Characterization and identification of forming features for 3-D sheet metal components

This paper presents a new classification system for forming operations, and concepts for extracting and recognizing forming feature from the 3-D sheet metal component created in a wireframe model. A set of principles is developed for characterizing forming features geometrically and topologically. Forming features are extracted by identifying 3-D component graph and subgraphs by vector normal method and vertex fusion methodology. Further, various planes and their type in the component graph are identified, and adjacency plane relationship between them is determined. Cross bend features are extracted by identifying common edges. Pattern recognition is then done using isomorphism principle and a set of characterization principles developed for forming features. A flat pattern is developed for the 3-D component and shearing features are identified. Recognized pressworking features help in the integration of Computer Aided Process Planning (CAPP), codification system, mapping of tools, inspection of tools, etc. The system has been tested for live components.     

汽车覆盖件冲压CAPP系统的研究

提出了引入KBE和优化方法的汽车覆盖件冲压工艺设计CAPP系统的框架结构,建立了基于特征/知识的产品/工艺信息模型,采用基于特征和知识的智能工艺决策方法制定了覆盖件冲压成形工艺路线,并利用几何优化的方法确定冲压方向,采用关联技术和参数化的方法进行冲压件图半智能化的详细设计和信息传递,直接生成工序件图的三维模型,有利于实现与CAE系统的结合,可直接用于模具设计和制造,实现无试模一次成功     

Modeling of plasma spraying of two powders

The behavior of metal and ceramic powders co-sprayed through a plasma jet was simulated using a commercial fluid dynamics model in which the particles are considered as discrete Langrangian entities. Computations were carried out for the plasma jet and the injected particles using (a) a steady-state three-dimensional (3-D) jet and (b) a simplified two-dimensional (2-D) model. An analytical method was used to estimate the appropriate injection velocities for the metal and ceramic particles, injected through opposing nozzles perpendicular to the plasma flow, so that their “mean” trajectories would impinge on the same area on the target surface. Comparison of the model projections with experimental measurements showed that this method of computation can be used to predict and control the behavior of particles of widely different properties.     

Experimental and numerical investigation of grid sheet bending behavior in four-roll bending

Grid sheet is a sandwich material consisting of two metal face sheets and a core of woven wire mesh that are joined by welding. It has been designed to act as an actively cooled heat shield, e.g. for steam turbine casings. For this purpose, cylindrical parts have to be produced from initially flat grid sheet. This paper focuses on four-roll bending of grid sheet. It is shown that springback and the number of failed spot welds after forming can be reduced by stress relief annealing and appropriate forming conditions. A finite element model of roll bending of grid sheet is presented, which has been set up to predict springback and spot weld failure.     

Laser digitizer-based sheet metal strain and surface analysis

This paper presents a new approach to sheet metal strain and surface analysis using data collected with a high-accuracy coordinate measuring machine mounted laser digitizer. First, the flat sheet metal blank is electrochemically etched with a hollow centre circular grid pattern. As the blank is pressed into the desired shape, the resulting strain deforms the circles into approximately elliptical shapes. The sheet metal is then laser digitized every 0.1 mm and the (X,Y,Z) surface coordinates plus reflected light intensity (grey level) are simultaneously recorded. Parallel computer-based image processing separates the darker ellipse grid points from the lighter background, and orthogonal least-squares data fitting estimates the major and minor surfaces strains. Results can be presented as a forming limit diagram, or as a derived thickness strain plot. Surface analysis is achieved by computing and plotting a maximum curvature map and then quantifying feature depth as the normal direction amplitude between the locally highest and lowest points. Implementation of the research for a representative industrial part is included.     

带下陷航空钣金零件展开及参数化建模研究

飞机钣金零件中有一类零件带有下陷,其下陷区域展开困难,目前主要采用经验方法展开,精度不高.提出一种针对下陷零件的展开算法,为下陷零件提供实用准确的处理流程,编程实现该类钣金展开的自动计算;对飞机钣金零件展开毛坯进行CATIA参数化建模.实践证明,本系统展开结果正确,精度满足要求,误差不超过0.3cm,方便操作.     

基于板料成形数值模拟的覆盖件模具结构优化

针对汽车覆盖件模具,提出一种基于板料成形模拟的模具结构拓扑优化方法,得到了新型的模具结构。先通过板料成形数值模拟得到板料对模具的作用力,经格式转换后,将模面节点力导入施加到模具的三维有限元模型上进行结构拓扑优化。运用该方法优化某后备门外板模具结构,经对比分析发现,优化后二次设计的模具结构相对于传统结构具有更高的刚度和更轻的质量,优于传统结构。     

Comparison of Material Models for Spring Back Prediction in an Automotive Panel Using Finite Element Method

Springback is a crucial factor in sheet metal forming process. An accurate prediction of springback is the premise for its control. An elasto-plastic constitutive model that can fully reflect anisotropic character of sheet metal has a crucial influence in the forming simulation. The forming process simulation and springback prediction of an automobile body panel is implemented by using JSTAMP/LS-DYNA with the Yoshida-Uemori, the 3-parameter Barlat and transversely anisotropic elasto-plastic model, respectively. Simulation predictions on spingback from the three constitutive models are compared with experiment measurements to demonstrate the effectiveness and accuracy of the Yoshida-Uemori model in characterizing the anisotropic material behavior of sheet metal during forming. With an accurate prediction of springback, it can provide design guideline for the practical application in mold design with springback compensation and to achieve an accurate forming.     

