Thermal contact resistance estimation: influence of the pressure contact and the coating layer during a hot forming process

The Thermal Contact Resistance R _C Estimation constitutes an encountered problem to be resolved in any forming process. To fairly simulate a part cooling during a hot stamping process, an experimental device was designed and developed by the Laboratoire de Thermocinétique de Nantes—France in collaboration with ArcelorMittal R&D Montataire—France. The object is to estimate the thermal contact resistance at the part/tool interface during the three stage of the hot stamping process. During hot stamping phases, different contact types occur at the part/tool interface. The forming phase is characterized by a dynamic contact due to the increasing effort applied by the punch. At the contact interfaces, thermal contact resistances R _C are estimated experimentally through a non-linear 1D inverse technique founded on sequential method of Beck. Experiments were carried out on hot stamping samples made of Usibor 1500P® and 22MnB5 galvanized steel. The range of prospected stamping pressure varies from 10 to 30 MPa. The analysis of the effort curves shows the same mechanical resistance law of the part during the forming phase, whatever the consign effort settled to reach the maximum stamping pressure. The R _C value estimated for the galvanized steel is 33% lower than the one estimated for Usibor 1500P®. It is due to a higher harmonic thermal conductivity of the coated material. Results have been established as correlation of type: R _C  = f(P) to be used for numerical simulation.