height, increase in section - open die forging Increase length, decrease cross-section, called drawing out. Decrease length, increase in cross-section on a portion of the length - upsetting Change length, change cross-section, by squeezing in closed impression dies - closed die forging. This results in favorable grain flow for strong parts

Types of forging Closed/impression die forging Electro-upsetting Forward extrusion Backward extrusion Radial forging Hobbing Isothermal forging Open-die forgig Upsetting Nosing Coining

Commonly used materials include • Ferrous materials: low carbon steels

• Nonferrous materials: copper, aluminum and their alloys

Open-Die Forging Open-die forging is a hot forging process in which metal is shaped by hammering or pressing between flat or simple contoured dies.

Equipment. Hydraulic presses, hammers. Materials. Carbon and alloy steels, aluminum alloys, copper alloys, titanium alloys, all forgeable materials.Process Variations. Slab forging, shaft forging, mandrel forging, ring forging, upsetting between flat or curved dies, drawing out. Application. Forging ingots, large and bulky forgings, preforms for finished forgings. Closed Die Forging In this process, a billet is formed (hot) in dies (usually with two halves) such that the flow of metal from the die cavity is restricted. The excess material is extruded through a restrictive narrow gap and appears as flash around the forging at the die parting line. Equipment. Anvil and counterblow hammers, hydraulic, mechanical, and screw presses. Materials. Carbon and alloy steels, aluminum alloys, copper alloys, magnesium alloys, beryllium, stainless steels, nickel alloys, titanium and titanium alloys, iron and nickel and cobalt super alloys. Process Variations. Closed-die forging with lateral flash, closed-die forging with longitudinal flash, closed-die forging without flash. Application. Production of forgings for automobiles, trucks, tractors, off-highway equipment, aircraft, railroad and mining equipment, general mechanical industry, and energy-related engineering production. Forward extrusion Forward extrusion reduces slug diameter and increases its length to produce parts such as stepped shafts and cylinders.

backward extrusion In backward extrusion, the steel flows back and around the descending punch to form cup-shaped pieces.

Upsetting, or heading Upsetting, or heading, a common technique for making fasteners, gathers steel in the head and other sections along the length of the part.

Electro-Upsetting (Fig. 2.4) Electro-upsetting is the hot forging process of gathering a large amount of material at one end of a round bar by heating the bar end electrically and pushing it against a flat anvil or shaped die cavity.

A, anvil electrode; B, gripping electrode; C, workpiece; D, upset end of workpiece Equipment. Electric upsetters. Materials. Carbon and alloy steels, titanium. Application. Preforms for finished forgings.

Hobbing Hobbing is the process of indenting or coining an impression into a cold orhot die block by pressing with a punch. Equipment. Hydraulic presses, hammers. Materials. Carbon and alloy steels. Process Variations. Die hobbing, die typing. Application. Manufacture of dies and molds with relatively shallow impressions. Nosing Nosing is a hot or cold forging process in which the open end of a shell or tubular component is closed by axial pressing with a shaped die. Equipment. Mechanical and hydraulic presses, hammers.

Materials. Carbon and alloy steels, aluminum alloys, titanium alloys. Process Variations. Tube sinking, tube expanding. Applications. Forging of open ends of ammunition shells; forging of gas pressure containers

Coining In sheet metal working, coining is used to form indentations and raised sections in the part. During the process, metal is intentionally thinned or thickened to achieve the required indentations or raised sections. It is widely used for lettering on sheet metal or components such as coins. Bottoming is a type of coining process where bottoming pressure causes reduction in thickness at the bending area.

Ironing Ironing is the process of smoothing and thinning the wall of a shell or cup (cold or hot) by forcing the shell through a die with a punch

Equipment. Mechanical presses and hydraulic presses. Materials. Carbon and alloy steels, aluminum and aluminum alloys, titanium alloys. Applications. Shells and cups for variousSwaging Uses hammering dies to decrease the diameter of the part

Defects in Forging

Extrusion and Drawing ProcessesExtrusion :Process by which long straight metal parts can be produced.

Cross-sections that can be produced vary from solid round, rectangular, to L shapes, T Shapes, tubes and many other different types Done by squeezing metal in a closed cavity through a die using either a mechanical or hydraulic press. Extrusion produces compressive and shear forces in the stock. No tension is produced, which makes high deformation possible without tearing the metal. Can be done Hot or cold Drawing :Section of material reduced by pulling through die. Similar to extrusion except material is under TENSILE force since it is pulled through the die Various types of sections: - round, square, profiles

Tube Drawing Utilizes a special tool called a MANDREL is inserted in a tube hollow section to draw a seamless tube Mandrel and die reduce both the tube's outside diameter and its wall thickness. The mandrel also makes the tubes inside surface smoother THE LATHE :

FUNCTION OF THE LATHE The main function of a lathe is to remove metal from a piece of work to give it the required shape and size.

TYPES OF LATHE Lathes of various designs and constructions have been developed to suit the various conditions of metal machining. 1. Speed lathe.

Woodworking Centering. Polishing. Spinning.

2. Bench lathe. 3. Tool room lathe. 4. Capstan and Turret lathe.

5. Special purpose. Wheel lathe. Gap bed lathe. T-lathe.

6. Engine lathe. Belt drive. Individual motor drive. Duplicating lathe. Gear head lathe. Spinning.

7. Automatic lathe.

The Speed Lathe: The speed lathe, in construction and operation, is the simplest of all types of lathe. It consists of a bed, a headstock, a tailstock and a tool-post mounted on an adjustable slide. There is no feed box, lead screw or conventional type of carriage. The tool is mounted on the adjustable slide and is fed into work purely by hand control. This characteristic of the lathe enables the designer to give high spindle speeds which usually range from 1200 to 3600 r.p.m. As the tool is controlled by hand, the depth of cut and the thickness of chip is very small

The engine lathe or centre lathe : This lathe is the most important member of the lathe family and is the most widely used. The term “engines is associated with the lathe owing to the fact that early lathes were driven by steam engines. Similar to the speed lathe, the engine lathe has got all the basic parts This is a small lathe usually mounted on a bench. It has practically all the parts of an engine lathe or speed lathe and it performs almost all the operations, its only difference being in the size. This is used fur small and precision work.

The bench lathe:

This is a small lathe usually mounted on a bench. It has practically all the parts of an engine lathe or speed lathe and it performs almost all the operations, its only difference being in the size. This is used fur small and precision work.

The tool room lathe: A tool room lathe having features similar to an. engine lathe is much more accurately built and has a wide range of spindle speeds ranging from a very low to a quite high speed up to 2500 r.p.m.

This is equipped, besides other things, with a chuck, taper turning attachment, draw in collet attachment, thread chasing dial, relieving attachment, steady and follower rest, pump for coolant, etc.

This lathe is mainly used for precision work on tools, dies, gauges and in machining work where accuracy is needed. The machine is costlier than an engine lathe of the same size.

