STUDIES ON THE WEAR CONDITIONS AND THE SHEARED EDGES IN PUNCHING

This paper presented the worn conditions of the punch cutting edges in punching holes on a larger thickness AISI 52100 steel plate using pun ches of different convex shear angles. The characteristic behaviors of the sheared edges and slugs were also investigated. Experimental resu lts indicated that when using a punch of the convex double shear angle of 12.5 degrees, the wear on punches is mainly side wear. It is a res ult of the combinations of the adhesive wear, fatigue wear and abrasiv e 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 degrees. A relatively longer p unch life is obtained. However, the plastic deformation and eccentrici ty of the punched hole and burr of the slugs are relatively higher. Th e maximum hardness of the hardening layer for the punch of shear angle s of 12.5 and 20 degrees is about twice the initial hardness of the wo rkpiece, and the depth of its layer with increasing number of the punc hed 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 f ractured 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 es timated through the characteristic observations of slugs. (C) 1997 Els evier Science S.A.