GMAW焊接熔滴长大和脱离动态过程的数学分析

考虑GMAW焊接过程中熔滴过渡的主要特点,利用“质量-弹簧”理论建立了熔滴过渡的数学模型,对连续电流条件下GMAW焊接熔滴过渡过程进行了动态力学分析。定量分析了熔滴过渡形式、振荡速度等对熔滴过渡行为的影响,预测出了不同焊接电流条件下的熔滴脱离尺寸和过渡频率。结果表明,在同一焊接电流条件下, 上一个熔滴的脱离会影响到下一个熔滴在焊丝末端的振荡,并影响熔滴的尺寸和过渡周期:熔滴尺寸和过渡频率的理论计算值与试验数据基本吻合。     

脉冲GMAW焊接熔滴过渡的动态模拟

本文建立了脉冲GMAW焊接熔滴过渡的动态模型,对熔滴的长大和脱离过程进行了模拟,为实现优质高效的脉冲GMAW焊接提供了科学的依据。     

脉冲GMAW焊接熔滴过渡的动态模拟

本文建立了脉冲GMAW焊接熔滴过渡的动态模型，对熔滴的长大和脱离过程进行了模拟，为实现优质高效的脉冲GMAW焊接提供了科学的依据。     

不同波长激光对激光—MAG电弧复合焊接熔滴行为的影响

通过计算分析了金属对Nd：YAG激光和CO2激光的吸收率;以8.0mm厚高强钢板为试验材料,采用高速摄像系统观测熔滴过渡模式和等离子体形态的变化.建立脉冲MAG焊接熔滴力学模型,从熔滴受力角度分析了不同波长两种激光YAG激光和C02激光在激光—MAG焊接中对熔滴过渡形式和熔滴过渡频率的影响.结果表明,Nd：YAG激光和CO2激光输出特性存在差异,金属表面对YAG激光的吸收率约为CO2激光的3倍多;在焊接电流180A、焊接电压26V、光丝间距3mm的相同条件下,YAG激光—MAG电弧复合焊接熔滴过渡频率高于CO2激光—MAG电弧复合焊接的熔滴过渡频率,且熔滴过渡频率均随着激光功率的增加而降低,但是增加等量的激光功率,YAG激光—MAG电弧复合焊接熔滴过渡频率下降幅度更大;CO2激光—MAG电弧复合焊接过程中,熔滴的过渡形式由射滴过渡转变为颗粒过渡,在YAG激光—MAG电弧复合焊接过程中,熔滴过渡形式主要为射滴过渡.     

脉冲DE-GMAW过程熔滴受力分析及电流波形设计研究

针对为了实现铝-钢高效高质量的连接,提出一种高效低热输入的脉冲旁路耦合电弧熔化极惰性气体保护焊(Double-electrode gas metal arc welding,DE-GMAW)方法。为了使其焊接过程熔滴平稳过渡,分析旁路电弧对熔滴过渡时电流密度的影响,确定脉冲DE-GMAW熔滴过渡时电磁力的作用机制,在主路为脉冲电流情况下,分别设计旁路波形与主路组合形式即为恒定电流、交替脉冲电流和同步脉冲电流三种形式的研究,并使用高速摄像拍摄熔滴过渡图像,进行对比分析试验验证。结果表明,焊接电流波形及组合形式不同会导致作用于焊接熔滴的受力发生改变,从而使得焊接过程的稳定性与焊接质量也发生变化,对比分析得出采用同步脉冲电流时的脉冲旁路耦合电弧熔化极惰性气体保护焊焊接过程稳定、熔滴过渡均匀一致且焊缝成形平整美观。     

双丝旁路耦合电弧GMAW高效焊接工艺

在介绍了双丝旁路耦合电弧熔化极气体保护焊(双丝旁路耦合电弧(Double-electrode gas metal arc welding,DE-GMAW))高效焊接工艺原理的基础之上,采用双闭环反馈解耦智能控制系统,进行双丝旁路耦合电弧GMAW高速焊接工艺试验,测量双丝旁路耦合电弧GMAW母材热输入,分析双丝旁路耦合电弧GMAW高效焊接工艺机理,并对双丝旁路耦合电弧GMAW高效焊接工艺方法进行改进,进一步研究混合气体保护下的双丝旁路耦合电弧GMAW及其熔滴过渡行为,且开发出单电源双丝旁路耦合电弧GMAW。研究表明:采用双闭环反馈解耦智能控制系统使双丝旁路耦合电弧GMAW焊接过程稳定性更好、精确度更高且响应速度更快;旁路分流是实现高效焊接的同时降低母材热输入的关键;采用混合气体保护下的双丝旁路耦合电弧GMAW能进一步提高焊接过程稳定性,单电源双丝旁路耦合电弧GMAW能形成良好的焊缝成形,且设备成本低。     