The capstan and turret lathe: These lathes are development of the engine lathe and are used for production work. The distinguishing feature of this type of lathe is that the tailstock of an engine lathe is replaced by a hexagonal turret, on the face of which multiple tools may be fitted and fed into the work in proper sequence. The advantage is that. several different types of operations can be done on a work piece without re- setting of work or tools, and a number of identical parts can be produced in the minimum time.

Special purpose lathe: As the name implies, they are used for special purposes and for jobs which cannot be accommodated or conveniently machined on a standard lathe. The wheel is made for finishing the journals and turning the tread on railroad car and locomotive wheels. The gap bed lathe, in which a section of the bed adjacent to the headstock is recoverable, is used to swing extra-large diameter pieces. The T-lathe, a new member of the lathe family, is intended for machining of rotors for jet engines. The axis of the lathe bed is at right angles to the axis of the headstock spindle is the form of a T. The duplicating lathe is one for duplicating the shape of a flat. or round template on to the workpiece. Mechanical, air, and hydraulic devices are all used to coordinate the movements of the tool to reproduce accurately.

Automatic lathe : These are high speed, heavy duty, mass production lathes with complete automatic control. Once the tools are set and the machine is started it performs automatically all the operations to finish the job

The changing of tools, speeds, and feeds are also done automatically. After the job is complete, the machine will continue to repeat the cycles producing identical parts even without the attention of an operator. An operator who has to look after five or six automatic lathes at a time will simply look after the general maintenance of the machine and cutting tool, load up a bar stock and remove finished products from time to time.

THE SIZE OF A LATHE: The size of a lathe is expressed or specified by the following items

1. The height of the centres measured from the lathe bed2. The swing diameter over bed.

This is the largest diameter of work that will FEED MECHANISM The movement of the tool relative to the work is termed as„ feed”. A lathe tool may have three types of feed —longitudinal, cross, and angular. When the tool moves parallel to the lathe axis, the movement is termed as Longitudinal! feed and is effected by the movement of the carriage. When the tool moves at right angle to the lathe axis with the help of the cross slide the movement is termed across feed, while the movement of the tool by compound slide when it is swiveled at an angle to the lathe axis is termed as angular feed. Cross and longitudinal feed are both hand and power operated, but angular feed is only hand operated.

The feed mechanism has different units through which motion is transmitted from the headstock spindle to the carriage. Following are the units: 1. End of bed gearing.2. Feed gearbox. 3. Feed rod and lead screw 4. Apron mechanism. End of bed gearing: This gearing serves the purpose of transmitting the drive to the lead screw and feed shaft, either direct or through a gear box. In modern lathes, tumbler gear mechanism or bevel gear feed reversing mechanism is incorporated to reverse the direction of feed. Tumbler gear mechanism:.

Tumbler gears are used to give the desired direction of movement to the lathe carriage, via lead screw or the feed shaft. Apron mechanism Different designs of apron mechanism for transforming rotary motion of the feed rod and the lead screw into feed motion of the carriage are constructed by different makers of the lathe

THREAD CUTTING MECHANISM The rotation of the lead screw is used to transverse the tool along the work to produce screw thread. The half-nut mechanism illustrated in Fig makes the carriage to engage or disengage with the lead screw. it comprises a pair of half nuts 7 capable of moving in or out of mesh with the lead screw.

LATHE ACCESSORIES AND ATTACHMENTS

Lathe accessories include centers, catch plates and carriers, chutes, collets, face plates, angle plates, mandrels, and rests. They are used either for holding and supporting the work or for holding the tool. Attachments are additional equipment used for specific purposes. They include stops, ball turning rests, thread chasing dials, and taper turning, milling, grinding, gear cutting, turret, cutter, relieving a id crank pin turning attachments.

LATHE OPERATIONS Operations which are performed in a lathe either by holding the workpiece between

centres or by a chuck are: Straight turning. Shoulder turning. Chamfering. Thread cutting. Facing. Knurling. Filing. Taper turning. Eccentric turning. Polishing. Grooving. Spinning. Spring winding. Forming.

Operation which is performed by holding the work by a chuck era faceplate or an angle plate are:

Drilling Reaming Boring Counterboring Taperboring Internal thread cutting Tapping Undercutting Parting-off

Operations which are performed by using special attachments Grinding Milling

Work Holding Devices:

Fig : (a) and (b) Schematic illustrations of a draw-in-type collets. The workpiece is placed in the collet hole, and the conical surfaces of the collet are forced inward by pulling it with a draw bar into the sleeve. (c) A push-out type collet. (d) Workholding of a part on a face plate.

Three jaw chuck: - -For holding cylindrical stock centered. – For facing/center drilling the end of your aluminum stock

Four-Jaw Chuck - This is independent chuck generally has four jaws, which are adjusted individually on the chuck face by means of adjusting screws

Collet Chuck: Collet chuck is used to hold small workpieces

Magnetic ChuckThin jobs can be held by means of magnetic chucks

CENTERING Where the work is required to be turned between centres or between a chuck and a centre, conical shaped holes must be provided at the ends of lbs workpiece to provide bearing surface for lathe centres. Centering is the process of producing conical holes in workpieces.

TURNING: Turning in a lathe is to remove excess material from the workpiece to produce a cone-shaped or a cylindrical surface. The various types of turning made in lathe work for various purposes are described below.

STRAIGHT TURNING: The work is turned straight when it is made to rotate about the lathe axis, and the tool is fed parallel to the lathe axis The straight turning produces a cylindrical surface by removing excess metal from the workpiece.

TAPER TURNING METHODS:

A taper may be turned by any one of the following methods: 1. By a broad nose form tool. 2. By setting over the tailstock centre. 3. By swivelling the compound rest. 4. By a taper turning attachment. 5. by combining longitudinal and cross feed in a special lathe. Taper Turning by a form tool-

A broad nose tool having straight cutting edge is set on to the work at half taper angle, and is fed straight into the work to generate a tapered surface The half angle of taper will correspond to 90 minus side cutting edge angle of the tool. In this method the tool angle should be properly checked before use. This method is limited to turn short length of taper only. This is due to the reason that the metal is removed by the entire cutting edge, and any increase in the length of the taper will necessitate the use of a wider cutting edge. This will require excessive cutting pressure, which may distort the work due to vibration and spoil the work surface.

Taper turning by setting over the tailstock: The principle of turning taper by this method is to shift the axis of rotation of the workpiece, at an angle to the lathe axis, feeding the tool parallel to the lathe axis. The angle at which the axis of rotation of the workpiece is shifted is equal to half angle of the taper. This is done when the body of the tailstock is made to slide on its base towards or away from the operator by a setover screw as illustrated The amount of setover being limited, this method is suitable for turning small taper on long jobs. The main disadvantage of this method is that the live and dead centres are not equally stressed and the wear is not uniform. Moreover, the lathe carrier being set at an angle, the angular velocity of the work is not constant.

Taper turning by swiveling the compound rest: This method employs the principle of turning taper by rotating the workpiece on the lathe axis and feeding the tool at an angle to the axis of rotation of the workpiece.

