基于双展开平面映射法的板料成形多步快速模拟

初始解的确定是板料冲压成形有限元快速分析中的一个重要环节,初始解的好坏严重影响分析计算的速度以及求解的收敛性。文章在总结前人研究成果的基础上提出一种新的网格映射方法——"双展开平面映射法"快速获得中间构型初始解。在此基础上,将上述方法用于板料成形的多步快速模拟,试算表明所提方法正确、有效,为板料成形多步快速模拟中的中间构型准确建立奠定了重要基础。     

板料零件应变测量的网格图像处理

基于网格测量板料冲压零件拉延成形的面内应变分布和厚度变化,是进行冲压成形分析的一种有效手段.结合实例研究了视觉测量中的关键技术之一——网格图像处理主要步骤、理论及方法.结果表明采用图像处理技术能改善网格图像的视觉效果,提高图像的清晰度;突出图像中的有用信息,削弱干扰和噪声,强调边缘,从而将图像转换成了一种更适合人或机器进行解释和分析处理的形式,是视觉技术进行板料零件应变测量的必备基础.     

基于全量理论的一步成形正算法

在一步成形逆算法的基础上,提出了一步成形正算法来模拟金属板料冲压成形过程。先利用映射关系和面积坐标,得到一步成形正算法的空间初始解。再采用Newton-Raphson方法,基于全量理论在空间坐标系下进行迭代求解。迭代过程中使用接触搜索方法保证节点不会脱离零件工艺面。正算法的求解过程更加符合零件的成形过程,既保持了一步成形逆算法高效率的优势,又提高了算法的模拟精度。利用方盒件拉伸实验验证了本文算法的有效性。     

板料拉延成形的数值模拟与网格试验法

为了对板料拉延进行缺陷预测,在分析板料成形数值模拟和网格试验技术的基础上,采用数值模拟进行拉延成形分析,以及网格试验法进行成形缺陷成因判断,并将两者综合应用进行拉延成形缺陷预测和工艺优化的实例中.     

一种基于有限元仿真的板料成形极限预测方法

从成形极限图试验中观察得到了板料发生缩颈的2条判断准则：1.板料发生缩颈时凸模与板料接触力出现峰值；2.缩颈区域应变路径向平面应变状态发生突变.在有限元仿真软件中建立成形极限图试验的模型，对不同尺寸的试件进行仿真，根据以上2种准则可以得到在不同应变状态下的缩颈应变成形极限和应力成形极限.在二维坐标系里标出得到的极限点并连成曲线，即为用有限元仿真方法得到的板料应变成形极限图（Forming Limits Diagram,FLD）和应力成形极限图（Forming Limit Stress Diagram,FLSD）.通过与理论计算方法和试验方法得到的结果对比发现用该方法得到的FLD以及FLSD比理论推导出的更接近试验得到的数据     

有限元数值模拟技术在汽车冲压件成形中的应用

板料冲压成形作为一种重要的塑性加工工艺,广泛应用于各种工业领域,在汽车制造业中显得尤为重要.介绍了板料冲压成形在汽车制造业中的重要地位以及国内外汽车冲压件成形的现状.综述了有限元数值模拟技术的发展状况、理论基础以及一些专用的有限元软件.板料在冲压成形过程中经常出现起皱、破裂及回弹等缺陷.通过对几种典型汽车冲压件的成形分析,证明了有限元数值模拟技术能够在成形过程中很好的预测成形缺陷.并指出数值模拟在冲压成形中正发挥着越来越重要的作用.     

