Finite element simulation of plate or sheet metal forming processes using tetrahedral MINI-elements

In this paper, finite element prediction of sheet metal forming process is investigated using solid elements. A three-dimensional rigidviscoplastic finite element method with linear tetrahedral MINI-elements is employed. This technique has traditionally been used for bulk metal forming simulations. The solid element approach with remeshing capability is applied to simulating a plate metal forming process to reveal its possible problems. The similar approach is also applied to a typical sheet forming process. Both single- and double-layer finite element mesh systems are studied, with particular attention to their effect on the deformed shape of the workpiece and thickness variation of a cold sheet forming process. The procedure is applied to the well-known problem of the NUMISHEET93 international benchmark. The resulting predictions are compared with experimental observations found in the literature, and good agreement is noted.     

有限元逆算法与板料成形工艺的评价

依据理想形变理论，研究开发了冲压成形过程模拟的有限元逆算法，根据变形体的整体塑性功取相对极值的条件，导出了塑算法有限元方程。提出了求逆算法初始解以及求解与给定形状的毛坯相对应的冲压件形状的迭代计算方法。采用有限元塑算法预测了与冲压件形状相对应的冲压件毛坯的展开形状，根据给定的板坯形状计算了冲压件最终构形及应变分布。分析计算实例表明，逆算法可用于对板料成形工艺方案进行快速评价，对冲压工艺参数进行优化。     

基于Dynafarm多角弯曲成型模拟及模具设计

板料成型数值模拟技术在工艺方案预测、毛坯尺寸估算和优化模具设计等方面具有重要的作用。板料成型模拟软件 Dynaform 具有强大的板料成型分析功能及前、后处理功能,主要用于板料成型工艺中模具的设计与开发。本文以汽车多角弯曲件为研究对象,根据板料成型特点,采用 Dynaform 软件,对零件冲压过程进行了成型模拟和回弹分析,确定了最佳工艺参数,优化了模具结构,完成了模具设计,改变了传统的依靠经验或反复试验和试模的模式,缩短了开发周期,提高了设计可靠性,降低了模具成本。     

考虑接触演变的板材回弹过程建模与优化

回弹是由工件在卸载后的弹性变形引起的。板料成形过程中为了控制成形件的最终形状,必须进行回弹设计优化。准确预测回弹对于板料成形过程的模具设计非常重要。降低回弹模拟结果与试验结果的偏差是设计过程中的难题。基于NUMISHEET’02的自由弯曲标准考题考虑板材与模具间的接触演变过程,建立了一个有限元模型来预测回弹。采用一个常规的优化方法对有限元分析中的材料和单元模型进行了分析,研究发现不同模型对回弹结果有较大影响。模拟结果与参考文献中的试验结果比较表明了模型的正确性和可行性。     

Optimization of drawbead restraining forces and drawbead design in sheet metal forming process

This paper presents an optimization procedure of drawbead restraining forces in order to improve the sheet metal formability in deep drawing process. A simplified finite element method called inverse approach (IA) has been developed for sheet forming analysis with the consideration of the drawbead restraining forces. This IA is combined with a mathematical programming algorithm to optimize the restraining forces and then to design the drawbeads. The obtained optimization procedure is very efficient due to the simplified assumptions of the IA and the analytical sensitivity analysis. The Square cup of Numisheet’93 and the Renault Twingo dashpot cup are presented to demonstrate the usefulness of the proposed optimization procedure for industrial applications. Verifications of the obtained results have been carried out using a precise incremental commercial code OPTRIS^TM based on explicit dynamic approach to show the effectiveness of our approach.     

