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.     

Arc characteristics and behaviour of metal transfer in pulsed current GMA welding of stainless steel

The variation in arc characteristics, stability in shielding of arc environment and behaviour of metal transfer with a change in pulse parameters have been studied by high speed video-photography during pulsed current gas metal arc (P-GMA) weld deposition using austenitic stainless steel filler wire. A comparative study of similar nature has also been carried out during gas metal arc (GMA) weld deposition in globular and spray transfer modes. The effect of pulse parameters has been studied by considering their hypothetically proposed summarized influence defined by a dimensionless factor ? = [(I_b/I_p) ft_b], mean current and arc voltage and correlation between welding parameters and arc characteristics have been established. The arc characteristics studied by its root diameter, projected diameter, length and stiffness measured in terms of arc pressure and the behaviour of metal transfer noted by the droplet diameter and velocity of droplet at the time of detachment have been found to vary significantly with the variation in ?. At a given ? the experimentally measured values of the behaviour of metal transfer are found well in agreement to their corresponding theoretical values estimated through mathematical expressions reported earlier. The increase of ? and the ratio of (I_b/I_p) have been found to adversely affect the stability of shielding jacket and arc profile especially at high arc voltage.     

Selection of filler wire for and effect of auto tempering on the mechanical properties of dissimilar metal joint between 403 and 304L(N) stainless steels

Weldability of the dissimilar weld joint between austenitic 304L(N) stainless steel (SS) and martensitic 403 SS made by gas tungsten arc welding process using ERNiCr-3 filler metal has been studied. For this study, 12 mm thick plates of these two materials were joined using a K-type weld groove joint, with the straight edge on the 403 SS side buttered using ERNiCr-3 filler wire. Two types of weld joints were prepared—one using as-buttered 403 SS and the other one with buttered and post-weld heat-treated 403 SS plate. The joint made with the as-buttered 403 SS plate exhibits good bend ductility and toughness on the heat-affected zone (HAZ) of the 403 SS side and it is comparable with that of the buttered and post-weld heat-treated 403SS weld joint properties. Thus, buttering of the 403 SS plate enabled dissimilar welding with the 304L(N) SS plate without any post-weld heat treatment because of auto tempering of the martensite present in the 403 SS HAZ formed due to weld thermal cycle.     

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 laser-MIG 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.     

Investigation of the stability of melting and electrode metal transfer in consumable electrode arc welding using power sources with different dynamic characteristics

The results of investigations carried out to study the effect of the dynamic characteristics of power sources on the stability of melting and electrode metal transfer to the weld pool in consumable electrode arc welding are presented. It is shown that when using a new generation of welding inverter power sources the heat and mass characteristics change and this has a decisive effect on the heat content of the weld pool, reduces the level of residual stresses in the heat-affected zone (HAZ) and also increases the susceptibility to reducing the size of structural components in the zone of permanent welded joints.     

Stationary GMAW-P weld metal deposit spreading

Abstract

Non-isothermal spreading of non-travelling pulsed gas metal arc weld (GMAW-P) deposits was studied by experiments and numerical simulation. After an initial transient period, metal from the melting welding wire was deposited as a regular stream of droplets into a molten weld pool whose spreading was enhanced by direct arc heating of the solid substrate and weld pool convection. Accurate predictions of the final weld cross-section and time histories of base metal temperature and weld pool radius were produced by this simulation, which included mass, energy and momentum of transferring filler metal droplets. Dimensional analysis showed that speed of weld pool spreading was initially dominated by the momentum of liquid droplets while thermal convection by surface tension-driven flow became important at intermediate times. Eventually, the rate of spreading was matched to the thermal diffusion rate in the liquid. Capillary forces were never important in weld pool spreading. The weld metal deposit shape was well-approximated as a spherical cap with increasing volume and constant contact angle.     

Studies on multipass welding with trailing heat sink considering phase transformation

A two pass butt welding of 6 mm mild steel plates was simulated using 3D finite element model using temperature and phase dependent material properties. Material phase transformations were simulated using suitable phase transformation kinetic models. Mechanical analysis is carried out using nodal temperature and phase proportions as input. Experiments were carried out using liquid nitrogen (LN2) as trailing heat sink. Trailing heat sink helped to reduce the residual stress in the fusion zone (FZ) and heat affected zone (HAZ) although distortions were found be increasing. A parametric study was conducted to study the effect of distance between weld arc and trailing heat sink. The heat sink closer to weld arc reduced both distortions and residual stresses.     

