Study On The Property Gradient Of Hot Stamping Parts Based On Different Cooling Zones

Hot stamping forming technology is an important means to realize the light weight of automobile,and its application is more and more extensive.Although the traditional hot stamping parts have high strength,their ductility is very poor,they cannot absorb energy when they collide,so they cannot guarantee the high safety of passengers.Based on this,on the basis of traditional hot stamping,a punching process,district cooling-hot stamping process,which makes the cooling speed difference in different regions by changing the initial temperature of different modules of the mold,and finally gets the favorable gradient distribution of the sheet material performance.On the premise of reducing the weight of the vehicle,the elongation of the forming parts is enhanced and the collision safety of the car is enhanced.In this paper,the basic theories of 22MnB5 materials in the process of district cooling-hot stamping are introduced,including heat transfer,mechanics and phase change dynamics.The contact mode of the district cooling stamping is determined and the thermal boundary condition of the district cooling is established.Through the hot tensile test,the high temperature rheology curve of the sheet was obtained,and the other thermal physical parameters of 22MnB5 were combined to establish the thermal force-phase transition coupling constitutive equation.The DEFORM software is used to simulate the non deformation flat plate holding,and to explore the influence of different gap sizes between the cold and hot modules on the cooling of the sheet metal,and to analyze the influence of different initial mold temperature on the partition cooling based on this premise.The geometric model of the mold is established,and the whole process simulation of the U-deformed district cooling-hot stamping process is carried out,including the four stages of transfer,forming,packing and air cooling.The influence of different factors on the cooling rate of sheet material is explored,including the initial die temperature,the pressure protection and the contact heat conduction coefficient.A physical experiment platform is designed and constructed,and the districtcooling-holding test is carried out by changing the temperature of the mold hot zone,and it is verified with the simulation results.The performance analysis of district cooling after the experiment specimen,using tensile testing machine,microhardness tester and optical microscope observe and analyze the strength,elongation,hardness and microstructure of specimen.The regular pattern of the performance gradient of the structure of the sheet is summarized and analyzed.