The tool mounted on the compound rest is attached to a circular base, graduated in degree, which may be swivelled and clamped at any desired angle.

The setting of the compound rest is done by swivelling the rest at the half taper angle, if this is already known. If the diameter of the small and large end and length of taper are known. Taper turning by a taper attachment: The principle of turning taper by a taper attachment is to guide the tool in a straight path set at an angle to the axis of rotation of the workpiece, while the work is being revolved between centres or by a chuck aligned to the lathe axis. Consists essentially of a bracket or frame which is attached to the rear end of the lathe bed and supports a guide bar pivoted at the centre. The bar having graduations in degrees may be swivelled on either side of the zero graduation and is set at the desired angle with the lathe axis.

SHAPERShaper is a reciprocating type of machine tool in which the ram moves the cutting tool backwards and forwards in a straight line. The basic components of shaper are shown in Fig. It is intended primarily to produce flat surfaces. These surfaces may be horizontal, vertical, or inclined. In general, the shaper can produce any surface composed of straight-line elements. The principal of shaping operation is shown in Fig. Modern shapers can also generate contoured surface as shown in Fig. A shaper is used to generate flat (plane) surfaces by means of a single point cutting tool similar to a lathe tool.

WORKING PRINCIPLE OF SHAPERA single point cutting tool is held in the tool holder, which is mounted on the ram. The workpiece is rigidly held in a vice or clamped directly on the table. The table may be supported at the outer end. The ram reciprocates and thus cutting tool held in tool holder moves forward and backward over the workpiece. In a standard shaper, cutting of material takes place during the forward stroke of the ram. The backward stroke remains idle and no cutting takes place during this stroke. The feed is given to the workpiece and depth of cut is adjusted by moving the tool downward towards the workpiece. The time taken during the idle

stroke is less as compared to forward cutting stroke and this is obtained by quick return mechanism. The cutting action and functioning of clapper box is shown in Fig. during forward and return stroke.

Fig: Working Principle of Shaping Machine

Fig: Surface Produced by Shaper

Fig: Cutting action and functioning of clapper Box

TYPES OF SHAPERSShapers are classified under the following headings:(1) According to the type of mechanism used for giving reciprocating motion to the ram(a) Crank type(b) Geared type(c) Hydraulic type(2) According to the type of design of the table:(a) Standard shaper(b) Universal shaper(3) According to the position and travel of ram:(a) Horizontal type

(b) Vertical type(c) Traveling head type(4) According to the type of cutting stroke:(a) Push type(b) Draw type.A brief description these shapers is given below-Crank ShaperThis is the most common type of shaper. It employs a crank mechanism to change circular motion of a large gear called “bull gear” incorporated in the machine to reciprocating motion of the ram. The bull gear receives power either from an individual motor or from an overhead line shaft if it is a belt-driven shaper.Geared ShaperGeared shaper uses rack and pinion arrangement to obtain reciprocating motion of the ram. Presently this type of shaper is not very widely used.Hydraulic ShaperIn hydraulic shaper, reciprocating motion of the ram is obtained by hydraulic power. For generation of hydraulic power, oil under high pressure is pumped into the operating cylinder fitted with piston. The piston end is connected to the ram through piston rod. The high pressure oil causes the piston to reciprocate and this reciprocating motion is transferred to the ram of shaper. The important advantage of this type of shaper is that the cutting speed and force of the ram drive are constant from the very beginning to the end of the cut.Standard ShaperIn standard shaper, the table has only two movements, horizontal and vertical, to give the feeUniversal ShaperA universal shaper is mostly used in tool room work. In this type of shaper, in addition to the horizontal and vertical movements, the table can be swiveled about an axis parallel to the ram ways, and the upper portion of the table can be tilted about a second horizontal axis perpendicular to the first axisHorizontal ShaperIn this type of shaper, the ram holding the tool reciprocates in a horizontal axis.Vertical ShaperIn vertical shaper, the ram reciprocates in a vertical axis. These shapers are mainly used for machining keyways, slots or grooves, and internal surfaces.Travelling Head ShaperIn this type of shaper, the ram while it reciprocates, also moves crosswise to give the required feed.Push Type ShaperThis is the most general type of shaper used in common practice, in which the metal is removed when the ram moves away from the column, i.e. pushes the work.Draw Type ShaperIn this type of shaper, the cutting of metal takes place when the ram moves towards the column of the machine, i.e. draws the work towards the machine. The tool is set in a reversed direction to that of a standard shaper.

PRINCIPAL PARTS OF SHAPERthe parts of a standard shaper. The main parts are given as under.1. Base2. Column3. Cross-rail4. Saddle5. Table6. Ram7. Tool head8. Clapper box9. Apron clamping bolt10. Down feed hand wheel11. Swivel base degree graduations12. Position of stroke adjustment hand wheel13. Ram block locking handle14. Driving pulley15. Feed disc16. Pawl mechanism17. Elevating screwSome of important parts are discussed as under.

BaseIt is rigid and heavy cast iron body to resist vibration and takes up high compressive load. It supports all other parts of the machine, which are mounted over it. The base may be rigidly bolted to the floor of the shop or on the bench according to the size of the machine.ColumnThe column is a box shaped casting mounted upon the base. It houses the ram-driving mechanism. Two accurately machined guide ways are provided on the top of the column on which the ram reciprocates.Cross rail

Cross rail of shaper has two parallel guide ways on its top in the vertical plane that is perpendicular to the rai1 axis. It is mounted on the front vertical guide ways of the column. It consists mechanism for raising and lowering the table to accommodate different sizes of jobs by rotating an elevating screw which causes the cross rail to slide up and down on the vertical face of the column. A horizontal cross feed screw is fitted within the cross rail and parallel to the top guide ways of the cross rail. This screw actuates the table to move in a crosswise direction.SaddleThe saddle is located on the cross rail and holds the table on its top. Crosswise movement of the saddle by rotation the cross feed screw by hand or power causes the table to move sideways.TableThe table is a box like casting having T -slots both on the top and sides for clamping the work. It is bolted to the saddle and receives crosswise and vertical movements from the saddle and cross rail.RamIt is the reciprocating part of the shaper, which reciprocates on the guide ways provided above the column. Ram is connected to the reciprocating mechanism contained within the column.Tool headThe tool head of a shaper performs the following functions-(1) It holds the tool rigidly,(2) It provides vertical and angular feed movement of the tool, and(3) It allows the tool to have an automatic relief during its return stroke.

