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Module-II of PDPT

Lecture Notes of Chinmay Das


Rule No.3:

For upsetting the stock which is longer than three times the diameter and free length of stock

outside the die is up to 2.5 times the diameter, the following conditions should be satisfied. The metal is to

be confined into a conical cavity made in the punch with the mouth diameter not exceeding 1.5 times the

stock diameter and the bottom size being 1.25 times the stock diameter. Also, it is necessary that the

heading tool recess be not less than two thirds the length of the working stock or not less than working

stock minus 2.5 times the stock diameter.

Figure 2.3.3: Application of rule three for proper upsetting

The above are the absolute limits for proper upsetting. But in practice it may be possible to cross these

absolute limits.

Location of Cavities

The upset cavities may entirely be kept in the gripper dies or in the heading tool or part in the

gripper and part in the heading tool. The choice of

location mainly depends on the severity of the

upsetting and the convenient location of flash for

trimming. Simple forgings requiring smaller upsetting

may contain the complete die cavity in the heading

tool. Also complex shapes requiring severe upsetting

are obtained with the die cavity completely in the

gripper die.

For very simple shapes, one pass may be enough to

obtain the final shape, but majority of forgings require

three or more passes. If trimming of flash is included,

then an additional pass is required. All these passes are

arranged on the die block in an order and the stock is

moved from one pass to the other sequentially. While

designing the heading tool or the punch to slide into the

gripper die, it is necessary to provide clearance

between the two such that no seizure takes place due to

uneven expansion or due to scales of the punch and die.

Figure 2.3.4: Location of cavities

This clearance should be of the order of 0.125 to 0.200 mm. The length of gripping portion of the gripper

die should be maintained between 3 and 4 times the stock diameter.

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