基于能量最小原理的熔化极气体保护电弧焊短路过渡液桥形状动态模型

基于能量最小原理,建立了熔化极气体保护电弧焊(Gas metal arc welding,OMAW)短路过渡液桥形状动态变化的模型.在一定的假设条件下,以电磁力、表面张力、重力共同作用下的液桥某体积元上具有的能量(势能)最小,建立 GMAW 短路过渡液桥形状动态变化的模型,结合焊接回路的动态模型,对液桥形状动态变化进行仿真计算,并在此基础上进一步进行模型的试验验证和模型的误差分析.研究结果表明,建立的GMAW短路过渡液桥形状模型所描述的液桥轮廓动态变化趋势与试验结果比较吻合,实际焊接过程中的液桥形状还受到磁偏吹、焊接运动过程、熔池作用、保护气体流动等的影响,这些影响是造成液桥形状模型误差的主要因素.     

EXPERIMENTAL STUDY ON METAL TRANSFER OF CELLULOSE ELECTRODE IN VERTICAL DOWN WELDING

A high-speed photographic method is mainly used to analyze metal transfer of a cellulose covered electrode in the vertical down welding. The experimental results show that fine droplets spraying transfer and globular transfer are the dominant transfer characteristic. The large droplet spatter, especially the upwards spatter, is a particular phenomenon. It is found that the combination action of gas blow force, surface tension, gravitational force and electromagnetic force lead to globular transfer. Gravitational force and electromagnetic force, which hasten big droplet spatter, should not be neglected.     

Numerical simulation of metal transfer process in tandem GMAW

A numerical model based on fluid dynamics theory and electromagnetic theory is developed to simulate the dynamic metal transfer process in tandem gas metal arc welding (T-GMAW). The relationship between welding current and surface tension coefficient is modified by analysis of regression in this model. The numerical simulation of the metal transfer process in T-GMAW is compared with that in single-wire gas metal arc welding (SW-GMAW). It is found that a droplet transfers axially in SW-GMAW, but the droplets transfer non-axially in T-GMAW. To verify the accuracy of simulated results, the welding experiments were performed in which the actual metal transfer processes were recorded by high-speed photography. The simulated results are in good agreement with the experimental ones. This transfer behavior in T-GMAW is analyzed by studying the distributions of physical quantities including pressure, velocity, and electric potential of the droplet. The simulated results reveal that the electromagnetic force between two droplets results in the different metal transfer process. With the increase of the welding current, the surface tension coefficient decreases and the electromagnetic force increases. As a consequence, the metal transfer process in T-GMAW is accelerated.     

Effect of forces on dynamic metal transfer behavior of cable-type welding wire gas metal arc welding

A cable-type welding wire (CWW) gas metal arc welding (GMAW) method was proposed as a novel approach, using CWW for the consumable electrode. Droplet transfer influences the welding process, and the forces on the droplet were analyzed to elucidate the metal transfer phenomenon observed during the welding process. The effects of the arc pressure, rotating force, and welding parameters were analyzed to understand the metal transfer. The special structure of the CWW affected the arc characteristics and forces during metal transfer as part of the welding process. The droplet formed by droplets from each thin wire, the arc, and electromagnetic forces on droplet formation and the coupling process were analyzed. The arc pressure and rotating forces are beneficial to metal transfer and increase the droplet transfer frequency. The droplet size decreases with increasing welding parameters.     

焊接电流影响GMAW双丝焊电弧等离子体的数值模拟研究

基于电磁学理论和流体力学理论,建立熔化极气体保护焊(Gas metal arc welding,GMAW)双丝焊焊接电弧等离子体三维数学模型,利用流体力学软件Fluent对其进行求解。重点研究焊接电流对GMAW双丝焊电弧等离子体行为的影响规律,获得了电弧温度、电流密度、热通量、磁场分布等结果。研究发现,随着焊接电流的变化,电弧等离子体形状变化显著。随着焊接电流的增大,电弧最高温度和电弧偏转角随之增大,电流密度和工件表面热通量由双峰分布转变为单峰分布,并且热通量峰值随焊接电流的增大而增大。此外,随着焊接电流的增大,磁感应强度和磁场力随之最大,磁场分布由独立两个磁场向耦合磁场转变。为有效、定量地证明模拟结果准确性,开展焊接试验,利用高速摄像监测电弧行为,利用光谱测温测量电弧温度。结果表明模拟结果同试验结果吻合良好,研究结果为合理选择GMAW双丝焊焊接电流参数提供理论依据。     

高强度X80钢的GMAW熔滴过渡行为研究

高强度X80钢管道的主线焊接方式为GMAW,根焊时采用内部短弧控制.本文研究了X80钢的GMAW熔滴过渡行为,采用高速摄影设备,拍摄观察了熔滴过渡过程,并提取了短路过渡中对应的电信号,研究了它们之间的动态响应过程.研究发现,熔滴过渡过程中受电磁力的影响较大,合适的焊接参数可以使熔滴平稳过渡.     

