Effect of Forming Conditions on Draw Bending Formability in Hot Stamping Process

Abstract

Formability in draw bending, i.e., deep drawing without shrink deformation at the flange part, in the hot stamping process was investigated and discussed in terms of the effect of the strength of the side wall near the punch shoulder on deep drawability. Furthermore, hot forging lubricants used in a wet condition in the hot stamping process were examined because the die temperature is below 100 °C for die quenching. The results showed that the forming limit of draw bending increased with a lower forming temperature, a lower forming speed, and a lower blank holder force. Under these forming conditions, the temperature of the side wall near punch shoulder, which is a critical part for fracture, decreased indicating an increase in the strength of the side wall. Accordingly, the temperature of the side wall near the punch shoulder is a dominant factor in the control of the draw bending formability in the hot stamping process. In addition, emulsion-type hot forging lubricant exhibited excellent lubricating ability and improved the forming limit of draw bending in the hot stamping process.