Numerical investigation of droplet impact on the welding pool in gas metal arc welding

A transient three‐dimensional model that describes physical phenomena inside a welding pool during gas–metal arc welding process is presented. The model considers such phenomena as heat‐mass transfer, electromagnetics, hydrodynamic processes and deformation of the weld pool free surface. The fluid flow in the weld pool is induced due to the presence of the mechanical impact of the droplets, thermo‐capillary surface tension, thermal buoyancy and electromagnetic forces. The weld pool surface deformation is calculated by considering arc pressure and droplet impact force. A comparative analysis of the impact of the electric current of the welding arc and different force factors causing the motion of liquid metal in the weld pool on the shape of the welded seam was carried out and discussed.     

固定电弧脉冲TIG焊接熔池流体流动与传热模型

在浮力、电磁力和表面张力梯度共同作用下对固定电弧脉冲ＴＩＧ焊接熔池中的流体流动与传热的动态过程建立了数学模型。在控制方程组强烈耦合的情况下，将处理导热问题边界条件的附加源项法应用于处理动量边界条件，同时采用交替方向隐式迭代法及双块修正技术，使求解非稳态控制方程组的迭代收敛速度大为提高。计算结果展示了脉冲ＴＩＧ焊接过程中，随着焊接电流的周期性变化，熔池流场与热场的周期性变化规律以及熔池形成的动态发展过程。根据该模型得出的计算结果与试验测定结果吻合程度良好。     

Numerical analysis of AC tungsten inert gas welding of aluminum plate in consideration of oxide layer cleaning

A unified numerical simulation model of AC TIG welding of the aluminum plate considering energy balance among the electrode, the arc and the base metal and employing an analytical model for calculating cleaning rate of the oxide layer has been developed for investigating heat transport properties and weld pool formation process in AC TIG welding of aluminum plate. As a result of this simulation, it was shown that although the heat flux from the arc onto the base metal increases in EN (Electrode Negative) phase due to the electron condensation, that in EP (Electrode Positive) phase conversely decreases because mainly of cooling caused by the electron emission. Furthermore, the validity of the simulation model was confirmed by comparing to experimental results such as the arc voltage, the area of cleaning zone and the shape of weld pool.     

Modelling of arc welding: The importance of including the arc plasma in the computational domain

We present results of computational simulations of tungsten-inert-gas and metal-inert-gas welding. The arc plasma and the electrodes (including the molten weld pool when necessary) are included self-consistently in the computational domain. It is shown, using three examples, that it would be impossible to accurately estimate the boundary conditions on the weld-pool surface without including the arc plasma in the computational domain. First, we show that the shielding gas composition strongly affects the properties of the arc that influence the weld pool: heat flux density, current density, shear stress and arc pressure at the weld-pool surface. Demixing is found to be important in some cases. Second, the vaporization of the weld-pool metal and the diffusion of the metal vapour into the arc plasma are found to decrease the heat flux density and current density to the weld pool. Finally, we show that the shape of the wire electrode in metal-inert-gas welding has a strong influence on flow velocities in the arc and the pressure and shear stress at the weld-pool surface. In each case, we present evidence that the geometry and depth of the weld pool depend strongly on the properties of the arc.     

高铝粉煤灰活性剂影响TIG电弧行为研究

为了研究高铝粉煤灰作为活性剂对钨极氩弧焊电弧特性的影响规律,继而明确复合成分活性剂调控焊接电弧增加焊缝熔深的机制。基于自行开发的数据采集平台,进行了实时焊接电流、电压、焊接热循环的数据采集;基于霍尔传感器测量了电弧电流密度及其作用半径;用自制的电弧力测量装置,研究了工件表面涂覆活性剂对电弧综合作用力的影响。实验结果说明,涂覆在工件表面的活性剂在高能的等离子弧的作用下将形成复杂气氛,复杂的气氛导致焊接过程中的电弧动态特性及其电弧力产生改变,继而影响焊缝的形貌。     

等离子+缆式焊丝脉冲GMAW复合焊熔池流体行为研究

目的 研究等离子+缆式焊丝脉冲GMAW复合焊过程的熔池流体行为.方法 综合考虑传热学以及流体动力学,建立Fluent数值分析模型.使用双椭球–锥体热源模型代表等离子弧焊传热模型,用双椭球热源表征GMAW电弧传热并考虑熔滴传热,同时考虑熔池受到的电磁力、浮力、表面张力、等离子流力等作用力.基于Fluent软件,对复合焊过...     

