Local heating-aided hot blanking of quenched ultra-high-strength steel BR1500HS

Abstract

Hot stamping and successive quenching can significantly improve the strength of the hot-stamped part to above 1.5 GPa and has been widely used in automobile manufacturing. However, ultra-high strength brings high difficulty in cold blanking of such hot-stamped part: low tool life and low surface quality of the sheared edge. Local heating-aided hot blanking of quenched ultra-high-strength steel (UHSS) is proposed in order to reduce the blanking loading and thus improve the tool life. In this method, conduction heating technology is employed to locally heat the shear zone of the blank prior to blanking. The surface quality of the sheared edge is investigated under different process parameters by experiments and simulations. Cooling methods used in obtaining the quenched blank and heating temperature (HT) play an important role in conditioning the surface quality of the sheared edge. Microstructure of the shear zone for different cooling methods and heating temperatures as well as its effect on the surface quality of the sheared edge and the mechanical properties of material in the vicinity of sheared edge are studied by experiments and simulations. A finite element (FE)-coupled thermo-mechanical model is developed to model hot blanking process. Good agreement between simulation and experimental results are achieved. Relationships among blanking force, heating temperature, and tool clearance (TC) are determined. Both experiment and simulation results demonstrate that for heating temperature at 800 °C, hot blanking loading decreases sharply and relative burnish height is significantly increased compared with the case of heating temperature at 400 °C.