Thermal Study of Hot Stamping with Heated and Cooled Tooling to Obtain Tailored Properties

To produce parts with tailored properties, i.e. parts with high strength in some areas and high ductility on some other areas, one of the most popular method, called the tailored tempering process, is to heat up locally the tools. In the hot areas, the blank follows a different thermal path leading to different microstructure evolutions and thus different final mechanical properties. In this paper, a tool is designed to have a side heated up to 500°C and a water cooled side. The hot side is heated up thanks to heated cartridges. A PID regulation is used to control the temperature of the hot side (from 200°C to 500°C) while the cold side is maintained at a low temperature using a thermostated water circulation. A uniform temperature on the working surface is successfully reached on both sides. Instrumentation by thermocouples is designed to be able to fully characterize the heat transfer: solving 2D heat conduction problems, the temperature fields in the tools and the thermal contact resistances at the blank/tool interfaces are estimated. Hardness measurements are also performed on the blank: the possibility to confer a distribution of mechanical properties is highlighted.