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#142 Design of Hole Punching Dies (2) Design of Hole Punching Punches

Category : Shear Forming
January25, 2013
Fig. 1 shows the different parts and their name in a hole punching punch.
Since very often the punch is made from a single material, it may be not so common to think of the different parts separately.
However, when designing a punch, knowing what are the functions required will be far different from just designing somehow.
The functional part is the part that constitutes the life of the punch. The desired forming is done by this part. This part has the same shape as the shape to be formed. The shank part is for holding a thin punch. It is embedded in the punch plate.
The adjustment part is the part that connects the functional part and the shank part.
The stopper is the part for ensuring that the punch that has been embedded in the punch plate does not come off.

Fig. 2 shows the concept of the design of a punch.


The figure (a) is the shape when the cross-section of the punch functional part is large, and when it is considered sufficient in terms of strength even if the shank part and the functional part are made of the same size. This is called a straight punch. This shape is ideal and is easy to prepare.
The figure (b) is the shape called a stepped punch in which the cross-section of the functional part is small, and when the limiting length of the punch is small due to strength considerations, a strong shank part is provided, and the shape is adjusted in the adjustment part, thereby acquiring the required length of the punch.
The figure (c) is the shape in which the functional part has become further smaller and weaker. The difference between this cross-section and the shank part cross-section being too large causes problems in the preparation and strength of the punch. Because of this, the countermeasure is taken of increasing the number of steps.

Fig. 3 shows the different types of punch stoppers.


The straight punch of (a) is embedded in the punch plate and is fixed by caulking or using an adhesive.
The punch in (b) has a small flange which acts as the stopper. This type is used very frequently in the case of round punches, etc. It may be difficult to prepare the flange in the case of square or odd-shaped punches.
The punch in (c) is one in which the punch is prevented from getting detached using a bolt. This type is used frequently in the case of straight punches that are prepared using a wire cut discharge machine.
The punches in (d) and (e) have the key stopper structure. These are also selected depending on the shape, size, and material of the punch. At the time of selecting, for the same die, as far as possible the method used for preventing the punch from slipping out is unified thereby making it easy to assemble and disassemble the dies.

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