Ansys下复杂拉伸成型件成型工艺研究

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。首先讨论了用有限元分析软件研究板料成形过程的重要意义;其次介绍了有限元分析成型件的成型工艺;然后介绍了用Ansys研究成型件成型工艺的国内外进展情况;最后对这一领域的发展趋势作了展望。     

Process optimal design in non-steady forming of porous metals by the finite element method

A new approach to process optimal design in non-steady forming of porous metals is presented. In this approach, the optimal design problem involving diverse objective functions and design variables is formulated on the basis of the finite element process model, and a derivative-based approach is adopted as the solution technique. The process model, the formulation for process optimal design, the schemes for the evaluation of the design sensitivity, and an iterative procedure for optimization are described in detail. The validity of the schemes for the evaluation of the design sensitivity is examined by performing a series of numerical tests. The capability of the proposed approach is demonstrated through application to a selected design problem.     

Formability analysis on the process of multi-point forming for titanium alloy retiary sheet

The multi-point forming (MPF) process of spherical surface parts of titanium alloy retiary sheet and titanium alloy sheet metal with different thickness and curvature radius was simulated by an explicit finite element software. Contradistinctive analysis between retiary sheet and sheet metal forming parts with different modes were done. The simulation results show that under the same forming conditions, titanium alloy retiary sheet is not easy to wrinkle and springback, whereas it is easy to form. The reason for differences in the formability of above-mentioned sheet metal is also analyzed. A non-wrinkling limited graph and a fracture critical graph for spherical surface parts of retiary metal sheet and metal sheet were obtained. Finally a forming test of titanium alloy cranial prosthesis was done in MPF press. Testing results indicate the customized 3D curved surface of prosthesis can be adequately shaped and the forming quality was guaranteed.     

Analysis of drawbead process by static-explicit finite element method

The problem analyzed here is a sheet metal forming process which requires a drawbead. The drawbead provides the sheet metal enough tension to be deformed plastically along the punch face and consequently, ensures a proper shape of final products by fixing the sheet to the die. Therefore, the optimum design of drawbead is indispensable in obtaining the desired formability. A static-explicit Finite element analysis is carried out to provide a perspective tool for designing the drawbead. The finite element formulation is constructed from static equilibrium equation and takes into account the boundary condition that involves a proper contact condition. The deformation behavior of sheet material is formulated by the elastic-plastic constitutive equation. The finite element formulation has been solved based on an existing method that is called the static-explicit method. The main features of the static-explicit method are first that there is no convergence problem. Second, the problem of contact and friction is easily solved by application of very small time interval. During the analysis of drawbead processes, the strain distribution and the drawing force on drawbead can be analyzed. And the effects of bead shape and number of beads on sheet forming processes were investigated. The results of the static explicit analysis of drawbead processes show no convergence problem and comparatively accurate results even though severe high geometric and contact-friction nonlinearity. Moreover, the computational results of a static-explicit finite element analysis can supply very valuable information for designing the drawbead process in which the defects of final sheet product can be removed.     

钣料成形过程动力分析中的惯性效应及对策

指出钣料成形过程中采用曲面压料面时,压边圈夹紧过程动力显式有限元分析存在惯性效应问题。提出“虚拟补实压边圈”方法克服惯性作用,高效实现曲面压边圈夹紧过程的动力工有限元模拟,拓展动力显式有限元方法在钣料成形数值模拟中的应用领域,对于连续快速地模拟曲面压边和拉延等多阶段钣料成形过程意义重大。     

A simple model to simulate electromagnetic sheet free bulging process

Electromagnetic sheet forming is a high-velocity forming process driven by the coupled electromagnetic and mechanical phenomena. The deformation of the workpiece is governed by the body forces (Lorentz forces) that results from a pulsed magnetic field produced by a flat spiral coil. Formability can be increased using this high-velocity forming technique due to the inertial forces and high strain rates. In this study, we consider the electromagnetic and the mechanical aspect of the process as two independent problems. The finite difference method has been employed to solve the electromagnetic equations. The pressure acting on the sheet and due to the Lorentz forces is estimated neglecting the influence of the sheet velocity on the magnetic field. Then it has been treated as a load in the mechanical problem. Numerical simulations of the mechanical problem have been performed with the commercial finite element code ABAQUS/Explicit. The magnetic pressure has been introduced in ABAQUS/Explicit as an analytical pressure distribution. The general objective of this study is to better understand the complex phenomenon of deformation and the influence of viscoplastic material behaviour during the simulation of a free bulging electromagnetic sheet forming process.     