Mathematical modelling as a means to bridge the gap between material and tooling

The mathematical modelling of sheet-metal forming is a major focal point of current research in the field of deep-drawing world-wide. To date, however, most research efforts have been concentrated within the automotive industry.

Mathematical modelling in its initial form can be seen as an aid in understanding the material behaviour as sheet metal is transformed from a flat sheet to a hollow body. On a more sophisticated level, mathematical modelling has come to be regarded as a powerful tool with tremendous economic impact.

Decision makers in the automotive industry are increasingly under pressure to reduce development time whilst simultaneously improving product quality, minimizing risks and preventing mis-development. By supporting decisions in the initial stages of research and development and by providing feasibility results before a product even exists, mathematical modelling can decrease product-to-market time significantly.

Taking an oil-pan, which is difficult to stamp, as an example, it will be demonstrated how the part is designed using CAD data and how these data are transferred into an appropriate part and tooling network. The stresses and strains of the sheet are calculated by means of a constitutive law for deep-drawing which takes into account an elastic region, a large inelastic deformation, general hardening behaviour and anisotropy. A state-of-the-art supercomputer is used to carry out the modelling and simulation.     

实用钣金展开CAD系统的开发技术与应用研究

在分析钣金展开计算和绘图方法的基础上，详细地讨论了实用钣金展开CAD的系统结构和开发方法。最后结合钣金展开应用实例。系统地说明利用几何数学计算法结合计算机辅助设计和AutoCAD系统的绘图环境，如何进行钣金件展开计算，自动生成钣金展开图和相应的展开计算数据文件。目前，该方法已经成功地用于开发钣金展开CAD系统。     

板料冲压成形有限元分析软件的智能化

用户在使用板料冲压成形有限元分析软件时由于掌握的知识有限 ,常常不知如何建立分析模型 ,如何应用该软件进行分析计算 ,这在一定程度上影响了板料冲压成形数值模拟技术的推广应用。本文针对这些问题 ,在建立分析模型时 ,提出了自动生成板料模型、自动确定冲压方向、自动定位有限元模型以及自动计算压边力等算法 ,这样就方便了用户使用该软件 ,而且有利于板料冲压成形数值模拟技术的应用推广。     

Analysis of the levelling process based upon an analytic forming model

Roller levelling is a complex forming process to minimize flatness imperfections and residual stresses by repeated forming of a sheet.At the Institute for Metal Forming and Metal Forming Machine Tools at the University of Hanover an analytic forming model is being developed which analyses the levelling process with sufficient precision in a shorter time than is possible with the finite element method (FEM).With this analytic forming model, the states of multiple forming under bending conditions during the levelling process can be investigated. The residual stresses and the residual bend of the sheet metal are calculated. Additionally, the forces acting on the rollers during levelling are determined. The controlling system assures setting of rollers automatically.     

板料增量成形的研究进展

板料增量成形是采用简单模具对板料进行逐次塑性加工的一种工艺,不需要专用的模具就可以成形较为复杂的零件,同时还具有成形力小、柔性高的特点,特别适合多品种小批量零件的生产方式,因此得到国内外学者的重视。本文重点从板料的增量压弯成形、增量拉深胀形、增量微成形3个方面对板料增量成形的发展进行综述,还对板料增量成形工艺的发展前景进行了展望,指出进行理论创新、开发新的模拟软件、探索新的成形方案、开发增量成形新设备是发展趋势。     

汽车覆盖件面畸变评价指标研究

汽车覆盖件现有的面畸变评价指标均有一定的局限性 ,难以满足工程实践和理论研究多方面的要求。本文提出了一种新的面畸变评价指标 ,该指标既能反映零件上各点相对标准型面曲率变化程度的几何本质 ,又能比较客观地评价复杂零件局部畸变的水平。并用实例验证了二维和三维面畸变评价指标的正确性。     

Computer simulation and experimental investigation of sheet metal bending using laser beam scanning

Computer simulation and experimental investigation of the sheet metal bending into a V-shape by the laser beam scanning without an external force exerted onto it have been performed. A 3-D FEM simulation has been carried out, which includes a non-linear transient indirect coupled thermal-structural analysis accounting for the temperature dependency of the thermal and mechanical properties of the materials. The bending angle, distribution of stress–strain, temperature and residual stresses have been obtained from the simulations. The sheet metal bending had been performed for different materials, thicknesses, scanning speeds and laser powers. The measurement of real-time temperature and bending angle was carried out. The bending angle is affected by the mechanical and thermal properties of the sheet metal material, the process parameters, and the output of laser energy. The bending angle is increased with the number of laser beam scanning passes and is the function of the laser power and the laser beam scanning speed. The simulation results are in agreement with the experimental results.     

