Three-dimensional turbulent model of heat transfer and fluid flow in GTAW process

A two-equation K-ε turbulent fluid flow model is built to model the heat transfer and fluid flow in gas tungsten arc welding (GTAW) process of stainless steel SUS310 and SUS316.This model combines the buoyancy force,lorentz force and marangni force as the driving forces of the fluid flow in the weld pool.The material properties are functions of temperature in this model.The simulated results show that the molten metal flowing outward is mainly caused by the marangoni convection,which makes the weld pool become wider and shallower.The comparison of the weld pool shape of SUS310 and SUS316 shows that the slight differences of the value of thermal conductivity mainly attributes to the difference of the weld pool shape and the distinction of heat transport in laminar and turbulent model makes large diversity in the simulated results.     

Weld pool boundary and weld bead shape reconstruction based on passive vision in P-GMAW

A passive visual sensing system is established in this research, and clear weld pool images in pulsed gas metal arc welding （ P-GMA W） can be captured with this system. The three-dimensional weld pool geometry, especially the weld height, is not only a crucial factor in determining workpiece mechanical properties, but also an important parameter for reflecting the penetration. A new three-dimensional （3D） model is established to describe the weld pool geometry in P-GMAW. Then, a series of algorithms are developed to extract the model geometrical parameters from the weld pool images. Furthermore, the method to reconstruct the 3 D shape of weld pool boundary and weld bead from the two-dimensional images is investigated.     

Numerical simulation of gas metal arc welding temperature field

The infrared camera is used to investigate the temperature field of gas metal arc welding.The results show that the temperature distribution of weld pool and adjacent area appears cone shape.A new heat source model combined by Gaussian distribution heat source of the arc and conical distribution heat source of the droplet is set up based on the experimental results, and with the combined boundary conditions,the temperature field of gas metal arc welding is simulated using finite element method.According to the comparison between the results of experiment and simulation in temperature field shows that the new combined heat source model is more accurate and effective than the Gauss heat source model.     

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.     

Determination of arc pressure and current density on the molten pool surface in plasma arc welding

A unified numerical model is developed to couple the plasma arc, weld pool and keyhole in a self consistent way. The plasma arc/anode interface and the melt/solid interface are treated specially, the VOF method is used to trace the moving keyhole wall, and the fluid flow and heat transfer in both the plasma arc and weld pool are numerically simulated. The distributions of current density and arc pressure on the weld pool surface during the keyhole formation process are analyzed using the coupled model. The predicted arc pressure and current density are compared with the experimentally measured results, and both are in good agreement.     

Numerical analysis on flow field of weld pool during deep penetration electron beam welding of titanium alloy

Flow field of weld pool during deep penetration electron beam welding of TA 15 titanium alloy was numerically and experimentally studied using a hybrid heat source of Gaussian surface heat source and rotational paraboloidal body heat source. And the formation mechanism of the weld pool flow field was analyzed. The results showed that the movement of the liquid metal in the top weld pool was the fiercest and weakened gradually in the middle and bottom of the weld pool. The maximum flow velocity of the liquid metal was about 0. 295 m/s in the top surface of weld pool. The primary driving forces of the movement of liquid metal in the weld pool were the recoil pressure of metal vapor and the surface tension.     

Formative mechanism of the undercut defect in horizontal variable polarity plasma arc welding

Abstract Horizontal welding is important for heavy or huge welding structures. Keyhole mode variable polarity plasma arc welding of aluminum alloy plates with medium thickness was carried out in horizontal position. The characteristic of welding defects was introduced. Preliminary experiments indicated that the undercut defect could not be eliminated easily. The relationship between welding parameters and the undercut defect showed that this deject could be lessened by using higher heat input. The fluid flow of weld pool was observed by a high speed camera. The fluid flow in weld pool was not symmetric and much of molten metal gathered in the lower part. The fluid flow velocity in the lower part was bigger than that in the upper part. To this end, the formative mechanism of the undercut defect was proposed. The flowability of the molten metal was an influential factor for the undercut defect. A preheating method was designed to verify the formative mechanism.     

Effect of groove angle and preheating temperature on temperature profile and fluid velocity in weld pool

The three dimensiotud transient weld pool dynamics are numerically analyzed ,for Forcearc welding, which is a new gas metal arc welding technology to get deep fusion penetration with smaller angle sf V groove to enhance welding efficiency significantly. The influence of groove angle and preheatin,g temperature on heat and .fluid .flow is studied and compared to get an optimal welding parameter. Good agreement is shown between the predicted and experimental results, such as weld bead cross-section and thermal cycles. It can he seen that an apprpriate groove angle could be used to replace high preheating temperature to get inproced penetration and thermal cycles.     

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.     

