Design And Optimization Of Variable Blank Holder Force In Large Complex Thin-walled Workpieces Deep Drawing Process And Its Applications

With the development of the science and technology,the tailor-welded processing mode for the large complex thin-walled workpiece in the field of aerospace and automobile manufacture has become the bottleneck which restrict the performance and reliability of products.As an important plastic working method,sheet metal deep drawing forming has got the attention of domestic and foreign researchers in the field of large complex thin-walled workpiece manufacturing.The method of sheet deep drawing forming has the advantages of high reliability,high dimensional accuracy and high production efficiency,but it also has many deficiencies in the situation of large complex thin-walled workpieces which has the features of great tensile depth,high material strength.In order to solve the problems:unreasonable drawing process caused by the unknown of internal mechanism,flange wrinkling caused by uneven distribution of blank holder force,optimization failure caused by uncertainty of hydraulic equipment forming parameters,this paper researched the modeling of the large complex thin-walled workpiece drawing process,designing of variable blank holder force in deep drawing and the hydraulic equipment forming parameters uncertainty optimization,propose the design and optimization technology of large complex thin-walled workpiece in deep drawing process,and applied this technology in the 150MN hydraulic drawing machine in Hefei.The main contents of this thesis were summarized as follows:In the first chapter,the significance and technical background of the subject were summarized.The present researches on numerical simulation technology of sheet metal forming,optimization method of forming parameters,technology and equipment of sheet metal forming were discussed.The problems of current sheet metal forming were pointed,and finally the main contents and organizational framework of this thesis were presented.In the second chapter,large complex thin-walled workpiece deep drawing forming model based on strain path were proposed.Through numerical simulation of the deep drawing process under different blank holder forces,the strain path of various parts of sheet were studied.The M-K method was applied to calculate the forming limit curve,obtained forming limit strain path,and the forming limit of complex thin-walled workpiece was obtained under real strain path.The internal mechanism of various blank holder force improving sheet metal formability was revealed,and the theoretical basis for optimizing BHF curve reasonably was provided.In the third chapter,a design method of VBHF in sheet deep drawing forming based on sequential approximation was proposed.The blank holder forces were taken as design variables,typical forming quality index which can be easily obtained were taken as the objective functions and constraints,VBHF multi-objective optimization model of deep drawing was built.The sequential approximate models of objectives and constraints were constructed based on a multi-width RBF neural network and sequential sampling strategy,and NSGA-? genetic algorithm was used to find the optimal solutions based on sequential approximate models.The deep drawing of the rocket bottom tank was studied as an example to verify the feasibility of the optimization method.In the fourth chapter,an uncertain optimization method of hydraulic equipment forming parameters based on interval variables.Uncertainty parameters were described as interval variables,and the optimization model of hydraulic equipment forming parameters uncertainty problem was built.Through a nonlinear interval number programming method,the multi-objective optimization problem under interval uncertainty was converted into a deterministic one.IP-GA genetic algorithm and NSGA-II genetic algorithm were employed to analysis uncertainty and search optimization,respectively.Based on the intermediate uncertainty optimization results,the approximation models were updated using uncertain sequential sampling strategy to improve the convergence efficiency precision of the algorithm.In the fifth chapter,functional modules of forming parameters design system of sheet metal deep drawing oriented to hydraulic equipment was developed combined with the enterprise project,and the proposed method in this paper was applied in the enterprise to verify the feasibility and the effectiveness.In the sixth chapter the research contents of the whole dissertation were summarized,and the further research direction was prospected.