Study on heat source model in twin-arc GMAW with a common weld pool

The heat input from arcs to weld pool in twin-arc gas metal arc welding (GMAW) with a common weld pool is investigated by high-speed photography. The characteristics of arc shapes and droplet transfer are studied and then the models for heat flux distribution on top surface of weld pool and enthalpy distribution of metal droplets transferred into weld pool are established. By using the model, 3-D geometries of weld pools in twin-arc GMAW with a common weld pool are predicted. Corresponding welding experiments on mild steel plates are carried out and the results indicate that the predicted shape of weld bead on cross section shows good agreement with measured one.     

基于ANSYS的GMAW温度场计算

根据传热学、流体力学、物理冶金等理论，建立了运动电弧下熔化极气体保护焊(GMAW)的三维非稳态熔池的数学模型。在数学模型的基础上建立了GMAW堆焊的有限元模型，并使用通用有限元软件ANSYS对熔池温度场进行了计算，在计算的过程对有限元模型进行了非均匀网格划分，加入了熔滴对熔池的能量和表面变形的影响，采用了双高斯热源叠加的双峰热源分布模型，应用有限元生死单元的处理方法。并通过不同工艺参数下的工艺试验的熔宽和熔深的测量值与ANSYS计算值进行了比较，熔池的熔宽和熔深的误差均控制在8％以内。结果表明，使用ANSYS和使用双峰分布的热流来计算GMAW温度场均是可靠和可行的。     

Numerical simulation of heat transfer and fluid flow in GTA/Laser hybrid welding

Abstract

In order to understand the temperature fields, cooling rates and mixing in the weld pool, a comprehensive, three-dimensional heat transfer and fluid flow model is developed and tested by comparing model predictions with two sets of experimental data. The first set of data was taken from the literature. The experiments varied the separation distance between the heat sources for three arc current levels at a constant laser power. The second set of experiments analysed the effect of varying laser power for a constant heat source separation distance. The results demonstrate that the distance between the two heat sources significantly affects the cooling rates. The calculated results showed that the hybrid weld pool was very well mixed with strong convection currents resulting from the interaction between the electromagnetic and Marangoni forces. The calculated and experimental results showed that hybrid welding increases the weld pool width and gap bridgability when compared with laser welding. The weld pool depth in hybrid welding was affected mainly by the characteristics of the laser beam. Hybrid weld pool penetration depth is maximised at an optimal distance between the arc electrode and laser beam. The cooling rate increases significantly when the heat sources are separated beyond a critical distance. At close separation between arc and laser, calculations show that the arc radius must be decreased to achieve the observed weld depths.     

铝/钢电弧辅助激光对接熔钎焊铺展特性

采用小功率TIG电弧辅助激光热源进行5A06铝合金和热镀锌ST04Z钢的预置粉末对接熔钎焊工艺试验,通过SEM,Photoshop来研究预留间隙、背面填涂钎剂、激光热输入、辅助电弧电流、热源中心间距、填加焊丝对熔钎焊接头铺展宽度的影响. 结果表明,预留小于0.5 mm的间隙与背面填涂钎剂均可增大铺展宽度;在未焊穿的前提下,随激光热输入和辅助电弧电流的增加,铺展宽度增大;随热源中心间距的增大,铺展宽度先增加后减小. 焊接熔池中填加Al-Si焊丝较未填加焊丝的铺展性更好,获得连续、美观的焊缝表面形貌.     

Analysis of submerged arc welding process by three-dimensional computational fluid dynamics simulations

The effect of torch angle and current polarities on the convection heat transfer in single wire submerged arc welding is analyzed. To develop arc models such as arc heat flux, arc pressure and electromagnetic force, this study adopts the Abel inversion method with CCD camera images for direct and alternating current polarities. The heat transfer by molten slag from the flux consumption is considered as an additional boundary heat source in the numerical simulation. The variation of arc forces, the direction of droplet flight with polarity and the torch angle significantly affect the molten pool flow and the resultant weld beads. The simulated weld pool profiles are validated with corresponding experimental results and found to be in good agreement.     

Numerical analysis of weld pool geometry in pulsed current plasma arc welding

Numerical analysis of weld pool shape and size is of great significance for selection and optimization of the process parameters in pulsed current plasma arc welding (PAW). In this paper, a mathematical model and relevant algorithm are developed to determine the temperature profiles and weld pool geometry in pulsed current PAW through employing an adaptive heat source model. The volumetric heat source consists of semi-ellipsoid at upper part and a conic body at lower part along the workpiece thickness direction. The dynamic variation features of weld pool shape during a pulse cycle are numerically simulated. The calculated weld cross-section is consistent with the measure one.     

