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#152 Design of Compound Punching Dies (1) Features of Compound Punching

Category : Die Design
April 5, 2013

Regarding compound punching, the most basic structure of a compound punching die has been shown in Lesson No. 31. First see this Lesson No. 31. Then, get a mental picture of the die form and structure.

Compound punching means simultaneously carrying out both outer shape punching and hole punching.
This has several merits. Products punched using a press are prepared as copies of the die. If the die is prepared accurately, that accuracy is obtained as a copy in the product. In compound punching, not only the relationship between the outer shape and the positional accuracies of the holes, but also the shape accuracies of the holes and outer shape can be obtained as die dimensions.

As is shown in Fig. 1, the points of concern in compound punching are the proximity between a hole and the outer border and the proximity between holes. The strength of the die is a concern. One would want to know the limits to these dimensions.
If we assume a material such as SPC with a thickness of about 1mm, if the hole is round it can come close by up to 50% of the material thickness. Although this would be a problem in ordinary situations, since the forming is done simultaneously from both sides in compound punching, it appears that the balance between the forces is prevents breakage.

Compound punching is a method of forming in which the outer shape and hole punching are combined together. It is necessary to pay attention to the precautions in both outer shape punching and hole punching.
For example, in the case of points like a corner without rounding (R) in Fig. 1, burrs are easily generated if the punching is done as it is. It is necessary to carry out an operation of providing rounding.

The blank layout is treated in the same manner as blanking as is shown in Fig. 2. However, it is safer to take the bridge width wider than in blanking.


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