Punching of small hole of die-quenched steel sheets using local resistance heating

A punching process of a small hole in a die-quenched steel sheet having high strength using local resistance heating of a shearing zone was developed to decrease the punching load. Uniform temperature in the circular shearing zone of the hole was obtained by optimising heating conditions for a pair of rectangular electrodes. The punch load and the burnished surface area for the heating at 500 °C were about 1/3 smaller and 2 times larger than those for the cold punching, respectively, and the occurrence of delayed fracture around the punched hole was prevented by the heating above 500 °C.