工程应用中的钛型CO_2气体保护药芯焊丝熔滴过渡

分析了GMAW熔滴过渡形态,重点探讨了钛型渣系CO2气体保护药芯焊丝的电弧、熔滴过渡特性,并以工程应用实例论证该类焊丝熔滴主流过渡形态。结果表明,GMAW用焊丝的工艺质量很大程度取决于熔滴过渡形态和电弧行为。熔化极气体保护电弧焊主要熔滴过渡形态是滴状过渡、短路过渡和喷射过渡。钛型渣系CO2气体保护药芯焊丝的电弧形态应属于活动、连续型,在大电流、强规范(含高的电弧电压)条件下施焊时,该焊丝熔滴主流过渡形态是非轴向滴状过渡。     

激光-电弧复合焊过程的熔滴过渡特征与受力分析

利用高速相机对高氮钢激光-电弧复合焊接过程的熔滴过渡、熔滴形态、等离子体形态进行采集与分析。采用图像处理与数学计算相结合的方法给出熔滴在电弧空间飞行时的受力大小和加速度。初步计算激光产生的金属蒸气对熔滴的反冲力的大小和分布。结果表明:熔滴呈现颗粒过渡的临界焊接电流为180 A附近;熔滴呈现射滴过渡的临界焊接电流200 A附近。激光的加入对电弧具有明显的压缩作用,在熔池表面这种压缩作用更为剧烈。通过观测和计算给出电弧焊和激光-电弧复合焊时熔滴刚脱离焊丝的加速度分别达到70 m/s~2和50 m/s~2。在实际复合焊接过程中,当熔滴落入熔池位置与激光匙孔间距为3 mm时,从激光匙孔喷发的金属蒸气对熔滴的反冲力非常小。激光的加入主要改变了电弧形态,近而改变熔滴上下表面的压力差,使得熔滴在接近熔池表面发生合并和过渡频率减慢。     

双丝旁路耦合电弧熔化极气体保护焊旁路熔滴过渡行为的模拟与分析

双丝旁路耦合电弧熔化极气体保护焊过程中,由于旁路电弧选择了直流正极性接法,采用常规纯氩气保护时旁路熔滴体积较大且过渡过程不稳定。为此,提出采用80%Ar+20%CO_2作为保护气体,通过改变熔滴表面的受力形式,改善旁路熔滴过渡过程。在此基础上,通过建立可以描述旁路熔滴过渡行为的动态数学模型,模拟分析不同受力形式下的旁路熔滴直径变化与过渡过程。结果表明:采用纯氩气保护时,不同旁路电流参数下的旁路熔滴直径为2.6~3.3 mm且难以过渡,采用80%Ar+20%CO_2混合气体保护时,旁路熔滴直径减小至0.6~1.1 mm且过渡频率加快;通过模拟分析不同保护气体成分下电磁力对旁路熔滴过渡的影响,发现采用80%Ar+20%CO_2混合气体保护时旁路熔滴直径减小了50%,与试验结果基本一致,证明了富氩保护气体中加入CO_2可以使得电磁力重新促进旁路熔滴向熔池过渡,从而改善了旁路熔滴过渡过程。     

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。     

Effect of shielding gas mixture on gas metal arc welding of HSLA steel using solid and flux-cored wires

In this work, gas metal arc welding of high strength-low alloy (HSLA) steel with solid- and flux-cored arc welding wires using different shielding gas compositions was performed. The composition of filler wire and shielding gas in gas metal arc welds of HSLA steel determines the inclusion characteristics, microstructure and mechanical properties. Thus, acceptable weld metal properties in HSLA steel using gas metal arc welding (GMAW) process could be achieved with the proper combination of filler wire and shielding gas composition.     

基于旁路耦合电弧的铝钢MIG熔钎焊研究

实现铝钢良好连接的关键是有效控制焊接热输入,尽量降低中间层铝铁金属间化合物的厚度,一般认为中间层金属间化合物厚度小于10μm时铝钢接头质量良好。提出旁路耦合电弧熔钎焊方法,通过调节旁路电弧电流的大小来控制焊接热输入。在优化控制系统和工艺参数的基础上采用脉冲旁路耦合电弧焊方法将铝镁合金ER5356堆焊到304不锈钢板上,获得结合良好的焊缝。对焊接接头进行扫描电镜(Scanning electron microscope,SEM)、能量色散光谱仪(Energy dispersive spectrometry,EDS)分析,结果表明:铝与不锈钢焊接接头中间层金属间化合物平均厚度约为8μm,小于10μm的临界厚度;脉冲旁路耦合电弧焊方法能够实现铝钢的连接,是一种新型低成本低热输入电弧焊方法。     

