【作者】 李雪；

【导师】 李明哲；

【作者基本信息】 吉林大学 ， 材料加工工程， 2004， 硕士

【摘要】 多点成形（Multi-point forming，简称 MPF）是三维曲面板类件柔性成形的新技术，与传统的模具成形相比在许多方面占有优势，例如可实现无模成形、优化变形路径、小设备成形大型件等等，因而有着良好的应用前景；但在其成形过程中也易于产生一些缺陷，如压痕和起皱等。这些缺陷影响工件的外观和内在质量，从而制约多点成形技术的实用化和进一步推广应用。目前，CAE 技术逐渐成为现代设计流程的核心和现代设计的聚焦点。因此，有必要对多点成形过程进行数值模拟，预测可能出现的成形缺陷，探讨合适的工艺参数，消除或减轻缺陷，从而提高成形质量和成形效率。多点成形过程从力学观点来看属于几何、物理、边界条件三重非线性和边界条件非连续性的复杂问题，而有限元方法是目前进行非线性分析的最强有力的工具。本文选用动态显式有限元算法对薄板多点成形过程进行数值模拟研究，为多点成形工艺的确定以及成形性的判断提供了依据，同时对多点成形技术的发展和完善起到重要的推动作用。本文的主要研究内容与结论如下：1）有限元数值模拟方法的探讨基于连续介质力学的理论，探讨了利用中心差分法使动力方程求解显式化的过程，并对质量矩阵和阻尼矩阵的计算进行了研究；利用振动理论的基本原理论述了临界时间步长的估算方法，保证了中心差分计算的稳定性；引用了基于流动理论的本构方程和基于罚函数方法及库仑摩擦规律处理多点不连续接触边界条件。2）具有压边功能，且使用弹性介质的多点成形有限元模型的建立 65<WP=71>吉林大学硕士研究生学位论文合理的有限元模型是进行有限元数值模拟计算的重要前提，本文探讨了使用弹性介质的压边多点成形过程有限元模型建立时的若干问题，如空间有限元离散化、有限单元的选择、材料模型的选择、边界条件等，为正确建立多点成形有限元模型提供了原则和依据。3）压边多点成形过程中起皱及拉裂成形缺陷的数值模拟研究采用压边功能可实现薄板三维曲面零件的多点成形。本文从压边力和压边间隙两种压边控制方式对压边多点成形过程进行了模拟，准确地反映了成形工件的实际变形状态，并就不同的压边条件、板料厚度以及材质等工艺参数对多点成形过程中起皱和拉裂现象的影响进行了数值模拟研究，成功地运用成形极限图对拉裂现象进行了判断，判断结果与实验结果一致，进一步说明了选择适当的工艺参数可以抑制或减少成形缺陷的产生，同时为多点成形工艺、成形性能的分析和研究提供了依据。4）使用弹性介质的压边多点成形过程中压痕的数值模拟研究使用弹性介质可实现薄板三维曲面零件的无压痕多点成形。本文对使用弹性介质和无弹性介质的多点成形过程进行了对比，指出使用弹性介质时在满足成形精度的前提下可以明显改善工件的成形质量，并通过对不同厚度和弹性模量的弹性介质对压痕的抑制作用进行了对比分析，探讨了最佳的弹性介质参数。模拟结果表明：压痕深度随着弹性介质的厚度和弹性模量的增加而减小，但当弹性介质较薄时，即使选择大弹性模量，对压痕的防止并无太大效果。因此，选择合适的弹性介质是消除多点成形压痕缺陷的关键。更多还原

【Abstract】 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<WP=73>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 68<WP=74>Abstractusing the elastic medium a更多还原