METAL FORMING METAL FORMING PROCESSESPROCESSES

FORGINGFORGING

INTRODUCTIONINTRODUCTION Forging is an oldest shaping process used for Forging is an oldest shaping process used for

the producing small articles for which accuracy the producing small articles for which accuracy in size is not so important. in size is not so important.

The parts are shaped by heating them in an The parts are shaped by heating them in an open fire or hearth by the blacksmith and open fire or hearth by the blacksmith and shaping them through applying compressive shaping them through applying compressive forces using hammers. forces using hammers.

Thus forging is defined as the plastic Thus forging is defined as the plastic deformation of metals at elevated temperatures deformation of metals at elevated temperatures into a predetermined size or shape using into a predetermined size or shape using compressive forces exerted through some compressive forces exerted through some means of hand hammers, small power means of hand hammers, small power hammers, die, press or upsetting machine.hammers, die, press or upsetting machine.

It consists essentially of changing or It consists essentially of changing or altering the shape and section of altering the shape and section of metal by hammering at a temperature metal by hammering at a temperature of about 980°C, at which the metal is of about 980°C, at which the metal is entirely plastic and can be easily entirely plastic and can be easily deformed or shaped under pressure. deformed or shaped under pressure.

The shop in which the various forging The shop in which the various forging operations are carried out is known operations are carried out is known as the smithy or smith’s shop.as the smithy or smith’s shop.

A metal such as steel can be shaped in a A metal such as steel can be shaped in a cold state but the application of heat lowers cold state but the application of heat lowers the yield point and makes permanent the yield point and makes permanent deformation easier. deformation easier.

Forging operation can be accomplished by Forging operation can be accomplished by hand or by a machine hammer.hand or by a machine hammer.

Forging processes may be classified into hot Forging processes may be classified into hot forging and cold forgings and each of them forging and cold forgings and each of them possesses their specific characteristics, possesses their specific characteristics, merits, demerits and applications.merits, demerits and applications.

Classification of forging Classification of forging processesprocesses

- Hammer or drop forging- Hammer or drop forging

- Press forging- Press forging

- Open-die forging- Open-die forging

- Closed-die forging- Closed-die forging

Applications of forgingApplications of forging Almost all metals and alloys can be forged. The low and Almost all metals and alloys can be forged. The low and

medium carbon steels are readily hot forged without medium carbon steels are readily hot forged without difficulty, but the high-carbon and alloy steels are more difficulty, but the high-carbon and alloy steels are more difficult to forge and require greater care. Forging is difficult to forge and require greater care. Forging is generally carried out on carbon alloy steels, wrought iron, generally carried out on carbon alloy steels, wrought iron, copper-base alloys, alumunium alloys, and magnesium copper-base alloys, alumunium alloys, and magnesium alloys. Stainless steels, nickelbased super-alloys, and alloys. Stainless steels, nickelbased super-alloys, and titanium are forged especially for aerospace uses. titanium are forged especially for aerospace uses. Producing of crank shaft of alloy steel is a good example Producing of crank shaft of alloy steel is a good example which is produced by forging. which is produced by forging.

Forging processes are among the most important Forging processes are among the most important manufacturing techniques utilized widely in manufacturing manufacturing techniques utilized widely in manufacturing of small tools, rail-road equipments, automobiles and of small tools, rail-road equipments, automobiles and trucks and components of aeroplane industries. These trucks and components of aeroplane industries. These processes are also extensively used in the manufacturing processes are also extensively used in the manufacturing of the parts of tractors, shipbuilding, cycle industries, of the parts of tractors, shipbuilding, cycle industries, railroad components, agricultural machinery etc.railroad components, agricultural machinery etc.

