Countersunk hole producing on sheet metal - involves star-shaped punch followed by impact-deforming of prongs with tapered tool

摘要

To produce a countersunk hole near the edge of a sheet metal part without risking the possibility of crack developing on the edge area, first a star-cross section punch is used, which produces a corresponding star-shaped hole (3'). The final clear opening in the workpiece has to be such as to allow passage of a circular part with an OD (25). After the punching operation the prongs (21) of the star-shaped hole are positioned along a circle with a dia. larger than the ID (25). An impact tool with a tapered underside is used, which deforms the prongs (21) in such a way that the sheet material thickness is driven in inward direction, until the tips (27) of the prongs reach the line (25).