动臂梁焊接顺序优化减小焊接变形模拟预测

利用热弹塑性有限元法对装载机动臂梁结构的焊接变形进行热 力耦合数值模拟.建立分析模型,定量对比在同一约束条件下动臂板与动臂圆筒、摇臂板与动臂圆筒的焊接顺序对整体结构焊接变形的影响,按照对称组焊的原则优化焊接顺序.结果表明,对称结构的动臂梁采用交替焊接顺序与沿一个方向顺次焊接顺序相比,动臂板与摇臂板变形量都减小,先焊动臂板比先焊摇臂板 动臂板角变形小.得出整体结构的最佳焊接顺序方案,并将预测的在最佳焊接顺序下的变形模拟值和试验值进行对比,二者吻合良好.     

基于主S-N曲线法的地铁制动箱焊接疲劳分析

为研究地铁车辆制动箱焊接接头的疲劳寿命,根据实际结构建立4节点壳单元有限元模型,给出搭接焊和T型焊的焊缝建模方法.在3种振动工况下,运用主S N曲线法计算焊缝的等效结构应力和对应损伤比.结果表明：该地铁车辆制动箱焊接结构设计合理可靠;通过与实体单元模型计算结果进行对比证明壳单元模拟焊缝的合理性;在不同尺寸单元下对比2种疲劳评估方法,结果表明名义应力法预测疲劳寿命的准确性较低.     

机器人小车焊接构架变形预测和分析

为探究焊接变形对机器人小车碰撞性能和使用寿命的影响,基于热弹塑性固有应变法,利用仿真软件VIRFAC对机器人小车焊接构架变形进行数值模拟。通过热源校核,模拟4种典型接头的热源分布,建立固有应变数据库,分析具有282条焊缝的机器人小车整体变形规律。结果表明：机器人小车焊接构架的最大变形为2.962 mm,位于顶层边框位置。研究结果为机器人小车的焊接设计、强度和稳定性分析提供支持。     

基于ANSYS的MV3车轮焊接变形分析

针对汽车轮辐焊接变形影响车轮精度的问题,用ANSYS仿真分析轮辐焊接变形.采用单丝MAG焊和双丝MAG焊技术,每种焊接方法又分"先外后内焊"和"先内后外焊"2种不同的焊接工艺,得到不同热输入条件下的温度梯度场、等效应力场和焊后结构变形.分析结果表明:"先内后外焊"工艺优于"先外后内焊",且单丝MAG焊产生结构变形的最大位移约为双丝MAG焊的2倍,因此采用"先内后外焊"工艺的双丝MAG焊优势明显.     

新一代计算机焊接模拟系统与应用

一、概述 焊接工艺在工业生产中扮演着重要的角色,特别是在汽车、船舶和航天航空工业中.焊接工艺在具有众多优点的同时,也存在一些缺点,例如,冶金过程中伴随金相转变导致的热膨胀和收缩、内应力和结构的扭曲与变形.这些问题都必须得到很好地控制,尽量减少其影响.从仿真的角度来说,其目的就是在焊接工艺进行之前对结构变形和内应力进行计算,通过调整焊接参数、焊接工艺、焊接顺序、焊接位置、约束条件和材料等,优化最终的焊接结果.     

基于有限元方法的车身B柱全工序焊接变形研究及应用

为研究不同车身结构对焊接变形的影响，对欧版原型车和产品安全措施(product safety measure, PSM)项目车型的B柱区域同时建立电阻焊有限元焊接模型。应用热弹塑性有限元方法模拟B柱区域的焊接变形量，并进行B柱区域全工序链式仿真，得到整体焊接变形量。结果表明，B柱区域在电阻焊后产生最大0.85 mm的变形，与实际变形量0.90 mm吻合。利用全工序链式仿真获得的整体变形量比各个工序简单累加的结果小，实际应用中效果良好。     

重型自卸车架模态分析和结构优化

针对受较大动载荷或作用力的频率与车架某些固有频率接近时,车架会产生强烈的振动,造成破坏或不允许的大变形的问题,采用有限元法对某自卸车冲压铆接车架进行仿真分析.采用刚性单元和梁单元的组合来模拟铆钉连接;用Lanczos方法求解特征值.模态分析结果表明,该车架具有合理的低阶振型和固有频率.利用网格变形技术对车架横梁的位置进行设计优化,使车架的1阶扭转固有频率得到提升.     

