Numerical analysis of flow-thermal coupling in micro-plasma welding pool of thin-wall part

The formed characteristics of thin-wall part is studied when it is in the process of MPAW. Finite element method is used to sinmlate the temperature field coupling flow field in the welding of thin-wall part. It is found that because of the obvious effect of heat accumution in cross-section, where the distribution of temperature field area presents trapezoidal inverted approximately in the molten pool and the non-molten pool area presents level. The surface tension, the electromagnetic force and buoyancy are considered for analyzing the effects on the fluid flow of welding-pool. It can be obtained that the surface tension is the main driving force in the welding pool, which is far greater than electromagnetic force and buoyancy.

NUMERICAL ANALYSIS OF THREE-DIMENSIONAL FLUID FLOW AND HEAT TRANSFER IN TIG WELD POOL WITH FULL PENETRATION

A model is established to analyze three-dimensional fluid flow and heat transfer in TICweld pools with full penetration.It considers the deformation of the molten pool surfaceat the condition of full penetrated workpieees,takes the are pressure as the drivingforce of the pool surface deformation,and determines the surface configuration of weldpool based on the dynamic balance of arc pressure,pool gravity and surface tension atdeformed weld pool surface. The SIMPLER algorithm is used to calculate the fluid flowfield and temperature distribution in TIG weld pools of stainless steel workpieces.TIGwelding experiments are made to verify the validity of the model.It shows the calculatedresults by the model are in good agreement with experimental measurements. professor,Dept of Welding Engineering,Harbin Institute of Technology,Harbin 150006,China

Modeling transient fluid flow and heat transfer phenothena in stationary pulsed current TIG weld pool

A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.

Mathematical analysis of the role of recoil pressure in weld pool dynamics during laser-MIG hybrid welding

A mathematical model was established to simulate the weld pool development and dynamic process in stationary iaser-MlG hybrid welding. Surface tension and buoyancy were considered to calculate liquid metal flow patter, moreover, typical phenomena of MIG welding, such as filler droplets impinging weld pool, electromagnetic force in the weld pool, and typical phenomena of laser beam welding, such as recoil pressure, Inverse Bremsstrahlung absorption, Fresnel absorption were all considered in the model. The laser beam and arc couple effect were introduced into this model by the plasma width during hybrid welding. The role of recoil pressure in the weld formation was discussed. Transient weld pool shape and complicated liquid metal velocity distribution from two kinds weld pool to an unified weld pool were calculated. The simulated weld bead geometry with consideration recoil pressure was in good agreement with experimental measurement.

Theoretical and experimental investigation of gas metal arc weld pool in commercially pure aluminum:Effect of welding current on geometry

Effects of welding current on temperature and velocity fields during gas metal arc welding(GMAW) of commercially pure aluminum were simulated. Equations of conservation of mass, energy and momentum were solved in a three-dimensional transient model using FLOW-3 D software. The mathematical model considered buoyancy and surface tension driving forces. Further, effects of droplet heat content and impact force on weld pool surface deformation were added to the model. The results of simulation showed that an increase in the welding current could increase peak temperature and the maximum velocity in the weld pool. The weld pool dimensions and width of the heat-affected zone(HAZ) were enlarged by increasing the welding current. In addition, dimensionless Peclet, Grashof and surface tension Reynolds numbers were calculated to understand the importance of heat transfer by convection and the roles of various driving forces in the weld pool. In order to validate the model, welding experiments were conducted under several welding currents. The predicted weld pool dimensions were compared with the corresponding experimental results, and good agreement between simulation and preliminary test results was achieved.

