52 巻 (2011) 609 号 p. 1114-1118
A punching process of a small hole using local resistance heating of a shearing region for a die-quenched steel sheet was developed. The shearing region in the sheet was locally heated by a pair of electrodes to decrease the flow stress in the punching. The effects of the distance between the electrodes, the length of the electrode and the current on the temperature distribution generated by the resistance heating were examined. A uniform distribution of temperature in the hoop direction of the hole was obtained by optimizing the heating conditions. 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. In addition, the occurrence of delayed fracture around the punched hole was prevented by decreases in tensile residual stress and hardness for the heating above 500 °C.