Inverse finite element approach and its application in sheet metal forming

The inverse finite element approach (IFEA) was derived from ideal forming to predict the development blank of sheet metal and the thickness strain distribution according to the geometry of final product. The flange portion of stamping product under blank-holder is a free parameter that is mostly dependent on the shape of the initial flat blank. Based on the IFEA, this paper proposed a node relocation technique to estimate the influence of flange shape and evaluate the final geometry and thickness strain distribution from the prescribed flat blank. The applications of the IFEA cover the backward and forward evaluations: from given product to initial blank and from given initial blank to final product. Those applications make the design of sheet metal forming easy and fast. A door-like product experiment confirmed that the precision of the IFEA satisfied the manufacturing requirement.     

板料成形中有限元模拟技术的应用

使用传统的靠经验和反复修模试模的方法研发模具，不仅难以掌握板料成形的真实过程，而且会造成人、财、物、时的浪费。将有限元技术引入冲压成形模拟中是解决这一问题行之有效的方法，对板料冲压成形模拟进行了讨论，并重点介绍了Dynaform软件的应用。     

有限元模型转换及其在金属板料成形数值模拟中的应用

本文根据CAD和CAE软件各自的功能和特点 ,探讨了板料成形数值模拟中CAD模型向CAE模型转换的方法 ;并针对有限元分析软件ANSYS与ABAQUS的实际特点 ,编写了有限元模型转换接口程序 ,用实例验证了所编接口转换程序的可行性与正确性。     

基于有限元逆向法和正向法的板料成形过程中合理毛坯形状的确定

合理的毛坯形状可以提高板料成形质量,降低成本.有限元逆向法确定简单形状零件的毛坯具有很高的可靠性,但不适合于单独用来确定带有拉深筋及切边余量大的覆盖件拉深成形板料毛坯.本文采用有限元逆向法和正向法结合的方法,确定覆盖件零件的成形毛坯,并用物理实验验证了其合理性.     

板料成形数值模拟研究进展

以历届国际板料成形数值模拟会议(NUMISHEET)及其标准考题研究结果为主要线索,对板料成形数值模拟的研究历史及发展现状作了简要综述,并对当前的研究热点和发展方向进行了探讨.     

板料冲压成形一步正向有限元分析

提出基于理想成形理论的板料冲压成形一步正向有限元分析方法。给出迭代初始解获取、线性化处理、收敛条件判定等具体算法,以及所使用的材料应力应变关系和屈服准则。运用该方法进行带凸缘盒形件和无凸缘筒形件的冲压成形模拟,将减薄率与增量有限元方法计算结果进行比较,并就无凸缘筒形件进行实验验证。结果表明,该方法计算结果可靠,使用简便,计算效率高。     

基于增量法有限元对钣金成形中毛坯展开形状的优化

钣金成形中,毛坯的形状不仅影响成形过程中材料的流动情况,而且影响材料的成形性和材料的用量等。合理的毛坯形状是钣金成形的一个重要工艺参数。文章基于商用软件ANSYS/LS-DYNA的动态显式算法和变形路径,提出了一种钣金毛坯优化的方法,并通过APDL参数化编程和C++语言实现了毛坯优化算法。以一个长方形盒形件为实例进行了优化。结果表明,此方法可行,有实际使用价值。     

An analytical finite element model for predicting three-dimensional tool forces and chip flow

A model of three-dimensional cutting is developed for predicting tool forces and the chip flow angle. The approach consists of coupling an orthogonal finite element cutting model with an analytical model of three-dimensional cutting. The finite element model is based on an Eulerian approach, which gives excellent agreement with measured tool forces and chip geometries. The analytical model was developed by Usui et al. [ASME J. Engng Indust. 100(1978) 222; 229], in which a minimum energy approach was used to determine the chip flow direction. The model developed by Usui required orthogonal cutting test data to determine the tool forces and chip flow angle. In this paper, a finite element model is used to supply the orthogonal cutting data for Usui's model. With this approach, a predictive model of three-dimensional cutting can be developed that does not require measured data as input. Cutting experiments are described in which good agreement was found between measured and predicted tool forces and chip flow angles for machining of AISI 1020 steel.     