润滑条件下铝合金板成形模拟中摩擦模型的研究

对润滑条件下铝合金薄板筒形件拉深成形过程进行了工艺分析，在作出一些简化和假设的基础上，建立了基于流体润滑的筒形件拉深成形过程摩擦模型；将该模型运用到板料成形过程有限元分析中，计算出筒形件成形时摩擦系数动态变化的数值；开发出基于探针测试的铝合金板温成形动态过程摩擦测试系统，并对筒形件成形时的摩擦系数进行了测试实验。计算结果与实验数据表明，板料成形过程中的摩擦系数不是一个常数，随着凸模行程的增加，摩擦系数具有增加的趋势。     

Comparison between three optimization methods for the minimization of maximum bending load and springback in wiping die bending obtained by an experimental approach

The sheet metal bending process is widely used in the automotive industries, and it is actually one of the most important manufacturing processes. The robustness and the reliability of the bending operation, like many other forming operations, depend of several parameters (geometry, material, and process). In this paper, the die radius and the clearance between the punch and the sheet are optimised in order to reduce the maximum bending load and the springback. Two optimization problems are formulated, and three optimization procedures based on the response surface method are proposed and used to find the optimum solutions. Global and local approximations are used to replace the initial optimization problem, which is implicit by an explicit problem, and the optimum is localised using two algorithms: a sequential quadratic programming and an evolution strategies. The objective functions are evaluated experimentally into a limited points number, which are defined using a design of experiments technique. Good results are obtained from the three optimization procedures. The ability of each technique to find the optimal solution is evaluated, and the results show a good agreement between those three methods.     

瑞风商务车托架拉延成形数值模拟及工艺参数优化

基于逆向工程建立瑞风商务车托架零件的几何模型,并基于Dynaform软件平台对不同工艺参数下该零件的拉延成形过程进行数值模拟。在此基础上,以压边力、拉延筋高度和拉延筋圆角半径作为设计变量,以零件不发生破裂为优化目标,以有限元数值模拟结果作为虚拟样本,建立目标函数的人工神经网络预测模型;将人工神经网络预测模型作为优化算法的知识源,采用遗传算法对压边力、拉深筋几何参数等工艺参数进行了优化设计。试验结果表明,数值模拟、神经网络预测和工艺优化是可靠的,从而可为制定金属板料最佳的冲压成形工艺提供一条先进、合理的途径。     

Analytical modeling and numerical simulation for three-roll bending forming of sheet metal

The three-roll bending forming of sheet metal is an important and flexible manufacturing process due to simple configuration. It is suitable for forming large sheet parts with complex, curved faces. Most researches on roll bending forming of large workpiece are mainly based on experiments and explain the process through macroscopic metal deformation. An analytical model and ABAQUS finite element model (FEM) are proposed in this paper for investigating the three-roll bending forming process. A reasonably accurate relationship between the downward inner roller displacement and the desired springback radius (unloaded curvature radius) of the bent plate is yielded by both analytical and finite element approaches, which all agree well with experiments. Then, the three-roll bending forming process of a semi-circle-shaped workpiece with 3,105 mm (length)?×?714 mm (width)?×?545 mm (height) is simulated with FEM established by the optimum tool and process parameters. Manifested by the experiment for three-roll bending forming of this workpiece, the numerical simulation method proposed yields satisfactory performance in tool and process parameters optimization and workpiece forming. It can be taken as a valuable mathematical tool used for three-roll bending forming of large area sheet metal.     

