Study on Process Parameters Optimization of Sheet Metal Forming Based on PFEA/ANN/GA

Sheet metal forming is widely applied to automobile, aviation, space flight, ship, instrument, and appliance industries.In this paper, based on analyzing the shortcoming of general finite element analysis (FEA), the conception of parametric finite element analysis (PFEA) is presented. The parametric finite element analysis, artificial neural networks(ANN) and genetic algorithm (GA) are combined to research thoroughly on the problems of process parametersoptimization of sheet metal forming. The author programs the optimization scheme and applies it in a research ofoptimization problem of inside square hole flanging technological parameters. The optimization result coincides wellwith the result of experiment. The research shows that the optimization scheme offers a good new way in die designand sheet metal forming field.

STUDY ON THE FINITE ELEMENT NUMERICAL SIMULATION OF SHEET METAL FORMING

Based on the Finite Element Theory of Rigid Plastic, relevant problems during plas-tic simulation on sheet metal forming were technologically studied and simplified; asimplified model of the blank holder during the drawing process was established andthe effects of related parameters on the forming processes were also studied. At thesame time, a finite--element numerical simulation program SPID was developed. Thedistribution of strain and relationship of stress--stroke simulated were compared withexperimented, the results are well coincided with each other. It is verified that theanalytical program is reliable.

FAST ACCURATE PREDICTION OF BLANK SHAPE IN SHEET METAL FORMING

By using the Finite Element Inverse Approach based on the Hill quadratic anisotrop-ically yield criterion and the quadrilateral element, a fast analyzing software-FASTAMP for the sheet metal forming is developed. The blank shapes of three typical stampings are simulated and compared with numerical results given by the AUTOFORM software and experimental results, respectively. The comparison shows that the FASTAMP can predict blank shape and strain distribution of the stamping more precisely and quickly than those given by the traditional methods and the AUTOFORM.

DEFORMATION ANALYSIS OF SHEET METAL SINGLE-POINT INCREMENTAL FORMING BY FINITE ELEMENT METHOD SIMULATION

Single-point incremental forming （SPIF） is an innovational sheet metal forming method without dedicated dies, which belongs to rapid prototyping technology. In generalizing the SPIF of sheet metal, the deformation analysis on forming process becomes an important and useful method for the planning of shell products, the choice of material, the design of the forming process and the planning of the forming tool. Using solid brick elements, the finite element method（FEM） model of truncated pyramid was established. Based on the theory of anisotropy and assumed strain formulation, the SPIF processes with different parameters were simulated. The resulted comparison between the simulations and the experiments shows that the FEM model is feasible and effective. Then, according to the simulated forming process, the deformation pattern of SPIF can be summarized as the combination of plane-stretching deformation and bending deformation. And the study about the process parameters＇ impact on deformation shows that the process parameter of interlayer spacing is a dominant factor on the deformation. Decreasing interlayer spacing, the strain of one step decreases and the formability of blank will be improved. With bigger interlayer spacing, the plastic deformation zone increases and the forming force will be bigger.

SECTIONAL FINITE ELEMENT ANALYSIS OF COUPLED DEFORMATION BETWEEN ELASTOPLASTIC SHEET METAL AND VISCO-ELASTOPLASTIC BODY

The present paper is devoted to developing a new numerical simulation method for the analysis of viscous pressure forming （VPF）, which is a sheet flexible-die forming （FDF） process. The pressure-carrying medium used in VPF is one kind of semisolid, flowable and viscous material and its deformation behavior can be described by the visco-elastoplastic constitutive model. A sectional finite element model for the coupled deformation analysis between the viscoelastoplastic pressure-carrying medium and the elastoplastic sheet metal is proposed. The resolution of the Updated Lagrangian （UL） formulation is based on a static explicit approach. The frictional contact between sheet metal and visco-elastoplastic pressure-carrying medium is treated by the penalty function method. Coupled deformation between sheet metal and visco-elastoplastic pressure-carrying medium with large slip is analyzed to validate the developed algorithm. Finally, the viscous pressure bulging （VPB） process of DC06 sheet metal is simulated. Good agreement between numerical simulation results and experimental measurements shows the validity of the developed algorithm.

