10.3.6 Combination Dies

A combination die is a simple-station complex die in which both cutting and non-cutting operations are accomplished at one press stroke. An example of such a die is shown in Fig. 10.13. The die in Fig. 10.13 consists of the punch holder (1), the die shoe (2), with guide system/guide post (10), and the guide post bushing (11). The punch holder carries the bending punch (3), which functions as a punch plate for the punch (4). The punch (4), bears the pressure pad (6), and the spring (15) is also attached to the punch holder as well as the strip cutting punch (13).

Fig.10.13 Combination die.

The die shoe carries a central die (7) for bending and punching operations; a side die (8) for bending one end of the workpiece; and a side die (9) for cutting the work strip (12), and bending the other end of the workpiece. The die shoe also supports the workpiece ejector (5) and spring (14).

In the first operating phase of the combination die in Fig. 10.13, the cutting punch (13) cuts the work strip, and the punch (4) then punches a hole. As the punch continues to descend, the bending punch (3), the central die (7), and the side dies (8 and 9), bend the workpiece into its final shape.

10.3.7 Progressive Dies

Individual operations in a progressive die are often relatively simple, but when they are combined into several stations it is often difficult to devise the most practical and economical strip design for optimum operation of the die.

In designing a die to produce good pieces, the sequence of operations for a strip and the details of each operation must be carefully developed. A tentative sequence of operations should be established and the following items should be considered as the final sequence of operations is developed:

     1. Arrange for piloting holes and piloting notches to be punched in the first station. Other holes may be punched that will not be affected by subsequent non-cutting operations.

     2. Develop the blank for drawing or forming operations for free movement of strip.

     3. Distribute punching areas over several stations if they are close to each other or close to the edge of the die opening.

     4. Analyze the shapes of blanked areas in the strip for division into simple shapes, so that commercially available punches may be used for simple contours. .

     5. Use idle stations to strengthen die blocks and stripper plates, and to facilitate strip movement.

     6. Determine if strip grain direction will adversely affect or facilitate any operation.

     7. Plan the bending or drawing operations in either an upward or a downward direction, whichever will assure the best die design and strip movement.

     8. The shape of the finished piece may dictate that the cutoff operation should precede the last noncutting operation.

     9. Design adequate carrier strips or tabs.

     10. Check strip layout for minimum scrap. – Use a multiple layout if feasible.

     11. Locate cutting and forming areas to provide uniform loading of the press slide.

     12. Design the strip so that the scrap and part can be ejected without interference.

Fig. 10.14 shows a progressive die with four workstations. In this die, after four press strokes down, every following press stroke down makes one final piece. The die block is machined from four pieces and fastened to the die shoe. This arrangement permits the replacement of broken or worn die blocks.

The stock is fed from the right. The first strip is stopped by a finger stop (not shown). The first down stroke of the press (Fig. 10.14-I ) produces a bigger hole and two notches. These notches form the left end of the first piece.

The press ram retracts, and the stock moves to the next station. The second station is idle (Fig. 10.14-II ). The right end of the second piece and a second bigger hole have now been punched.

The press ram retracts a second time, and the scrap moves to the third station (Fig. 10.14-III ). The third ram stroke punches the four small holes as shown in Fig. 10.14-III . The fourth ram stroke (Fig. 10.14-IV ) bends the sides, and cuts off and forms the end radii of the finished piece. Thereafter every press down stroke produces a finished piece, as shown in Fig. 10.14-V.

Fig. 10.14 Progressive punching, notching, bending and cutting-off die.

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