TC4合金等离子–MIG复合焊过程温度场的数值模拟

目的 研究TC4合金在等离子-MIG复合焊(Plasma–MIG Hybrid Welding)过程中的温度场特性,探究不同电弧功率对熔池形貌的影响。方法 进行了2组4 mm TC4合金板堆焊试验,根据实验结果提出了一种改进的复合热源模型并进行了相应的仿真分析。结果 仿真与实验获得的焊缝截面相吻合;等离子电流的增大使熔池尺寸增大且余高减小,等离子电弧功率的变化对熔池宽度的影响相对较小。结论 等离子–MIG复合电弧对工件的热作用非常集中,更易实现深熔焊、焊接效率更高;所提出的热源模型适用于TC4合金等离子–MIG复合焊温度场模拟。     

AC TIG welding with single-component oxide activating flux for AZ31B magnesium alloys

Magnesium-based alloys are finding extensive applications foreground in aerospace and automotive applications. Weldability of magnesium alloys has recently been investigated with a variety of processes. In this article, the activating flux TIG (ATIG) welding of magnesium alloys with three single-component fluxes (TiO₂, Cr₂O₃ and SiO₂) under alternating current (AC) mode was studied. The effects of welding speed, weld current and electrode gap on the weld shape and the weld arc voltage in AC TIG welding with oxide fluxes were investigated on an AZ31B magnesium alloy substrate. The mechanisms of oxide fluxes on the arc shape and the arc voltage on the weld shape are discussed. The result showed that the TiO₂ and Cr₂O₃ increase the weld penetration of AC TIG welding of magnesium with good bead cosmetics. The SiO₂ increased the weld penetration with very poor formation of the weld surface. However, the arc voltage decreased with the used of TiO₂ flux, and increased with the used of Cr₂O₃ flux. The mechanism of TiO₂ and Cr₂O₃ fluxes increasing penetration should not accord with the “arc constriction”. It would comply with some potential effects of the flux interacting with the liquid metal of fusion zone.     

Numerical simulation of variable polarity vertical-up plasma arc welding process

Three-dimensional transient governing equations were developed based on conservation laws of energy, momentum and mass. These equations described physical phenomena of convection in weld pool and heat transfer in workpiece during variable polarity vertical-up plasma arc welding process. Boundary conditions for the developed governing equations were given. Welding energy input for variable polarity vertical-up plasma arc welding process was quantitatively expressed. Free surface deformation of the keyhole molten pool was coupled into calculation. Effect of wire filling on the geometry of molten pool and weld reinforcement was considered in the simulation. Correlations of temperature and thermophysical properties for aluminum alloy 2219 were quantitatively established. A control volume based finite difference method was used to solve the discrete governing equations. Moreover, dynamic evolutions of geometrical profile, dimension and fluid flow for the molten pool and keyhole were simulated through the developed computational routines, which achieved transient solution of fluid flow field coupling with thermophysical properties, temperature field and weld pool free surface deformation. Besides, the effect of the workpiece thickness on the moments of keyhole formation and stable keyhole establishment was analyzed, and thermal cycles for the main welding stage were calculated. In addition, experiments via variable polarity vertical-up plasma arc welding technique were conducted, and the established models were experimentally verified through weld cross-section profiles.     

Numerical Simulation of the TIG Welding Arc Behavior

Achieving an effective utilization and exploitation of TIG welding arcs require a thorough understanding of the plasma properties and its physical processes.Through simultaneous solutions of the set of conservation equations for mass,momentum, energy and current, a mathematical model has been developed to predict the velocity,temperature,and current density distributions in argon welding arcs.The predicted temperature fields in arc regions, and the distribution of current density and heat flux at the anode agree well with measurements reported in literatures.This work could lay the foundation for developing a comprehensive model of the TIG welding process where a dynamic, two-way coupling between the welding arc and the weld pool surface is properly represented.     

埋弧堆焊WC颗粒增强复合层的工艺及性能

目的针对传统钢材硬度低、不耐磨损的问题,选用WC颗粒来增强传统钢材性能,研究不同工艺对WC颗粒增强钢基材料的影响。方法采用埋弧焊方法,将含有WC颗粒的药芯焊丝在钢板表面进行堆焊,采用SVS3020显微镜、光学显微镜和显微硬度计对焊缝的显微组织进行观察与分析。结果随着焊接电流、电压的增大,焊缝成形逐渐完好,无焊缝缺陷,焊接速度增大,焊缝有夹渣缺陷产生;焊缝硬度随着电流、速度的提升而增大,但随电压的提升而下降。结论埋弧焊焊接选用350 A电流、32 V电压和20 m/s速度成形的焊缝质量最佳,基体的稀释作用对堆焊合金层的显微硬度也有明显影响。     

Numerical simulation on interaction between TIG welding arc and weld pool

The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established in this paper. The moving interface was solved by updating the calculation region of arc and weld pool continually. Fluid flow and heat transfer of TIG welding arc and weld pool were analyzed basing on this model. The weld pool shape calculated by dynamic coupling welding arc and pool is more close to the experiment than that of non coupling calculation.     

