Development of Estimation Procedure of Contact Heat Transfer Coefficient at the Part–Tool Interface in Hot Stamping Process

Abstract

Energy efficiency, a high level of passenger safety, and weight reduction of the vehicles still constitute the main functional elements for the design of modern car body structures. Toward this objective, the usage of advanced sheet-metal forming technologies like hot stamping of quenchable boron manganese steel is developing nowadays. Hot stamping is a combination of hot forming and simultaneously quenching and hardening of the blank. In this article, an experimental procedure developed to estimate the thermal conductance at the part–tool interface during a hot stamping procedure is presented. The tools set (punch and die) has been designed to form omega-shaped samples. This work represents the first stage of the procedure development where the standard experiment is a simple compressive load of sample in the bottom of the omega-shape die, considering the real hot-stamping conditions. Tests are carried out under different contact pressure values for two different blank materials (Usibor 1500P and a material B). The results show that the thermal conductivity increase contributes to the reduction of the thermal contact resistance and therefore to a more rapid cooling of the part.

Acknowledgments

Bakri Abdulhay is an assistant professor at the Ecole Polytechnique, University of Nantes, France. He worked on the flow characterization in the presence of instability due to Gortler vortex for his master's thesis, and received his M.S. in 2006 from the Ecole Polytechnique, University of Nantes, France. He obtained his engineering diploma in 2006 from the Lebanese University, Tripoli, Lebanon. He worked on the thermal and mechanical aspects of the hot stamping process for his Ph.D. thesis, and he received his Ph.D. degree in mechanical engineering, specialty in thermal energetics, from the University of Nantes, France.

Brahim Bourouga is a graduate of the Polytechnic School of Algiers (1977), and received his Ph.D. from the Ecole Centrale of Nantes (1986). He was an associate professor in University of Annaba in Algeria until 1991. Since 1991, he has been a professor of mechanics and heat transfer in Ecole Polytechnique, University of Nantes (France), in the Thermal Engineering Department. He is a member of Laboratoire de Thermocinétique de Nantes UMR-CNRS 6607, and his research activity is mainly focused on heat transfer and associated phenomena at interfaces.

Christine Dessain is a research engineer at ArcelorMittal R&D Automotive Applications in Montataire, France. Prior to joining ArcelorMittal group in 1990, she worked at the research center of ORKEM in Verneuil en Halatte on the characterization of thermal properties of the polymers developed in the center. Then she followed her work of thermal and thermomechanical characterization of polymer paints and composites in the research center of Arcelor. She studied the rheological behavior of cross-linked powder coatings at the University of Saint Etienne to develop the direct extrusion and the lamination of those solid paints on the steel coils. She also studied the kinetics of the cross-linking reaction of those powder coatings to develop their rapid cure on industrial lines. Since 2004, she has worked in the field of the hot stamping process of Usibor 1500P and is a leader in the tribological and thermal activities of the hot stamping projects. She graduated as a polymer industrial materials engineer from the Conservatoire National des Arts et Métiers in Paris, France.

Gilles Brun is head of the Innovative Forming Technique Department of ArcelorMittal R&D Research Center in Montataire, France. He is a graduate of the Ecole Centrale de Lyon, France, and received his Ph.D. in mechanics from Claude Bernard University in Lyon, France. He had been appointed as associate professor at the Ecole Nationale d’Ingénieurs de Saint-Etienne, France, for four years. After several years of work for aeronautics, he joined ArcelorMittal to work on the forming of steel, first in the stainless steel division of the group and then in its flat carbon division.

Joël Wilsius is a senior research engineer at ArcelorMittal Automotive Applications Research Center, Montataire France. He leads a research and development project dedicated to the simulation of the hot stamping process. He is also in charge of the customer technical support for the feasibility assessment of hot-stamped automotive components. He received his Ph.D. in mechanical engineering from the University of Lille in 1999.