The various parts of tool head of shaper are apron clamping bolt, clapper box, tool post, down feed, screw micrometer dial, down feed screw, vertical slide, apron washer, apron swivel pin, and swivel base. By rotating the down feed screw handle, the vertical slide carrying the tool gives down feed or angular feed movement while machining vertical or angular surface. The amount of feed or depth of cut may be adjusted by a micrometer dial on the top of the down feed screw. Apron consisting of clapper box, clapper block and tool post is clamped upon the vertical slide by a screw. The two vertical walls on the apron called clapper box houses the clapper block, which is connected to it by means of a hinge pin. The tool post is mounted upon the clapper block. On the forward cutting stroke the clapper block fits securely to the clapper box to make a rigid tool support. On the return stroke a slight frictional drag of the tool on the work lifts the block out of the clapper box a sufficient amount preventing the tool cutting edge from dragging and consequent wear. The work surface is also prevented from any damage due to dragging

SHAPER OPERATIONSA shaper is a machine tool primarily designed to generate a flat surface by a single point cutting tool. Besides this, it may also be used to perform many other operations. The different operations, which a shaper can perform, are as follows:1. Machining horizontal surface

2. Machining vertical surface 3. Machining angular surface 4. Slot cutting 5. Key ways cutting 6. Machining irregular surface 7. Machining splines and cutting gears

MILLING

A milling machine is a machine tool that removes metal as the work is fed against a rotating multipoint cutter. The milling cutter rotates at high speed and it removes metal at a very fast rate with the help of multiple cutting edges. One or more number of cutters can be mounted simultaneously on the arbor of milling machine. This is the reason that a milling machine finds wide application in production work. Milling machine is used for machining flat surfaces, contoured surfaces, surfaces of revolution, external and internal threads, and helical surfaces of various cross-sections. Typical components produced by a milling are given in Fig. In many applications, due to its higher production rate and accuracy, milling machine has even replaced shapers and slotters.

PRINCIPLE OF MILLINGIn milling machine, the metal is cut by means of a rotating cutter having multiple cutting edges. For cutting operation, the workpiece is fed against the rotary cutter. As the workpiece moves against the cutting edges of milling cutter, metal is removed in form chips of trochoid shape. Machined surface is formed in one or more passes of the work. The work to be machined is held in a vice, a rotary table, a three jaw chuck, an index head, between centers, in a special fixture or bolted to machine table. The rotatory speed of the cutting tool and the feed rate of the workpiece depend upon the type of material being machined

MILLING METHODSThere are two distinct methods of milling classified as follows:1. Up-milling or conventional milling, and2. Down milling or climb milling.UP-Milling or Conventional Milling ProcedureIn the up-milling or conventional milling, as shown in Fig.the metal is removed in form of small chips by a cutter rotating against the direction of travel of the workpiece. In this type of milling, the chip thickness is minimum at the start of the cut and maximum at the end of cut. As a result the cutting force also varies from zero to the maximum value per tooth movement of the milling cutter. The major disadvantages of up-milling process are the tendency of cutting force to lift the work from the fixtures and poor surface finish obtained. But being a safer process, it is commonly used method of milling.

Down-Milling or Climb MillingDown milling is shown in Fig. It is also known as climb milling. In this method, the metal is removed by a cutter rotating in the same direction of feed of the workpiece. The effect of this is that the teeth cut downward instead of upwards. Chip thickness is maximum at the start of the cut and minimum in the end. In this method, it is claimed that there is less friction involved and consequently less heat is generated on the contact surface of the cutter and workpiece. Climb milling can be used advantageously on many kinds of work to increase the

number of pieces per sharpening and to produce a better finish. With climb milling, saws cut long thin slots more satisfactorily than with standard milling. Another advantage is that slightly lower power consumption is obtainable by climb milling, since there is no need to drive the table against the cutter.

TYPES OF MILLING CUTTERSTypes of milling cutters along with workpieces. Milling cutters are made in various forms to perform certain classes of work, and they may be classified as:(1) Plain milling cutters,(2) Side milling cutters,(3) Face milling cutter,(4) Angle milling cutters,(5) End milling cutter,(6) Fly cutter,(7) T-slot milling cutter,(8) Formed cutters,(9) Metal slitting saw,Milling cutters may have teeth on the periphery or ends only, or on both the periphery and ends. Peripheral teeth may be straight or parallel to the cutter axis, or they may be helical, sometimes referred as spiral teeth.

TYPES OF MILLING MACHINESMilling machine rotates the cutter mounted on the arbor of the machine and at the same time automatically feed the work in the required direction. The milling machine may be classified in several forms, but the choice of any particular machine is determined primarily by the size of the workpiece to be undertaken and operations to be performed. With the above function

or requirement in mind, milling machines are made in a variety of types and sizes. According to general design, the distinctive types of milling machines are:1. Column and knee type milling machines(a) Hand milling machine(b) Horizontal milling machine (c) Universal milling machine(d) Vertical milling machine

2. Planer milling machine3. Fixed-bed type milling machine(a) Simplex milling machine.(b) Duplex milling machine.(c) Triplex milling machine.4. Machining center machines5. Special types of milling machines(a) Rotary table milling machine.(b) Planetary milling machine.

(c) Profiling machine.(d) Duplicating machine.(e) Pantograph milling machine.(f) Continuous milling machine.(g) Drum milling machine(h) Profiling and tracer controlled milling machineSome important types of milling machines are discussed as under.Column and Knee Type Milling MachineA simple column and knee type milling machine. It is the most commonly used milling machine used for general shop work. In this type of milling machine the table

is mounted on the knee casting which in turn is mounted on the vertical slides of the main column. The knee is vertically adjustable on the column so that the table can be moved up and down to accommodate work of various heights. The column and knee type milling machines are classified on the basis of various methods of supplying power to the table, different movements of the table and different axis of rotation of the main spindle. Column and knee type milling machine comprises of the following important parts-1. Base 2. Column3. Saddle 4. Table5. Elevating screw 6. Knee7. Knee elevating handle 8. Cross feed handle9. Front brace 10. Arbor support11. Arbor 12. Overhanging arm13. Cutter 14. Cone pulley

15. Telescopic feed shaft.The principal parts of a column and knee type milling machine are described as under.BaseIt is a foundation member for all the other parts, which rest upon it. It carries the column at its one end. In some machines, the base is hollow and serves as a reservoir for cutting fluid.ColumnThe column is the main supporting member mounted vertically on the base. It is box shaped, heavily ribbed inside and houses all the driving mechanism for the spindle and table feed. The front vertical face of the column is accurately machined and is provided with dovetail guide way for supporting the knee.KneeThe knee is a rigid grey iron casting which slides up and down on the vertical ways of the column face. An elevating screw mounted on the base is used to adjust the height of the knee and it also supports the knee. The knee houses the feed mechanism of the table, and different controls to operate it.SaddleThe saddle is placed on the top of the knee and it slides on guide ways set exactly at 90° to the column face. The top of the saddle provides guide-ways for the table.TableThe table rests on ways on the saddle and travels longitudinally. A lead screw under the table engages a nut on the saddle to move the table horizontally by hand or power. In universal machines, the table may also be swiveled horizontally. For this purpose the table is mounted on a circular base. The top of the table is accurately finished and T -slots are provided for clamping the work and other fixtures on it

Overhanging armIt is mounted on the top of the column, which extends beyond the column face and serves as a bearing support for the other end of the arbor.

