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#147 Design of Hole Punching Dies (7) Design of the Spring of a Movable Stripper

Category : Shear Forming
March 1, 2013
A movable stripper is held by a stripper bolt and a spring. Its movements are restrained by the stripper bolt, and a pressing force is generated by the spring.

The figure shows a typical method of using a spring and a stripper bolt.

Fig. 1(a) is a structure in which the spring is set between the stripper plate and the backing plate. This is used frequently when a moderate amount of deflection is to be obtained.
The spring is compressed by tightening the stripper bolt. There is a disadvantage that, to do this, unless the stripper bolts are tightened by small amounts alternatingly, the tightening of the stripper bolt becomes hard.
It is also difficult to mate the die and the punch because the spring is present in between.
The strength of the spring can be adjusted by placing a washer, etc.

This is used frequently in blanking, etc., wherein it is sufficient to have a small amount of stripper movement.
Since the spring is assembled after tightening the stripper bolt, it is not necessary to tighten the stripper bolts by small amounts alternatingly as described above (it is necessary to tighten them alternatingly, though).
The strength of the spring is adjusted by the amount of tightening the press screw (screw plug).

Fig. 1(c) is a method used when a long stroke is required. Since the spring and the stripper bolts are placed separately, the number of steps in the manufacturing of the die becomes large.
Using this method is very rare in the dies for blanking including hole blanking.
The adjustment of the strength of the spring is done by tightening the screw plug.

See Lesson No.58 "Coil springs (1)" and Lesson No.59 "Coil springs (2)" for information about the design of the spring. 		Fig.1

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