Comparisons between different models for thermal simulation of GTAW process

0IntroductionIn arc welding processes,final microstructure andmechanical properties of the weldments mainly depend onthe thermal cycle undergoing during the heating and cool-ing process.The accurate analysis of the welding thermalprocess is the foundation…     

Modeling of the Weld Shape Development During the Autogenous Welding Process by Coupling Welding Arc with Weld Pool

A numerical model of the welding arc is coupled to a model for the heat transfer and fluid flow in the weld pool of a SUS304 stainless steel during a moving GTA welding process. The described model avoids the use of the assumption of the empirical Gaussian boundary conditions, and at the same time, provides reliable boundary conditions to analyze the weld pool. Based on the two-dimensional axisymmetric numerical modeling of the argon arc, the heat flux to workpiece, the input current density, and the plasma drag stress are obtained. The arc temperature contours, the distributions of heat flux, and current density at the anode are in fair agreement with the reported experimental results. Numerical simulation and experimental studies to the weld pool development are carried out for a moving GTA welding on SUS304 stainless steel with different oxygen content from 30 to 220 ppm. The calculated result show that the oxygen can change the Marangoni convection from outward to inward direction on the liquid pool surface and make the wide shallow weld shape become narrow deep one. The calculated result for the weld shape and weld D/W ratio agrees well with the experimental one.     

Three-dimensional turbulent weld pool convection in gas metal arc welding process

Abstract

A three-dimensional model has been developed to study turbulent fluid flow and heat transfer in a gas metal arc weld pool. The phase change process during melting and solidification is modelled using the enthalpy–porosity technique. Mass and energy transports by droplet transfer are considered through a thermal analysis of the electrode. The droplet heat addition into the molten pool is considered to be in the form of a volumetric heat source distributed in an imaginary cylindrical cavity within the weld pool ('cavity' model). A two-equation k-ε model capable of addressing turbulent weld pool convection, taking into account the morphology of the phase change, is presented. The weld pool dynamics and geometry (shape and size) in a moving gas metal arc welding (GMAW) process are studied and the effects of enhanced diffusivities on the turbulent weld pool are discussed. The predicted weld pool geometry using laminar and turbulent models is also compared with corresponding experimental post-weld sections.     

外加磁场对镁合金焊接熔池形态的影响

以镁合金焊接熔池为研究对象,建立了移动热源作用下焊接熔池的三维数学模型. 利用大型通用有限元软件ANSYS将电磁场分析结果导入到热流场分析中,实现电磁场和热流场之间的耦合分析. 模拟了无外加磁场作用下以及外加磁场作用下镁合金焊接熔池的温度场分布和流体流动的速度矢量分布. 结果表明,外加磁场产生的电磁力驱动熔池中熔融的液态金属发生旋转运动,改变了液态金属原有的运动方式和传热方式,流体流动速度和流动范围增加,焊缝熔宽增大,熔深减小. 试验结果验证了模拟结果的可靠性.     

Particles migration behavior during laser keyhole welding of ZLIO1/TiB2 composites

Particle redistribution occurred with the flow of pool fluid in laser welding aluminum composites. In order to investigate particle migration behavior, a numerical model was established on laser welding of ZL101-TiB2 composite. TiB2 migration coupling with fluid was realized. The volume-of-fluid (VOF) method was employed to track free fluid surfaces. The travel heat source was realized utilizing the workpiece motion in place of heat source motion, which made the heat load stable. Melting and evaporation enthalpy, recoil force, surface tension and buoyancy were considered in this model. Through the calculation it showed that the simulated weld cross section shape and particle distribution were in good agreement with experimental results.     

激光+GMAW复合热源焊流体流动数值分析模型

基于FLUENT软件,建立了适用、高效的激光+GMAW复合焊流体流动数值分析模型. 将电弧热输入视为双椭球热源模型,采用基于小孔尺寸的锥体热源模型描述激光热流分布;将金属填充过程视为液态金属从熔池上部边界以一定速度流入熔池过程,并通过对液态金属流速施加时间脉冲函数,模拟熔滴的过渡频率;模型简化了小孔的计算过程,主要考虑熔池中存在的弯曲小孔对流体的影响. 利用FLUENT软件,对激光+GMAW复合热源焊熔池流体流动及小孔形态进行了模拟计算和分析. 结果表明,模型能够合理反映小孔及复合焊流体流动模式的主要特征,且提高了计算效率.     

