Inverse evaluation of equivalent contact heat transfer coefficient in hot stamping of boron steel

Abstract

It is of significance to evaluate the equivalent contact heat transfer coefficient (ECHTC) at the sheet-die interface in hot stamping of boron steel (HSBS) for controlling the local cooling rate of the sheet and hence obtaining components with tailored microstructure and properties. Moreover, accurate evaluation of the ECHTC can provide a reliable thermal boundary condition for numerical simulation of the HSBS process. In the study, a simple and effective physical simulation setup for die quenching of boron steel (DQBS) was developed, where the temperatures at measurement points are related only to the ECHTC so as to improve the evaluation accuracy. A FE-based optimization model for inverse evaluating the ECHTC was established. The ECHTCs at the B1500HS sheet-H13 die steel interface were identified under various contact pressures, and it was found that the ECHTC increases exponentially with the pressure increasing. Both the physical simulation of DQBS and the HSBS experiment were performed to verify the ECHTC evaluated, and the maximum relative errors of 9.6 and 19.7 % were observed, respectively, between the predicted and measured temperature histories.