Advantages of Forging

AUTOMOBILE MANUFACTURING PROCESSES

2010

1.7 Advantages of forging Strength: Forging reduces the failures. In this process work piece yields with high strength to weight ratio. Due to this, it can be able to withstand  fluctuating stress caused by sudden shock  loading. I.

Metal co conservation: Practically there is no waste of metals.

II.

Weight saving: Strong thin-walled parts may be produced without damaging

important physical requirements.

III.

Machining ti time: Forging can be made to close tolerances, which reduces

machining time for finishing operations of the products.

Speed of production: High rate of production is possible.

IV.

Incorporation in welded structures: 4

Dhaigude.P.B.

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AUTOMOBILE MANUFACTURING PROCESSES Parts can be welded easily due to fibrous structure.

V.

VI.

VII.

It maintains uniform and same quality all over parts.

Close tolerances.

Smooth surfac face fi finish.

1.8 Disadvantages of forging parts I. II.

High tool cost. High igh tool mai maintenance.

III.

No cord holes.

IV. IV.

Limi Limita tati tion on in size size and and sha shape pe..

V.

Heat Heat tre treat atmen mentt proc proces ess s incr increa ease ses s cost cost of of the the prod produc uct. t.

VI.

Brittle materials like cast iron can c an not be forged.

VII. VII.

Comp Comple lex x sha shape pe ca can n not not be prod produc uced ed by forg forgin ing. g.

1.9 Classification of forging f orging process: Mainly forging process classified into two parts. I. Open die forging:

a) Hand Hand forg forging ing

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AUTOMOBILE MANUFACTURING PROCESSES ii .

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Press forging

II. Close die forging:

a) Drop Drop forg forgin ing g b) Pres Press s forg forging ing c) Ma Mach chin ine e for forgi ging ng

I. Open Open die die for forgi ging ng:: It is the simplest forging process. This process also known as smith die forging or flat die forging. A solid workpiece placed between two flat face dies as shown in fig.1.1 (a) and reduces their height by compressing it.

Fig. 1.1 Open Die Forging Processes The die surfaces have some cavity to produce relatively

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part gets developed in barrel shape as shown in fig.1.1 (c). This barreling is caused due to friction force between workpiece and die surfaces. Barreling can be reduced easily with help of lubricant. Smith die forging process sub-divided into two parts

a) Hand process:

According to the name this process purely done by hand. The forging is done on a anvil by hammering the workpiece at suitable temperature. This temperature attained by heating the workpiece with tongs. Hand forging consist of two formers as shown in fig.1.2. These formers are made of high carbon steel in different size to suit various types of workpiece. It has two formers top and bottom formers. Bottom formers also known as fuller. Working edges of the fullers and formers are normally rounded. These are us ed for making necks by reducing cross-section of a workpiece. Generally are used in maintenance shops as well as rework area. But now a days, a new forging process is developed known as power forging.

 b) Power forging:

Heavy machine parts can not be forged by hand. Low blow of  a hand or hammer is not able ab le to produce a great degree of  deformation in a workpiece.

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Power forging also sub-divided into two parts

i.

Hammer fo forging: Machine which is work by blow or impact to perform forging

process is known as hammer forging

ii.

Press forging: Machine which is work on pressure p ressure to perform forging process is known as press forging.

II. II. Clos Close e die die forg forgin ing: g: In open die forging Complex shape with great accuracy is very difficult to forged. Close die forging process consist of specially prepared dies to manufacturing forged parts in large quantities. It is also known as impression die forging.

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It consist of two dies as shown in fig.1.3. the workpiece takes the shape of the die cavities ( impression ) during forging process. Some materials comes outwards and forms a flash. The flash has a very important role in the grain flow of material in close die forging. Thin flash cools very easily. Flash have frictional resistance gives high pressure to the material in die cavity. So it helps to filling of die cavity. Generally this process is used for mass production with high degree of accuracy. This process sub-divided into two parts

a) Drop Drop forgin forging: g: Drop forging is used when mass production of identical parts is required. It is also called as stamping. It consist of special type of  hammer known as drop hammer or drop stamp. Perfectly made steel dies are used for forging. these dies are made into two parts as shown in fig.1.4. One part is connected to the top side and other part is fastened fas tened to the anvil block at the bottom side. The top part of the die is raised by mechanical links to a certain height. The heated metal placed accurately in the bottom part of the die. The top part of the die is then allowed to fall suddenly. This gives a high blow and completes the workpiece in a single operation. This process done due to squeezing of the metal into the die cavities. The devices are used for raising the top part of the die is given gi ven below

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Working process: At

b) Press Press forging forging:: The machine which is work on pressure to perform forging process is known as press forging. This process consist of slow squeezing of metal in closed impression dies, instead of Appling repeated blow by hammers. Generally two types of presses are used

i.

Hydraulic presses: These presses are used for heavy work. Hydraulic presses are

less faster than mechanical presses. But hydraulic presses produce greater squeezing force than mechanical presses.

ii.

mechanical pr presses: These presses are used for light work. Mechanical presses are

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AUTOMOBILE MANUFACTURING PROCESSES c) Machin Machine e forgi forging: ng: This process also known as hot heading or up-setting. This process consist of applying pressure longitudinally on a hot bar clamped or gripped between grooved dies. Forging is done on the end of the bar. Forging is done on various shapes of metals. But most commonly used shape is round shape metals. The equipments used for forging is forging machine or up-setter. Generally it gives forging pressure in a horizontal directions.

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Many strokes of the heading tool may be needed to complete the forging. In this process dies does not have draft as well as flash, so it gives better dimensional accuracy.

