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#143 Design of Hole Punching Dies (3) Design of Hole Punching Dies

Category : Shear Forming
February 1, 2013

Fig. 1(a) shows the basic shape of a hole punching die.


Here, p is the die hole. It is made larger than the punch by the amount of the clearance between them. (See Lesson 5 which discusses the clearance in blanking operations.)
B is the part which is called the die cutting edge length. This is determined considering the re-grinding margin.
If we assume that the thickness of the work material is 1cm, the state in which 3 to 4 scraps have got accumulated is good. It is not good if this die cutting edge becomes too long, because it can lead to jamming of the scrap.
Further, d is the scrap ejecting part. It is said that scrap jamming can occur easily when the dimension d is about twice the dimension p.
The countermeasures for this are the shapes (b) and (c). A taper is provided thereby making it difficult for scrap to stick. The shape (c) is one in which the shape is made larger in small steps when it is difficult to machine the taper. This can be said to be a substitute for tapering.

Fig. 2 is a button die. This is used when one does not want to carry out maintenance or hardening of the entire plate.This is also good at meeting changes.
Although this is easy to use in the case of a round hole since there is no orientation, since an odd shaped hole has a proper orientation, it becomes necessary to have stopper for preventing the rotation of the die button.
Sometimes, a square button die is also made considering the difficulties of a rotation stopper and the difficulties of adjustment.

Fig. 3 shows the precautions regarding the relationship with the hole pitch. When there are many holes formed, the error in the pitches between the holes becomes a problem. The problem becomes particularly serious when the work material is thin and the clearance is small. The design of the die is changed considering the machining error of metal working machines, and the deformation due to heat treatment. The decision has to be made of whether to make the die have an integrated structure, or to use a button die, or to use the insert type die and carry out adjustment machining. Fig.3

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