板料成形摩擦特性的实验研究与有限元分析

采用MPX-2000盘-销式摩擦试验机研究了边界润滑条件下滑动速度与界面载荷对304不锈钢与SKD11模具钢之间摩擦系数的影响。运用Matlab软件对实验数据进行处理分析,得出摩擦系数随滑动速度与界面载荷变化的规律,建立了基于滑动速度与界面载荷的变摩擦系数模型。并对典型U形件进行了实际冲压实验与有限元仿真,比较了定摩擦系数模型和变摩擦系数模型的回弹预测结果与测量值之间的误差。分析结果表明:滑动速度为30.615~44.22 mm·s~(-1)时,304不锈钢与SKD11模具钢之间的摩擦系数随滑动速度的增加而逐渐减小;界面载荷为2.038~4.076 MPa时,摩擦系数随界面载荷的递增而递减,且随着载荷的增加,摩擦系数减小的趋势逐渐变缓。采用修正后摩擦模型的回弹预测结果与测量值之间误差较小,预测精度较高。     

基于动态显式算法的薄板冲压成形回弹量工程估算研究

采用动态显式算法仿真了LDH (LimitingDomeHeight)实验的成形与回弹过程 ,确定了冲压后薄板回弹量与压边力、材料特性和冲压高度之间的关系曲线 ,分析了脱模前成形件内的能量和等效应力 ,以及脱模后由于成形件发生回弹导致的薄板内能量和等效应力的变化情况。计算结果表明 ,纯显式算法对于回弹量的计算是可以保证一定精度的。     

Optimum finite element for simulation of elasto-plastic bending of sheet metal

This paper concerns the optimum condition of finite elements in simulation of elasto-plastic bending. The effect of the integration scheme and the number of finite element layers on calculation of the stress and the strain is thoroughly investigated and some remedies are suggested. As a benchmark problem, an elasto-plastic bending problem is studied for the calculation of the stress and the strain. The calculation directly estimates stress and strain distribution along the thickness direction and shows the oscillatory behavior ol the stress and the incompatible behavior of the strain. The results tully demonstrate that the finite: element simulation in the usual way is sometimes very dangerous since it could lead to a fatal pitfall. This study proposes the optimum condition of finite elements especially in simulation of elasto-plastic bending with a proper integration scheme.     

Industrial applications of sheet stamping simulation using new finite element models

The paper is aimed to present industrial applications of sheet stamping simulation using new finite element formulations developed in the International Center for Numerical Methods in Engineering in Barcelona. Theoretical formulation is briefly reviewed. Both continuum and shell elements have been considered. The new shell elements developed are based on a geometrically exact shell model treating the shell as one-director Cosserat surface. The formulation of the continuum elements employs the multiplicative decomposition of the deformation gradient tensor into its elastic and plastic parts. The new finite element models have been implemented in the in-house explicit dynamic code STAMPACK. A number of practical problems of sheet metalforming have been solved with the program. Some of the problems, namely stamping of a kitchen sink, hydraulic forming of an aeronautical part and stamping of a food can, have been presented in the paper. The examples give an idea of practical information that can be obtained from the computer simulation of a forming process. The results confirm a good behaviour of the formulation and program used in the industrial applications.     

Finite element simulation of the manufacturing process chain of a sheet metal assembly