1.10 Difference between drop forging and press forging:

Sr. No. 1)

Drop forging

Press forging

This process involves fast

This process involves slow

squeezing of metal in dies by

squeezing of metal in dies by

applying repeated blows by

applying pressure force.

hammers. The dies used relatively more

The dies used relatively less

draft and therefore more

draft and therefore more

complicated shape can not be

complicated shape can be

3)

forged. Alignment of two dies halves is

forged. Alignment of two dies halves is

4)

difficult. The life of machines and dies

easy. The life of presses and dies are

are shorter.

longer.

2)

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AUTOMOBILE MANUFACTURING PROCESSES

1.11 Difference between open die forging and close die forging: Sr.

Open die forging

Close die forging

No. 1)

It is the simplest forging

It is the complex forging

2)

process. This process requires simple

process. This process requires complex

3)

and inexpensive dies. It is useful only for small scale

and expensive dies. It is useful for small scale as

4)

production. It is very difficult to hold close

well as large scale production. It is very easy to maintain close

5)

tolerances. Relatively poor utilization of 

tolerances. Relatively good utilization of 

6)

materials. This process requires highly

materials. This process does not requires

7)

skilled operator. This forging process have less

highly skilled operator. This forging process have better

8)

dimensional accuracy. This forging process have less

dimensional accuracy. This forging process have better

9)

reproducibility. This forging process have less

reproducibility. This forging process have high

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AUTOMOBILE MANUFACTURING PROCESSES The design of forging dies requires a knowledge of  strength, ductility, sensitivity to deformation rate and melting point of the workpiece material.

Fig. 1.6 Standard Terminology of Forging Die

The terminology for forging die is as shown in fig. 1.6. Some of these consideration are similar to those for casting. For most of the forging, the parting line li ne is usually at the largest l argest cross-

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forging shrinks both radialy and longitudinally. To overcome overcome this cause, internal draft angles are made mad e larger than external draft angles. Internal draft angles are about 7° to 10°, and external draft angles are about 3° to 5°. Selection of proper radii for corners and fillets is important to give smooth flow of metal in a die cavity as well as to improve die life. Small radii and fillets are not allowed due to stress concentration and fatigue cracking of the dies. Allowances are provided in forging die design because machining of forging of forging may be necessary to obtain final desired dimensional as well as surface finish. To produce a smooth and accurate cavity with parting plane more care is required. In a die, better and economical results are will be obtained if the following points are considered: I.

The die should part along a single flat plane, if at all possible. If 

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AUTOMOBILE MANUFACTURING PROCESSES X.

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Too Too thin thin sec secti tion on s sho hould uld be avoi avoide ded d for for easy easy flo flow w of met metal al..

1.13 Die materials materials and lubricants lubricants:: The die material and lubrication is the important aspects of forging.

I.

Die ma materials: In most of the forging operation large parts are forged

at elevated temperature. Therefore the general requirements for die materials are: a) Good strength strength and and toughness toughness at elevated elevated temperature temperatures. s.  b) Good harden ability and ability to harden uniformaly.

c) Resistance Resistance to mechanical mechanical and and thermal thermal shocks. shocks. d) It should should have have high high wear resistance. resistance.

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II.

Lubrication: Lubricants generally reduces friction and wear. They

also act as thermal conductor between hot workpiece w orkpiece and cool dies. It can slows the cooling rate of workpiece and improving metal flow or grain flow. It also act as a parting agent. Wide variety of lubricants can be used in forging:

a)

For hot forging: i.

Graphite.

ii .

Glass.

iii iii.

Molybd ybdenum di disul sulfide. de. In hot forging lubricants are usually applied

directly in to the dies.

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b) Presence Presence of cold shuts shuts or cracks at corners; corners; Reason Reason – improper improper forging and faulty die design. c) Incomplete Incomplete componen component; t; Reason Reason – less metal metal used, faulty faulty die design and inadequate metal flow. d) Mismatched Mismatched forging; forging; Reason – die halves not properly properly aligned. aligned. e) Burnt and overhe overheated ated metal; metal; Reason – improper improper heating. heating. f) Fiber flow flow lines lines or grain grain flow flow lines disconn disconnected; ected; Reason – very rapid plastic flow of metal. g) Scale pits; pits; Reason – formed formed by squeezing squeezing of scale into into metal during forging. h) Oversize Oversize components; components; Reason Reason – worn out dies, incorrect incorrect dies.

Also fig. 1.7 shows common examples of defects in forged parts

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Fig. 1.7 Examples Of Defects In Forged Parts

1.15 1. 15 Forg Forged ed par parts ts::

I. Gear blan lank: It can be made by upsetting the bar stock. The pattern of the grain flow lines in the bar stock is as shown in fig. 1.8 (a). When bar stock is placed in dies such that the flow lines are vertical. The grain pattern produced will be radial and gear blank will give greatest strength to the

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AUTOMOBILE MANUFACTURING PROCESSES teeth as shown in fig. 1.8 (b).

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strength . because gear blank have hav e expected stresses are perpendicular to the flow lines of bar stock.

II. II. Co Conn nnec ecti ting ng rod: rod: It can be made by forging the bar stock. The blank shape gradually changes, as shown in fig. 1.9 (a) of connecting rod.

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Performing processes, such as fullering and edging [fig. 1.9(b) and fig. 1.9(c)] are used to distribute the material into various regions of the blank. In fullering, fullering, material is distributed away from an area. In edging, edging, it is gathered into a localized area. The part is then formed into the rough shape of a connecting rod by a process called blocking using blocker dies. The final operation is the finishing of the forging in close die forging that give the forging its i ts final shape. The flash is removed

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AUTOMOBILE MANUFACTURING PROCESSES usually by a trimming operation (fig. 1.9)

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