CAE-based process design for improving formability in hot stamping with partial cooling

A CAE-based process design method was developed to improve formability in hot stamping by controlling the temperature distribution during the forming step. Specifically, areas where deformation is not desired should be cooled to make them harder, and areas where deformation is desired should be kept at higher temperature. In this study, a tailored initial temperature distribution was calculated through three-step analysis of the deformation behavior by a thermo-mechanical forming simulation. First, the deformation severity was evaluated from the damage value for each finite element by using a forming limit diagram (FLD) at elevated temperature. The cautionary damage value was then defined to determine whether the element should be cooled. Finally, the tailored initial temperature was calculated based on the temperature-dependent flow stress. This procedure was applied to a high-rigidity pillar model that could not be formed by the conventional hot stamping process without cracking. The improved formability was confirmed experimentally. Thus, controlling the temperature distribution increases the diversity of shapes achievable by hot stamping.