Studies on the wear conditions and the sheared edges in punching

Abstract

This paper presented the worn conditions of the punch cutting edges in punching holes on a larger thickness AISI 52100 steel plate using punches of different convex shear angles. The characteristic behaviors of the sheared edges and slugs were also investigated. Experimental results indicated that when using a punch of the convex double shear angle of 12.5°, the wear on punches is mainly side wear. It is a result of the combinations of the adhesive wear, fatigue wear and abrasive wear. The punch life is characteristically lower. The punch displays dominantly the face wear with a larger round cutting edge for a punch of the convex double shear angle of 20°. A relatively longer punch life is obtained. However, the plastic deformation and eccentricity of the punched hole and burr of the slugs are relatively higher. The maximum hardness of the hardening layer for the punch of shear angles of 12.5 and 20° is about twice the initial hardness of the workpiece, and the depth of its layer with increasing number of the punched holes is about 0.17–0.35 times the thickness of the workpiece. The punched slugs during shearing have two smooth sheared and two rough fractured appearances. With increasing number of the punched holes, the primary rough-fractured portion of the slug becomes larger while the secondary smooth-sheared portion of the slug would become shorter or, in an extreme case, vanish. Hence, the punch life can be indirectly estimated through the characteristic observations of slugs.