Experimental and theoretical study of thermal aspects of the hot stamping process

The objective of the present article is the thermal conductance estimation to improve the Usibor 1500P® blank cooling during the hot stamping process. An experimental device was designed and developed to estimate the thermal contact resistance at the part/tool interface. The designed stamping tool is composed of a die and a punch made in Z160CDV12 steel and presenting an omega shape. Samples and tools are thermally instrumented with thermocouples type K sheathed with silky glass, forming heat-flux meters in the most interesting locations in the tools. Reproducibility tests showed a good repeatability of recorded and estimated parameters with a mean dispersion less than 5%; it was noticed that a re-heating of the cooled part due to its microstructure transformation occurring systematically at 400 °C. At the surface boundary of the part, thermal conductances are calculated using convective/radiation modeling of both phases: approach and forming. At the contact interfaces, thermal contact resistances RC are estimated experimentally through a non-linear 1D inverse technique founded on sequential method of Beck. Results have been established as correlation of type: RC = f(P) to be used for numerical simulation.