Numerical analysis of influence of expansion joints on welding residual stress of an EGR cooler

The influence of expansion joints on the welding residual stress at the tube-plate junction of an exhaust gas recirculation (EGR) cooler was studied by numerical simulation method. The simulation results show that the expansion joints set on the housing of the EGR cooler mainly for the sake of protecting the tube-plate joints from bearing additional heating stress can also reduce the welding residual tensile stress. The expansion joints set on the EGR cooler can mitigate the tensile force acting on the edges of the main plates through its elastic extension, and thus reduce the magnitude of welding residual tensile stress at the tube-plate junction.     

常压/真空环境激光焊接焊缝成形特性及残余应力与变形对比

在高功率激光焊接中,采用增大激光功率的方法以获得更大熔深时,面临焊接过程稳定性差、焊接缺陷频发等问题,目前国内外普遍认为真空激光焊接是解决以上问题的有效手段. 文中采用工艺试验和数值模拟的方法,研究了常压和真空环境下中厚度全熔透激光焊接在焊缝成形及残余应力与变形分布的差异. 结果表明,降低环境压力可显著增加激光焊接熔透深度,真空环境可以将常压环境10 mm全熔透激光焊接所需激光功率从10 kW降低到6 kW,并获得更好的焊接质量. 常压环境和真空环境下,全熔透激光焊接工件展现出类似的横向残余应力、纵向残余应力和变形分布规律,但由于真空环境下热输入较低,焊缝深宽比大,焊后残余应力的峰值和变形程度均显著小于常压环境.     

铝合金激光-MIG复合焊熔滴对匙孔作用的模拟

将复合焊接过程中的反冲压力、表面张力等驱动力及熔滴过渡行为考虑在内,建立5A06铝合金激光-MIG复合焊接数值模拟热流耦合模型,由于熔池内的流动及匙孔稳定性对焊接性能有重要影响,因此针对熔滴与匙孔及熔池稳定性的影响进行了系统讨论,并且通过采用不同的熔滴落入位置进行计算.结果表明,当熔滴落入位置距激光中心较近时,熔滴对匙孔的冲击作用较大,匙孔壁的平均流速和波动频率有所增加,匙孔更易由于周期性的熔滴过渡而产生液桥发生闭合,熔滴落入位置还会影响匙孔深宽比,进而影响激光能量的菲涅尔吸收.     

K-TIG焊接接头的应力与变形

采用SYSWELD软件对Q345低合金钢板的匙孔型钨极气保焊（keyhole gas tungsten arc welding,K-TIG）焊接过程进行了模拟,选用了3种形式的组合热源对K-TIG焊接过程的温度场进行数值模拟,并与实际焊缝轮廓进行对比,发现采用上半部分双椭球热源和下半部分3D高斯热源的组合热源所得温度场与实际情况较为相似.并通过K-TIG焊接数值模拟,分别研究板厚、间隙和焊接速度对K-TIG焊接接头变形和应力的影响.结果表明,减小焊接板厚有利于减小焊后z向变形和横向残余应力,留出适当的间隙有利于减小焊后残余应力,增大焊接速度有利于减小焊后变形,但不利于控制焊后残余应力.     

Numerical simulation of stress and deformation of in-service welding onto gas pipeline

SYSWELD was used to simulate in-service welding process of gas pipeline of X70 pipeline steel. Welding thermal cycle, stress and deformation of in-service welded joint were studied. The results show that peak temperature of coarse grain heat-affected zone （CGHAZ） of in-service welding onto gas pipeline is the same with routine welding, but ts/5, ts/3 and ts/1 decrease at certain degree. For the zone near welded seam, axial stress and hoop stress in the inner pipe wall are compressive stress when welding source passes through the cross-section that is studied, but residual axial stress and residual hoop stress after welded are all tensile stress. Transient deformation and residual deformation are all convex deformation compared with the original pipe diameter size. Deformation achieves maximum when welding thermal source passes through the cross-section that is studied and then decreases during the cooling process after welding.     

缆式焊丝CO2气体保护焊接头残余应力高效数值计算和试验

文中采用基于焊缝形貌的温度热源模型高效计算其热过程,通过单丝CO2气体保护焊堆焊件的温度场计算和焊缝形貌比较验证该热源模型的正确性,采用小孔法测试表面应力验证基于该热源模型的残余应力计算结果.结果表明,基于焊缝形貌的给定温度热源模型适用于缆式焊丝CO2气体保护焊的焊接温度场高效数值模拟;缆式焊丝CO2气体保护焊的上表面焊缝区域及焊缝中心沿厚度方向的应力分布与埋弧焊基本一致,但远离焊缝区域的纵向压缩应力幅值大于埋弧焊纵向压缩应力.     

