Numerical Simulation And Multi-objective Optimization Of Partition Cooling In Hot Stamping Of The Automotive B-pillar

Designing parts with performance gradients is a hot research topic in the industrial field.In the context of automobile lightweight,in order to solve this problem,researchers have designed a variety of molding processes to produce automotive parts with both local high plasticity and local high strength.At present,partition cooling for hot stamping technology,which capable of preparing automotive parts with performance gradients has been becoming a hot spot in research and application development.In this thesis,the design and finite element simulation analysis of hot stamping forming process were carried out on an automobile B-pillar by the forming method of partition cooling for hot stamping technology.Based on the method of "Finite Element Simulation + Optimal Latin Hypercube Experimental Design + Response Surface Approximation Model + Multi-Objective Optimization",the parameters of stamping process affecting thickening and thinning are mathematically modeled and multi-objective solution optimization was carried out.Finally,the quality of the forming was verified by trial-manufacturing the B-pillar and inspecting the mechanical properties and microstructure.The main research work and progress of the thesis are as follows:(1)The principle of partition cooling for hot stamping,metal thermoplastic deformation process and heat transfer process were discussed,solid heat transfer model and flow-solid coupling heat transfer model were established,and the heat transfer coefficients were determined.The process of stress,strain and phase transition during the partition cooling for hot stamping were analyzed,and then the heat-mechanical-phase transition coupling model was established.These provide theoretical basis for finite element simulation analysis and experimental verification.(2)The process of the partition cooling for hot stamping was designed,and a better performance and quality of the forming scheme was analyzed by using the AutoForm software.And the temperature change,thickness change,stress and strain state,microstructure change,tensile strength,hardness and forming limit diagram of the B-Pillar were analyzed during the partition cooling for hot stamping.(3)In order to study the effect of process parameters on the thickness and thinning of the B-pillar after hot stamping,the optimal Latin Hypercube Design was selected to choose a simulation scheme;a third-order response surface approximation model was established based on the simulation results;and the accuracy and credibility of the model were tested;the interactive influence of multiple factors on the thickening rate and thinning rate were analyzed,which lay the foundation for subsequent process parameter optimization.(4)Based on the established response surface model,in order to minimize the maximum thickening rate and maximum thinning rate in rapid cooling zone and in slow cooling zone,both the global optimization algorithm PSO and the multi-objective optimization algorithm NSGA-? were used for optimization solution.The comparison shows that the NSGA-? is more suitable for the optimization of the thickening and thinning of the B-pillar,which could obtain better optimization results.(5)The trial production of parts was carried out according to the optimized process parameter combination to ensure that the parts were free from obvious defects such as wrinkling and cracking.The microstructure and mechanical properties of different zone of the B-pillar were tested.The results show that the rapid cooling zone could obtain martensite structure,which tensile strength reached 1390 MPa,the elongation was 7%,the hardness was 478.78 HV,while the pearlite and ferrite microstructure were obtained in the slow cooling zone,the tensile strength could be reduced to 680 MPa,the hardness was 230.56 HV,the elongation was 11.4%.In this thesis,combining with scientific numerical simulation,experimental design methods,approximate models,and optimized algorithms can effectively achieve the control of the thinning and thickening rate of the auto B-pillar by using partition cooling for hot stamping.The research has important theoretical significance and practical application value for guiding the production of forming structural parts with partition hot stamping.