Numerical Simulation And Shaping Analysis On The Process Of Multi-Point Forming For Thin Sheet Metal

Multi-point forming (MPF) is a flexible manufacturing technology forthree-dimensional surface part of thin sheet metal. Relative to the traditionalstamping technique, the MPF has more advantages, such as forming instead ofsolid dies, optimum deformed path and using the MPF press to form large parts.Therefore, the MPF technology can be applied extensively in many fields.However in the process of multi-point forming, dimple and wrinkle are themain defects which influence the forming ability and quality of the parts andlimit the development of the multi-point forming technology. At the present dayCAE is becoming the focus of modern design processes. So the numericalsimulation is carried out to analyze the multi-point forming process, andpredicts the possible defects. The different models and parameters are discussedand compared in details; finally the best model which deform well is suggestedfor the forming process. According to the simulations, those defects can berestrained or even eliminated, so that the forming quality of the parts andefficacy can be improved. MPF process concerns nonlinear fields on geometry, physics, andboundary, as well as complex discontinuous boundary problem. Nowadays thefinite element method (FEM) is a cogent tool to deal with the nonlinearproblems. In this paper, dynamic explicit algorithm FEM is successfully used toanalyze the MPF process of thin sheet metal. It provides an effective means foroptimizing the technique design and judging forming ability and quality of theparts. Also it promotes the development of the MPF technology. The main contents and results are as follows: 67吉林大学硕士研究生学位论文 1) Research on the numerical simulation using finite element method Based on the continuum mechanics theory, dynamic explicit algorithmusing centre difference method is studied including how to compute massmatrix and damp matrix. According to the oscillation theory, critical time step isdiscussed to assure the computing stabilization using centre difference method.Furthermore, the constitution equation on the basis of the flow rule isformulated in this thesis, and penalized function method and coulomb's law offriction are adopted to deal with the discontinuous boundary problem. 2) Building finite element model for MPF process The reasonable finite element model is constructed for MPF process withblank-holder device and elastic medium, such as spatial discretization formulti-point process, the choice of finite element unit, the choice of materialpattern, boundary condition etc, have a great influence on the numericalsimulation. It provides the principles and basis for the correct finite elementmodel of MPF process. 3) Numerical simulation on the wrinkle and crack during the MPF processwith blanker-holder device MPF technique with blank-holder device can be applied to threedimensional surface parts. In this thesis, both blank-holder force andblank-holder clearance controlling means are considered to simulate the MPFprocess, which can reflect the real deformation well. The influence of thedifferent parameters, such as blank-holder condition, thickness of blank sheetand material pattern on the wrinkle and the crack is analyzed. FLD is used tojudge the crack on the multi-point forming process successfully. The predictionof crack accords with the experiment ones, which shows choosing the properparameters can eliminate or restrain the defects, and also benefits the MPFtechnique and the shaping analysis. 4) Numerical simulation on the dimple during the MPF process usingelastic medium technique MPF process with the elastic medium can be applied to the forming ofthree dimensional surface part of thin sheet metal and be considered asdeformation with no dimples. In this thesis, the numerical simulation between 68Abstractusing the elastic medium a...