“<Emphasis Type="SmallCaps">disassembly plan approach based on subassembly concept</Emphasis>”

A three-dimensional numerical model is established to study the temperature and fluid flow fields in the twin-wire gas metal arc welding (GMAW) process. The high-speed photography system is used to capture the images of the weld pool during the welding. Based on simulation and experimental results, the weld pool formation, convection, and stability in twin-wire GMAW process are investigated. Both “push-pull” and outward flow patterns exist in the twin-wire GMAW weld pool, which can contribute to decreasing the height of the bulge and increasing the width of the pool. The convection in the weld pool can proceed adequately, the arc force between the leading and trailing arcs is relatively balanced, surface tension normal force is uniform along the liquid channel, and the liquid channel is capillary stable, all of those contribute to the stability of the weld bead. The simulation results are in good agreement with those in the experiment.     

CO2气体保护焊短路过渡与电弧电压关系的研究

针对CO2短路过渡气体保护焊过程中的飞溅问题，通过焊接质量分析仪采集电压、电流动态信息，找到与飞溅相关的熔滴缩颈、熔滴短路和熔滴小桥爆断时刻的标志信息，为短路过渡气保焊过程在线监控提供高品质的信息源。     

短路过渡CO2焊接熔滴形状数值模拟与控制

为了进一步提高短路过渡CO2气体保护电弧焊的工艺性能和焊接质量,根据高速CCD摄像获得的熔滴及其短路过渡图像,分析了熔滴与熔池短路前的形状对熔滴与熔池的短路、熔滴在熔池中的铺展及液桥缩颈形成的影响.采用熔滴静力平衡模型研究了电磁力(燃弧电流)、表面张力、重力与熔滴形状的关系,并通过对燃弧电流的精确控制实现了对熔滴形状的有效控制.当熔滴与熔池短路前为细长形状时,短路过渡过程稳定柔顺,而当熔滴为扁平形状时,则不利于熔滴的短路过渡,甚至产生瞬时短路.燃弧阶段的熔滴形状体现了各种力对熔滴的作用,而电磁力(燃弧电流)是决定熔滴形状的主要因素.根据燃弧电流对熔滴形状的影响规律,提出了采用前期大、后期小的燃弧电流控制原则,以在燃弧的不同阶段获得不同的熔滴形状.试验结果表明该控制方法获得了良好的适合于熔滴短路过渡的短路前熔滴形状,短路过渡过程柔顺稳定,消除了瞬时短路以及由此导致的飞溅,改善了熔滴的短路过渡行为,短路过渡结束后焊丝端部的残余液态金属具有良好的一致性.     

高强钢厚板激光-GMAW复合双面同步横焊特性研究

针对30 mm厚船用高强钢10Ni5Cr Mo V对接接头横焊应用需求,开展激光-熔化极气体保护电弧(Gas metal arc welding,GMAW)复合双面同步横焊特性研究。研究结果表明,针对横焊位姿因重力、非对称坡口对熔滴、电弧的影响,利用激光对电弧的吸引和收缩作用,通过减小光-丝间距,有效地抑制了电弧侧壁燃弧,熔滴在电磁力和等离子流力的作用下,稳定过渡到熔池中,实现了熔滴过渡稳定性控制,解决了激光-GMAW复合横焊位姿电弧偏离和熔滴下落等过程控制难题与侧壁未熔合问题;厚板激光-GMAW复合双面同步横焊包括打底层和填充层焊接,其中打底层焊接是保证接头焊接质量的关键;采用激光-GMAW复合双面同步横焊新方法,4道焊接完成了30 mm厚船用高强钢10Ni5Cr Mo V横焊位姿的高强、高效连接。焊缝表面成形良好,无裂纹、未焊透和侧壁未熔合等缺陷。接头的抗拉强度高于母材,且其–50℃冲击吸收能量为57.3 J。     

