Study Of B-pillar Hot Stamping With Tailored Mechanical Properties And Its Optimization

Automobile lightweight technology is particularly important for energy conservation and emission reduction in the world.Hot stamping technology is an important means of automobile lightweight.With the help of hot stamping technology,the microstructure in the original state can be changed,the tensile strength can be improved,and the body-in-white weight can be reduced.At present,the traditional heat treatment process can only enhance the tensile strength of boron steel,which can effectively resist deformation,but the elongation is low,and the energy absorption capacity is poor,so there are some deficiencies in protecting the safety of people and vehicles.However,with the increasing research of hot stamping process,the hot stamping process with tailored mechanical properties can solve this problem well.The principle is to make the same hot stamping sheet have different mechanical properties,that is,different region of the same steel sheet,one part has higher tensile strength to resist deformation,the other part has good toughness to absorb collision energy.In this paper,the forming process of B-pillar was simulated.In order to obtain the reasonable tailored distribution of mechanical properties,the main process parameters were optimized according to the modelFrontier optimization platform.Finally,the research results were verified by the hot stamping experiment of B-pillar.In order to obtain the hot stamping process parameters of B-pillar tailored mechanical properties,this paper used Ls-dyna to carry out the finite element numerical simulation.The tool temperature was set as 400?,450?,500?,550?,the unheated tool was set as 25?,the initial temperature of sheet metal was 930?,and the holding time was set as 20s.According to the CCT diagram of' boron steel B1500HS,we can judge the miscrostructure distribution of sheet metal performance at different temperature of heating tool,and determine whether there was the best tailored mechanical property distribution in the given temperature range of hot stamping process parameters.Taking the set temperature parameter as the optimization variable,multi-objective optimizations were carried out with the help of modeFrontier platform,and the most important parameters were identified by DOE analysis.Driven by MOGA-? algorithm(including multi-objective genetic algorithm in modeFrontier),the heating temperature of the heating tool,the initial temperature of the non-heating tool and the sheet metal with the best quality were obtained by Kriging model.In the optimization results,the tailored mechanical property distribution of hot stamping process parameters was the initial temperature of sheet metal 930?,the heating temperature of heating tool 500?,the temperature of non-heating tool 25?,and the holding time 20s.By means of these process parameters,the automobile parts with martensite region of high tensile strength to resist deformation and bainite region of good elongation to absorb crash energy can be obtained.In order to further test the rationality of the results,the traditional B-pillar hot stamping tool was redesigned.The tool was divided into heating tool and non-heating tool.The temperature of the heating tool(upper and lower)was set as 400?,450?,500?,550?,the temperature of the sheet in the heating furnace was 950?,and the non-heating tool was not made.The treatment temperature was about 25? and the holding time was 20s.Boron steel B1500HS was used as experimental sheet,which was punched by modified tool,and the sheet obtained under different temperature of heating tool was tested and analyzed.The samples were cut at different positions on the hot stamped parts with tailored mechanical distribution,and the hardness distribution at different positions was determined by Vickers hardness test with microhardness tester.The miscrostructure was observed to judge the content of different metallographic structures,and the tensile strength and elongation at different locations were obtained by tensile tests.Finally,the optimized parameters of hot stamping process for the tailored mechanical property distribution were verified and determined.