激光辅助活性焊接法

提出了激光辅助活性焊接的方法,研究了焊接参数对激光熔化处理后TIG焊接熔深、熔宽的影响.首先,使用极小功率激光在氧气保护下熔化焊件表面,使焊缝表面的氧含量增加.然后使用普通的TIG焊接,覆盖激光焊缝,达到增加熔深的目的.利用此方法,不使用活性剂就可以使TIG焊焊接熔深增加约2倍,与A-TIG焊相比没有表面熔渣,表面成形较好.小功率激光处理后焊缝中O元素含量增加,熔池表面张力温度系数由负变正,导致激光辅助活性焊熔深增加.

Abstract：

On the bases of the study for the mechanism of the increasing of A-TIG welding penetration, a new method of activating TIG welding, the laser aided activating TIG welding was proposed. At first, the surface of weld was melt by the mini power laser protected by oxygen. As a result, the oxygen content increases in the weld pool surface. Then the conventional TIG welding was used to cover the weld. The oxygen could change the direction of fluid flow in molten pool, which leads to the weld beads with narrower width and deeper penetration. Without the activating flux, the penetration can be increased by 2 times. There is no slag in the surface of weld and the appearance is good. The oxygen can change the temperature dependence of surface tension gradient from a negative value to a positive value; and cause the significant changes in the weld penetration. Fluid flow could be inward along the surface of the weld pool toward the center and then down. This fluid flow pattem transfers heat to the weld root and produces a relatively deep and narrow weld efficiently. This change is the main cause to increase the penetration.     

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。     

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。     

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。     

基于示踪粒子的摆动TIG填丝焊熔池行为数值分析

为了使TIG焊熔池液态金属分布更加均匀,在普通TIG填丝焊的基础上,研究焊枪摆动对熔池行为的影响.建立了焊枪摆动的TIG填丝焊的数学模型,并利用示踪粒子的方法,对比普通TIG填丝焊和摆动TIG填丝焊的熔池温度场、流场及熔滴质量分布.结果表明,普通TIG填丝焊与摆动TIG填丝焊熔池轮廓基本一样,但摆动TIG焊通过摆动电弧,导致熔池内流场行为发生了改变,进而影响了温度场的分布,使熔池内温度分布更加均匀;示踪粒子分布表明,在TIG填丝焊中,摆动TIG填丝焊能够使熔滴金属更加均匀的分布在熔池中.     

氧元素分布模式与AA-TIG焊熔池形貌的数值模拟

文中结合电弧辅助活性TIG焊熔池氧元素分布的试验研究结果,提出焊接熔池表面氧元素分别与熔池表面温度和位置相关两种分布模式,建立了更完善的电弧辅助活性TIG焊熔池模型,求解结果与已有的试验结果和理论研究吻合良好. 结合求解结果,利用格拉晓夫数G_r,磁雷诺数R_m和表面张力雷诺数M_a分析了浮力、电磁力和表面张力的相对作用大小; 利用Peclet数分析了熔池热对流和热传导的相对强弱. 结果表明,电弧辅助活性TIG 焊熔池表面张力作用远大于电磁力和浮力,并决定熔池流动形式;熔池热对流主导熔池的传热过程,揭示了不锈钢活性TIG焊活性元素决定深而窄的熔池形貌的内在本质.     

活性元素氧对AA-TIG焊熔池传输行为影响的数值模拟

电弧辅助活性TIG焊(arc assisted activating TIG welding,AA-TIG焊),采用辅助电弧以Ar+O₂作为保护气体预熔待焊母材表面以形成氧化层,再进行常规TIG焊,可使熔深明显增加.文中结合AA-TIG焊熔池氧元素分布的实验研究,提出焊接熔池表面氧元素的两种不均匀分布模式,考虑浮力、电磁力和表面张力,建立了更完善的电弧辅助活性TIG焊熔池模型,模拟研究氧元素在熔池表面呈不均匀分布时,AA-TIG焊瞬态熔池中动量及能量的传输行为.假设熔池内部液态金属是湍流、不可压缩Newton流体,使用FLUENT RNG k-ε湍流模型进行处理.结果表明,当氧在熔池上表面呈非均匀分布,并且氧的不均匀分布模型为低氧模型时,熔池内部仍然以内对流流动为主.     

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.     

Numerical analysis of heat transfer process for double sided tungsten inert gas – metal inert gas weld pool

Abstract

Double sided arc welding is a new type of technology developed in recent years. Many experiments show that this technology has great advantages over single arc welding for the joining of intermediate thickness stainless steel and aluminium alloy base metals. In the present work, a three-dimensional transient numerical model is created to reveal the heat transfer process for a double sided tungsten inert gas (TIG) - metal inert gas (MIG) weld pool from the viewpoint of heat transfer literature and hydrodynamics. Considering of the features of the model, effective calculation software using finite element technology is adopted. The temperature fields in the weld pool for double sided TIG - MIG welding are successfully calculated; in addition, the configuration of the weld pool is also calculated.Comparisons show that thecalculatedresults agree approximately with the experimentally measured results. STWJ/310