An exploration of the piercing of round holes in metal sheets in the presence of frictionally induced radial compressive stress

A new concept of using an annular urethane disc to apply radial compressive stress in blanking or piercing is presented. As the punch advances prior to piercing a hole in the sheet metal, it compresses a urethane disc which is enclosed within a die ring. Friction between the urethane and the sheet metal being pierced induces radial compressive stress in the sheet metal. The tooling used for the process and the results of experiments conducted with mild steel and brass are presented. A theoretical model is used to estimate the induced compressive stress and the force needed for the piercing operation. The results show that some improvement in the quality of the hole is produced, as compared with conventional piercing.