前副车架焊缝疲劳分析和寿命优化

为评估前副车架的耐久性能,利用FEMFAT分析某汽车前副车架的疲劳寿命.提出焊缝不同区域单元的尺寸要求和焊缝连接单元的厚度要求,以保证前副车架焊缝的局部应力真实可信;采用S-N法预测焊缝疲劳寿命,计算得到的开裂位置和行驶距离与道路试验吻合良好;通过加强局部结构并重新布置焊缝位置,使前副车架通过耐久试验测试.分析表明:通过规范焊缝的建模要求,根据实际结构设置合适的焊缝类型,可准确预测焊缝的疲劳寿命,指导焊缝布置,优化产品结构.     

金属波纹管焊接过程的应力及变形特性

针对焊接引起的变形及其所产生的残余应力和应变会影响金属波纹管正常使用的问题,用有限元法分析波纹管的焊接过程,研究焊接过程中金属波纹管的变形和应力.基于单元生死技术,考虑材料的性能随温度变化而非线性变化的影响,通过提取焊缝周边参考点和参考路径的应力和变形,重点研究热源移动对金属波纹管应力和变形分布、类型以及大小的影响.     

机器人多层多道焊接的路径规划

为了运用机器人实现多层多道复杂空间轨迹的自动化焊接,提高特定焊接结构的加工质量与效率,针对中厚壁管件的相贯线焊缝进行了路径规划.在满足焊接工艺要求的基础上,建立了焊接坡口模型以作为预制管件的制造依据与路径规划算法的设计基础.通过对围绕接管轴线旋转任一角度的焊缝截面的分析,提出了多层多道的焊道排布策略,确定了每条焊道的位置,同时规划了机器人焊枪末端位姿,开发了多层多道机器人焊接离线编程系统.仿真结果表明,各条焊道位置准确.在实际焊接实验中,机器人焊接连续性好、效率高,焊缝填充均匀、致密且美观.     

Effect of cold bending and welding on buckling of ring-stiffened cylinders

The BOSOR5 computer program for elastic plastic buckling of shells of revolution is used for calculation of bifurcation buckling of cold bent and welded ring-stiffened cylinders under external pressure. Residual stresses and deformations from cold bending and welding are included in the model for buckling under service loads by introduction of these manufacturing processes as functions of a time-like parameter which ensures that the material in the analytical model experiences the proper sequence of loading prior to and during application of the service loads. The cold bending process is first simulated by a thermal loading cycle in which the temperature varies linearly through the shell wall thickness, initially increasing in time to simulate cold bending around a die and then decreasing in time to simulate springback to a final somewhat larger design radius. The welding process is subsequently simulated by the assumption that the material in the immediate neighborhoods of the welds is cooled below the ambient temperature by an amount that leads to weld shrinkage amplitudes typical of those observed in tests. Buckling loads are calculated for a configuration including and neglecting the cold bending and welding processes. These predictions are compared to values obtained from tests on two nominally identical specimens, one carefully machined and the other fabricated by cold bending the shell and then welding machined ring stiffeners to it.     

Effect of welding sequences on residual stresses

Accurately predicting welding residual stresses and developing an available welding sequence for a weld system are pertinent tasks since welding residual stress is inevitably produced in a welded structure. This study analyzes the thermomechanical behavior and evaluates the residual stresses with various types of welding sequence in single-pass, multi-pass butt-welded plates and circular patch welds. This is achieved by performing thermal elasto-plastic analysis using finite element techniques. Furthermore, this investigation provides an available welding sequence to enhance the fabrication process of welded structures.     

