The important affecting variables are given below: Radius on punch: A general rule to prevent excessive thinning is to design the punch with a radius of from 4 to 10 times the metal thickness. Otherwise a sharp radius will require higher forces when the metal is folded around the punch nose & may result in excessive thinning on tearing at the bottom of the cup. Draw radius on die: Theoretically the radius on the draw die should be as large as possible to permit fall freedom of metal flow as it passes over the radius. If the draw radius is too large, the metal will be released by the blank holder too soon & wrinkling will result. To sharp a radius will hinder the normal flow of metal & cause uneven thinning. Friction: The force of static friction between the work piece blank & draw die surface must be overcome in a drawing operation. Since the blank holder pressure causes higher frictional forces, it should be only high enough to prevent wr
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