Numerical simulation of transient welding angular distortion with external restraints

Abstract

A multibody coupling finite element model, in which worktable, clamping strip, welding plate and fixture are included, is built to simulate the welding transient distortions under restraining forces. Overlaying welding experiments are also carried out to measure transient welding distortions and dynamic restraining forces to validate the model. The effects of the restraining force location and magnitude, release of restraining force and restraining moment on welding distortion are discussed. Results show that the variation of the restraining force is similar to that of the welding angular distortion during welding, and the minimum initial restraining force for a specified restraining location and the appropriate restraining distance from welding centreline for a specified restraining force to restrain the welding angular distortion can be optimised using the model. However, the welding plate would spring back to some extent after the restraining force release. The restraining moment plays an important role in controlling the welding angular distortion under the same welding parameters, the angular distortion almost the same with the same restraining moment no matter the location and magnitude of the restraining force, the angular distortion decreases rapidly with increasing restraining moment, the distortion before restraining force release can be fully restrained and the values of spring back keep almost the same when the restraining moment is larger than a threshold.     

Welding distortion investigation in fillet welded joint and structure based on iterative substructure method

Abstract

In this paper, prediction and controlling angular distortion in fillet welded joint and structure were investigated. First, two methods to reduce angular distortion in fillet welded joint were investigated by experimental and numerical analysis. One was to apply a constant external force in-process and the other was rigid clamping. In numerical analysis, a new in-house finite element code has been developed based on the idea of iterative substructure method (ISM) to calculate welding distortion in rational time. During experimental analysis, the constant external force was designed and applied in-process to reduce angular distortion of fillet welded joint. The results showed that the distortion can be efficiently predicted by ISM, which were in good agreement with the experimental ones. Applying constant external force in process was a more effective method to reduce distortion than using rigid clamping. In addition, with a constant load distance from weld bead, the locations of the applied constant external force and rigid clamping along the longitudinal direction (welding direction) have little influence on the magnitude of welding angular distortion. Finally, the angular distortion of a large fillet welded structure was predicted with ISM and also controlled with applying a constant external force based on the simulation results of the fillet welded joint.     

环形拉深筋阻力计算及影响因素分析

拉深筋可以用来防止内皱的出现 ,本文对使用环形拉深筋拉深的变形机理进行了理论分析和试验研究 ,得到了使用环形筋压边时的拉深力公式及筋的阻力公式。此外 ,本文还讨论了筋的结构参数对拉深力以及筋的阻力的影响。其结果是 :上述两种力的大小主要受板料对筋的最终包角、筋及槽的圆角半径 3个因素影响     

A LOOP DRAWBEAD RESTRAINING FORCE MODEL IN SHEETMETAL DEEP DRAWING PROCESS

1. IntroductionIn the sheet metaJ fOrming process9 deep drawing is used frequently in the automotiveor packaging industry to manufacture products with comPlicated shapes and ctirvatures.In the deep drawing process, a sheet metal, the blank, is clamped between a die and a blankholder. The specific shape of the punch and the die is transferred to the blank during thedefor.atio.[1--4].In the deep drawing process, the material flow is restrained by both the friction con-dition and the blankholde…     

多元非线性回归的非对称薄壁件装夹位置优化

采用Johnson-Cook动态本构和剪切失效准则,从装夹位置角度对非对称航空薄壁件加工变形问题进行研究,获得加工变形与装夹位置关系数据;利用多元非线性回归手段,得到装夹位置与加工变形的数学模型;采用全局寻优能力较强的遗传算法优化装夹位置。结果表明:采用优化后的装夹位置较大幅度的降低了加工变形,与传统装夹位置(夹紧元件均匀分布)相比,平均变形量降低62%。     

基于数值模拟的拉延筋约束阻力计算方法研究

在汽车覆盖件拉深成形中,拉延筋可以在较大范围内调节和控制板料的变形程度和变形分布,抑制多种成形质量问题的产生.其中,拉延筋几何参数起着重要的作用.本文以矩形拉延筋为例,建立了拉延筋约束阻力计算有限元模型,对拉延筋几何参数与约束阻力之间的关系进行分析研究.结果表明:拉延筋约束阻力与凹槽圆角半径和凸筋圆角半径成反比,与筋高成正比.结合某轿车B柱加强板实例,通过优化其拉延筋结构参数,得到当1号等效拉延筋高8mm、凸筋和凹槽圆弧半径3mm;2号等效拉延筋高4 mm、凸筋和凹槽圆弧半径6mm时,该制件成形质量达到最佳.     

半圆形拉深筋尺寸参数对其阻力的影响

通过数值模拟和实验相结合的方法 ,研究了半圆形拉深筋的高度、圆角半径等参数对拉深筋阻力的影响 ,分析了不同尺寸参数下拉深筋阻力的构成特点。研究表明 ,拉深筋高度和拉深筋圆角半径对阻力均有显著的影响。其中拉深筋高度与阻力之间存在较好的线性关系 ,是控制拉深筋阻力的首选参数。拉深筋的高度变化主要影响拉深筋的摩擦阻力 ,而圆角半径主要影响局部圆角的变形阻力。最后在实验和分析的基础上 ,给出了半圆形拉深筋的设计调整原则     

CAE技术在解决注塑机锁模力不足中的应用

基于CAE模拟技术,验证注塑机锁模力不足,找到塑件充不满的原因,并通过调整产品厚度,解决了因设备锁模力不足及注射压力低而导致的充不满问题。该文的案例为一模两件的模具,零件1的厚度增加22.2%,零件2的厚度增加20%,锁模力降低了23.5%。锁模力大大降低,有利于注塑成型。     

夹紧力对7075铝合金薄板件铣削变形影响

针对薄板件装夹及加工时易变形的问题,为研究夹紧力对7075铝合金薄板件铣削变形的影响,对铝合金薄板件进行铣削实验,采用面支撑、四点夹紧的装夹方式,通过改变初始夹紧力的值,对铣削后平面度进行测量。结果表明:在铣削过程中,夹紧力一直处于动态变化中,最大变化幅度为9%,且铣削结束时,夹紧力不会恢复到初始值,初始与结束时夹紧力的最大差值为42N;增大初始夹紧力,切削力也随之增大;铣削后表面的平面度随着初始夹紧力的增大呈现出先增大后减小再增大的趋势。这说明,初始夹紧力的大小对工件变形的影响显著;加工过程中夹紧力的不断变化是影响工件变形的重要原因。     

Influence of clamping support distance on distortion of welded T joints

Abstract

A study is presented on the influence of the clamping support distance on welding distortion of 6 mm thick gas metal arc welded structural steel T joints. Experiments were performed for two clamping conditions and are compared to simulations based on a previously presented model. It was found that clamping closer to the weld seam reduces angular as well as bending distortion. In order to assess the accuracy of the results, sensitivity analyses were performed on the influence of predeformation and material parameters. It is shown that an initial predeformation has an influence on the final welding distortion. Additionally, it has been found that selection of material properties within the range of variations permitted by the material norms has a strong influence on the predicted distortion. Results were improved using material specific data rather than generic data for the relevant material class. Also the assumed phase volume change plays an important role.