Experimental Investigation of Wire Arrangements for Narrow-Gap Triple-Wire Gas Indirect Arc Welding

A new narrow-gap welding process is proposed by applying triple-wire gas indirect arc (TW-GIA). There are double power supplies and triple wires in this system. Power supplies are only connected between electrode wires and base materials are not linked to power supplies. Since there are different wire arrangements with TW-GIA, this article studies these wire arrangements and their effects on sidewall fusion for narrow-gap welding. Results show that different wire arrangements lead to variant arc behaviors and metal transfer, and consequently they lead to different situation of sidewall fusion. The heat to melt sidewalls is mainly from the indirect arc column and metal transfer with narrow-gap TW-GIA. When side wires deviate from the main wire to opposite directions, heat from arc columns and metal transfer can concentrate toward groove sidewalls. When the whole weld torch is lowered, heat from the indirect arc column and metal transfer increases at the weld bead root.     

等离子弧焊接熔池和小孔形成过程数值分析

目的 研究等离子弧焊接穿孔过程中熔池内部的金属流动情况和小孔动态变化过程。方法 通过“传热-熔池流动-小孔”之间的相互耦合关系,建立了等离子弧焊接穿孔过程的数值分析模型,通过VOF方法追踪了小孔界面,采用FLOW-3D软件模拟了等离子弧焊接熔池和小孔的形成过程,定量计算了等离子弧焊接温度场、熔池流场及小孔形状;分析了等离子弧焊接熔池和小孔行为;并通过等离子弧焊接实验数据验证了模拟结果。结果 当焊接时间为0~1.0 s时,小孔深度曲线与熔深曲线几乎相同,小孔底部紧贴熔池底部;在2.8 s以后,小孔深度曲线与熔深曲线有一定距离,小孔深度曲线在一定范围内波动,等离子弧焊接电弧挖掘作用到达极限,电弧压力与其他力达到平衡状态。模拟的焊缝熔深为8.04 mm、熔宽为13.20 mm,实验测得的焊缝熔深为8.00 mm、熔宽为13.42 mm。结论 构建的随小孔动态变化的曲面热源模型和电弧压力模型可以描述等离子弧焊接过程中的电弧热-力分布;模拟出了等离子弧焊接熔池和小孔动态演变过程;模拟得到的等离子弧焊接焊缝形貌与实验测得的焊缝形貌基本吻合。     

Numerical and experimental investigation on temperature distribution of the discontinuous welding

The main objective of this study is to generate new understanding and improve computer methods for calculating the thermal cycles and temperature distribution of 5A06 aluminum alloy structure during discontinuous welding. Predicting the thermal cycle also provides an estimate of the weld penetration and weld width. The submodeling technique was used to save computing time and improve calculation accuracy. The arc heat input was applied in the weld zone using different forms of surface, volumetric and combined heat flux distribution functions. In order to validate the thermal simulation model, temperature distribution at the weld backside was precisely measured by infrared thermography during the welding process. The simulation results showed that the model is quite sensitive to the energy distribution during the welding process, the effects of the pre-heating and re-heating are significant. The present simulation model can be used as a proper tool to investigate the effect of different metal inertia gas (MIG) process parameters.     

Electric arc modeling of the EAF using differential evolution algorithm

?tore Steel Ltd. makes more than 1400 steel grades. The highest costs in steel production from scrap stems from the electric arc furnace electric energy consumption. Electrical energy is used to produce heat energy generated by the burning arc between the graphite electrodes and steel scrap. In general, the balanced heat input of all electrodes is essential. Based on the input of thermal energy from all electrodes, also the possibility of occurrence of hot and cold spots in the electric arc furnace can be determined. Perception of and the elimination of the unequal heat load of electrodes have a major impact on reducing operating costs and increasing the efficiency of the electric arc furnace production. Most authors have modeled the arc furnace as an electrical equivalent circuit, where the electric arc is modeled using the macroscopic approach. In this paper, the microscopic approach to the electric arc model is described, where a set of equations (electrical neutrality, Dalton law, Saha–Eggert) was solved using differential evolution algorithm. The results of modeling were practically confirmed by measuring electric parameters (voltage, current, active power) during the electric arc furnace operation. In November 2016, the investment in a new electrode controller using implemented logic will be carried out.     