Experimental Study on Metal Transfer and Welding Spatter Characteristics of Cellulose Electrode

Welding spatter cause many problems during the welding process and this issue is particularly important for cellulose electrode welding.The hot flying spatter balls often deteriorate the working environment,and decrease the welding efficiency.Many factors affect the welding spatter,and metal transfer behavior is one of the main factors.Many studies concerning the spatter mechanism in arc welding process were made;most of them focused on the solid wire welding and the study on cellulose electrode is rarely reported.In this paper the metal transfer behavior and the weld spatter characteristics of three commercial cellulose electrodes were studied experimentally by using a high speed camera for visually capturing the metal transfer.The relationship between the metal transfer and the welding spatter was analyzed experimentally by comparing the spatter loss coefficient,which is for quantitative evaluation of welding spatter,with the statistical analysis of the large droplet transfer mode.The results showed that short circuiting transfer,large droplet spray transfer,fine droplet spray transfer and explosive transfer govern the metal transfer modes in cellulose electrode welding.Weld spatter occurred mainly in the deflection of large droplet process,explosive transfer process and fine droplet spraying process.Different metal transfer modes lead to different spatter.The deflection of large droplet and explosive transfer are the main factors of the spatter formation.Minimizing the droplet size and reducing the deflection of large droplet and explosive transfer leads to the reduction the amount of spatter in cellulose electrode welding.     

A Comparison of Gas Metal Arc Welding with Flux-Cored Wires and Solid Wires Using Shielding Gas

In the present work, gas metal arc welding (GMAW) with flux-cored wires and solid wires using shielding gas has been adopted for welding stainless steel. Five different compositions of shielding gas are used with flux-cored wire and three with solid wire. Spatter rates, chemical compositions, tensile strength and elongation tests have been performed and are reported. The spatter rates of the sample made using flux-cored wires are less than that for the sample made using solid wire. The ultimate tensile strength and elongation are not influenced by the composition of the shielding gas.     

Investigation on droplet momentum in VPPA-GMAW hybrid welding of aluminum alloys

Variable polarity plasma arc-gas metal arc welding (VPPA-GMAW) is a superior technology for welding thick plates of high-strength aluminum alloys. It integrates the advantages of energy focusing and high penetration depth in VPPA welding, and those of high welding efficiency and wide range of technological parameters in GMAW process. In this work, we investigated the droplet momentum in paraxial VPPA-GMAW hybrid welding of 7A52 aluminum alloys, and the technological parameters of welding process was also optimized. The images of droplet transfer were captured by high-speed camera, while the droplet speeds and sizes were statistically analyzed by t tests of independent samples. The results showed that the speeds of droplet arriving at the weld pool were significantly between GMAW and VPPA-GMAW processes, and the droplet speed increases with increasing plasma currents within a certain range. Meanwhile, the droplet momentum in VPPA-GMAW process is larger than that in conventional GMAW process. We also found that as the droplet momentum increased, the depression of weld pool grew more obvious and greatly facilitated the deep-penetration welding. In VPPA-GMAW process, it became more and more easier for the droplet to fall off the wire when the electromagnetic force gradually increased during pulse period. Droplet movement through the arc zone was further accelerated since the central pressure of arc column increased during base period. This research can provide some theoretical support for thick plate welding of high-strength aluminum alloys and help for deeper understanding of the hybrid arc coupling mechanism.     

Selection of welding process for hardfacing on carbon steels based on quantitative and qualitative factors

Weld hardfacing techniques are employed mainly to extend or improve the service life of engineering components either by rebuilding or by fabricating in such a way as to produce a composite wall section to combat wear, erosion, corrosion, etc. In this paper, an attempt has been made to determine the best welding process to hardface boiler grade steels based on quantitative factors (by measuring percentage of dilution) and qualitative factors (using the analytic hierarchy process [AHP]). Five different welding processes including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), submerged arc welding (SAW), and plasma transferred arc welding (PTAW) have been compared. Based on the quantitative and qualitative factors, the PTAW process is found to be the best method to hardface boiler grade steels.     

