In this process the desired shape is obtained by the application of a compressive force over the metal. In hot forging process the metal is heated above the recrystallization temperature. This hot metal is then compressed to the desired shape using hammer or press tool.
There are three types of forging process.
· Open die forging process
· Closed die forging process
· Roll forging process
OPEN DIE FORGING
In this type of forging process the work piece is heated to a very high temperature and it is placed on a flat surface and hit using a hammer to obtain the desired shape. This type of forging is very simple and flexible. It is very much useful in producing rough components like chisel, bolts, and rectangular, circular, hexagonal shapes. In this the forging hit is given either by hand or by power.
CLOSED DIE FORGING
1. DROP FORGING
The impression dies used in this process is called as closed dies. The upper die is fitted on the ram and the lower die is fitted on the anvil. Both the dies have impression. Two rollers are held on the board supporting the ram. These rollers rotate in opposite direction to each other. This makes it to drive the board upwards and lifts the ram. By releasing the rollers the ram falls down producing the working stroke. For producing simple parts a single stroke is enough. large components are produced by number of steps.
It is generally used for making spanner, automobile parts, and machine parts.
2. PRESS FORGING
Press forging is done with the help of a press. The press may either be operated mechanically or hydraulically. It is a slow squeezing process rather than delivering heavy blows. The lower die is fitted with the anvil and the upper die is fitted with the ram. The ram is slowly a moved down and it slowly presses the metal. The finished component may be removed from the die with the help of ejectors in the die set. The speed of press forging varies from 34 to 40 strokes per minute.
Press forging is used for making components such as connecting rods, machining components, spanner, etc.
3. UPSET FORGING
This process is generally used to make head of bolts, rivets or pins. The shape of the head may be square, hexagonal or hemispherical. The machine holds a die set which consists of a fixed die and movable punch. The heated metal bar is held in the die and the force is given to the punch. So the desired shape is obtained with the help of die cavity.
The roll forging machine consists of two horizontal rolls. The heated metal bar is passed between the two rolls. Roll forging is performed in an impression-die.
A bar of heated rod is passed between the rolls. As the rolls rotate the heated metal is squeezed between them. This method is used for reducing the cross sectional area and for producing taper ends.