Study On Heat Transfer Phenomenon Of Hot Stamping Process

Hot stamping process is an important approach to achieve light weightcar in automotive industry. The process arises researchers’ andentrepreneurs’ wide-spread attention. Some key structural parts havealready been put into manufacturing in recent years. However, manyproblems in hot stamping still need further research. Based on the heattransfer phenomena inside the die in hot stamping process, cold rolleduncoated boron steel B1500HS produced by Bao Steel is for the study inthe thesis. Theoretical model, experimental measurement and numericalsimulation are respectively conducted to study heat transfer phenomenonin hot stamping process.A theoretical model for heat transfer in the hot stamping process isestablished. Contact heat transfer between hot blank and cold dies is themain reason to arise blank temperature change. A roughness-joint model ispresented to describe the relationship between the heat transfer coefficientand those material and contact parameters concerned in the hot stampingprocess, including interface roughness, hardness, material conductance andcontact pressure etc.. The parameters in the model are easy to measurecompared with the existed models. Therefore, it is easy to use in practice.In addition, the heat transfer phenomenon during the transfer stage is alsostudied.It is hardly to measure the hot blank temperature changesimultaneously by those conventional measurement methods by usingthermocouple, since the blank temperature rate in the die is extremely high.In this thesis, two new measurement methods are designed to measure thetemperature of hot blank inside the dies. One method is with thermocouple, which is fixed with the blank and measure the temperature for wholeprocess including the heating stage. The other one is called as non-contactmeasurement method, the heated blank is moved to a designed flat die withobservation hole, and the temperatures under different pressures aremeasured by a thermal infrared imager through the observation hole. Theresults show that the theoretical values agree with the experimental valueswell.Numerical simulation for hot stamping process is conducted based onthe LS_DYNA finite element software. A new model integrated withtheoretical and experimental heat transfer coefficient is obtained by usingsecondary development method in LS_DYNA. In the new model, the heattransfer coefficients rely on node pressures. Numerical simulations of hotstamping process for a flat blank and a typical U-CAP part are performed.The effectiveness of the simulations are verified by comparing with theexperimental results.