外加磁场对高速GMAW电弧和熔池行为的主动调控效应

在熔化极气体保护焊(Gas metal arc welding,GMAW)过程中,当焊接速度超过临界值后,焊缝成形变差,出现咬边和驼峰焊道,无法满足生产要求。研究证明,熔池中动量很大的后向液体流是产生驼峰焊道的主要原因。自主研发外加磁场发生装置,向熔池施加横向电磁力,对后向液体流进行主动干预,并调控熔池流态,从而抑制驼峰焊道的形成。在Q235低碳钢板上开展焊接工艺试验,获得了不同磁感应强度下的焊缝表面成形;采用高速摄像技术,拍摄焊接过程中的电弧和熔池图像,分析外加磁场对电弧形态、熔池流场和焊缝成形的影响规律,初步揭示外加磁场抑制驼峰焊道的机理。试验结果表明,外加横向磁场能明显调控熔池流态,减小后向液体流的动量,并能有效抑制驼峰焊道和咬边等缺陷,显著改善焊缝成形,提高临界焊接速度。     

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。     

Unsupervised droplet identification during the pulsed laser enhanced GMAW process

Pulsed laser-enhanced gas metal arc welding (GMAW) is an innovative arc welding process developed recently at the University of Kentucky. It uses the recoil pressure force generated by a pulsed laser to provide an additional force to reduce the needed electromagnetic detaching force (which is produced by the current) to assure the detachment of the droplet and the arc stability. The reduction in the current needed to detach droplets and maintain the arc stability improves the controllability of the most widely used arc welding process—GMAW—and its application range. To accurately control the detachment of the droplets, the force generated by the pulsed laser needs to be computed. Since this force is proportional to the distance from the center of the droplet to the welding wire, the problem can thus be changed to compute the distance between the droplet and the wire. To compute this distance, image processing method is the most effective way. Hence, different well-known image processing algorithms are implemented to address this problem and their performances are evaluated in this paper. Considering the robustness, processing speed, and automation, none of the evaluated image processing methods produce an acceptable result. To solve this specific problem, a novel image processing method is proposed. It is unsupervised and fast. Experimental results indicate that this proposed method can also achieve adequate computation accuracy.     

CO2气体保护焊产生飞溅的原因及控制措施

熔滴飞溅是CO2气体保护焊影响生产效率、焊接稳定性和焊缝质量的主要因素。大滴过渡和短路过渡都会产生飞溅。分析飞溅的成因,采取有针对性的控制飞溅的有效措施,采用合理的焊接工艺、选择合理的焊接工艺参数降低飞溅率,对CO2气保焊有着十分重要的意义。     

Prevention of humping bead associated with high welding speed by double-electrode gas metal arc welding

Manufacturing productivity can be improved by increasing the welding speed. However, humping bead will occur when welding speed is beyond a certain value. An experimental system of double-electrode gas metal arc welding (DE-GMAW) was developed to implement high speed welding and prevent from humping bead formation. The DE-GMAW appropriately partition the heat energy between the wire and the base metal so that higher deposition rate of filler wire and suitable shape and size of weld pool are ensured. The arc images captured during DE-GMAW process were used to optimize the geometric parameters between the gas tungsten arc welding and the gas metal arc welding (GMAW) torches. The main arc and bypass arc integrated well and satisfactory weld bead formation was obtained. Through observing the weld pool behaviors from side view during DE-GMAW process, it was found that the height of both solidified and molten region at the pool tail is almost flat so that no humping bead was formed during DE-GMAW with the welding speed up to 1.7?m/min. The side view images of weld pool in DE-GMAW were compared with those in conventional GMAW, and the reason why DE-GMAW can suppress humping bead is shortly discussed.     

Numerical analysis for effect of process parameters of low-current micro-PAW on constricted arc

A model was put forward to simulate the electromagnetic phenomena and fluid field in plasma arc occurring during the low-current microplasma arc welding (low-current micro-PAW) process. The effects of the nozzle neck-in and welding current of micro-plasma arc on the arc electromagnetic field distribution were discussed. Finally, under the condition of different welding current, welding voltage, arc length, shield gas flow rate, and plasma flow rate, welding experiments of image sampling were carried out. Three types of microplasma arc, namely, needle plasma arc, columnar plasma arc, and opening model plasma arc, are founded by experiment. Based on the unified model, a thorough investigation of the low-current microplasma arc characteristics during the micro-PAW process was conducted. It was found that the process parameters have significant effects on the microplasma arc and the distributions of current density and electromagnet force distribution.