基于Al2O3纳米流体的槽式太阳能热发电集热器传热建模及性能分析

基于计算流体动力学中的有限体积法,研究了Al₂O₃/Syltherm800导热油纳米流体作为传热介质时槽式太阳能热发电集热器的性能,建立了真空管集热器的三维模型,进行了光学模拟和传热数值模拟,并通过实验进行了验证。在非均匀热流密度分布的情况下,研究了进口温度、进口流速等运行参数对采用纳米流体的槽式集热器传热性能的影响规律。结果表明:随着Al₂O₃体积分数的增加,槽式集热器的换热性能及热效率均有所提高;进口温度、进口流速等运行参数对集热器的传热性能影响很大,随着进口温度的上升和进口流速的减小,纳米流体对传热性能的影响程度逐渐增大。     

Longitudinal propagation of a normal phase along a superconducting wire and its transient heat evacuation to a normal helium bath

The longitudinal destruction of the superconducting state along a wire by an electrical subcritical current can occur if a strong enough thermal disturbance appears somewhere along the wire. The longitudinal expansion velocity of the normal phase along the wire is then strongly dependent on the different heat production and evacuation processes. As for a wire in a superfluid helium bath, a steady boundary thermal conductance across the wire wall and the normal helium bath can be deduced by adjusting the theoretical data with the experimental data. For the temperature range considered in this paper, the steady boundary thermal conductance seems to be independent of the helium bath temperature but not of the wire surface morphology. It is also shown that the experimental and theoretical data are in strong disagreement unless a transient term in the heat transferred across the wire wall and the liquid He I separating interface is introduced in the theoretical model. A transient heat transfer coefficient is defined, and its dependence on the different wire characteristics is investigated. An empirical relationship between the transient heat transfer coefficient and the wire characteristics is deduced for a given bath temperature. The transient heat transfer coefficient is shown to depend on the maximum thermal flux released into the bath across the wire wall and not on the wire surface morphology.     

核用小直径传热管自动化衬管焊接系统的研制

目的 针对核用小直径传热管长期服役于高温高压环境时易产生表面腐蚀缺陷等问题,研制一套自动化衬管焊接系统,以高效修复腐蚀传热管,并验证该焊接系统的可行性。方法 采用以STM32F405RGT6微处理器为控制核心、植入FreeRTOS实时操作系统的方式设计了一款焊接控制系统;以微型TIG焊枪为执行机构、数字化焊接电源为功率输出设备,研制了一套自动化衬管焊接系统;最后以304不锈钢管为试样进行了衬管脉冲焊接试验。结果 焊接试验过程稳定,无断弧现象,得到的焊缝衬管完全焊透,基管适度熔透,焊缝成形良好。可通过调整基值电流、峰值电流、脉冲频率和占空比等参数调控焊接热输入,获得优质的焊缝。结论 研制的微型焊枪可适应传热管内部的狭小焊接工况;焊接电源能够满足焊接过程中的能量需求,提高了焊接过程的动态响应能力;焊接控制系统在硬件和软件层面上实现了焊枪和焊接电源的宏观调度,能够对焊接波形进行精细化调控。所研制的衬管焊接系统各项性能优秀,满足压水堆核用蒸汽发生器水箱内不锈钢传热管内衬管焊接高质量修复的需求。     

Robust sensing of arc length

During arc welding, the arc heats and melts the workpiece as heat flux. When the welding current is given, the distribution and the intensity of the heat flux are determined by the length of the are. The measurement and control of the are length are fundamental in robotic and automated welding operations. Length of welding arc determines the distribution of the arc energy and thus the heat input and width of the weld. This work aims at improving the measurement accuracy of arc length using the spectrum of are light at a particular wavelength during gas tungsten arc welding (GTAW) with argon shield. To this end, effects of welding parameters on spectral distributions were studied. To verify the effects of base metal and arc length, the arc column was also sampled horizontally as Layers for spectral analysis. Results show that spectral lines of argon atoms are determined by are length, independent of welding parameters other than the current. Based on these findings, a compact arc light sensor has been designed to measure the arc length with adequate accuracy. A closed-loop arc length control system has been developed with the proposed sensor