The Research On Heat Transfer Coefficient Of 22MnB5 High Strength Steel During Hot Forming

High strength boron steel hot stamping process can reduce the vehicle's curb weight on the premise of meeting the overall safety of the vehicle.At the same time,hot stamping is also one of the important ways to lighten the vehicle.The process can reduce the springback of sheet metal and improve the formability of the material.However,the formability and microstructure of the final part are closely related to the good heat exchange behavior between the material and the die.As one of the key factors of heat transfer in the hot stamping process,the interface heat transfer coefficient can affect the temperature field,stress field and organization field of the leading part,and finally affect the forming quality of the part.At the same time,as one of the key boundary conditions in the numerical simulation,the accurate setting of the interface heat transfer coefficient is the premise to ensure the accuracy of the finite element simulation.Therefore,the accurate solution of the interface heat transfer coefficient can provide a reference for the setting of the heat transfer coefficient in the numerical simulation of metal hot stamping,and explore a new way for the research of the interface heat transfer coefficient of high-strength steel hot forming.In this paper,the temperature change of 22MnB5 high strength steel in hot stamping process under different working conditions is studied,and the heat exchange process in hot stamping process is studied by using the inverse heat transfer method and the finite element numerical simulation method,and the interface heat transfer coefficient under different working conditions is solved and reverse verified.The specific research contents are as follows:(1)Taking the typical U-bend as the research object,the experiment of hot stamping die/blank metal contact heat transfer is carried out through the existing whole set of sheet metal hot stamping forming device.The temperature change curve of sheet metal under different technological conditions in the experiment was obtained by using the self-developed temperature acquisition system.The temperature curves and cooling of sheet metal under different conditions are compared and analyzed.(2)Based on Beck's nonlinear estimation method,the mathematical model of the algorithm of the reverse heat transfer method is established,and the reverse program of the interface heat transfer is established by using programming language.The interface heat transfer coefficient under different working conditions is obtained by using the inverse heat transfer method.The corresponding curves are drawn and analyzed under different conditions.(3)The finite element model is established by using the nonlinear finite element analysis software,and the interface heat transfer coefficient obtained by the above solution is substituted as the boundary condition to simulate the hot stamping process of the sheet metal.Finally,the temperature distribution of the numerical simulation is output.The accuracy of the heat transfer coefficient is verified by comparing with the experimental temperature.(4)A series of mechanical properties of U-shaped parts in the process of contact heat transfer experiment were tested,and the quality of U-shaped parts after forming was verified by the test.