Hole-flange forming of high-strength steel sheet using one-step hot stamping-forging method

Abstract

A process of one-step hot stamping-forging for increasing the tensile strength of the hole-flanging of the high-strength steel sheets with flange thickening was developed. In this proposed method, the high-strength steel sheet is directly formed within the designed die, which is simultaneously accompanied with a resistance heating, a hole punching, and the flanging and forging processes. The electrode material is SKD61. This material is not only used as the forming of the high-strength steel sheet but also directly served as the heating of the high-strength steel sheet within the die. The experimental results indicated that the high-strength steel sheet could be heated to 850 °C in 30 s by the SKD61 die. It demonstrates the successful completion of heating, hole punching, flanging and forging in a one-step process. Furthermore, it is found that the tensile strength of M18 tapped hole with forged part is increased by about 7.4% than that without forged part, and the breaking toughness is increased by about 33%.