The Research In Simulation On The Hot Stamping Of High Strength Steel Sheet

With the application of ultra high strength steel in vehicle manufacturing field, the hotforming method, in which a high strength part （like A-pillar, B-pillar, bumper, roof rail,rocker rail and tunnel）can be produced by forming at high temperature and rapid cooling indies, has been studied extensively. However, the hot stamping process, which covers the fieldsof mechanics, thermal, microstructure evolution and surface oxidation, is more difficult andchallengeable than the cold stamping process to the engineer and researcher. With high-costand long production cycle of the hot stamping process, the strict technology process and specialequipment is required in the production of hot stamping parts in the enterprises requirement.Especially for the cool duct design, improper design may results in a large waste of human workand financial resources easily. In order to shorten the cycle of design and reduce the cost, thecomputer-aided design becomes very important. The application of FEM in the designcontributes to assessment of initial design and subsequent optimization for the stampingprocess design and die design.In this paper, the thermal-mechanical property of22MnB5steel was represented by theJohnson Cook constitutive equation. The inverse analysis approach, which is combined byFEM and optimization algorithm, was applied to calculate the material parameters of JohnsonCook constitutive equation. By making a comparison of the tested and simulated compressionforces as function of time, the Johnson Cook flow stress expression with the initial materialparameters showed a more insufficient ability to describe the deformation behavior of materialthan the expression with the optimized parameters. Therefore, the inverse approach wasfeasible and practical for the engineering application and offered the effective material modeland method for simulation on the subsequent hot stamping process and cooling process, whichcan improve the precision of simulation and guide the design of project effectively.Also in this paper, the FE model that contained thermal-mechanical-microstructure andstrain model represented by a mixture law for hot forming was discussed, and further beenapplied to the simulation of hot forming and quenching process of22MnB5metal sheet partwith U-shape constant section. The computed results of final part shape and hardness aftercooled in air, in water without dies and cooled within dies were compared respectively.