Front braceIt is an extra support, which is fitted between the knee and the over-arm to ensure further rigidity to the arbor and the knee.SpindleIt is situated in the upper part of the column and receives power from the motor through belts, gears. and clutches and transmit it to the arbor. ArborIt is like an extension of the machine spindle on which milling cutters are securely mounted and rotated. The arbors are made with taper shanks for proper alignment with the machine spindles having taper holes at their nose. The draw bolt is used for managing for locking the arbor with the spindle and the whole assembly. The arbor assembly consists of the following components.1. Arbor 2. Spindle

3. Spacing collars 4. Bearing bush5. Cutter 6. Draw bolt7. Lock nut 8. Key block9. Set screwPlaner Type Milling MachineIt is a heavy duty milling machine. It resembles a planer and like a planning machine it has a cross rail capable of being raised or lowered carrying the cutters, their heads, and the saddles, all supported by rigid uprights. There may be a number of independent spindles carrying cutters on the rail as two heads on the uprights. The use of the machine is limited to production work only and is considered ultimate in metal re-moving capacity.Special Type Milling MachinesMilling machines of non-conventional design have been developed to suit special purposes. The features that they have in common are the spindle for rotating the cutter and provision for moving the tool or the work in different directions.

OPERATIONS PERFORMED ON MILLING MACHINEUnlike a lathe, a milling cutter does not give a continuous cut, but begins with a sliding motion between the cutter and the work. Then follows a crushing movement, and then a cutting operation by which the chip is removed. Many different kinds of operations can be performed on a milling machine but a few of the more common operations will now be explained. These are:Plain milling or slab millingThe plain and slab milling operation. It is a method of producing a plain, flat, horizontal surface parallel to the axis of rotation of the cutter. Face millingIllustrates the face milling operation. It is a method of producing a flat surface at right angles to the axis of the cutter.Side millingIllustrates the side milling operation. It is the operation of production of a flat vertical surface on the side of a work-piece by using a side milling cutter.Angular millingIllustrates angular milling operation. It is a method of producing a flat surface making an angle to the axis of the cutter.Gang-millingIllustrates the gang milling operation. It is a method of milling by means of two or more cutters simultaneously having same or different diameters mounted on the arbor of the milling machine.Form millingIllustrates the form milling operation. It is, a method of producing a surface having an irregular outline.End milling

Illustrates end milling operation. It is a method of milling slots, flat surfaces, and profiles by end mills.Profile millingIllustrates profile milling operation. It is the operation of reproduction of an outline of a template or complex shape of a master die on a workpiece.Saw millingIllustrates saw milling operation. It is a method of producing deep slots and cutting materials into the required length by slitting saws.T-slot millingIllustrates T-slot milling operation.Keyway millingIllustrates keyway milling operation.Gear cutting millingIllustrates gear cutting milling operation.Helical millingIllustrates helical milling operation.Flute millingIt is a method of grooving or cutting of flutes on drills, reamers, taps, etc,

Straddle millingIt is a method of milling two sides of a piece of work by employing two side-milling cutters at the same time.

Thread millingIt is a method of milling threads on dies, screws, worms, etc. both internally and externally. As an alternative to the screw cutting in a lathe, this method is being more extensively introduced now a day in modern machine shops.Grinding Machines Grinding Machines are also regarded as machine tools. A distinguishing feature of grinding machines is the rotating abrasive tool. Grinding machine is employed to obtain high accuracy along with very high class of surface finish on the workpiece. However, advent of new generation of grinding wheels and grinding machines, characterised by their rigidity, power and speed enables one to go for high efficiency deep grinding (often called as abrasive milling) of not only hardened material but also ductile materials. Conventional grinding machines can be broadly classified as: (a) Surface grinding machine (b) Cylindrical grinding machine (c) Internal grinding machine (d) Tool and cutter grinding machine

Surface grinding machine: This machine may be similar to a milling machine used mainly to grind flat surface. However, some types of surface grinders are also capable of producing contour surface with formed grinding wheel. Basically there are four different types of surface grinding machines characterised by the movement of their tables and the orientation of grinding wheel spindles as follows: • Horizontal spindle and reciprocating table • Vertical spindle and reciprocating table • Horizontal spindle and rotary table • Vertical spindle and rotary table

Horizontal spindle reciprocating table grinderthis machine with various motions required for grinding action. A disc type grinding wheel performs the grinding action with its peripheral surface. Both traverse and plunge grinding can be carried out in this machine as shown in Fig

Vertical spindle reciprocating table grinder

This grinding machine with all working motions is shown in Fig. The grinding operation is similar to that of face milling on a vertical milling machine. In this machine a cup shaped wheel grinds the workpiece over its full width using end face of the wheel as shown in Fig. This brings more grits in action at the same time and consequently a higher material removal rate may be attained than for grinding with a peripheral wheel

Horizontal spindle rotary table grinder Surface grinding in this machine is shown in Fig. In principle the operation is same as that for facing on the lathe. This machine has a limitation in accommodation of workpiece and therefore does not have wide spread use. However, by swivelling the worktable, concave or convex or tapered surface can be produced on individual part as illustrated in Fig.

Vertical spindle rotary table grinder The principle of grinding in this machine is shown in Fig.The machine is mostly suitable for small workpieces in large quantities. This primarily production type machine often uses two or more grinding heads thus enabling both roughing and finishing in one rotation of the work table

Creep feed grinding machine :

This machine enables single pass grinding of a surface with a larger down feed but slower table speed than that adopted for multi-pass conventional surface grinding. This machine is characterised by high stiffness, high spindle power, recirculating ball screw drive for table movement and adequate supply of grinding fluid. A further development in this field is the creep feed grinding centre which carries more than one wheel with provision of automatic wheel changing. A number of operations can be performed on the workpiece. It is implied that such machines, in the view of their size and complexity, are automated through CNC.

High efficiency deep grinding machine: The concept of single pass deep grinding at a table speed much higher than what is possible in a creep feed grinder has been technically realized in this machine. This has been made possible mainly through significant increase of wheel speed in this new generation grinding machine

Cylindrical grinding machine This machine is used to produce external cylindrical surface. The surfaces may be straight, tapered, steps or profiled. Broadly there are three different types of cylindrical grinding machine as follows: 1. Plain centre type cylindrical grinder 2. Universal cylindrical surface grinder 3. Centreless cylindrical surface grinder Plain centre type cylindrical grinder this machine and various motions required for grinding action. The machine is similar to a centre lathe in many respects. The workpiece is held between head stock and tailstock centres. A disc type grinding wheel performs the grinding action with its peripheral surface. Both traverse and plunge grinding can be carried out in this machine as shown in Fig.

Universal cylindrical surface grinder Universal cylindrical grinder is similar to a plain cylindrical one except that it is more versatile. In addition to small worktable swivel, this machine provides large swivel of head stock, wheel head slide and wheel head mount on the wheel head slide.