QUANTITATIVE PREDICTION FOR SPRINGBACK OF UNLOADING AND TRIMMING IN SHEET METAL STAMPING FORMING

Based on the elastic-plastic large deformation finite element formulation as well as the shell element combined discrete Kirchhoff theoretical plate element (DKT) with membrane square element, deep-drawing bending springback of typical U-pattern is studied. At the same time the springback values of the drawing of patterns' unloading and trimming about the satellite aerial reflecting surface are predicted and also compared with those of the practical punch. Above two springbacks all obtain satisfactory results, which provide a kind of effective quantitative pre-prediction of springback for the practical engineers.

Process of back pressure deep drawing with solid granule medium on sheet metal

The experimental die apparatus of the solid granules medium forming on sheet metal was designed and manufactured.Typical parts,such as conical,parabolic,cylindrical and square-box-shaped components,were successfully trial-produced as well.According to the analysis of the changing trends of the cross-section shape and the wall thickness during the process,it can be found that the shape of the free deformation zone of the sheet metal,which is the most critical thinning area,can be described as an approximately spherical cap.According to this forming feature,back pressure deep drawing technology with solid granules medium on sheet metal was proposed to restrain drastic thinning at the bottom of the part through the joint friction effect of solid granules medium,the back pressure tringle and the sheet metal.Therefore,the deep drawing limit of the sheet metal is significantly improved.In order to fabricate thin-walled rotary parts with great drawing ratio and complex cross-sections,a finite element model based on the material property test of the solid granules medium was established to optimize the scheme of the back pressure deep drawing.The effects on the forming performance of sheet metal from back pressure load and the approach of blank holding control were analyzed through this model.

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.

Evaluation of forming limit in viscous pressure forming of automotive aluminum alloy 6k21-T4 sheet

A ductile fracture criterion is introduced into numerical simulation to predict viscous pressure forming limit of the automotive body aluminum alloy 6k21-T4. The material constant in the ductile fracture criterion is determined by the combination of the viscous pressure bulging (VPB) test with numerical simulation. VPB tests of the aluminum alloy sheet are carried out by using various elliptical dies with different ratios of major axis to minor axis(β), and the bugling processes are simulated by the aid of the finite element method software LS-DYNA3D. On the basis of the stress and strain calculated from numerical simulations, the forming limits of bulging specimens obtained are predicted by the ductile fracture criterion, and compared with experimental results. The fracture initiation site and the minimal thickness predicted by the ductile fracture criterion are in good agreement with the experimental results.

家电用热镀锌板减薄后的冲压成形性能

某家电厂将DC51D+Z钢冰箱用热镀锌板的厚度由0.3 mm减薄至0.27 mm,直接减薄时出现了冲压开裂问题。采用有限元仿真分析方法研究了零件冲压成形的要求,并提出了优化方案。结果表明:在材料不变、冲压工艺不变的前提下,直接减薄热镀锌板无法满足该零件冲压成形的要求;采用增加镀锌板碳元素含量、降低镀锌板硼元素含量、提高退火温度等方法,可以降低材料的屈服强度,提高材料的时效性能和冲压成形性能,改进后材料成形极限满足零件的冲压成形要求。

基于概率热力图的钣金件抓取点生成与评估

为快速确定钣金件抓取位置,提高抓取自动化程度,提出一种基于概率热力图的钣金件抓取点生成方法。基于钣金件与端拾器投影计算单因素概率热力图,评估钣金件与端拾器重叠程度、钣金件几何中心位置、钣金件表面起伏程度;融合各单因素概率热力图对概率热力图进行随机网格划分,并以数值最高处作为抓取位置;最后通过有限元仿真验证抓取点有效性。结果表明,所提抓取点生成与评估方法可以适应不同抓取工况,单次概率热力图计算及抓取点生成需1.58 s。Q345b钣金件被抓取最大形变为7.993 mm,最大等效应力为158.42 MPa,小于钣金件材料屈服强度。

