Research On Fast Simulation And Optimization Technology For The Stamping Product Design

The sheet metal forming simulation technology based on the incremental finite element method has been widely used at the stamping process design stage to validate the process feasibility. However, the application level of the numerical simulation which is used at the automotive stamping product design and the earlier stamping process design stage is still very lower. At the present, the life cycle of automotives become shorter and shorter, the automotive enterprises and die manufacturing companies have put more attention on the ability of the product design and the process design to improve the key competitiveness. As a key analysis tool at the design stage, the inverse approach should be improved in both the analysis accuracy and its scope of application.On the support of the National Natural Science Foundation and other projects (5057508, 2006BAF01A43, 2006AA04Z140), an updated inverse approach is proposed based on shell element and real process treatments to improve the accuracy and to expand its scopes of application.An updated inverse approach is proposed for complicated stamping process. Based on the finite deformation theory, the kinematic relationship of a material point has been built between the initial flat configuration and final configuration with the DKQ shell element model adopted. Based on the Hencky deformation theory and the Hill's yield criteria with the anisotropy in plane, the constitutive equation is derived. In the inverse finite element model, real process conditions, such as blank-holder force, pad force and drawbead have been considered.A trimming line design and flanging analysis method has been proposed based on the updated inverse approach. In the analysis method, the material property and the process conditions, such as addendum, blank-holder model and friction can be considered. A trimming line design and flanging analysis system is developed on UGS / NX platform, which can be used as a fast analysis tool to assist the process engineer for trimming line design and flanging analysis.A multi-step unfolding method has been developed for blank design and formability prediction of complicated progressive stamping part, especially with freeform surface. In the method, a finite element model of the inverse approach is developed at a local area according to the stamping process, and the intermediate shape is unfolded on a reference surface at the local area. Not only the influence of the bridge, blank-holder force and the friction, but also the influence of the offsetting of the strain neutral layer at different radius of curvature on the blank shape size, are considered in the finite element model, so that the calculation accuracy of the blank shape at each step is increased. The key intermediate blank shapes and initial blank shape can be calculated repeatedly by the method in an inverse sequence. The optimum blank shape can also be designed according to the formability of the stamping part. The key intemmediate shapes of a progressive die stamping part strip is unfolded to illustrate the method to verify the feasibility of the method.A hybrid element based method is proposed, which can be assist product designers to estimate springback in sheet metal forming process at the earlier design stage. In the hybrid method, the forming analysis results obtained firstly by the updated inverse finite element approach. Then, a rotation-free shell element with only three displacements at the corner nodes of the element is employed to calculate the springback.A multiple objectives optimization algorithm for the drawbead process is built based on the update inverse approach and the sensitivity analysis algorithm. The objectives include thickness strain distribution, rupture, wrinkle and insufficient forming.The reliability of the developed methods is verified by the examples given in the paper. The method developed can not only improve the robustness of the stamping part design, but also greatly shorten the cycle of the stamping design and manufacturing. Therefore, a useful and quantitative analysis tool for the product design engineers and stamping process planning engineers and die design engineers has been successfully developed.