基于FLOW-3D的GMAW焊熔池行为数值分析模型

基于FLOW-3D软件,建立了GMAW焊传热和熔池流场的三维瞬态数值分析模型.电弧热输入和电弧压力均采用双椭圆分布模式描述,熔滴过渡过程则通过高温液态金属的质量和动量源项表征;同时,模型还考虑了电弧等离子体切应力、电磁力、重力、浮力等作用于熔池的主要应力.利用该模型对碳钢温度场及熔池流体流动进行模拟计算.结果表明:受熔滴冲击影响,熔池始终处于周期性震荡过程中,无法真正达到准稳态;同时,该模型能够模拟飞溅等焊接成形缺陷,继而可以更为全面、合理地描述焊接物理过程,为深入理解焊接内部机制提供有力支撑.

基于摆动激光扫描的GMAW焊缝成形调控

将摆动激光与GMAW工艺复合,利用“8”字形摆动激光扫描液态熔池,对其温度场和流场进行调控,以改变熔池温度梯度,主动调控熔池流动以改善焊缝成形.在6061铝合金板材表面进行堆焊试验,重点探究了光丝间距、摆动幅度、激光功率对于焊缝成形的影响,采用高速摄像机拍摄激光扫描熔池过程.结果表明,摆动激光扫描可以有效抑制成形缺陷的发生,当摆动激光扫描熔池中部时可以获得最佳的焊缝成形效果.摆动激光扫描降低了熔池温度梯度分布,同时激光扫描产生的激光蒸发反力可以驱动熔池流动,促进了液态熔池的流动铺展,从而有效抑制了不规则焊缝成形缺陷,减少焊缝内部气孔和裂纹缺陷.调节摆动激光摆幅可以在一定范围内对焊缝宽度进行调控.

奥氏体不锈钢薄板激光焊表面张力驱动熔池形成的数值模拟分析

为探究奥氏体不锈钢薄板激光焊接过程中表面张力对熔池形状、熔池流速、熔池静压的影响,以期优化焊接工艺并提高焊接质量。基于数值模拟分析方法,建立了移动旋转高斯曲面体热源模型,通过改变Marangoni对流系数来模拟不同表面张力条件,分析其对熔池形成过程、熔池形状、流速及熔池内静压力的影响。模拟结果表明,表面张力是影响熔池形态和内部静压力的关键因素,表面张力指向熔池内部,驱动熔池向中心汇聚,从而促进熔池的形成;表面张力的大小与熔池峰值温度、熔深、深宽比呈负相关,与峰值流速、熔宽、熔池内部静压力呈正相关;铜衬底的加入显著增大了过冷度,加速了熔池的冷却,有助于避开奥氏体不锈钢的敏化温度区间。

Inconel-52M焊丝高频脉冲TIG电弧及熔池流动行为研究

基于高速摄像机和图像处理技术,分析了脉冲频率(0~60 kHz)对焊接电弧和Inconel-52M镍合金焊丝熔池流动行为的影响及其作用规律.结果表明,在常规低频脉冲电流上复合高频脉冲电流会使电弧形态显著收缩,随着高频脉冲频率的增加,电弧弧根尺寸逐渐减小.与常规低频脉冲焊相比,高频脉冲电弧的整体面积减小,核心区面积及其占比增加,电弧能量集中度和温度(能量)得到提高.在高频脉电流的作用下,电弧轴向压强和径向电磁力增大,最大可分别提高18.0%和8.1%.电弧轴向电磁压强增大导致熔池流动性增强,使焊缝液态金属流动更充分,从而易形成大焊缝宽度和低润湿角的焊缝形貌.

光束倾角对激光深熔焊304不锈钢焊缝力学性能及熔池流动的影响

在激光深熔焊接中光束倾角会直接影响匙孔形态,光束倾角对熔池流动也具有一定的影响.采用激光深熔焊接白板试验结合“半三明治”熔池流动直接观测试验,以激光倾角作为变量,研究其对304不锈钢激光深熔焊接焊缝力学性能及熔池流动的影响.结果表明,在焊缝的力学性能上,不同激光倾角对焊缝上、中部的影响差异性较小,对下部的影响较大,焊缝底部拉伸件出现较多气孔缺陷,正激光入射角下的焊缝抗拉强度和断后伸长率小于负激光入射角.正激光入射角下“上小下大”的匙孔形貌使其底部易产生涡流,不利于气泡的排出,且匙孔坍塌频率较负激光入射角大,导致熔池稳定性较差,焊缝气孔缺陷的形成概率呈现为正激光入射角高于负激光入射角态势.