This allows grinding of any taper on the workpiece. Universal grinder is also equipped with an additional head for internal grinding. Schematic illustration of important features of this machine is shown in FigSpecial application of cylindrical grinderPrinciple of cylindrical grinding is being used for thread grinding with specially formed wheel that matches the thread profile. A single ribbed wheel or a multi ribbed wheel can be used as shown in Fig.

Roll grinding is a specific case of cylindrical grinding wherein large workpieces such as shafts, spindles and rolls are ground.External centreless grinder This grinding machine is a production machine in which out side diameter of the workpiece is ground. The workpiece is not held between centres but by a work support blade. It is rotated by means of a regulating wheel and ground by the grinding wheel. In through-feed centreless grinding, the regulating wheel revolving at a much lower surface speed than grinding wheel controls the rotation and longitudinal motion of the workpiece. The regulating wheel is kept slightly inclined to the axis of the grinding wheel and the workpiece is fed longitudinally as shown

The grinding wheel or the regulating wheel or both require to be correctly profiled to get the required taper on the workpieceTool post grinder A self powered grinding wheel is mounted on the tool post or compound rest to provide the grinding action in a lathe. Rotation to the workpiece is provided by the lathe spindle. The lathe carriage is used to reciprocate the wheel head

Internal grinding machine This machine is used to produce internal cylindrical surface. The surface may be straight, tapered, grooved or profiled. Broadly there are three different types of internal grinding machine as follows: 1. Chucking type internal grinder 2. Planetary internal grinder 3. Centreless internal grinder

Chucking type internal grinder This machine and various motions required for grinding action. The workpiece is usually mounted in a chuck. A magnetic face plate can also be used. A small grinding wheel performs the necessary grinding with its peripheral surface. Both transverse and plunge grinding can be carried out in this machine as shown in Fig.

Planetary internal grinder Planetary internal grinder is used where the workpiece is of irregular shape and can not be rotated conveniently as shown in Fig. this machine the workpiece does not rotate. Instead, the grinding wheel orbits the axis of the hole in the workpiece.

Centreless internal grinder This machine is used for grinding cylindrical and tapered holes in cylindrical parts (e.g. cylindrical liners, various bushings etc). The workpiece is rotated between supporting roll, pressure roll and regulating wheel and is ground by the grinding wheel as illustrated in Fig.

Tool and cutter grinder machine Tool grinding may be divided into two subgroups: tool manufacturing and tool resharpening. There are many types of tool and cutter grinding machine to meet these requirements. Simple single point tools are occasionally sharpened by hand on bench or pedestal grinder. However, tools and cutters with complex geometry like milling cutter, drills, reamers and hobs require sophisticated grinding machine commonly known as universal tool and cutter grinder. Present trend is to use tool and cutter grinder equipped with CNC to grind tool angles, concentricity, cutting edges and dimensional size with high precision.

DRILLING MACHINE

Drilling is an operation of making a circular hole by removing a volume of metal from the job by cutting tool called drill. A drill is a rotary end-cutting tool with one or more cutting lips and usually one or more flutes for the passage of chips and the admission of cutting fluid. A drilling machine is a machine tool designed for drilling holes in metals. It is one of the most important and versatile machine tools in a workshop. Besides drilling round holes,

many other operations can also be performed on the drilling machine such as counter- boring, Counter sinking, honing, reaming, lapping, sanding etc.

CONSTRUCTION OF DRILLING MACHINEWorkpiece. Different parts of a drilling machine are shown in Fig. and are discussed below: (i) The head containing electric motor, V-pulleys and V-belt which transmit rotary motion to the drill spindle at a number of speeds. (ii) Spindle is made up of alloy steel. It rotates as well as moves up and down in a sleeve. A pinion engages a rack fixed onto the sleeve to provide vertical up and down motion of the spindle and hence the drill so that the same can be fed into the workpiece or withdrawn from it while drilling. Spindle speed or the drill speed is changed with the help of V-belt and V-step-pulleys. Larger drilling machines are having gear boxes for the said purpose. (iii) Drill chuck is held at the end of the drill spindle and in turn it holds the drill bit. (iv) Adjustable work piece table is supported on the column of the drilling machine. It can be moved both vertically and horizontally. Tables are generally having slots so that the vise or the workpiece can be securely held on it. (v) Base table is a heavy casting and it supports the drill press structure. The base supports the column, which in turn, supports the table, head etc. (vi) Column is a vertical round or box section which rests on the base and supports the head and the table. The round column may have rack teeth cut on it so that the table can be raised or lowered depending upon the workpiece requirements.

This machine consists of following parts1. Base2. Pillar3. Main drive4. Drill spind5. Feed handle6. Work table

Fig: Construction of drilling machine

TYPES OF DRILLING MACHINEDrilling machines are classified on the basis of their constructional features, or the typeof work they can handle. The various types of drilling machines are:(1) Portable drilling machine(2) Sensitive drilling machine(a) Bench mounting(b) Floor mounting(3) Upright drilling machine(a) Round column section(b) Box column section machine(4) Radial drilling machine(a) Plain(b) Semi universal(c) Universal(5) Gang drilling machine(6) Multiple spindle drilling machine(7) Automatic drilling machine(8) Deep hole drilling machine

(a) Vertical(b) Horizontal

Few commonly used drilling machines are described as under.

Portable Drilling MachineA portable drilling machine is a small compact unit and used for drilling holes in worpieces in any position, which cannot be drilled in a standard drilling machine. It may be used for drilling small diameter holes in large castings or weldments at that place itself where they are lying. Portable drilling machines are fitted with small electric motors, which may be driven by both A.C. and D.C. power supply. These drilling machines operate at fairly high speeds and accommodate drills up to 12 mm in diameter.

Sensitive Drilling MachineIt is a small machine used for drilling small holes in light jobs. In this drilling machine, the workpiece is mounted on the table and drill is fed into the work by purely hand control. High rotating speed of the drill and hand feed are the major features of sensitive drilling machine. As the operator senses the drilling action in the workpiece, at any instant, it is called sensitive drilling machine. A sensitive drilling machine consists of a horizontal table, a vertical column, a head supporting the motor and driving mechanism, and a vertical spindle. Drills of diameter from 1.5 to 15.5 mm can be rotated in the spindle of sensitive drilling machine. Depending on the mounting of base of the machine, it may be classified into following types:

1. Bench mounted drilling machine, and2. Floor mounted drilling machine

Upright Drilling Machine The upright drilling machine is larger and heavier than a sensitive drilling machine. It is designed for handling medium sized workpieces and is supplied with power feed arrangement. In this machine a large number of spindle speeds and feeds may be available for drilling different types of work. Upright drilling machines are available in various sizes and with various drilling capacities (ranging up to 75 mm diameter drills). The table of the machine also has different types of adjustments. Based on the construction, there are two general types of upright drilling machine:(1) Round column section or pillar drilling machine.(2) Box column section.The round column section upright drilling machine consists of a round column where as the upright drilling machine has box column section. The other constructional features of both are same. Box column machines possess more machine strength and rigidity as compared to those having round section column.