FORGABLE MATERIALSFORGABLE MATERIALS1. Aluminium alloys 1. Aluminium alloys 2. Magnesium alloys2. Magnesium alloys3. Copper alloys. 3. Copper alloys. 4. Carbon and low alloy steels4. Carbon and low alloy steels5. Martensitic stainless steels 5. Martensitic stainless steels 6. Austenitic stainless steels 6. Austenitic stainless steels 7. Nickel alloys 7. Nickel alloys 8. Titanium alloys 8. Titanium alloys 9. Columbium alloys 9. Columbium alloys 10. Tantalum alloys10. Tantalum alloys11. Molybdenum alloys 11. Molybdenum alloys 12. Tungsten alloys12. Tungsten alloys13. Beryllium.13. Beryllium.

EFFECT OF FORGING ON EFFECT OF FORGING ON METAL CHARACTERISTICSMETAL CHARACTERISTICSGenerally a forging material is selected Generally a forging material is selected based on certain desirable mechanical based on certain desirable mechanical properties inherent in the composition properties inherent in the composition and/or for those which can be developed by and/or for those which can be developed by forging. Such properties may be one or forging. Such properties may be one or several, such as strength, resistance to several, such as strength, resistance to fatigue, shock or bending, good machining fatigue, shock or bending, good machining characteristics, durability etc. A continuous characteristics, durability etc. A continuous and uninterrupted grain flow in a forged and uninterrupted grain flow in a forged component results in higher strength and component results in higher strength and toughness.toughness.

Fuels used in forging shopFuels used in forging shop The fuels used in forging shop are classified as solid, liquid The fuels used in forging shop are classified as solid, liquid

and gaseous fuels which are discussed as under.and gaseous fuels which are discussed as under. Solid fuelsSolid fuels

Wood, coal, anthracite, peat, charcoal, coke, pulverized fuel Wood, coal, anthracite, peat, charcoal, coke, pulverized fuel etc.etc.

Liquid fuelsLiquid fuelsCrude oil, petroleum, kerosene, tar oil etc.Crude oil, petroleum, kerosene, tar oil etc.

Gaseous fuelsGaseous fuelsNatural gas and some artificially produced gases are used Natural gas and some artificially produced gases are used generate heat.generate heat.

A good fuel should have always possesses the following A good fuel should have always possesses the following essential characteristic which are given as under.essential characteristic which are given as under.1. The fuel should be able to generate the required heat.1. The fuel should be able to generate the required heat.2. It should have complete combustion.2. It should have complete combustion.3. It should be highly efficient.3. It should be highly efficient.4. It should not produce excess smoke and flying ash.4. It should not produce excess smoke and flying ash.5. It should be easy to fire, cheap and easily available.5. It should be easy to fire, cheap and easily available.

FORGING FORGING TEMPERATURESTEMPERATURES

The temperature to start the forging for The temperature to start the forging for soft, low carbon steels is 1,250 to soft, low carbon steels is 1,250 to 1,300°C, the temperature to finish forging 1,300°C, the temperature to finish forging is 800 to 840°C. The corresponding is 800 to 840°C. The corresponding temperatures for high carbon and alloy temperatures for high carbon and alloy steels which are hard in nature are 1100 steels which are hard in nature are 1100 to l140°C and 830 to 870°C. Wrought iron to l140°C and 830 to 870°C. Wrought iron is best forged at a temperature little is best forged at a temperature little below 1,290°C. Non ferrous alloys like below 1,290°C. Non ferrous alloys like bronze and brass are heated to about 600 bronze and brass are heated to about 600 to 930°C, the aluminium and magnesium to 930°C, the aluminium and magnesium alloys to about 340 to 500°C.alloys to about 340 to 500°C.

COMMON HAND FORGING COMMON HAND FORGING TOOLSTOOLS

For carrying out forging operations For carrying out forging operations manually, certain common hand manually, certain common hand forging tools are employed. These forging tools are employed. These are also called blacksmith’s tools, for are also called blacksmith’s tools, for a blacksmith is one who works on a blacksmith is one who works on the forging of metals in their hot the forging of metals in their hot state. The main hand forging tools state. The main hand forging tools are as under.are as under.

