【作者】 徐建丽；

【导师】 刘纯国；

【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)是金属板材三维曲面成形的一种柔性加工方法，其基本思想是将传统的整体模具离散化为规则排列、高度可调的基本体群，由基本体球头的包络面（或称基本体群成形曲面）来完成板材成形。多点成形采用计算机控制基本体的位移和速度，实现基本体群包络面的变化，从而实现板材柔性成形。它在航空航天、造船、车辆覆盖件、城市雕塑等诸多领域有广泛的应用前景。由于板类件多点成形是一个材料非线性、几何非线性的过程，分析成形件卸载后的回弹量，预测成形过程中可能产生的缺陷就变得十分复杂。而数值分析方法是金属成形中优化模具设计、预测成形缺陷及分析成形质量必不可少的工具，有限元技术则是各种数值方法中最为有效的方法。近几十年来，有限元分析在板材成形工艺分析中的应用越来越广泛。它不仅用于典型成形工艺分析及成形过程模拟，而且用于起皱、压痕等成形缺陷预测、成形件回弹计算以及用于原始坯料设计等问题。对于薄板类件多点成形过程，由于基本体和板材之间接触状态不断发生变化，加载条件复杂，应用动态显式有限元算法求解具有明显的优势。因此，本文采用动态显式有限元算法对薄板类件多点成形过程进行数值模拟。在薄板类件多点成形中，需要使用压边装置以提高成形质量。多点压机的压边装置是由上下各数十个压边缸组成，每一个压边缸都由独立的液压装置驱动，再配以合适厚度的压边圈，可以实现高柔性压边。由于使用刚性压边装置的多点成形易产生起皱、拉裂和压痕等成形缺陷，尤其是薄板类件的成形。这些缺陷严重影响工件的成形质量，制约多点成形技术的推广应用。本文借助于有限元数值模拟软件，对采用高柔性压边的多点成形过程进行了详细的数值模 58<WP=63>吉林大学硕士研究生学位论文拟研究，并与采用刚性压边的多点成形过程进行比较，分析了成形缺陷产生的原因，探讨合适的工艺参数，从而消除或减轻缺陷，提高成形质量。 本文的所做的主要工作如下： 1) 多点成形有限元模型的建立及数值模拟关键算法和参数的研究 根据动力松弛法的概念，利用中心差分法使动力方程求解显式化，并对接触和摩擦模型进行了研究；探讨了采用刚性及高柔性压边的多点成形有限元模型建立过程中的若干问题，如有限单元的选择、边界条件、虚拟成形速度对模拟结果的影响、材料模型的选择等，建立了合适的采用刚性及高柔性压边的多点成形有限元模型。 2) 针对多点成形过程，对采用刚性压边和高柔性压边的多点成形过程进行了数值模拟对比研究 对采用刚性压边成形时的成形缺陷如起皱、压痕和拉裂等进行了数值模拟。起皱是由面内压应力引起的，通常通过增加压边力来解决，但压边力增加容易导致直壁传力区的破裂以及压痕的出现。通过对分别采用刚性压边和高柔性压边的多点成形过程的模拟研究证明，采用高柔性压边装置能够有效地抑制各种成形缺陷，板材的拉裂力以及成形力都要比采用刚性压边成形时小。 3) 根据多点压机柔性压边特点，对采用高柔性压边的多点成形工艺过程进行了数值模拟研究 系统研究了采用高柔性压边装置的多点成形过程，对成形过程中影响压边圈柔性的各种工艺因素进行了模拟研究，重点探讨了压边圈厚度、板料厚度、不同材料参数和不同压边力等对成形质量的影响，并对不同参数时压边圈的柔性对板材成形质量的影响进行分析，总结出了不同工艺因素对压边圈柔性的影响规律，以及不同柔性程度的压边圈对板材成形质量的影响规律。更多还原

【Abstract】 Multi-point forming (MPF) is a flexible manufacturing technology forthree-dimensional sheet metal parts. In MPF, the conventional monolithic die isdivided into a matrix of discrete elements. Each element’s height and velocity canbe controlled by computer. The forming process of sheet metal is implemented bythe contour surface of elements group. MPF has found its extensive applicationfields such as the manufacturing of the fuselage of aircraft, the hull of ship,covering components of vehicle, city sculpture and modern architecture etc. Based on the plasticity theory, the MPF of sheet metal parts is a nonlinearprocess which includes both material and geometry nonlinearity. It is difficult toanalyse spring-back and the defects during process of MPF. Numerical analysismethod is necessary for optimizing mould&die design, predicting defects andanalyzing forming quality. Among the Numerical analysis methods, finite elementanalysis is the most efficient one. In recent years, it has been extensivly applied intechnical analysis of sheet metal forming, not only in the analysing of practicalforming process, but also predicting wrinkle, dimple, calculating the magnitude ofspring-back, improving the raw material design, and so on. During the MPFprocess, because the contacting condition between elements and sheet metal variescontinuously and the load condition is complex, so the dynamic explicit algorithmFEM is the best choice. In this thesis, dynamic explicit finite element algorithm isused in the simulation of the MPF process. In multi-point forming, a blankholder is used to improve the forming quality ofsheet metal which is composed of dozens of hydraulic cylinders, and each of themis driven by its respective independent hydraulic equipment. When an appropriatethickness blankholder is selected in MPF, the rigid blankholder or the high flexibleblankholder multi-point forming can be realized. But when the rigid blankholder isused, forming defects such as wrinkles, fractures and dimples easily occur, With thecommercial FEA software, both the MPF process with the high flexibleblankholder and the MPF process with the rigid blankholder have been simulated.The results show that MPF with high flexible blankholder can eliminate or avoidforming defects and improve the forming qauality. Main works are as following: 60<WP=65>吉林大学硕士研究生学位论文 1) Building of the finite element analysis model for MPF and research on the keyalgorithms and parameters of numerical simulation. Based on the concept of dynamic explicit algorithm, how to make the dynamicequation solution explicit utilizing the central difference method has been discussed.the key parameters and algorithms that have a great influence on the simulationprecision and efficiency have been studied, such as, element formulas, materialmodels, fictitious velocity and the algorithms for the spring-back analysis. And thefinite element models for different multi-point forming principles have been built. 2) Comparision reasearch on the numerical simulation of MPF with the highflexible blankholder and with the rigid blankholder Simulation with forming defects, such as wrinkle, dimple and crack and so on,have been done in MPF with the rigid blankholder. Wrinkle is arose by press stress,which can be eliminated by increasing BHF. But increasing BHF easily bringscracks and dimple at the vertical transmiting force area. By comparesion researchon MPF with high flexible blankholder and rigid blankholder, it is clear thatmulti-point forming with high flexible blankholder can effectively restrict formingdefects, and the crack force and the forming force during the forming are bothsmaller than that with rigid blankholder. 3) Research on the numerical simulation of MPF with high flexible blankholder The multi-point forming process with high flexible blankholder has beensystemicly studied by means of fi更多还原