旋转电弧GMAW堆焊短路过渡熔池动态仿真

为探究旋转电弧GMAW堆焊短路过渡时熔池的温度和对流分布规律，利用Flow-3D软件建立三维数学模型，采用球形旋转热源模型，考虑重力、熔滴拖拽力、表面张力、浮力作用，模拟了堆焊状态下，工件材料为Q235的旋转电弧GMAW短路过渡的熔池成形规律. 采用流体体积法追踪熔滴过渡和熔池表面的自由变形,并分析熔滴进入熔池时熔池内部温度场和流场的变化. 结果表明，熔池形成过程中，旋转熔滴对熔池有搅拌作用，并使熔池内部液态金属活性增强，流速变快，熔池内部液态金属体积变大，熔池的宽度变大. 模拟预测的焊缝尺寸、形状与试验吻合良好. 为优化焊接工艺参数、改善旋转电弧GMAW堆焊焊缝质量提供参考依据.     

TIG焊接熔透熔池的数学模型

根据流体力学理论和变分法原理，推导出了熔透情况下ＴＩＧ焊接熔池上表面和下表面变形的方程，建立了ＴＩＧ焊接熔透熔池流场与热场的数值分析模型，采用非正交贴体曲线坐标系成功地处理了熔池表面的曲面边界，将熔透情况下熔池上下表面变形的计算，与熔池流场与热场的计算相结合，不仅较好地计算出熔池的流场与热场，同时求得了焊接熔池的上下表面变形。焊接工艺试验表明，根据该模型计算的焊缝成形与试验测试结果吻合程度良好。     

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。并提出了今后的发展方向     

焊接电弧与活性组元对TIG焊熔池形貌影响的数值模拟

通过对FLUENT软件进行二次开发,建立了焊接电弧和焊接熔池模型,模拟分析了不同活性组元O元素含量下定点和移动TIG焊熔池形貌变化,对比了氩弧和氦弧的电弧参量及其对熔池形貌的影响.结果表明,由活性组元O元素含量变化导致的熔池内Marangoin对流变化是熔深增加的主要因素;在氩弧下,来自于电弧的气体剪切力对熔池形貌有较大影响;与氩弧相比,氦弧明显收缩,电流密度更大,更多的热量传递到熔池,增大了电磁力引起的内对流运动,可获得更深熔深.焊缝深宽比的模拟结果与试验结果吻合较好.

Abstract：

Welding arc and weld pool modeh were established by FLUENT software for spot and moving TIG welding of SUS304 stainless steel to investigate the effect of the surface-activating element oxygen on the weld shape and analyze the properties of argon arc and helium arc and their effects on the weld shape. The results show that the change of the Marangoni convection induced by different oxygen contents can be considered as one of the principal factors to increase penetration. The plasma drag force from the argon arc has obvious effect on the weld shape. Compared with the argon arc, the hehum arc is more constricted, the welding current density is much greater and the much more heat flux is transferred into the weld pool, which increase the inward convection induced by the electromagnetic force, thus the deeper weld depth can be obtained.The calculated weld D/W ratio agrees with that of the experiment.     

脉冲电流作用下TIG焊接熔池行为的数值模拟

建立了脉冲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：熔池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。溶池中的流场随电流作周期性变化。     

Numerical simulation of molten pool dynamics in high power disk laser welding

A single-phase problem is solved rather than a multiphase problem for numerical simplicity: and the solution is based on the assumption that the region of gas or plasma can be treated as a void because solid or liquid steel has a greater density level than gas or plasma. The volume-of-fluid method, which can calculate the free surface shape of the keyhole, is used in conjunction with a ray-tracing algorithm to estimate the multiple reflections. Fresnel's reflection model is simplified by the Hagen-Rubens relation for handling a laser beam interaction with materials. Factors considered in the simulations include buoyancy force, Marangoni force and recoil pressure; furthermore, pore generation is simulated by means of an adiabatic bubble model, which can also lead to the phenomenon of a keyhole collapse. Models of the shear stress on the keyhole surface and of the heat transfer to the molten pool via a plasma plume are introduced in simulations of the weld pool dynamics. Analysis of the temperature profile characteristics of the weld bead and molten pool flow in the molten pool is based on the results of the numerical simulations. The simulation results are used to estimate the weld fusion zone shape; and the results of the simulated fusion zone formation are compared with the results of the experimental fusion zone formation and found to be in good agreement. The effects of laser beam profile (Gaussian vs. measured), vapor shear stress, vapor heat source and sulfur content on the molten pool behavior and fusion zone shape are analyzed.     

