Study On Hot Stamping Process Of High Strength Steel22MnB5Based On Numerical Simulation

Using high strength steel in vehicle body manufacture is an effective way to achieve lightweight vehicles. To reduce the disadvantages of high strength steel cold stamping such as forming difficultly and poor dimensional accuracy of parts, hot stamping technology that integrates deformation and phase transformation emerges at the right moment and has advantages of lower forming resistance, making parts acquire good dimensional accuracy and high strength etc. Hot stamping forming is a complex thermo-mechanical coupled analysis process. The differences of temperature field and stress-strain field of parts caused by different process parameters will lead to different performance of parts. Study on the influences of process parameters on part quality and process parameters optimization are of great significance for obtaining parts that satisfy the requirement of organization performance and dimensional accuracy.Taking high strength steel22MnB5as the research object, the study on high strength steel hot stamping process is carried out by the methods of theoretical analysis, numerical simulation and experiment.Firstly, the hot stamping finite element model of U-shape parts is established and simulated by Dynaform. The rationality of finite element model is confirmed by analyzing the deformation process, temperature field, stress field, plastic strain field and thinning ratio of blank during hot stamping process.Then, taking the max temperature difference of U-shape part after packing process and the max thinning ratio as experimental indexes, process parameters including initial forming temperature of blank, stamping speed, holding time and friction coefficient are optimized by using range and variance analysis methods, then the optimal process parameters combination is determined. The results show that the max temperature difference of U-shape part is99.98℃and the max thinning ratio is4.73%under the condition of initial forming temperature of blank750℃, stamping speed40mm/s, holding time10s, friction coefficient0.20. And both of them achieve the optimal values.Based on the optimal process parameters combination, the influences of process parameters on the max temperature difference of U-shape parts after packing process and the max thinning ratio are studied. The results show that the max temperature difference of U-shape part after packing process and the max thinning ratio increase with initial forming temperature of blank increasing, decrease with stamping speed increasing; with the increase of holding time, the max temperature difference of U-shape parts after packing process decreases significantly and the max thinning ratio increases gently; with the increase of friction coefficient, the max thinning ratio increases significantly, while the max temperature difference of U-shape parts after packing process remains almost unchanged.Finally, the optimal process parameters combination is used for U-shape parts hot stamping experiment. The experiment and simulation results match basically with the same distributions of temperature field and thinning ratio, and the accuracy of simulation is verified. The results of microstructure observations and mechanical performance show that the microstructure of parts after hot stamping is mainly martensite, and yield strength and tensile strength of parts reach more than1000MPa and1300MPa respectively. More and uniformer martensite generates at the flange and lower sidewall because of higher cooling rate during hot stamping, so their strengths are higher than that of the upper sidewall and bottom reaching1500MPa. The experiment results are consistent with the cooling rates distribution of u-shape parts of simulation results, and the reliability and accuracy of numerical simulation are verified further. It verifies the feasibility of hot stamping process obtained based on numerical simulation by experiment and provides important guiding significance for hot stamping production.