Q345/316L异种钢焊接残余应力与变形数值模拟

文中基于SYSWELD有限元分析软件对Q345/316L异种钢焊接过程的瞬态温度分布、残余应力及变形进行了数值模拟,并通过试验对其模拟结果进行了验证. 试验测量结果与数值模拟结果吻合良好,证明了利用SYSWELD模拟异种钢焊接的可靠性. 结果表明,异种钢焊接温度场呈不对称分布,Q345侧的高温区域范围更大. 不论是横向残余应力还是纵向残余应力,沿焊缝方向均呈帽状分布且在焊缝中部位置存在最大残余应力;在垂直于焊缝中央截面上,纵向残余应力与横向残余应力在焊缝和焊缝附近区域分布是不连续的,存在较大的应力梯度且应力状态也较复杂,而最大残余应力出现在Q345侧的熔合线处. 不同的热输入下模拟结果表明,在保证焊接接头质量的前提下,最好采用小热输入的焊接工艺.     

Q345/SUS304异种钢对接接头残余应力和变形的分析

以ABAQUS软件为平台,开发了热-弹-塑性有限元计算方法用于模拟Q345/SUS304异种钢多层多道焊对接接头的温度场、残余应力和焊接变形. 同时,采用试验方法测量了焊接接头的残余应力、横向收缩和角变形. 计算得到的残余应力、横向收缩和角变形与实测值吻合良好,验证了计算方法的妥当性. 结果表明,Q345母材与焊缝交界处的应力分布有明显的不连续性,靠近交界处Q345侧的较窄范围内纵向拉伸应力明显低于该区的两侧;SUS304侧的高纵向拉伸应力区明显宽于Q345侧. 此外,试验和数值分析表明,Q345/SUS304异质接头有较明显的角变形.     

Double-sided gas tungsten arc welding process on TC4 titanium alloy

TC4 titanium alloy was welded by double-sided gas tungsten arc welding（GTAW） process in comparison with conventional GTAW process, the microstructure and mechanical performance of weld were also studied. The results indicate that double-sided GTAW is superior over regular single-sided GTAW on the aspects of increasing penetration, reducing welding deformation and improving welding efficiency. Good weld joint was obtained, which can reach 96.14% tensile strength and 70.85% elongation percentage of the base metal. The grains in heat-affected zone（HAZ） are thin and equiaxed and the degree of grain coarsening increases as one moves to the weld center line, and the interior of grains are α and α′ structures. The coarse columned and equiaxed grains, which interlace martensitic structures α′ and acicular α structures, are observed in weld zone. The fracture mode is ductile fracture.     

Analysis of keyhole geometry in plasma arc welding

The key problem for numerical simulation of plasma arc welding （PAW） process is to develop a suitable and adaptive volumetric heat source mode which reflects the physical characteristics of keyhole PAW. To this end, the keyhole geometry under different PAW process conditions must be predicted. In this paper, a mathematical model for determining the keyhole shape is developed with considering the mass and momentum conservation of the in-keyhole plasma jet as well as the pressure equilibrium at the plasma jet/liquid metal boundary. A suitable heat source model related to the keyhole shape is applied to the calculation of PAW weld dimensions. The predicted results are in good agreement with the experimental ones.     

沟槽蒙皮结构激光焊接应力和变形的数值模拟

利用有限元分析软件MARC对"沟槽-蒙皮"结构的激光焊接过程进行三维数值模拟,涉及了激光焊接复合热源模型的确定,热力学边界条件的简化,数值模拟温度场的验证,以及残余变形和应力分布结果的分析和讨论.研究了结构上规则排列的多道焊缝的施焊顺序对焊接残余应力和变形的影响.结果表明,不同焊接顺序所产生的变形态相同,变形量有区别,而残余应力的分布则不同,以由外向中的对称顺序进行焊接时,结构的焊后残余变形最小,残余应力的分布比较均匀,峰值最小.     

片状偏钨极电弧特性的数值模拟

基于流体力学和麦克斯韦方程组,建立片状偏钨极电弧三维数学模型,计算得到电弧温度场、流场、电场及电流密度分布.结果表明,片状偏钨极厚度方向电弧温度场、流场、电场及电流密度呈对称分布;相同焊接工艺参数下,片状偏钨极电弧最高温度、最大流速及电流密度小于圆柱钨极电弧;电流密度受片状偏钨极前端斜边引导作用和电弧惯性后拖效应的共同影响,其分布范围沿钨极宽度方向扩展,且电弧等温线在该方向上扩张;片状偏钨极前端斜边倾角的改变,会引起电流密度在钨极前端局部集中,并导致阴极下方高温区和阴极射流沿斜边偏移.     

