Forging is one of the manufacturing operations it can be done by submission of pressure and with or without the submission of heat. During the forging process the metal should be heated and apply compressive forces within the limit to obtained final shape. Forging are generally hot forging process and cold forging process. Based on the temperature and die arrangement forging are classified.
Based on the temperature forging is divided in to three types they are
- Hot forging
- Cold forging
- Warm forging
Hot forging is the common method used by every one for the process. Above the recrystallization temperature hot forging is carried out.
The temperature at which new grains are found in the metal is known as recrystallization. To avoid strain hardening high amount of heat is required for deformation. This is known as hot forging process related to temperature basis.
|S.No||Metal||Maximum temperature||Minimum temperature|
- Forces require for the easy flow of metal, high strain amounts, recrystallization is less.
- Scale formation is obtained
- Ductility of the metal is increases
- Elimination of chemical oddness
- Production of different parts
- Normal grain structure is observed
- At high temperatures lubrication is difficult
- Due to cooling process deformation is occurred in the material
- Oxidation occurs on the work
- During the process poor surface finish is obtained
Below the recrystallization temperature cold forging process is takes place on the metals. Mainly the cold forging is suitable for the soft metal like aluminium etc. Compare with the hot forging cold forging is inexpensive. To harden the material heat treatment is required and strengthen of the material is also increases. Carbon alloy steels are used for the cold forging process.
- Production rate is high
- Less friction is developed between the die and the work piece material
- Lubrication is easy
- No oxidation on the work
- High mechanical properties
- Dimensional control is high
- High accuracy is obtained
- Design and manufacture of tool is difficult
- Residual stress are occurred
- Less ductile material
- Improve reproducibility
- Increase dimensional control
- Maintain clean metal surface
Warm forging :
The temperature varies from above room temperature to below recrystallization temperature. Compare with the cold forging process warm forging gives better results. Warm forging is used to produce components with close tolerances.
- Tooling loads and press loads are reduced
- Increase ductility of the steel material
- Lower forming process
- No annealing is required
- Deformation ratio is high
- High tool cost
- Based on the arrangement die forging is divided in to
- Open die forging
- Impression dies forging
Bases on the die arrangement forging is divided in to three types they are
- Open die forging
- Impressive die forging
- Closed die forging
Open die forging
Open die forging is used to compress the metal which was placed in between the dies. During the process the height of the work piece material is reduced or compressed. This process is also known as flat die forging are upsetting. Under friction less condition the work piece material must be deformed.
Forging Forces required is
- = flow stress
- μ = coefficient of friction
- r = radius
- h = height of the work piece
Impressive die forging
In this process the dies are manufactured according to the requirement of shapes. Work piece is places between the shaped dies when force is applied on the work piece in upward directions which results in the impressed die.
Forging Forces required is
- k= multiplying factor
- = material flow stress
Closed die forging
Closed die forging is also one of the types of the forging process. The dies are interchanging each other and cover the whole work piece material.
The heated work piece material is placed on the bottom die the shape of the top die is obtained on the work piece material. High accurate shapes are formed.
There is no waste age of the material during the process.
Forging operations are drawing, swaging, upsetting, fullering, forged welding, flatting and setting down, edging, bending, cutting and punching.
This operation is performed to elongate of the metal and decrease in the cross sectional area when the forces are acting towards the perpendicular direction of the longitudinal axis.
Swaging is a cold working process of forging. This operation is used to alternate the dimensions of the work piece by using the dies force is applied on the material.
To increase the cross sectional area of the standard length upsetting operation is applied. To get the required result operation is performed along parallel direction of the longitudinal axis. This is known as upsetting operation. Mainly we can see this operation in but and bolts.
This operation is used to increase the length and decrease the cross sectional area of the material. For this process the bottom fuller is place with an angle in the heated stock and the upper fuller is also placed in the stock. With the help of sledge hammer force is applied on the upper fuller to obtain required shape.
In this operation to increase the length at that case two metal pieces are joined. Applying the hammer or pressure when it reaches the forging temperature the process is done.
Flatting and setting down
During the process fuller is used on the surface of the work piece. At that case it leaves some marks on the work piece material. To avoid or clean those marks hammers and flatters used on the work piece. Smooth surface is obtained on the work piece by using this operation process.
During the process work piece material is placed between the two edges and striking the edges to obtain a required shape. This is known as the edging operation.
To bend the roads and sheets this type of forging operation is performed.
With the help of hammers and chisel the rods and plates are cutting in to two pieces when the rod is in hot condition the cutting operation is performed.
By using the punching operation holes are produced with the help of the hollow cylinder. When we are applying the pressure on the cylindrical die holes then it moves downwards to make a hole on the plate.
During the design of the forging process some defects are occurred .In hot forging process it causes hot shortness, shear bands, grain boundary cavitation. In the cold forging process it causes surface cracks, shear band and center burst.
- Cold shut
- Die shift
- Unfilled section
- Scale pits
- Improper grain flow
- Residual Stresses
- Surface cracking
- Incomplete forging
- Cracking at the flash
Due to in-complete welding process the two surfaces of the work pieces material are touching each other. The main cause for the cold shut is excessive chilling, sharp corners and high friction. To avoid the cold shut radius of the fillet is increase on the die.
Misalignment of the dies halves results in the die shift. To improve the shapes make the die in to two halves. To avoid the die shift you need to align the die halves properly and provide half notches on the upper and lower side of the die. So during the alignment if the notch is matches on the both the sides then it give the proper shapes.
The moving metal does not fill the die chamber completely. So it causes the improper defect in the design of the forging die, poor heating and fewer raw materials. To avoid this defect proper raw material, proper heating and proper design of the die is required.
Irregular cleaning on the exterior surface of forging leads to the scale pits. The scales and oxide are get rooted in to the finished surface.to avoid the scale pits proper cleaning of the surface is required.
Improper grain flow
Due to improper proper design of the die the flowing material does not flow downwards. To avoid the improper grain flow proper design of die is arranged.
Internal disagreements are basically found in the arrangement. They are mainly cause because of improper cooling. To avoid the flakes defect proper cooling procedures are followed.
Improper cooling and non-uniform deformation of the forging are results in residual stresses. To avoid this defect during a period of time slow cooling in a furnace or under ash the forging is done.
Due to low temperatures and excessive work is result in the surface cracking. To avoid the surface cracking suitable temperatures are used for the forging process.
Mainly the forging is takes place at the surfaces so never broke the interior of the forging. So always try to use light hammer blowers for the process.
Cracking at the flash
To avoid the cracking at the flash try to increase the thickness of the flash.
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