Radial Drilling Machine The radial drilling machine consists of a heavy, round vertical column supporting a horizontal arm that carries the drill head. Arm can be raised or lowered on the column and can also be swung around to any position over the work and can be locked in any position. The drill head containing mechanism for rotating and clamped at any desired position. These adjustments of arm and drilling head permit the operator to locate the drill quickly over any point on the work. The table of radial drilling machine may also be rotated through 360 deg. The maximum size of hole that the machine can drill is not more than 50 mm. Powerful drive motors are geared directly into the head of the machine and a wide range of power feeds are available as well as sensitive and geared manual feeds. The radial drilling machine is used primarily for drilling medium to large and heavy workpieces. Depending on the different movements of horizontal arm, table and drill head, the upright drilling machine may be classified into following types-1. Plain radial drilling machine2. Semi universal drilling machine, and3. Universal drilling machine.

In a plain radial drilling machine, provisions are made for following three movements -1. Vertical movement of the arm on the column,2. Horizontal movement of the drill head along the arm, and 3. Circular movement of the arm in horizontal plane about the vertical column.In a semi universal drilling machine, in addition to the above three movements, the drill head can be swung about a horizontal axis perpendicular to the arm. In universal machine, an additional rotatory movement of the arm holding the drill head on a horizontal axis is also provided for enabling it to drill on a job at any angle.

Gang Drilling MachineIn gang drilling machine, a number of single spindle drilling machine columns are placed side by side on a common base and have a common worktable. A series of operation may be performed on the job by shifting the work from one position to the other on the worktable. This type of machine is mainly used for production work.

Multiple-Spindle Drilling MachineThe multiple-spindle drilling machine is used to drill a number of holes in a job simultaneously and to reproduce the same pattern of holes in a number of identical pieces in a mass production work. This machine has several spindles and all the spindles holding drills are fed into the work simultaneously. Feeding motion is usually obtained by raising the worktable.

TYPES OF DRILLSA drill is a multi point cutting tool used to produce or enlarge a hole in the workpiece. It usually consists of two cutting edges set an angle with the axis. Broadly there are three types of drills:1. Flat drill,

2. Straight-fluted drill, and3. Twist drillFlat drill is usually made from a piece of round steel which is forged to shape and ground to size, then hardened and tempered. The cutting angle is usually 90 deg. and the relief or clearance at the cutting edge is 3 to 8 deg. The disadvantage of this type of drill is that each time the drill is ground the diameter is reduced. Twist drill is the most common type of drill in use today. The various types of twist drills (parallel shank type and Morse taper shank type) are shown in Fig

Number sizesIn metric system, the drill is generally manufactured from 0.2 to 100 mm. In British system the drills sizes range from No. 1 to No. 80. Number 80 is the smallest having diameter equal to 0.0135 inch and the number 1 is the largest having diameter equal to 0.228 inch. Number 1 to number 60 is the standard sets of drills. The numbers 61 to 80 sizes drills are not so commonly used. The diameter of drills increases in steps of approximately by 0.002 inch.

Letter sizesThe drill sizes range from A to Z, A being the smallest having diameter equal to 0.234 inch and Z being the largest having diameter equal to 0.413 inch, increasing in steps of approximately O.010 inch fractional sizes: The drill sizes range from 1/64" inch to 5 inch in steps of 1/64 inches up to 1.75 inches, then the steps gradually increase. The drill sizes range from A to Z, A being the smallest having diameter equal to 0.234 inch and Z being the largest having diameter equal to 0.413 inch, increasing in steps of approximately O.010 inch fractional sizes: The drill sizes range from 1/64" inch to 5 inch in steps of 1/64 inches up to 1.75 inches, then the steps gradually increase. The drill is generally removed by tapping a wedge shaped drift into the slot in the drilling machine spindle as shown in Fig.

Twist Drill GeometryTwist drill geometry and its nomenclature are shown in Fig. A twist drill has three principal parts:(i) Drill point or dead center(ii) Body(iii) Shank.

Drill axis is the longitudinal centre line.Drill point is the sharpened end of the drill body consisting of all that part which is shaped to produce lips, faces and chisel edge.Lip or cutting edge is the edge formed by the intersection of the flank and faceLip length is the minimum distance between the outer corner and the chisel-edge corner of the lip.Face is that portion of the flute surface adjacent to the lip on which the chip impinges as it is cut from the work.Chisel edge is the edge formed by the intersection of the flanks.Flank is that surface on a drill point which extends behind the lip to the following flute.Flutes are the grooves in the body of the drill, which provide lips, allow the removal of chips, and permit cutting fluid to reach the lips.Flute length is the axial length from the extreme end of the point to the termination of the flutes at the shank end of the body.Body is that portion of the drill nomenclature, which extends from the extreme cutting end to the beginning of the shank.Shank is that portion of the drill by which it is held and driven,Heel is the edge formed by the intersection of the flute surface and the body clearance.Body clearance is that portion of the body surface reduced in diameter to provide diametric clearance.Core or web is the central portion of the drill situated between the roots of the flutes and extending from the point end towards the shank; the point end of the core forms the chisel edge.Lands are the cylindrically ground surfaces on the leading edges of the drill flutes. The width of the land is measured at right angles to the flute.

Recess is the portion of the drill body between the flutes and the shank provided so as to facilitate the grinding of the body. Parallel shank drills of small diameter are not usually provided with a recess.Outer corner is the corner formed by the intersection of the lip and the leading edge of the land.Chisel edge comer is the corner formed by the intersection of a lip and the chisel edge.Drill diameter is the measurement across the cylindrical lands at the outer corners of the drill. .Lead of helix is the distance measured parallel to the drill axis between corresponding points on the leading edge of a flute in one complete turn of the flute.Helix angle is the angle between the leading edge of the land and the drill axis.Rake angle is the angle between the face and a line parallel to the drill axis. It is bigger at the face edges and decreases towards the center of the drill to nearly 0°. The result is that the formation of chips grows more un-favorable towards the centre.Lip clearance angle is the angle formed by the flank and a plane at right angles to the drill axis; the angle is normally measured at the periphery of the drill. To make sure that the main cutting edges can enter into the material, the clearance faces slope backwards in a curve. The clearance angle is measured at the face edge, must amount to 5° up to 8°. Point angle is the included angle of the cone formed by the lips

OPERATIONS PERFORMED ON DRILLING MACHINEA drill machine is versatile machine tool. A number of operations can be performed onit. Some of the operations that can be performed on drilling machines are:1. Drilling 2. Reaming3. Boring 4. Counter boring5. Countersinking 6. Spot facing7. Tapping 8. Lapping9. Grinding 10. Trepanning.The operations that are commonly performed on drilling machines are drilling, reaming,lapping, boring, counter-boring, counter-sinking, spot facing, and tapping. These operations

Drilling:This is the operation of making a circular hole by removing a volume of metal from the job by a rotating cutting tool called drill as shown in Fig. Drilling removes solid metal from the job to produce a circular hole. Before drilling, the hole is located by drawing two lines at right angle and a center punch is used to make an indentation for the drill point at the center to help the drillin getting started. A suitable drill is held in the drill machine and the drill machine is adjusted to operate at the correct cutting speed. The drill machine is started and the drill starts rotating. Cutting fluid is made to flow liberally and the cut is started. The rotating drill is made to feedInto the job. The hole, depending upon its length, may be drilled in one or more steps. After the drilling operation is complete, the drill is removed from the hole and the power

ReamingThis is the operation of sizing and finishing a hole already made by a drill. Reaming is performed by means of a cutting tool called reamer as shown in Fig. Reaming operation serves to make the hole smooth, straight and accurate in diameter. Reaming operation is performed by means of a multitooth tool called reamer. Reamer possesses several cutting edges on outer periphery and may be classified as solid reamer and adjustable reamer.