紫铜厚大结构件钨极氩弧焊热裂纹形成机理

对紫铜厚大结构件钨极氩弧焊(GTAW)热裂纹形成机理进行了研究.对热裂纹的动态形成过程进行观察和分析,在普罗霍罗夫理论基础上优化了热裂纹形成判据,并建立了基于刚性拘束热裂纹试验的紫铜厚板GTAW有限元模型.结果表明,内部变形率Δε是促使开裂的内因,得到HS201焊缝金属在脆性温度区间内(BTR)的横向拉伸应力及Δε的变化规律,并与其高温延性进行对比,得到不预热工艺下热裂纹产生的原因.为了防止热裂纹的出现,模拟并分析了不同预热温度下HS201焊缝金属的Δε的变化规律,预热温度由500℃降为420℃即可避免热裂纹出现.     

Numerical analysis of keyhole establishment time in keyhole plasma arc welding

Numerical analysis of keyhole shape and keyhole establishment time is of great significance for selection and optimization of the process parameters in keyhole plasma arc welding. In this paper, a three-dimensional transient model is developed to analyze the evolutions of keyhole shape and keyhole establishment time in continuous current plasma arc welding process. Firstly, a combined volumetric heat source model is used to simulate the transient variation of temperature field. And then the surfaced formation equation is adopted to calculate dynamic features of the keyhole shape and keyhole establishment time inside weld pool, in which the force action on weld pool surface is considered. Experiment is conducted to validate the numerical simulation results. The predicted keyhole size and keyhole establishment time are in agreement with the experimental measurement. And the calculated fusion zone geometry is consistent with the measured one.     

等离子弧焊中小孔检测的研究

在小孔等离子弧熔透焊接中，利用等离子云电压能够检测小孔的成形。本文首次应用等离子鞘层理论，指出尾焰电压和等离子云电压的本质特点，提出计算尾焰电压和等离子云电压公式。为用简单方法检测小孔成形奠定了基础。     

天然气管道在役焊接径向变形数值模拟

采用焊接模拟软件SYSWELD研究了压力及修复时间对天然气管道在役焊接径向变形的影响,并进行了试验验证.结果表明,在0~4 MPa压力范围内,径向变形量随压力的增大而增大,在4~6 MPa压力范围内,径向变形随着压力的增大而减小,并在6 MPa压力时近似等于常压焊接的变形量;随着焊接修复时间的增加,径向变形量逐渐增大,具有时间效应;预测焊接烧穿时,瞬时径向最大变形法优于内部点径向变形法.     

基于温度函数法的铝合金电弧增材制造残余应力与变形数值模拟

电弧增材制造是制造大型复杂铝合金部件的新方法,但残余应力和变形对制造件的性能有重要影响. 建立了铝合金电弧增材制造件残余应力和变形的顺序热-力耦合有限元模型,采用移动热源法计算了增材过程的温度场,根据峰值温度的分布和演变特征确定了温度函数的提取方案,并分别采用移动热源法和温度函数法进行了残余应力和变形计算.结果表明,1段,3段,5段温度函数法分别将力学分析时间缩短91%,79%,63%,残余应力和基板变形误差均在20%以内,在满足计算精度的前提下显著提高了计算效率,为大型铝合金电弧增材制造件残余应力与变形的预测提供了途径.     

热源形状参数对薄板焊接残余应力和变形的影响

采用热-弹-塑性有限元方法模拟焊接残余应力和变形时,对于移动热源模型形状参数的选取,在大多数情况下大都是根据研究者的经验来确定.然而对于热源模型形状参数对焊接残余应力和变形的影响尚不十分明确.基于ABAQUS有限元软件,以高强钢SM490A单道TIG焊为例,通过建立三维有限元模型和采用双椭球体积移动热源模型,研究了热源模型形状参数对焊接残余应力和变形的影响.结果表明,热源模型形状参数对焊接残余应力影响较小,而对焊接变形,尤其是对角变形有一定程度的影响.     

以空气为舱内加压气体的钨极氩弧焊接

研究了1～700 kPa空气作用下的钨极氩弧焊接.气体爆炸试验表明,压缩空气虽然不爆炸但是显著助燃,高压焊接试验舱舱内设备需要采取抗燃措施.采用较大的氩气流量,可以实现高压空气之下良好的电弧和熔池保护.自动焊机用于舱内焊接时,解决了线缆密封、摄像系统适应性等特殊问题,此外,以弧长代替电压作为控制变量消除了焊接电缆影响.16Mn钢平板焊接试验证明,虽然不同空气压力、不同位置实现单面焊自由双面成形的工艺参数明显不同,但是,采用脉冲焊接均可以获得性能优良的焊接接头.     

不锈钢冷金属过渡焊角接接头应力及变形规律研究

在高速列车轻量化课题中,不锈钢薄板作为车体结构的关键部分越来越受重视。针对异种厚度的SUS301L不锈钢薄板,采用冷金属过渡技术进行角接试验,通过热电偶采集焊接时距焊缝不同位置的温度变化。用3D激光扫描仪测量焊接变形,由于采用焊缝悬空的约束方法,底板焊后发生了较大的呈波浪状的变形,最大变形量达到6.545 mm。用μ-X360分析仪检测接头残余应力,应力呈M型分布。