机器人柔性焊接系统在汽车半壳封装式后消声器焊接中的应用

根据汽车半壳封装式后消声器焊接的生产需要,研制了专用的机器人柔性焊接系统。从系统布置形式、变位机结构特性、气液增压系统特性、模具结构设计特点、模具快换结构设计几方面介绍了整套焊接系统的优点。与传统焊接方式相比,其突出特点是维护简单、通用性强、可实现多种半壳式后消声器互换生产。使工装系统的使用寿命延长,经济性提高。     

Reliability-based optimum design of a welded stringer-stiffened steel cylindrical shell subject to axial compression and bending

The economy of stiffened shells vs the unstiffened version depends on loading, type of stiffening and stiffener profile. The stiffening is economic when the shell thickness can be decreased in such a measure that the cost savings caused by this decreasing is higher than the additional cost of stiffening material and welding. The present work deals with cylindrical shell columns fixed at the bottom and free at the top subject to axial compression and horizontal force acting on the top of the column. The shell is stiffened outside with stringers welded by longitudinal fillet welds. Half rolled I-section (UB) stiffeners are used to reduce welding cost. The cost function to be minimized includes the costs of the materials, forming of shell elements into the cylindrical shape, assembly, welding and painting. The design variables are the shell thickness, number and profile of stiffeners for the stiffened shell, but only the first type of variable in the unstiffened case. Randomness is considered both in loading and material properties. A level II reliability method (first-order reliability method) is employed. Individual reliability constraints related with shell buckling, stringer panel buckling and the limitation of the horizontal displacement of the column top are considered. The overall structural reliability is obtained by using Ditlevsen's method of conditional bounding. The costs of both the stiffened and unstiffened shells designed to ensure a stipulated probability of failure will be compared with the solutions obtained for a code-based method, which employs partial safety factors. Results are given illustrating the influence of the constraint on the horizontal displacement.     

A general three-dimensional L-section beam finite element for elastoplastic large deformation analysis

In this paper, the development of a general three-dimensional L-section beam finite element for elastoplastic large deformation analysis is presented. We propose the generalized interpolation scheme for the isoparametric formulation of three-dimensional beam finite elements and the numerical procedure is developed for elastoplastic large deformation analysis. The formulation is general and effective for other thin-walled section beam finite elements. To show the validity of the formulation proposed, a 2-node three-dimensional L-section beam finite element is implemented in an analysis code. As numerical examples, we first perform elastic small and large deformation analyses of a cantilever beam structure subjected to various tip loadings, and elastoplastic large deformation analysis of the same structure under reversed cyclic tip loading. We then analyze the failures of simply supported beam structures of different lengths and slenderness ratios under elastoplastic large deformation. The same problems are solved using refined shell finite element models of the structures. The numerical results of the L-section beam finite element developed here are compared with the solutions obtained using shell finite element analyses. We also discuss the numerical solutions in detail.     

Detection of fillet weld joints using an adaptive line growing algorithm for robotic arc welding

One of the main challenges for robotic welding in low to medium volume manufacturing or repair work is the time taken to programme the robot path for a new job. It is often cheaper and more efficient to weld the parts manually. There are many papers published on the detection of butt welds, however there is no mature method for the identification of fillet welds which are more common. This paper presents a novel method that can autonomously identify fillet weld joints regardless of the base material, surface finish and surface imperfections such as scratches, mill scale and rust. The new method introduces an adaptive line growing algorithm for robust identification of weld joints regardless of the shape of the seam. The proposed method is validated through experiments using an industrial welding robot in a workshop environment. The results show that this method can detect realistic fillet weld joints for industrial arc welding applications.     

基于假定应变法的协同转动四边形复合材料壳单元

为对复合材料层合板壳结构进行精确的大变形数值模拟,提出一种采用假定应变法的能分析层合结构大转动问题的协同转动四边形壳单元.该方法在建立有限元公式时引入假定应变法以克服膜闭锁和剪切闭锁的不利影响.与其他能分析大转动问题的复合材料壳单元相比,在新的协同转动框架中采用矢量型转动变量,可大大降低在非线性增量求解过程中更新转动变量的难度,且能得到对称的单元切线刚度矩阵,提高单元的计算效率.分析两个典型算例,并与其他学者的结果进行对比,结果表明在计算层合结构大转角问题时拥有较好的精度和收敛性.