Simulation of hot stamping processes

Abstract

Hot stamping is a thermo-mechanical technique that enables to give to a metallic blank the desired geometry and properties in a single step, where deformation at high temperature, phase transformations and heat transfer are occurring simultaneously and affect mutually. They are several variables controlling the quality of the final component and their relationships are, in some cases, complex. Therefore, a methodology able to take into account all the phenomena involved is necessary in order to understand the influence of the parameters characterising the deformation system. In this work, numerical simulation techniques are implemented as a tool to evaluate the effect of different process parameters in the hot stamping of a Boron steel, with special emphasis on the thermal conductivity of the material of the dies, the cooling system of the tooling and the main features of the contact between metallic blank and tools. A very simple experimental test has been very useful to validate the simulation and to adjust the thermal contact conductance, responsible up to a point for the cooling velocity of the sheet. As a result, the importance of the quality of the thermal contact between the workpiece and tools has to be pointed out. The high thermal conductivity of the material dies allows reducing the duration of the forming cycle. An efficient cooling system limits the maximum temperature in the dies and assures a stable thermal state and consequently, the manufacturing of pieces with a uniform quality in long series is favoured