1. Tongs 1. Tongs 2. Flatter2. Flatter3. Swage 3. Swage 4. Fuller4. Fuller5. Punch 5. Punch 6. Rivet header6. Rivet header7. Hot chisel 7. Hot chisel 8. Hammers8. Hammers9. Anvil 9. Anvil 10. Swage block10. Swage block11. Drift 11. Drift 12. Set-hammer12. Set-hammer13. Brass scale 13. Brass scale 14. Brass14. Brass15. Black smith’s gauge 15. Black smith’s gauge 16. Heading too16. Heading too

HAND FORGING TOOLSHAND FORGING TOOLS

TYPES OF HAMMERSTYPES OF HAMMERS

Set hammerA set hammer generally used in forging shop is shown in Fig. It is used for finishing corners in shouldered work where the flatter would be inconvenient. It is also used for drawing out the gorging job.

ANVILANVILAn anvil is a most commonly tool used in forging shop which is shown in Fig. Itacts as a support for blacksmith’s work during hammering. The body of the anvil is made of mild steel with a tool steel face welded on the body, but the beak or horn used for bending curves is not steel faced. The round hole in the anvil called pritchel hole is generally used for bending rods of small diameter, and as a die for hot punching operations. The square or hardie hole is used for holding square shanks of various fittings. Anvils in forging shop may vary up to about 100 to 150 kg and they should always stand with the top face about 0.75 mt. from the floor. This height may be attained by resting the anvil on a wooden or cast iron basein the forging shop.

SWAGE BLOCKSWAGE BLOCK

Swage block generally used in forging shop is shown in Fig. It is mainly used for heading, bending, squaring, sizing, and forming operations on forging jobs. It is 0.25 mt. or even more wide. It may be used either flat or edgewise in its stand.

Forging OperationsForging Operations

1. Upsetting 1. Upsetting 2. Bending2. Bending3. Drawing down 3. Drawing down 4. Cutting4. Cutting5. Setting down 5. Setting down 6. Punching6. Punching7. Flattening 7. Flattening 8. Fullering8. Fullering9. Forge Welding 9. Forge Welding 10. Swaging10. Swaging

The hand forging The hand forging operationsoperations

HAND FORGINGHAND FORGINGHand forging is performed in the black smithy shop. The job is heated at the forging temperature in hearth and it is then brought on anvil using tong. It is then forged using hand hammers and other hand forging tools for imparting specific shape.

DRAWING OUTDRAWING OUTDrawing out is used to reduce the thickness of a bar and to increase its length. It may be carried out by working the metal over the horn the anvil as shown inFig. 14.17, then by hammering it on the anvil face. The rounded horn of the anvil acts as a blunt edge, which forces the metal to flow lengthwise when struck by the hammer. For drawing down very heavy work, fuller may be used for drawing down a bar over the horn (round portion) of anvil.

FULLERINGFULLERINGFullering operation generally used in forging shop is shown in Fig. It involves heating the stock in the black smith hearth. Then heated stock is placed on the fuller fixed on anvil. A fuller is put over the sock and hammering is done to reduce the cross section of job at required point.

Power ForgingPower Forging Hand hammer blows impact will not be always sufficient Hand hammer blows impact will not be always sufficient

enough to affect the proper plastic flow in a medium enough to affect the proper plastic flow in a medium sized or heavy forging. It also causes fatigue to the sized or heavy forging. It also causes fatigue to the hammer man. To have heavy impact or blow for more hammer man. To have heavy impact or blow for more plastic deformation, power hammer are generally plastic deformation, power hammer are generally employed. These hammers are operated by compressed employed. These hammers are operated by compressed air, steam, oil pressure, spring and gravity. They are air, steam, oil pressure, spring and gravity. They are generally classified as spring hammer and drop generally classified as spring hammer and drop hammers. The capacity of these hammers is given by the hammers. The capacity of these hammers is given by the total weight. A 100 kg hammer will be one of which the total weight. A 100 kg hammer will be one of which the falling pans weigh 100 kg. falling pans weigh 100 kg.