基于FLUENT的船用铝合金板激光焊接数值仿真分析

为得到最佳激光焊接工艺参数,以船用铝合金板为研究对象,利用FLUENT软件建立焊接温度场与流场模型进行仿真分析,按照实际的力和边界条件进行加载,得到不同激光焊接速度下的熔池形貌和温度、速度分布云图。结果表明,在焊接工况一定的条件下,激光焊接速度对熔池形貌和温度场产生重要影响:焊接速度较快时,金属流体流动不均衡,温度场分布紊乱,熔池形貌复杂且不稳定;焊接速度较慢时,熔池出现大梯度温度分布,金属流体流动较弱;选择合适的焊接速度才能得到较优的产品。

TIG焊熔池表面流动行为的研究

针对钨极惰性气体保护(Tungsten inert gas,TIG)焊熔池表面流动行为,在确定TIG焊熔池表面可采用粒子示踪的方法来进行其表面流动行为示踪的基础上,在以激光为试验背光光源,通过激光在TIG焊熔池表面镜面反射后,使得熔池及示踪粒子清晰成像于成像屏上。在此基础上,开展对304不锈钢和Q235普通碳钢的熔池表面流动行为的试验研究,对所获得这两种材料的TIG焊熔池试验数据进行处理与对比分析,探究熔池表面流动规律。研究结果表明:在TIG焊过程中,其焊接熔池存在两种运动模式,在304不锈钢焊接过程中熔池表面的液态金属由边缘向熔池中心流动;在Q235碳钢焊接过程中熔池表面的液态金属不定向、不规则地由熔池中心向熔池边缘流动,并测量304不锈钢TIG焊过程中熔池表面的液态金属流动速率为12 mm/s左右,Q235碳钢的熔池表面的流动速率为15 mm/s左右。

外加纵向磁场GTAW焊接熔池流动机理

以外加纵向磁场GTAW (钨极氩弧焊 )焊接LD10CS铝合金过程为研究对象 ,建立外加纵向磁场GTAW焊接熔池流体流动和传热数学模型 ,对固定电弧的外加纵向磁场GTAW焊接熔池流体流动过程进行数值分析 ,研究外加纵向磁场GTAW焊接熔池流体流动和传热行为。

脉冲电流作用下TIG焊接熔池行为的数值模拟

建立了脉冲TIG（TungstenInertGas）焊接熔池行为的数值分析模型，分析了脉冲电流对TIG焊接熔池流场、热场及熔池形状的影响规律计算结果表明：熔地体积对电流的脉冲作用较敏感；脉冲TIG焊接熔池内流体流动的主要驱动力是表面张力梯度；熔池中的流场随电流作周期性变化.利用自行研制的计算机视觉实验系统，测试了一个脉冲周期内熔池宽度的动态变化过程，计算值与测试值基本吻合.

外加高频磁场下电弧快速成形过程的电磁-流体耦合数值模拟

外加电磁作用是改善电弧快速成形零件组织和性能的有效方式之一。为了揭示高频磁场对熔池传热、对流和形态的影响机理,采用有限元电磁计算和有限体积流体分析耦合的方法,建立电磁场、熔池温度场和流体流动场分析的三维模型,分析工件和熔池中高频电磁力/热的分布特征,研究高频电磁力与表面张力、电弧力以及熔滴冲击共同作用下的熔池表面动态变形,对比分析有/无外加高频磁场情况下熔池温度分布和流体流动模式上的差异,并由此预测外加高频磁场对凝固组织和熔池形态的改变。结果表明,高频电磁力驱动熔池流体在垂直焊接方向的平面内形成单漩涡旋转对流,有利于熔断枝晶细化晶粒,熔池表面形状向远离线圈一侧倾斜,熔宽增大。金相和焊道横截面测试证实了上述模拟结果。

