Press Forging is done in presses rather than with hammers. The action is relatively slow squeezing instead of delivering heavy blows and penetrates deeply because it gives the metal time to flow. Dies may have less draft, and the forgings come nearer to the desired sizes. Pressed forgings are shaped at each impression with a single smooth stroke and they stick to the die impression more rigidly. Unless some provision is, therefore, made, the escape of air and excess die lubricant may be difficult. Thus press forging dies require a mechanical means for ejecting the forgings are venting for the escape of the air and lubricant. Press forgings are generally more accurate dimensionally than drop forgings.
Press for closed - die forgings may be two classes :
(1) Hydraulic Press
(2) Mechanical Press
HYDRAULIC PRESS :
A Hydraulic press for closed-die forging has the same principle as that of a press for smith or flat-die forging except the construction of the dies. In smith forging the press dies have the flat surface , while in a closed - die forging the press dies have shaped impressions cut on dies. Moreover, They form an integral part of the frame to maintain accurate alignment of the dies.
MECHANICAL PRESS :
Mechanical Forging presses of the cranks type have found wide application in forging practice.
The operative units of the press are powered from motor mounted on the press frame. By means of the V-belt drive , power is transmitted from the pulley to the flywheel mounted on the auxiliary shaft. The fly wheel is equipped with a friction safety device to prevent the overloading of the shaft. The flywheel stopped by the auxiliary brake which is automatically engaged when the motor is switched off. On the other end of the shaft gear is mounted. It meshes with the gear which drives crankshaft. The latter, through the pitman, reciprocates in slide. The crank mechanism is engaged by a pneumatic clutch which is controlled by a pedal. A band brake stops the crankshaft and slide when the pneumatic clutch is disengaged. The top half of the die is secured to the slide and the bottom half to the bed which is provided with a double-edge device for adjusting the die space.
They are used for the production of rivets , screws, and nuts where a high operating speed is desired. In a capacity, they range from 50,000 to 8,000,000 kg and speeds from 35 to 90 strokes per minute.
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