Abstract:The hot stamping process of ultra high strength (UHS) sheet metal is an innovative way which is used in automobile increasingly for the manufacturing of components with a ultra high ultimate tensile strength (UTS). Due to the high nonlinear elastoplastic and thermo-mechanical responses of material during the hot forming process, practically it is difficult to investigate such hot forming presses only via experiments. Therefore, it is necessary to develop a 3D elastoplastic coupled thermo-mechanical finite element model (FEM) of UHS sheet metal hot forming. Meanwhile, the mechanical properties of UHS steel at elevated temperatures were characterized and the corresponding material constitutive, which is strain, strain rate and temperature dependent, is developed on the basis of unaxial tensile test at elevated temperatures. In addition, hot stamping experiments were conducted and combined with the simulation to investigate the effect of tool temperature and punch speed on the hot stamping of UHS sheet metal for the square-box-shaped (SBS) component. Considering the UTS of hot formed component, the optimum tool temperature and the punch speed are achieved.

Key words: hot stamping; ultra high strength steel; FEM; thermo-mechanical coupling; tool temperature; punch speed