An increasing number of components in automotive structures are today made from advanced high strength steel (AHSS). Since AHSS demonstrates more severe springback behaviour than ordinary mild steels, it requires more efforts to meet the design specification of the stamped parts. Consequently, the physical fine tuning of the die design and the stamping process can be time consuming. The trial-and-error development process may be shortened by replacing most of the physical try-outs with finite element (FE) simulations of the forming process, including the springback behaviour. Still it can be hard to identify when a stamped part will lead to an acceptable assembly with respect to the geometry and the residual stress state. In part since the assembling process itself will distort the components. To resolve this matter it is here proposed to extend the FE-simulation of the stamping process, to also include the first level sub-assembly stage. In this study a methodology of sequentially simulating each step in the manufacturing process of an assembly is proposed. Each step of the proposed methodology is described, and a validation of the prediction capabilities is performed by comparing with a physically manufactured assembly. The assembly is composed of three sheet metal components made from DP600 steel which are joined by spot welding. The components are designed to exhibit severe springback behaviour in order to put both the forming and subsequent assembling simulations to the test. The work presented here demonstrates that by using virtual prototyping it is possible to predict the final shape of an assembled structure.     

板料成形多步反向模拟法的中间构型与运动约束

考虑到一步反向模拟法无法考虑变形历史的影响、无法计算各中间步之间的应变等信息,文章提出一种新型的多步反向模拟法。根据当前工步凸凹模信息,采用最小面积法,并结合可行域二次序列规划算法(FSQP)快速获取当前工步零件的构型。提出一种基于重心坐标的穿越搜索策略来提高接触搜索速度,计算复杂度仅为O(n1/d)(d为网格所在空间的维数)。提出的快速接触搜索算法来实现中间构型各个节点在约束滑移面上的移动,其理论成果成功地在自行开发的板料成形反向模拟法软件InverStamp/Multi-step模块中实现。在圆筒形件多步拉深实例中,通过中间工序及最终成形零件厚度分布与基于增量理论的LS-DYNA求解器计算结果的比较,验证了多步反向模拟法的有效性。     

Post-processing of finite element results and prediction of the localized necking in sheet metal forming

We propose a method based on the linear perturbation technique to predict the localized necking phenomenon in post-processing of finite element results for the simulation of deep-drawing processes. Numerous numerical results compared to experimental ones show the validity of such an approach. Numerical investigations have been performed to demonstrate the good behaviour of this technique in front of the process parameters as the friction value between the sheet and the tools, the blankholder force value or the tools radius. The paper is concluded by the interesting perspectives offered by this approach.     

Analysis of plastic flow localization under strain paths changes and its coupling with finite element simulation in sheet metal forming

Formability of sheet metal is usually assessed by the useful concept of forming limit diagrams (FLD) and forming limit curves (FLC) represent a first safety criterion for deep drawing operations. The level of FLC is strongly strain path dependent as observed by experimental and numerical results and therefore non-proportional strain paths need to be incorporated when analyzing formability of sheet metal components. Simulations using finite element method allow accurate predictions of stress and strain distributions in complex stamped parts. However, the prediction of localized necking is a difficult task and the combination of forming limit diagram analysis with finite element simulations often fail to give the right answer, if complex strain paths are not included in these predictions.     

板料冲压成形有限元反向分析中初始解确定方法的研究概况

初始解的确定是板料冲压成形有限元反向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。本文就国内外关于反向分析中的初始解确定方法进行了综述和分析。     

限制自由度单元及其在板料成形过程数值模拟中的应用

根据板料成形过程的特点，提出一种用于板料成形分析的新单元模型－三维限制自由度单元模型，这种单元既没有膜单元不能考虑横向剪应力的遗憾，也不受壳单元对于局部大的限制毛坯后机加工同时克服了体单元解决板结构问题时刚度矩阵奇异的缺点。     

An analytical finite element technique for predicting thrust force and torque in drilling

An analytical finite element technique was developed for predicting the thrust force and torque in drilling with twist drills. The approach was based on representing the cutting forces along the cutting lips as a series of oblique sections. Similarly, cutting in the chisel region was treated as orthogonal cutting with different cutting speeds depending on the radial location. For each section, an Eulerian finite element model was used to simulate the cutting forces. The section forces were combined to determine the overall thrust force and drilling torque. Good agreement between the predicted and measured forces and torques was found in orthogonal and oblique cutting and in drilling tests. The drilling tests were performed on AISI 1020 for several drill diameters, spindle speeds, and feed rates. An extension of the technique for predicting drill temperatures has also been described.