CuZnSnSi合金钎料相变过程的热分析动力学

CuZnSnSi合金钎料在钎焊钢工件中具有良好的综合性能.为进一步探究其合金性能,借助差示扫描分析(DSC)和热重分析(TG)技术,分别采用微分非等温法和积分非等温法分析了CuZnSnSi合金钎料相变过程的热分析动力学.结果表明,CuZnSnSi合金的相变温度范围为1150.5~1221.5 K,吸热峰温度为1174.46 K,在相变过程中没有化学反应,但出现升温段的吸热峰温度滞后于降温段的放热峰,说明了合金钎料在结晶过程需要一定的过冷度;非等温分析法计算得到合金钎料相变表观活化能为615.72 kJ/mol;由Arrhenius公式得出合金钎料相变速率常数k的变化规律为1.71×1027exp(-6.16×10⁵/RT).     

熔透情况下三维TIG焊接熔池流场与热场的数值分析

建立了熔透情况下三维运动TIG焊接熔池中流体动力学状态及传热过程的数值分析模型。该模型考虑了试件全熔透情况下液态金属熔池表面的变形。采用贴体曲线坐标系处理熔池曲面,利用SIMPLER方法对不锈钢焊接试件熔池中的流场与热场进行了数值分析,并进行了焊接工艺试验对模型加以验证。结果表明,根据该模型得出的计算结果与实验值吻合情况良好。     

A study on keyhole evolution and weld ripple formation in dissimilar welding under pulsed laser

A three-transient multiphase model is developed to study the dissimilar metal welding of pure niobium plate to titanium alloy Ti–6Al–4V sheet under pulsed laser. The physical process of dissimilar metal welding involves melting, resolidification, mass transfer, self-consistent keyhole, and weld bead formation. The major physical factors, such as recoil pressure induced by vapourisation, surface tension, heat transfer, fluid flow, Marangoni shear stress, buoyancy force, and their coupling are considered. The results show that the keyhole mainly occurs on the Ti–6Al–4V side due to the differences in physical properties of the materials. The effects of pulse overlapping factor on the weld bead are studied. It is found that the pulsed laser has a significant influence on the weld bead formation. The mixing of materials mostly occurred in the upper part of the molten pool. The simulated weld bead profile and the phase distribution agree well with the experimental results.     

Molten pool behavior in the tandem submerged arc welding process

A three-dimensional numerical heat transfer and fluid flow model is developed to examine the temperature profiles, velocity fields, weld pool shape and size in a two-wire tandem submerged arc welding process. The model solves the equations of the conservation of mass, momentum, and energy along with the volume of fluid method. The volume of fluid method is used to track the shape of the free surface. Further, a novel scheme is proposed to handle the arc interaction and its influence on the molten droplet transfer direction. Using the computational fluid dynamics simulations, it is found that the droplet movement and arc forces from the leading electrode heavily affect the molten pool flow patterns and the resultant bead shapes, even though the same heat inputs are applied. The computed weld width and penetration are in fair agreement with the corresponding experimental results.     

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

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可调拘束实验测量的焊接凝固裂纹阻力曲线的有限元法修正

利用有限元法对横向可调拘束实验进行了数值模拟,得到了不同弯曲应变条件下熔池尾部的局部应变,结果表明：在进行可调拘束实验过程中,焊接熔池尾部确实存在应变集中,从而对实验测得的平均应变即材料凝固裂纹阻力进行了修正．此外,将横向可调拘束实验模拟得到的局部应变与采用高速摄影和可调拘束相结合测量得到的局部应变进行了对比,能够较好的吻合．同时,计算了不锈钢SUS310焊接凝固裂纹驱动力,并与修正后的阻力曲线进行比较,预测了凝固裂纹敏感性,预测结果与实验结果相符．说明利用横向可调拘束实验结合数值模拟方法,能够定量预测焊接凝固裂纹．     

激光-等离子弧复合焊接熔池流动和传热的数值分析

建立了激光-等离子弧复合焊接过程中液相区、糊状区和固相区的统一模型,在模型中同时考虑了表面张力、热浮力和电磁力的作用,通过数值计算得到了熔池的速度场和温度场,重点研究了电磁力对熔池流动和传热的影响.结果表明,在熔池形成的初始阶段,表面张力对熔池中的对流和传热起主要作用,而电磁力的作用受到抑制,随着熔深增加,电磁力作用增强并引起涡旋,导致熔深和下表面熔宽增加.针对1420铝锂合金的复合焊工艺试验表明计算结果与实际相符合.