Al6063管件渐进成形壁厚减薄率研究

基于正交试验法定量分析某种管件单点渐进成形机对Al6063铝合金管件的塑性成形工艺;通过有限元软件ABAQUS仿真,探究各工艺参数对Al6063管件成形后最大减薄率的影响规律,找到最佳工艺参数组合。结果表明:各工艺参数影响顺序由大到小依次为径向进给距离、工具头半径、轴向进给距离、摩擦因数。在半径60 mm、壁厚1 mm的管件尺寸下,最优工艺参数组合为工具头半径6 mm、径向进给量0.5 mm、轴向进给量1.5 mm、摩擦因数0.100。最优工艺参数组合会随着管件尺寸的改变发生小幅变化。

APPLICATION OF INTEGRATION ALGORITHEMS FOR ELASTO-PLASTICITY CONSTITUTIVE MODEL FOR ANISOTROPIC SHEET MATERIALS

Two algorithms of computing stress increment by using the elasto-plasticity constitutive model are firstly formulated, which are the Euler integration method and the radial return method. Hill＇48 anisotropic yield criterion is used. The Euler integration method can not obtain more accurate computation of the stress increment as the radial return method unless enough subintervals are taken,by which the Euler integration method will take excessive computing time. Without docreasing any accuracy, the radial return method can save much time. Finally, a square cup deep drawing from NUMISHEET＇93 benchmarks is simulated with a self-developed code SheetForrn in order to investigate the accuracy and efficiency of the radial return method.

Automobile Roof Panel Forming: Prediction and Compensation of Springback and Application of Numerical Simulation Based on Dynaform

The forming of sheet metal in a desired and attractive shape is a process that requires an understanding of materials, mechanics and manufacturing principles. Manufacturing a consistent sheet metal component is challenging due to the nonlinear interactions of various material and process parameters. One of the major issues in the manufacturing of inconsistent?sheet metal?parts is springback. Springback is the elastic strain recovery in the material after the tooling is removed and the final shape of the product depends on the springback amount formed. In this study according to the result of simulation the inverted compensation method is adopted to optimize die surface design. Similarly, to predict and compensate the springback error this study presented an analytical approach of forming process in a stepwise modification of the automobile roof panel. Moreover, based on?Dynaform?and?finite element analysis of sheet metal stamping simulation the sprinback in automobile roof panel is predicted and compensated.?In addition, this study examines the significant requirements of the sheet metal forming precision of automobile body and the simulation of forming, stamping and springback of automobile roof panel is carried out, and the result of simulation also is analyzed.

小直径薄壁航空导管双翻边成形端头质量控制

针对小直径薄壁航空导管双翻边成形管件端头实际接触区宽度不均匀的问题,研究了模具参数对成形管件接触区宽度的影响。结果表明:第1道次和第3道次模具参数对结果影响很小,第2道次模具参数影响较大,其中圆角半径和圆角所占夹角有较大影响,半锥角度影响较小,成形管件端头接触区宽度随着第2道次凸模圆角半径的增大明显变宽,随着第2道次圆角所占夹角角度的增大先增宽后变窄,而第2道次半锥角度对接触区宽度影响较小。半锥角度应大于等于圆角所占夹角,基于正交优化方法,得到了最优参数组合为圆角半径R=20 mm,半锥角度为85°,圆角所占夹角为80°,此具有最好的成形效果,成形管件端头接触区宽度得到提升,使管件安装时有较大的密封区域,能有效提升双翻边管端头的密封性能。