The heavier these parts and greater the height from The heavier these parts and greater the height from which they fall, the higher will be intensity of blow the which they fall, the higher will be intensity of blow the hammer will provide. Power hammers are of different hammer will provide. Power hammers are of different types e.g. spring power hammers, pneumatic power types e.g. spring power hammers, pneumatic power hammers etc. These hammers are named due to their hammers etc. These hammers are named due to their construction, according to their way of operation and construction, according to their way of operation and according to the type of fuel they use for getting the according to the type of fuel they use for getting the required power for operation. Besides these, a large required power for operation. Besides these, a large number of forging presses are also used in forging work.number of forging presses are also used in forging work.

Spring HammerSpring Hammer

Drop HammersDrop Hammers

Design Principles for drop Design Principles for drop forgingforging

1. The sections of the forging should be 1. The sections of the forging should be balanced about the parting line. Where balanced about the parting line. Where this is impossible, design for the simplest this is impossible, design for the simplest irregular parting line which approaches irregular parting line which approaches a balanced condition.a balanced condition.

2. Generous inside fillets and external 2. Generous inside fillets and external radio should be allowed. Minimum radius radio should be allowed. Minimum radius should be 2 mm for small parts and 4 should be 2 mm for small parts and 4 mm for large parts.mm for large parts.

3. Sufficient draft should be allowed for 3. Sufficient draft should be allowed for easy removal of: the parteasy removal of: the part

DEFECTS IN FORGED DEFECTS IN FORGED PARTSPARTS

((ii) Defects resulting from the melting practice such as dirt, slag ) Defects resulting from the melting practice such as dirt, slag and blow holes.and blow holes.

((iiii) Ingot defects such as pikes, cracks scabs, poor surface ) Ingot defects such as pikes, cracks scabs, poor surface and segregation.and segregation.

((iiiiii) Defect due to faulty forging design.) Defect due to faulty forging design.

((iviv) Defects of mismatched forging because of improper ) Defects of mismatched forging because of improper placement of the metal in the die.placement of the metal in the die.

((vv) Defects due to faulty design drop forging die.) Defects due to faulty design drop forging die.

((vivi) Defects resulting from improper forging such as seams cracks ) Defects resulting from improper forging such as seams cracks laps. etc.laps. etc.

((viivii) Defects resulting from improper heating and cooling of the ) Defects resulting from improper heating and cooling of the forging part such as burnt metal and decarburized steel.forging part such as burnt metal and decarburized steel.

DEFECTS IN FORGED PARTS DEFECTS IN FORGED PARTS (contd…)(contd…)

1. Mismatched forging1. Mismatched forgingReasonsReasonsDue to non alignment of proper die halves.Due to non alignment of proper die halves.

2. Brunt and overheated metal2. Brunt and overheated metalReasonsReasonsThis is caused by improper heating the metal at high This is caused by improper heating the metal at high temperature or for a long time.temperature or for a long time.

3. Fibred flow lines discontinued3. Fibred flow lines discontinuedReasonsReasonsThis will occur because of very rapid plastic flow of metal.This will occur because of very rapid plastic flow of metal.

4. Scale pits4. Scale pitsReasonsReasonsThese are formed by squeezing of scale into the metal surface These are formed by squeezing of scale into the metal surface during forging.during forging.

5. Oversize components5. Oversize componentsReasonsReasonsDue to worn out dies, incorrect dies, misalignment of die Due to worn out dies, incorrect dies, misalignment of die halves.halves.

REMOVAL OF DEFECTS IN REMOVAL OF DEFECTS IN FORGINGFORGING

((ii) Surface cracks and decarburized areas are removed ) Surface cracks and decarburized areas are removed from forging parts by grinding on special machines. from forging parts by grinding on special machines. Care should also be taken to see that the job is not Care should also be taken to see that the job is not under heated, decarburized, overheated and burnt.under heated, decarburized, overheated and burnt.

((iiii) Shallow cracks and cavities can be removed by ) Shallow cracks and cavities can be removed by chipping out of the cold forging with pneumatic chisel chipping out of the cold forging with pneumatic chisel or with hot sets.or with hot sets.