小孔等离子弧焊接热场的有限元分析

根据小孔等离子弧焊接的工艺特点，建立了相应的热源模型和焊接热场的分析模型。数值模拟结果表明，一般的双椭球体热源和三维锥体热源不能准确描述小孔等离子弧焊接热过程。提出了改进型的三维锥体热源模型，可以较准确地计算焊缝的正面和背面熔宽，但熔合线走向的计算精度仍较低。在此基础上，考虑等离子弧对熔池的热-力作用，建立了符合小孔形态的热源模型，对小孔等离子弧焊接热场进行了有限元分析，计算出的小孔等离子弧焊缝形状与试验结果吻合良好。     

基于FLUENT的TIG焊瞬态熔池三维形态的数值模拟

根据流体力学和传热学原理,建立了 TIG 焊瞬态熔池三维数值分析模型.电弧热源模型采用典型的高斯热源分布模型,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、熔池流体的紊流特性、材料的热物理性能参数随温度变化等因素.用 enthalpy-porosity 方法处理工件熔化/凝固过程中的问题,FLUENT RNG k-ε湍流模型对 TIG 焊熔池模型进行求解.给出了熔池形状的可视化图形结果,熔池形状特征参数随时间的动态变化.结果表明,计算值与实测值吻合良好.

Abstract：

Based on theories of fluid dynamics and heat zransfer, a transient three-dimensional model of TIG weld pools is established, in which Gaussian distribution is used to describe the heat flux source of arc. Many factors are considered in the model including the convective heat transfer of liquid metal and the heat conduction of solid metal, latent heat in welding process, the turbulence characteristics of welding pool fluid, material thermo physical properties as the function of temperature and so on. The enthalpy-porosity technology is adopted to solve the problem with workpiece phase transformation. The graphics results of weld pools and the variation of shape parameters with time are given by using FLUENT RNG k-ε model to calculate the TIG wielding pool. The experiments show that the calculated results agree well with measured value.     

电弧热流分布模式对GMAW焊接温度场的影响

提出了ＧＭＡＷ熔池表面产生较大变形时的电弧热流分布模式,以此为基础并考虑熔滴过渡过程及焊缝余高,建立了焊接温度场的数值分析模型,通过数值模拟,定量分析了焊接工艺参数－ＧＭＡＷ熔池表面变形－电弧热流分布－熔池形态及其温度是之间的相互影响。焊接工艺试验结果,与高斯热源模型相比,采用本文给出的ＧＭＡＷ电弧热液分布模型的计算结果更符合实际。     

激光+GMAW复合热源焊焊缝成形的数值模拟III.电弧脉冲作用的处理与热源模型的改进

针对激光+脉冲GMAW复合焊时电弧脉冲的热作用特点,将电弧热流处理为脉冲电流和基值电流阶段分布参数不同的双椭圆模式,同时适当减小焊件表面的热导率,以间接考虑脉冲电流和基值电流的间歇式作用.根据平均焊接电流大小确定熔滴热焓椭球体分布的作用区域,并考虑激光热源的作用位置.从以上几方面对前期研究采用的热源模型进行了改进,建立了两类新的适用于复合焊的组合式体积热源模型.利用改进后的热源模型对不同工艺条件下复合焊的焊缝横断面形状尺寸进行了模拟计算.计算得到的熔深、熔宽以及熔合线走向都与实验结果吻合,使数值模拟精度有了较大提高.     

基于改进热源模型的铝合金MIG焊数值分析

采用CMOS高速摄像机检测和分析铝合金熔化极气体保护焊(MIG焊)熔滴过渡行为,确定MIG焊熔滴的过渡频率和速度.在理论分析MIG焊热源特性、热作用模式以及焊缝形貌前提下,从宏观焊接热过程出发,提出并开发了适用于MIG焊的组合体积热源分布模式,MIG焊电弧被处理描述为经典的双椭球体热源模型,熔滴能量作用模式被表示成均匀球体热源模型.同时,在均匀球体热源模型中加入了熔滴热能和动能,实现了熔滴对MIG焊熔池冲击作用的影响.基于上述热源模型,建立了铝合金MIG焊温度场有限元模型,对厚板铝合金MIG焊温度场进行了模拟.结果表明,模拟获取的焊缝熔合线走势及形貌和实际焊接结果相吻合,证明开发的热源模型能够准确描述MIG焊指状熔深特性和热传导过程.     

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.