基于解耦计算的多步快速成形有限元法

钣金零件是构成飞机机体和汽车车身的重要零部件。为缩短钣金件的生产周期,将有限元法用于零件设计初期评估零件的可制造性。为提高现有板料成形有限元法的计算效率,同时保证模拟精度,在一步快速成形有限元法的理论基础上,研究多步快速成形有限元法,通过引入中间构形的方式来考虑板料成形过程中加载路径与变形历史的影响。中间构形的构造是多步快速成形有限元法的关键,采用解耦思想将中间构形分解为弯曲变形和拉伸变形两个独立的过程进行计算。在弯曲变形阶段,不考虑材料的流动,根据板料与模具之间的位置关系计算获得滑移约束面;在拉伸变形阶段,材料的流动限制在滑移约束面上,通过应力平衡迭代以及节点修正后获得中间构形。以典型的钣金零件为例进行成形模拟,与现有商业有限元软件在计算精度和效率上进行对比,验证了该算法的可行性和有效性。结果表明,所提出的算法能够快速地构造出合理的中间构形,且能够准确地预测零件的成形性和厚度分布。

TO56金属管帽多工位级进模设计

根据TO56金属管帽的结构特点,分析了制件的结构工艺性,计算制件的工艺参数,拟定制件的工艺路线,并针对首次拉深成形开展有限元分析;在此基础上完成拉深、冲孔、切边等关键工序的工位结构设计,设计了该制件多工位级进模的整体结构。

基于有限元的汽车后备箱外板冷冲压成形分析

采用有限元软件Dynaform对某汽车后备箱外板冲压成形进行仿真分析,解决零件开裂、起皱和回弹等质量缺陷;以压边力、冲压速度、模具间隙和摩擦因数为优化因素,以最小厚度、最大厚度和最大回弹量为优化目标,获得各自的最优工艺参数;使用Design-Expert软件完成多目标优化求解,获得多目标最优工艺参数组合并进行仿真分析。分析结果表明,多目标最优工艺参数组合零件成形质量良好,厚度分布和最大回弹量均符合零件设计要求。

航空发动机钣金件多工序连续工艺链式仿真方法研究及实验验证

目的针对航空发动机上挡溅盘钣金件的多工序成形过程,进行有限元仿真分析与实验验证。方法以ABAQUS和DEFORM为仿真平台,先采用ABAQUS对钣金件第一道次的拉深回弹过程进行仿真,在此基础上,将第一道次仿真结果导入DEFORM中,作为初始状态进行退火热处理;然后将仿真结果导入ABAQUS中作为初始状态进行第二道次的拉深回弹仿真,重复上一道次的数据传递过程,再进行热处理与第三道次整形模拟,在每一道次拉深成形后对比模拟与实验结果。结果实现了钣金件在同一软件和不同软件之间几何形状及物理场的数据传递,完成了钣金件的多工序连续工艺仿真成形。第一道次拉深卸载后零件回弹较小,模拟得到的零件几何尺寸与实验结果误差较小,但卸载后零件中有较大残余应力,通过热处理可以很大程度地消除残余应力,增强高温合金后续的成形性能,经过多工序成形仿真后,几何特征尺寸累计误差值略有增大,但仍在可接受范围内。结论包含中间退火热处理的多工序成形仿真可以较好地描述实验结果,证明了仿真结果的准确性与有效性,可以为改进和优化钣金件的设计及成形过程提供科学指导。

TC4钛合金大深腔反向变曲率复杂蒙皮零件成形工艺

以TC4钛合金大深腔反向变曲率复杂蒙皮零件为研究对象,设计了两种成形工艺方案,分别为超塑成形工艺方案、热成形+超塑成形工艺方案,采用PAM-STAMP软件进行了工艺仿真分析,得到了零件成形过程中厚度的变化,预测了零件的成形质量,确定了采用热成形+超塑成形工艺方案,并设计了相应的成形模具进行试验验证。结果表明,采用热成形+超塑成形组合工艺可成功制备出合格的TC4钛合金大深腔反向变曲率复杂零件,成形后零件最薄处厚度约为1.24 mm,减薄率约为22.5%,满足设计强度要求,同时成形结果与仿真结果一致。