In simple die, the dies are designed to perform only one operation. But, by proper design of the dies, it is possible to carry out several operations in one stroke of the ram. The dies of the first type are known as single operation dies and second type are known as multi-operation dies.
The single operation dies could be further classified according to their functions, i.e. cutting dies and forming dies. Cutting dies are used for preparing blanks for further shaping operations like bending, forming, drawing etc.
The cutting dies could be further defined by the specific nature of operation like blanking piercing, performing, notching, trimming, shaving dies etc. The forming dies change the appearance of the blank without removing any stock, e.g., bending, curling and drawing dies.
The multi-operation dies can be further classified as:
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(i) Compound dies,
(ii) Combination dies and
(iii) Progressive dies.
In compound dies, two or more cutting operations such as blanking and piercing can be performed simultaneously in a single stroke. A simple compound die explaining its function is shown in Fig. 29.4. In this die first upper punch connected to the ram comes in contact with metal and pierces the hold.
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As this punch goes on moving down, the springs keep on compressing and after certain limit the lower punch moves upwards and blanks the outer portion. In this die, as the whole operation is performed at single station, it produces accurate result, but die design is complicated.
In combination dies, the cutting and forming operations are combined and carried out in a single operation. First blank is prepared in the die and then it is held by pressure pads and drawn. All this is achieved entirely within the die assembly by use of cam actuated punch and die members or by designing the die for use on a double action press which has two independent rams or slides on moving inside another.
In progressive dies, the work piece moves from one station to another, with separate operations, being performed at each station. All stations work simultaneously and the work piece is retained in stock till it reaches the final station which cuts off the finished piece.
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After each stroke, the stock is moved ahead by one station and in this way complete operation is carried out in single stroke, of course, at various stations. A simple progressive die for piercing and blanking is shown in Fig. 29.5, but it can be designed for complicated operations of bending, forming etc. also. In these dies, indexing at every station is very important and, therefore, accuracy is not much. However, it is simple in design.
