Identification methods on blank-die interfacial heat transfer coefficient in press hardening

Abstract

The interfacial heat transfer behaviors between blank and tools play a great effect on final mechanical property of hot stamping parts. Accurate description on the interfacial heat transfer coefficient (IHTC) can make great improvement on simulation accuracy of hot stamping process. However, it is still a big challenge due to the difficulty in direct measurement on instantaneous interface temperature, pressure and heat flux. So an accurate and efficient identification method of IHTC based on indirect measurement is indispensable. In this paper, an improved test machine with a high-accuracy infrared thermometer and well-controlled interface pressure is constructed. Two groups of IHTC identification methods, including Inverse Heat Conduction (IHC) and Finite-Element-Method based OPTimization (FEM-OPT) methods are developed. Several numerical procedures have been implemented for determining the IHTC between the blank and tools. The error of the proposed methods is further analyzed and calibrated by finite element simulation and experiments. The identified IHTC curves with double peaks reveal the interfacial heat transfer behavior during hot stamping clearly. The comparison among different identification methods shows that the constant equivalent IHTC is not a rational assumption, and IHC method gives the best accuracy on temperature prediction, FEM-OPT method with temperature dependent IHTC takes the next place.