A typical sketch of die assembly is shown in Fig. 29.3, and all the components used in it are described below:
Component # 1. Punch:
The punch is the member which forces the sheet strip down and may pierce it or draw it. It takes assistance of die to do this. It should be made of a hard, wear resistant metal and finally ground to a predetermined size providing just optimum clearance between die and punch. It should be made as small as possible consistent with required strength and rigidity and is secured by punch holder.
ADVERTISEMENTS:
The punch and die are generally made of cast steel hardened and tempered or of one of the alloy steels recommended for the purpose. The advantages of alloy steel are that the risk of distortion or cracking in hardening is minimised, and the working edges of the tools are less likely to chip or crumble.
Component # 2. Punch Retainer of Punch Pad:
Its purpose is to hold the punch in its proper relative position. It may be a solid body around the body of the punch and is itself bolted to the punch holder. Generally between the top of the punch and the punch holder a pressure plate is also introduced to provide some cushioning effect.
Component # 3. Punch Holder:
On its top, it ends in a shank which is anchored to the press ram and it exactly fits into the ram opening for proper positioning and aligning of the punch.
Component # 4. Pressure Plate:
It is introduced between the back of the punch and punch holder in order to distribute the pressure over a wide area and thus reduces the intensity of pressure on the punch holder and ultimately avoids any possibility of its getting crushed under heavy loads.
Component # 5. Die:
ADVERTISEMENTS:
It is also made of a hard, wear resistant metal and is finish ground to predetermined size and tolerance. In size, it is made as small as possible consistent with the required strength. It is a good fit and is nicely bedded in the slot which accommodates it, in order to avoid the heavy stresses and also to eliminate slackness developing with the shock conditions of service.
Component # 6. Die Retainer:
It holds the die block at proper position with respect to punch and is itself mounted in the die shoe or holder which in turn is bolted or clamped to the bolster plate.
Component # 7. Stripper:
These are of many designs. When the punch has completed its downward movement and starts returning, it has the tendency to carry the material with it. The stripper plate prevents this upward movement of the scrap strip and frees the punch of this for next stroke.
Suitable guide plates are also provided for locating the strip as well as a stop to control the amount by which the strip must be pushed forward for each blank. The stop controls this by contacting the farther side of the hole left by the previous blank.
Component # 8. Guide Posts and Bearings:
ADVERTISEMENTS:
The punch and die members once properly located and aligned, are held in alignment by means of guide posts and bushings which resists movement or deflection of die members as operating pressures increase.
Presses used for long runs are provided with automatic feed for the blanking strip. This consists of power-fed rolls driven from the crankshaft or slide-feed mechanism which advances the strip the exact amount each time the punches are clear. The strip is supplied in coils and the waste coiled up again after passing through the press thus making the operations automatic and eliminating any need of stop pins.