一种基于有限元仿真的板料成形极限预测方法

从成形极限图试验中观察得到了板料发生缩颈的2条判断准则：1．板料发生缩颈时凸模与板料接触力出现峰值；2．缩颈区域应变路径向平面应变状态发生突变，在有限元仿真软件中建立成形极限图试验的模型，对不同尺寸的试件进行仿真，根据以上2种准则可以得到在不同应变状态下的缩颈应变成形极限和应力成形极限．在二维坐标系里标出得到的极限点并连成曲线，即为用有限元仿真方法得到的板料应变成形极限图（Forming Limits Diagram-FLD）和应力成形极限图（Forming Limit Stress Diagrmn-FLSD）．通过与理论计算方法和试验方法得到的结果对比发现用该方法得到的FLD以度FLSD比理论推导出的更接近试验得到的数据．     

一种快速模拟复杂冲压件成形过程的截面分析单元

基于有限变形虚拟功率增量原理的弹塑性大变形有限元理论,建立了两点高效率平面应变板壳单元截面分析模型,并应用非均匀有理Ｂ样条曲线描述模具截面线进行接触判断,能快速获得较理想的板料冲压成形模拟结果。     

高强度钢板热成形三维温度场数值模拟分析

基于三维温度场有限元理论,考虑高强度钢板实际热成形过程中板料和水冷模具的温度边界条件,开发了用于热成形的KMAS_HF(King mesh analysis system_Hot forming)温度场分析模块,其中分别采用壳体单元和三维四面体单元模拟板料和模具温度场,将板料相变潜热释放引入温度场分析过程中。以典型U型试件为例,对其热成形过程进行数值模拟分析,并与实际试验进行对比研究。结果表明:板料与三维实体模具温度变化的数值模拟结果与试验结果一致,该模块对于热成形温度场分析预测具有重要指导意义。     

板料多点与渐进复合成形方法及数值模拟

提出了多点成形与渐进成形技术相结合的板料复合成形新方法,说明了两种复合成形方式的成形原理和成形过程。建立了复合成形分析的有限元模型,对球面件的复合成形过程进行数值模拟,分析了复合成形过程产生的压痕问题及其抑制方法。结果表明,采用弹性垫技术可以有效抑制复合成形过程产生的压痕缺陷,使成形件表面光滑;球面件上等效应力和厚度的变化过程及分布规律表明,随着增量步的加大,板料接触点处的等效应力随之增加,板料的厚度逐渐减薄。复合成形实验显示,数值模拟结果与实验结果基本吻合。     

基于理想成形理论的板料设计

将基于理想成形理论的板料设计方法推广到一般的各向同性硬化的弹塑性材料。从理想成形的必要条件出发,推导了包括弹塑性理想成形的本构关系在内的有关板料设计公式。推导了线性三角形薄膜单元的变形运动学关系,采用线性三角薄膜元的有限元素法计算了一个弹塑性材料的轴对称拉深实例,并和刚塑性材料的计算结果以及边界元的计算结果进行了对比。结果表明,使用本文的方法可以取得较为精确的板料展开尺寸。该方法具有快速、准确以及实用面广的优点。     

Meshfree Method Numerical Simulation of Sheet Metal Forming Process

Metal forming plays an important role in manufacturing industry and is widely applied in industries. The traditional finite element method (FEM) numerical simulation is commonly used to predict metal forming process. Conventional finite element analysis of metal forming processes often breaks down due to severe mesh distortion, therefore time-consuming remeshing is necessary. Meshfree methods have been developed since 1977 and can avoid this problem. This new generation of computational methods reduces time-consuming model generation and refinement effort, and its shape function has higher order connectivity than FEM's. In this paper the velocity shape functions are developed from a reproducing kernel approximation that satisfies consistency conditions and is used to analyze metal tension rigid viscoplastic deforming and Magnesium Alloy (MB15) sheet superplastic tension forming. A meshfree method metal forming modeling program is set up, the partition of unity method is used to compute the integrations in weak form equations and penalty method is used to impose the essential boundary condition exactly. Metal forming examples, such as sheet metal superplastic tension forming and metal rigid viscoplastic tension forming, are analyzed to demonstrate the performance of meshfree method.     

