Volumetrically deformed polymeric support for punches

Claim 1

In a punch press for punching a hole in a thick blank of metal, the combination comprising a ram having means for powered reciprocation, a bed mounting a die plate below the ram, a punch on the ram having an extended nib of constant diameter for entering a hole in the die plate, a horizontal stripper plate spaced below the ram and movable therewith, a punch bushing fixed in the stripper plate and having a central clearance opening the guiding the nib of the punch therethrough, stripper springs interposed between the ram and the stripper plate for urging the stripper plate downwardly away from the ram, means defining a normal extended position for the stripper plate with respect to the ram in which the face of the stripper plate extends downwardly a short distance beyond the tip of the punch, the punch bushing having a coaxial annular recess in its underside, an annular insert of volumetrically incompressible resilient polymeric material completely filling the recess and presenting an inwardly-directed collar surface substantially aligned with the clearance opening of the associated bushing, the insert being dimensioned to normally project downwardly a short distance beyond the recess to provide an exposed striking surface for engaging a workpiece interposed between the stripper plate and the die plate as the ram descends, the stripper springs being sufficiently strong so that when the striking surface of the insert engages the workpiece accompanied by compression of th stripper springs, the reaction force is sufficient to volumetrically deform the insert causing the inwardly-directed collar surface thereof to crowd inwardly against the nib of the punch to provide lateral support for the punch as the punch penetrates the workpiece.