基于有限元逆算法的拉深筋工艺设计和优化

汽车覆盖件拉深成形中，一般通过设置适当的拉深筋控制成形过程中的板料塑性流动规律来提高覆盖件成形质量。针对覆盖件工艺设计需求，提出一种基于有限元逆算法的拉深筋工艺优化算法。该算法以灵敏度优化方法为基础，考虑了板料的成形度、破裂和起皱等成形缺陷。在板料成形模拟FASTAMP系统中，开发了拉深筋优化模块，并以实际覆盖件为例，验证了该算法能快速准确地模拟等效拉深筋力的布置情况以及优化板料的成形性。     

汽车覆盖件模具冲压有限元仿真分析

针对汽车覆盖件难以成形以及在冲压过程中易产生各种质量问题等特点,采用基于动力显式算法的有限元分析软件DYNAFORM,以某汽车内覆盖件前隔板为例,对模拟得到的成形极限图（FLD）、材料厚薄图进行分析,优选工艺设计。阐述了CAE技术在模具开发中的重要作用。     

基于ANSYS Workbench的橡皮囊成形过程有限元建模功能模块开发

橡皮囊成形是航空企业中钣金件成形的主要方法之一,经常需要采用有限元软件进行成形过程分析,其中传统有限元建模不仅对技术人员操作水平要求高,而且建模效率低。针对橡皮囊成形有限元建模过程进行了分析,总结归纳出可以自动实现建模的部分,包括几何建模、材料定义和网格划分等,基于ANSYS Workbench软件的DM模块以及DS模块进行二次开发,建立专用的橡皮囊成形分析模块,实现橡皮囊成形有限元模型的快速构建,操作界面友好。应用所开发的模块对某钣金件橡皮囊成形过程进行有限元建模,并与传统有限元建模方法进行对比分析,结果表明,采用所开发的模块建模分析与传统有限元建模方法的模拟结果吻合较好,证明了所开发模块的有效性。     

基于多目标遗传算法优化板料拉深成形工艺参数

利用人工神经网络构建了板料拉深成形的目标函数模型,建立了板料拉深成形工艺参数和性能评价指标之间的映射关系.以多种工艺参数(压边力、摩擦因数等)作为优化变量,多种成形缺陷(起皱、破裂等)作为优化目标,结合多目标遗传算法和数值模拟,建立了板料拉深成形工艺参数的优化设计模型,大大提高了优化的效率.以油底壳下盖为例,对其拉深成形工艺参数进行了优化,通过对优化结果进行数值模拟可以看出,该优化参数完全避免了各种缺陷的产生,这说明该优化算法具有较好的优化结果.     

Electromagnetic blank restrainer in sheet metal forming processes

Electromagnetic blank restrainer (EMBR) is a new technology that was recently developed to control material movement in sheet metal forming processes. Magnetic attraction on the ferrous sheet metal is the intrinsic property of EMBR. Such magnetic force is quantified using Maxwell's stress tensor to assess the feasibility of EMBR in the sheet metal forming process. The 3D finite element analysis (FEA) of an electromagnetic system is conducted to determine the distribution of magnetic flux density on contacting surfaces of the sheet metal. The distribution is then used to estimate the magnetic force. Experiments have been conducted to measure the magnetic force and compare with results from the FEA. Biaxial-loading apparatus has been built to measure restraining forces on the sheet metal with blankholder, drawbead, and EMBR. All the restraining forces are put together in a chart to see where each method stands with respect to one another. In order to evaluate the quality of forming with each method, an experimental die has been built. The die forms a channel in a single stroke and provides a direct indication of how each restraining method controls blank movement in the die. The real advantage of EMBR lies in the effectiveness of force control and its flexible location in a sheet metal forming die. To prove this, a prototype has been built in a tryout die where house appliance panel is formed with blankholder and EMBR. EMBRs are locally installed in the die and actively controlled during the forming process. The part formed with EMBR shows a significant improvement in the forming quality. At the end of this paper, two immediate impacts that EMBR can bring to the sheet metal forming industry are also discussed.