Meshfree Method Numerical Simulation of Sheet Metal Forming Process

Metal forming plays an important role in manufacturing industry and is widely applied in industries.The tradi- tional finite element method(FEM)numerical simulation is commonly used to predict metal forming process.Conventional finite element analysis of metal forming processes often breaks down due to severe mesh distortion,therefore time-consuming remeshing is necessary.Meshfree methods have been developed since 1977 and can avoid this problem.This new generation of computational methods reduces time-consuming model generation and refinement effort,and its shape function has higher order connectivity than FEM's.In this paper the velocity shape functions are developed from a reproducing kernel approximation that satisfies consistency conditions and is used to analyze metal tension rigid viscoplastic deforming and Magnesium Alloy(MB 15)sheet superplastic ten- sion forming.A meshfree method metal forming modeling program is set up,the partition of unity method is used to compute the integrations in weak form equations and penalty method is used to impose the essential boundary condition exactly.Metal forming examples,such as sheet metal superplastic tension forming and metal rigid viscoplastic tension forming,are analyzed to demon- strate the performance of mesh free method.     

脉冲电流频率对电磁成形板料变形高度的影响

用ANSYS/LS-DYNA对平板件电磁成形进行了有限元分析,其中成形载荷简化为正弦载荷,载荷沿板料径向也是正弦变化。在载荷幅值相同的情况下,对各向同性薄板材料进行了不同加载时间的分析,结果表明:随加载时间的增大,板料的最大变形高度先是增大,然后减小,当加载时间增大到一定程度时,板料的最终变形程度差别不大。通过推导加载时间与脉冲电流频率的关系,得出了脉冲电流频率对板料变形高度的影响:随脉冲电流频率的减小,板料的最大变形高度先是增大,然后减小,当脉冲电流频率减小到一定程度时,板料的最终变形程度差别不大。     

Improvement of springback prediction of wide sheet metal air bending process

Accurate springback prediction of wide sheet metal air bending process is important to improve product quality and ensure the precision in dimension. The definition of elastic limit bend angle was proposed. Based on cantilever beam elastic deforming theory, the geometrical parameters of forming tools, sheet thickness and the material yielding strain were derived and validated by the finite element method (FEM). Employing the degree of elastic limit bend angle, the equation for springback prediction was constructed, the results calculated fit well with experimental data. Especially for the small bend angle, the predicted results by equation were applied to conduct the springback prediction and compensation in industries and give closer correlation to the experimental data than those calculated by engineering theory of plastic bending.     

金属板料二次成型的有限元分析

为了实现同台压力机加工多品种、多型号的板料,大型板料的成型采用同机分步成型,通过采用板料成型动力显式有限元模拟,采用四节点退化壳单元对板料进行离散化,利用中心差分法离散时间域,建立动力显式计算格式,采用罚函数法和修正库仑定理计算接触力和摩擦力.对二次成形过程,建立有限元分析计算模型,通过Dynaform软件仿真得出同机分步成形法的可行性.     

板材多点成表时复杂边界条件的研究

给出了多点成形时非连续接触边界及库化磨擦边界条件的处理方法,引用经典的J2流动理论研究了马鞍面的多点模具和多点压机成形时金属的流动规律。     

Numerical simulation and experimental investigation of incremental sheet forming process

In order to investigate the process of incremental sheet forming （ISF） through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model （FEM） was developed to simulate the process and the simulated results were compared with those of experiment. The results of numerical simulations, such as the strain history and distribution, the stress state and distribution, sheet thickness distribution, etc, were discussed in details, and the influences of process parameters on these results were also analyzed. The simulated results of the radial strain and the thickness distribution are in good agreement with experimental results. The simulations reveal that the deformation is localized around the tool and constantly remains close to a plane strain state. With decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces, leading to less thinning and more homogeneous plastic strain and thickness distribution. During ISF, the plastic strain increases stepwise under the action of the tool. Each increase in plastic strain is accompanied by hydrostatic pressure, which explains why obtainable deformation using ISF exceeds the forming limits of conventional sheet forming.     

韧性断裂准则在板料成形中应用研究进展

对板料成形中的成形极限应力图、最大变薄率、成形极限图以及韧性断裂准则等预测成形极限的方法进行了综述和分析,提出了利用韧性断裂准则能够较好地预测塑性差的板料成形极限,而且还能考虑应变路径的变化.利用有限元方法模拟时,韧性断裂准则既可以运用到完全耦合的弹塑性损伤模型的增量方法中,也可以运用到一步有限元逆算法中.指出了为准确地预测成形极限,除了提高有限元模拟精度外,应找到一种本质地反映材料性能的准则.