BoringShows the boring operation where enlarging a hole by means of adjustable cutting tools with only one cutting edge is accomplished. A boring tool is employed for this purpose

Counter-BoringCounter boring operation is shown in Fig. It is the operation of enlarging the end of a hole cylindrically, as for the recess for a counter-sunk rivet. The tool used is known as counter-bore.

Counter-SinkingCounter-sinking operation is shown in Fig. This is the operation of making a cone shaped enlargement of the end of a hole, as for the recess for a flat head screw. This is done for providing a seat for counter sunk heads of the screws so that the latter may flush with the main surface of the work.

LappingThis is the operation of sizing and finishing a hole by removing very small amounts of material by means of an abrasive. The abrasive material is kept in contact with the sides of a hole that is to be lapped, by the use of a lapping tool.

Spot-FacingThis is the operation of removing enough material to provide a flat surface around a holeto accommodate the head of a bolt or a nut. A spot-facing tool is very nearly similar to theCounter-bore.TappingIt is the operation of cutting internal threads by using a tool called a tap. A tap is similar to a bolt with accurate threads cut on it. To perform the tapping operation, a tap is screwed into the hole by hand or by machine. The tap removes metal and cuts internal threads, which will fit into external threads of the same size. For all materials except cast iron, a little lubricate oil is applied to improve the action. The tap is not turned continuously, but after every half turn, it should be

reversed slightly to clear the threads. Tapping operation is shown in Fig. The geometryand nomenclature of a tap is given in Fig.

Core drillingCore drilling operation is shown in Fig. It is a main operation, which is performed on radial drilling machine for producing a circular hole, which is deep in the solid metal by means of revolving tool called drill.

SIZE OF A DRILLING MACHINEDifferent parameters are being considered for different types of drilling machines to determine their size. The size of a portable drilling machine is decided by the maximum diameter of the drill that it can hold. The sensitive and upright drilling machines are specified by the diameter of the largest workpiece which can be centered under the drill machine spindle. A radial drilling machine is specified by the length of the arm and the diameter of the column. To specify a drilling machine completely, following other parameters may also be needed:1. Table diameter2. Number of spindle speeds and feeds available3. Maximum spindle travel4. Morse taper number of the drill spindle5. Power input6. Net weight of the machine7. Floor space required, etc.

CUTTING SPEEDThe cutting speed in a drilling operation refers to the peripheral speed of a point on the surface of the drill in contact with the work. It is usually expressed in meters/min. The cutting speed (Cs) may be calculated as: Cs = ((22/7) × D × N)/1000 Where, D is the diameter of the drill in mm and N is the rpm of the drill spindle.FEEDThe feed of a drill is the distance the drill moves into the job at each revolution of the spindle. It is expressed in millimeter. The feed may also be expressed as feed per minute. The feed per minute may be defined as the axial distance moved by the drill into the work per minute. The feed per minute may be calculated as:F = Fr × NWhere, F = Feed per minute in mm.Fr = Feed per revolution in mm.N = R.P.M. of the drill.

Computer-controlled lathes (CNC lathes)Computer-controlled (numerically controlled, NC, CNC) lathes incorporate a computer system to control the movements of machine components by directly inserted coded instructions in the form of numerical data. A CNC lathe is especially useful in contour turning operations and precise machining. There are also not chuck but bar modifications. A CNC lathe is essentially a turret lathe. The major advantage of these machines is in their versatility - to adjust the CNC lathe for a different part to be machined requires a simple change in the computer program and, in some cases, a new set of cutting tools.

UNIT V

PART-A (Important Questions and Answers)

1. List out types of lathe. Speed lathe.

Woodworking Centering. Polishing. Spinning.

Bench lathe. Tool room lathe. Capstan and Turret lathe.

Special purpose. Wheel lathe. Gap bed lathe. T-lathe.

Engine lathe. Belt drive. Individual motor drive. Duplicating lathe. Gear head lathe. Spinning.

Automatic lathe.

2. Define Cold working.The process is usually performed at room temperature, but mildly elevated temperatures may be used to provide increased ductility and reduced strength

3. Classifications of Squeezing Processes Rolling Cold Forging Sizing Staking Staking Coining Burnishing Extrusion Peening Hubbing Riveting Thread Rolling

4. What is Rolling?Process used in sheets, strips, bars, and rods to obtain products that have smooth surfaces and accurate dimensions; most cold-rolling is performed on four-high or cluster-type rolling mills A sheet or block or strip stock is introduced between rollers and then compressed and squeezed. Thickness is reduced. The amount of strain (deformation) introduced determines the hardness, strength and other material properties of the finished product. Used to produce sheet metals predominantly

5. Define Cold Forging.Process in which slugs of material are squeezed into shaped die cavities to produce finished parts of precise shape and size

6. List out the Types of forging.Closed/impression die forging Electro-upsetting Forward extrusion Backward extrusion Radial forging Hobbling Isothermal forging Open-die forging Upsetting Nosing Coining

7. Define Shaper machine. Shaper is a reciprocating type of machine tool in which the ram moves the cutting tool backwards and forwards in a straight line. The basic components of shaper are shown in Fig. It is intended primarily to produce flat surfaces

8. Define Milling machine.A milling machine is a machine tool that removes metal as the work is fed against a rotating multipoint cutter. The milling cutter rotates at high speed and it removes metal at a very fast rate with the help of multiple cutting edges.

9. List out type of Milling methods Up-milling or conventional milling, and Down milling or climb milling.

10. Write down the Types of milling cutters(1) Plain milling cutters,(2) Side milling cutters,(3) Face milling cutter,(4) Angle milling cutters,(5) End milling cutter,(6) Fly cutter,(7) T-slot milling cutter,

(8) Formed cutters,(9) Metal slitting saw,

PART B (Important Questions)

1. Explain in detail rolling, extrusion and forging process.

2. Write down the principle and operation shaper.

3. What is the working principle of lathe and write down its types?

4. Write down the operation done in drilling machine.

5. What do you mean by milling and write down its operation?

6. Explain CNC Machine and spark Erosion Process.