((iiiiii) The parting line of a forging should lie in one plane ) The parting line of a forging should lie in one plane to avoid to avoid

mismatching.mismatching.((iviv) Destroyed forgings are straightened in presses, if ) Destroyed forgings are straightened in presses, if

possible.possible.((vv) Die design should be properly made taking into ) Die design should be properly made taking into

consideration all relevant and important aspects that consideration all relevant and important aspects that may impart forging defects and ultimate spoilagemay impart forging defects and ultimate spoilage

((vivi) The mechanical properties of the metal can be ) The mechanical properties of the metal can be improved by forging to correct fibre line. The internal improved by forging to correct fibre line. The internal stresses developed due to heating and cooling of the stresses developed due to heating and cooling of the job can be removed by annealing or normalizing.job can be removed by annealing or normalizing.

HEAT TREATMENT OF HEAT TREATMENT OF FORGINGFORGING

Heat treatment is carried out for Heat treatment is carried out for releasing the internal stresses arising in the releasing the internal stresses arising in the metal during forging and cooling of work metal during forging and cooling of work piece. piece.

It is used for equalizing the granular It is used for equalizing the granular structure of the forged metal and improving structure of the forged metal and improving the various mechanical properties. Generally the various mechanical properties. Generally forged parts are annealed, normalized and forged parts are annealed, normalized and tempered to obtain the desired results.tempered to obtain the desired results.

Orbital ForgingOrbital Forging

In orbital forging, a metal blank is In orbital forging, a metal blank is placed in the lower half of a die and placed in the lower half of a die and deformed incrementally by the rotating deformed incrementally by the rotating upper half of the die.upper half of the die.

Synchronous to this rotation, the Synchronous to this rotation, the part can be raised upward by a piston that part can be raised upward by a piston that is part of the lower half of the die Fig. is part of the lower half of the die Fig.

This process is also referred to as This process is also referred to as rotary forging and can be performed as a rotary forging and can be performed as a hot or cold operation. Bearing rings, hot or cold operation. Bearing rings, bearing end covers, bevel gears, and bearing end covers, bevel gears, and various other disc-shaped and conical various other disc-shaped and conical parts can be rotary forged.parts can be rotary forged.

Orbital ForgingOrbital Forging

Roll ForgingRoll ForgingRoll forging forms a metal blank into a desired Roll forging forms a metal blank into a desired

shape by feeding it through a pair of rolls with shape by feeding it through a pair of rolls with shaped grooves (Fig). shaped grooves (Fig).

The rolls are in operation for only a portion of The rolls are in operation for only a portion of their rotational cycle. This hot-forming process is their rotational cycle. This hot-forming process is termed forging although it does not employ a moving termed forging although it does not employ a moving hammer/punch. hammer/punch.

It can be utilized for the production of long It can be utilized for the production of long and thin parts, including tapered shafts, leaf springs, and thin parts, including tapered shafts, leaf springs, and, occasionally, drill bits (when the blank is also and, occasionally, drill bits (when the blank is also rotated with respect to the rolls as it advances rotated with respect to the rolls as it advances between them).between them).

In a process similar to roll forging, alloyed In a process similar to roll forging, alloyed steel gears can be manufactured by forming gear steel gears can be manufactured by forming gear teeth on a hot blank fed between two toothed-die teeth on a hot blank fed between two toothed-die rolls (wheels).rolls (wheels).

Roll ForgingRoll Forging

Advantages of forgingAdvantages of forging 1. Forged parts possess high ductility and offers great 1. Forged parts possess high ductility and offers great

resistance to impact and fatigue loads.resistance to impact and fatigue loads. 2. Forging refines the structure of the metal.2. Forging refines the structure of the metal. 3. It results in considerable saving in time, labor and 3. It results in considerable saving in time, labor and

material as compared to the production of similar item by material as compared to the production of similar item by cutting from a solid stock and then shaping it.cutting from a solid stock and then shaping it.