活性剂对GH4169薄板电子束焊接焊缝成形的影响

选用镍基高温合金GH4169进行试验,分析了不同种类活性剂对焊缝成形的影响规律,发现添加不同的氧化物对焊缝表面成形、熔深均有影响,而添加氟化物却影响不大.在此基础上,进行配比和优化,得到了能改善焊缝成形,提高表面质量的电子束焊活性焊剂.分析活性剂改善电子束焊接焊缝成形的原因,认为添加活性剂改变了熔池内部的表面张力梯度,从而影响了熔池的流动方式,形成了窄而深、表面成形较好的焊缝.结果表明,活性剂电子束焊接能改善焊缝表面成形,并可进一步消除咬边等表面缺陷,这对薄板的电子束焊接技术很有帮助.

活性MAG焊电弧特征及熔池流动分析

提出了活性熔化极气体保护焊新方法,可增加焊接熔深,改善难熔焊接结构的熔合不良,获得高质量的焊接接头.对活性熔化极气体保护焊电弧状态和熔池表面形态进行了采集和分析,用钨粒子示踪法进行试验,分析了电弧形态和熔池流动.结果表明,活性熔化极气体保护焊电弧收缩显著,电弧形态更加集中,熔池内部液态金属的流动方向为从熔池周边向中心流动,熔池流动更为有序.对于钢的活性熔化极气体保护焊方法,熔池流动行为改变是增加焊接熔深的主要因素.

铍材钎焊熔池动态行为的影响因素研究

在综合分析激光钎焊的焊缝形状特征和热源作用特点的基础上,根据流体力学和传热学原理,建立瞬态熔池三维数值分析模型和混合热源分布模型,模型考虑熔池液态金属对流传热、熔池外工件的固态导热、焊接过程中的相变潜热、侧吹气流方式、对接界面的结构几何特性以及材料热物理性能参数随温度变化等因素。利用Visual Fortran语言编写数值分析程序,分析相变潜热、侧吹气流和对接间隙等对熔池内流场和温度场分布的影响。研究表明,相变潜热的影响不是总可以忽略的,尤其是在移动热源作用下相变潜热的影响比固定热源更为突出。侧吹气流主要是通过改变熔池内液态金属的流动状态进而影响到熔池的三维形态,因此,选择合适的吹气方式能够有效地提高激光钎焊的稳定性和焊深。间隙的存在造成温度场分布不连续造成熔池形状呈'钉头'形,考虑间隙时计算得到的熔池形状与试验结果吻合更好。

焊接熔池的传热与流体流动模拟进展

焊接熔池的传热与流体流动模拟是焊接模拟的一个重要领域 ,目前对焊接熔池的传热和流体流动的模拟主要是基于Navier strokes方程基础上而建立的。文中概括了近年来焊接熔池传热与流体流动模拟所取得的一些进展 ,总结了影响熔池传热和流体流动的一些主要因素。

A-TIG焊熔池流体流动形态的测试

为了验证A-TIG焊时的熔池流场计算结果,利用自行研制的活性剂FS12对不锈钢A-TIG焊时熔池流体流动变化进行了测试。利用高熔点双薄钨板挡住熔池流体流动的方法试验,对比焊缝中钨板周围钨颗粒的分布,从而对流体流动的方向进行试验验证。试验结果表明:无活性剂时钨颗粒在焊缝中心浓度比较小,而在焊缝边缘浓度比较大,钨板外侧浓度最大。证实了熔池流体流动是从中心流向边缘。有活性剂时的钨颗粒在焊缝边缘浓度比较小,焊缝中心的浓度比较大,而熔池底部浓度最大。证实了熔池流体流动是从边缘流向中心。通过以上试验说明,活性剂的加入改变了熔池流体流动的方向,使用活性剂FS12后强烈的熔池流体向内对流是A-TIG焊时熔深增加的根本原因。