Angular distortion analysis of the multipass welding process on combined joint types using thermo-elastic–plastic FEM with experimental validation

In this research, the capability of the multipass welding advisor (MWA) is to be evaluated in analyzing the angular distortion that is induced by gas metal arc welding (GMAW) process used to join a combination of butt and T-joint with thickness of 9 mm. The MWA in SysWeld 2010 is applied to develop and compare 2D/3D finite element analysis (FEA) based on the thermal elastic–plastic approach with low manganese carbon steel S355J2G3 as parent and weld material. For this simulation, the heat source of GMAW follows the Goldak's double ellipsoid model that is available within the FEA code. Detailed procedures of MPA are presented throughout this study followed with a comparison between 2D and 3D results of distortion and computational time on the combined types. To validate the simulation results, a series of experiments was conducted on low carbon steel using robotic welding process, GMAW power source with shielding gas composition of Ar (80 %)/CO₂ (20 %), and both-sided clamping method. It was established that the results of 3D simulation and experiments showed acceptable accuracy, while 2D results offers a fast solution analysis time in estimating distortion trend.     

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.     

Adaptive volumetric heat source models for laser beam and laser + pulsed GMAW hybrid welding processes

Laser + pulsed gas metal arc welding (GMAW) hybrid welding process is an attractive joining technology in industry due to its synergy of the two processes. It is of great significance to conduct fundamental investigations involving mathematical modeling and understanding of the hybrid welding process. In this study, an adaptive heat source model is first developed for laser beam welding. Through combining the ray-tracing method with the keyhole profile determination technique based on the local energy balance, the keyhole shape and size are calculated and correlated to the distribution parameters of the volumetric heat source model. Then, thermal action characteristics in laser + pulsed GMAW hybrid welding are considered from viewpoint of macro-heat transfer, and a combined volumetric heat source model for hybrid welding is developed to take consideration of heat input from laser, pulsed gas metal arc, and overheated droplets. Numerical analysis of thermal conduction in hybrid welding is conducted. The shape and size of fusion zone and weld dimension in the quasi-steady state are calculated for various hybrid welding conditions, which have a fair agreement with the experimental results.     

Impacts of external longitudinal magnetic field on arc plasma and droplet during short-circuit GMAW

In gas metal arc welding, electromagnetic force, plasma stream force, gravity, and surface tension are the most important factors that affect metal transfer and spatter generation rate. In this paper, different kinds of external electromagnetic fields were introduced to gas metal arc welding (GMAW). The photos of arc plasma and droplet and electric signals covering welding current and arc voltage were acquired synchronously by an analysis and evaluation system based on LabView for GMAW. It was confirmed that the metal transfer frequency was improved, and spatter generation rate was diminished under controls of external electromagnetic fields. The influencing rules of external electromagnetic fields on electromagnetic force, the gravity, the plasma stream force, and surface tension were studied by three physical models, and the mechanism of external electromagnetic fields was revealed. This paper is for the purpose of discussing these factors and will make a profit for the application of electromagnetic coupling control to short-circuit GMAW.     

Weldability of Copper-bearing Aging Steel

The weldability of copper-bearing aging steel is evaluated using calculated cracking susceptibility index Pcm,oblique Y-groove cracking test,heat-affected zone (HAZ) maximum hardness measurement,submerged arc welding (SAW) test and gas metal arc welding (GMAW) test.The results show that this copper-bearing aging steel has low hardenability and cold cracking susceptibility.SAW test of 40 mm thick plate with WS03 wire matched by CHF101 flux reveals that the welded joints obtain high strength and good impact toughness at low temperature.The HAZ has no hardening but there exists a slightly softening phenomenon.Thus,line energy should be limited or controlled strictly to avoid softening behavior in HAZ during SAW.GMAW tests of 12mm and 24mm thick plates using WER70NH wire show that the tensile strength of joints reaches 720MPa,higher than the stipulated strength requirement of base metal.The average impact energy at-40℃ in the welded joints is more than 140J exceeding minimum stipulated requirement by a wide margin.There are no hardening and softening behaviors in the heat-affected zones of GMAW.All weld metals exhibit acicular ferrite (AF) plus small amount of proeutectoid ferrite (PF) structure,of which the former can significantly improve impact toughness of weld metal.The predominant microstructure in coarse grain HAZ is bainite.     

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.