4. Forging distorts the previously created unidirectional 4. Forging distorts the previously created unidirectional fiber as created by rolling and increases the strength by fiber as created by rolling and increases the strength by setting the direction of grains.setting the direction of grains.

5. Because of intense working, flaws are rarely found, so 5. Because of intense working, flaws are rarely found, so have good reliability.have good reliability.

6. The reasonable degree of accuracy may be obtained in 6. The reasonable degree of accuracy may be obtained in forging operation.forging operation.

7. The forged parts can be easily welded.7. The forged parts can be easily welded.

Disadvantages of forgingDisadvantages of forging1. Rapid oxidation in forging of metal surface at high 1. Rapid oxidation in forging of metal surface at high

temperature results in scaling which wears the temperature results in scaling which wears the dies.dies.

2. The close tolerances in forging operations are 2. The close tolerances in forging operations are difficult to maintain.difficult to maintain.

3. Forging is limited to simple shapes and has 3. Forging is limited to simple shapes and has limitation for parts having undercuts etc.limitation for parts having undercuts etc.

4. Some materials are not readily worked by forging.4. Some materials are not readily worked by forging.5. The initial cost of forging dies and the cost of their 5. The initial cost of forging dies and the cost of their

maintenance is high.maintenance is high.6. The metals gets cracked or distorted if worked 6. The metals gets cracked or distorted if worked

below a specified temperature limit.below a specified temperature limit.7. The maintenance cost of forging dies is also very 7. The maintenance cost of forging dies is also very

high.high.

Residual stresses in Residual stresses in forgingforging• • The residual stress produced in forgings as a results The residual stress produced in forgings as a results

of inhomogeneous deformation are generally small of inhomogeneous deformation are generally small because the deformation is normally carried out well because the deformation is normally carried out well into the hot-working region.into the hot-working region.

• • However, appreciable residual stresses and warping However, appreciable residual stresses and warping can occur on the quenching of steel forgings in heat can occur on the quenching of steel forgings in heat treatment.treatment.

• • Large forgings are subjected to the formation of small Large forgings are subjected to the formation of small cracks, or flakes at the centre of the cross section. cracks, or flakes at the centre of the cross section. This is associated with the high hydrogen content This is associated with the high hydrogen content usually present in steel ingots of large size, coupled usually present in steel ingots of large size, coupled with the presence of residual stresses.with the presence of residual stresses.

•• Large forgings therefore have to be slowly cooled Large forgings therefore have to be slowly cooled from the working temperature. from the working temperature.

Finite element analysis is used to predict residual Finite element analysis is used to predict residual stresses in forgingsstresses in forgings

Calculation of forging Calculation of forging loadsloads

Die materialsDie materials((Required properties)Required properties)

• • Thermal shock resistanceThermal shock resistance

• • Thermal fatigue resistanceThermal fatigue resistance

• • High temperature strengthHigh temperature strength

• • High wear resistanceHigh wear resistance

• • High toughness and ductilityHigh toughness and ductility

• • High hardenabilityHigh hardenability

• • High dimensional stability during hardeningHigh dimensional stability during hardening

• • High machinabilityHigh machinability

Die materialsDie materials

Alloyed steels (with Cr, Mo, W, V), Alloyed steels (with Cr, Mo, W, V), tool steels, cast steels or cast iron. tool steels, cast steels or cast iron.

(Heat treatments such are nitriding (Heat treatments such are nitriding or chromium plating are required to or chromium plating are required to improve die life)improve die life)

Die materialsDie materials(contd…)(contd…)

1) Carbon steels with 0.7-0.85% C are 1) Carbon steels with 0.7-0.85% C are appropriate for small tools and flat appropriate for small tools and flat impressions.impressions.

2) Medium-alloyed tool steels for 2) Medium-alloyed tool steels for hammer dies.hammer dies.

3) Highly alloyed steels for high 3) Highly alloyed steels for high temperature resistant dies used intemperature resistant dies used in

presses and horizontal forging presses and horizontal forging machines.machines.

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