AZ31镁合金板材纵波轧制形变规律及边部损伤分析

纵波轧制+平辊轧制(LFR)是一种减轻镁合金轧制边裂的新型轧制工艺,通过一道次纵波轧制+二道次平轧,可有效减少镁合金板材边裂。为了进一步明晰LFR变形规律,本文通过对比AZ31镁合金板材纵波轧制+平轧(LFR)及平轧+平轧(FFR)热-力耦合有限元虚拟轧制对比和物理实验,分析了纵波轧制变形区金属变形规律及其对板材边部损伤的影响。结果表明：纵波轧制形成了异形搓轧区,板材各部位受到较大的三向剪切作用;急速金属流动产生的塑性变形热避免了板材边部温降,有利于提升塑性;剪切及温度影响促使LFR板材形成混晶组织,降低了波谷部位损伤,进而有效抑制了镁合金板材边裂的产生及发展。     

基于混合位移-压力有限元的厚板精冲数值模拟和损伤断裂预测

在MSC／MARC有限元分析软件中建立了轴对称精冲有限元模型，利用基于混合位移一压力的更新Lagrange有限元方法对精冲局部剧烈塑性变形进行模拟，克服了剪切自锁和体积自锁，结合网格自适应技术，对剪切区进行网格细化，精确捕捉了应变集中现象并通过MARC用户子程序实现了Schiffmann损伤功密度的半耦合计算，预测了精冲过程中材料损伤的发展，并预测了不同工艺参数下零件的塌角高度、光亮带高度和精冲力．最后，利用模拟得出的最佳工艺参数获得了合格的零件．     

Pulsed electromagnetic attraction of nonmagnetic sheet metals

This paper is dedicated to a study of pulsed electromagnetic attraction based upon recently developed inductor design – “Inductor System with an Attracting Screen”. The concept of attraction in this inductor system is based upon inducing currents flowing in the same directions in the screen and in the sheet metal blank, which, according to Ampere law, results in attraction forces between the screen and sheet metal blank. This system is capable of applying attraction forces to non-ferromagnetic sheet metal materials, for example, stainless steel or aluminum using low frequency discharges. An analytical model based upon solution of Maxwell equations was developed to estimate the attracting forces for low frequency discharges. In addition to the analytical model, the described concept is illustrated by the experimental results on attraction of sheet metal blanks of stainless steel employing a single turn inductor and a flat screen.     

Development of an analytical 3D-simulation model of the levelling process

Sheet metal often shows shape defects, which is not complying with the increasing requirements for the quality of the products needed to satisfy the highest demands on finer tolerances. Due to the market's high requirements on the quality of products, new high-technology levelling machines were developed. The adjustment of these levellers is very complicated and a successful adjustment depends mainly on the experience of the line operator. As the computational power has developed over the past years, simulation becomes more important in the production process and is used in analysing the effects of leveller adjustments on the unflattened sheet metal. In this study, edge- and centre waves are investigated. In order to find a suitable adjustment of the leveller to reach a flat sheet metal, an analytical 3D simulation model has been developed using the Matlab programming environment. The sheet metal will be firstly analyzed and visualized before and after deformation. A user-friendly interface has been developed to enter the required parameters before starting the simulation. Different methods have been used to investigate the effect of the levelling process on the sheet metal and to calculate the remaining shape defects after levelling. The simulation results were validated by experiments and are represented in this paper.     

The non-hydrostatic response of polymer melts as a pressure medium in sheet metal forming

The polymer injection forming process is a recent invention for producing plastic?Cmetal hybrids. It is a combination of injection molding and sheet metal hydroforming process in which polymer melt serves as a pressure medium. This paper presents the experimental investigations on the non-Newtonian nature of thermoplastic melt as pressure medium. The objective of this work is to identify the presence of non-hydrostatic pressure distribution within the cavity and its influence on the final shape of the formed sheet metal component. Experiments are conducted with center-gated injection mold under varying processing conditions. The development of localized cavity pressure during the process is recorded and evaluated against the final shape of formed sheet metal. It has been observed that higher injection rate, higher injection temperature, and higher melt flow index of the processed polymer is necessary for the uniform pressure distribution and subsequently uniform forming of the sheet metal.