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。     

熔化极气体保护焊焊接过程的分析

以流体动力学、电磁理论及VOF法(Volume of Fluid Method)为基础建立了熔滴过渡的动态模拟模型,模型中考虑电磁收缩力、表面张力、等离子流力的影响。利用建立的模型模拟了熔滴的形成、长大及脱离过程,计算了电流对过渡熔滴尺寸及频率的影响,计算结果与实验结果吻合较好。计算了不同阶段的熔滴中的流场,并利用计算的流场分析了熔滴的脱离机制。     

双旁路耦合电弧MIG焊熔滴过渡受力分析

针对双旁路耦合电弧熔化极惰性气体保护(Metal inert gas,MIG)焊过程,使用高速摄像采集不同旁路电流下的熔滴过渡图像,通过图像处理提取熔滴过渡数据信息,并对熔滴所受的主要作用力进行定量计算。根据计算结果对比分析不同参数下熔滴受力的动态变化情况,研究旁路电弧对熔滴过渡的促进机理。结果表明,在焊接总电流较大的情况下电磁力对双旁路耦合电弧MIG焊熔滴过渡的影响最显著,旁路电弧可以促进熔滴上弧根面积的扩展和熔滴缩颈的形成,通过增加向下的电磁力来促进熔滴过渡,且旁路电流越大旁路电弧对熔滴过渡的促进作用越明显;在焊接总电流不变的情况下,随着旁路电流的增加熔滴过渡频率随之增加,熔滴尺寸随之减小,熔滴过渡形式逐渐由大滴过渡转变为喷射过渡。     

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.     

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.     

直流正接MAG焊电弧及熔滴过渡特性

借助高速摄像手段研究不同保护气氛下(Ar+CO2和Ar+O2)、不同焊接电流大小的直流正接MAG焊的电弧及熔滴过渡特性,分析电弧烁亮球的成因及其对直流正接MAG焊接过程稳定性的影响特点,并在此基础上确立直流正接MAG焊的工艺区间,同时比较焊丝极性对MAG焊焊丝熔化系数的影响。试验结果表明,当保护气体采用Ar+CO2时,熔滴过渡方式基本上呈大滴排斥过渡,焊接过程不稳,飞溅较大,难以应用;当保护气体采用98%Ar+2%O2时,稳定的直流正接MAG焊的熔滴过渡方式可分为小电流滴状过渡和大电流射流过渡,其中前者为下垂滴状过渡,并且熔滴尺寸随着焊接电流的增大而减小,而熔滴过渡频率相应提高,后者的电弧烁亮区分为上下相串联的两部分,调节电弧电压可以控制电弧烁亮球的活动范围并能改善焊接过程的稳定性。     

激光功率对CO2激光-MAG电弧复合焊电弧与熔滴行为的影响

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,并采集焊接过程中的电弧和熔滴图像,利用电弧分析仪记录电弧信号,通过试验深入研究激光功率对CO2激光-熔化极活性气体保护焊(Metal active gas,MAG)电弧复合焊接的电弧形态、焊接稳定性、熔滴过渡频率的影响。研究表明,焊接电流的增加减小了实际热源间距,并且实际热源间距在2 mm附近效果最佳;带电粒子在主辅导电通道内的运动产生扰动或漂移、焊接模式的跳变和过渡模式的改变是电流、电压波形出现紊乱和尖角波形的主要原因;激光的加入降低了熔滴过渡频率和过渡稳定性;焊接电流为160A、180 A时,激光-电弧复合焊接的熔滴过渡频率均随着激光功率的增加而先减小后增大,但其过渡频率介于160 A和180 A电弧焊接时熔滴过渡频率之间。     

CMT电弧增材制造过程电弧特性对熔滴过渡行为的影响机理研究

冷金属过渡(CMT)电弧增材制造技术具有沉积效率高、制造成本低等优势，在航空用大尺寸构件的快速成型领域应用前景广阔。对于电弧增材制造大型构件需采用大电流来进一步提高沉积效率，但在此高电流模式下电弧放电过程对熔滴过渡行为的影响机理尚不明确。因此，本研究采用高速摄像仪观察了电弧增材制造过程中电弧形态及熔滴过渡行为，同时通过建立电弧模型及熔滴过渡模型，分析了在不同电流波段及工艺参数下熔滴过渡频率及熔滴尺寸变化规律，最终揭示了电弧放电过程中电流密度、洛伦兹力等物理因素对熔滴过渡的作用机理。结果表明，电弧宽度与洛伦兹力决定熔滴在电弧放电过程中的受力大小，进而决定熔滴尺寸及其过渡频率。随着送丝速度从5.5 m/min增大至7.0 m/min时，电流峰值持续时间增加了1倍左右，同时电弧宽度与电流密度的随之增加，使得熔滴过渡过程中电磁力上升，熔滴尺寸下降14%且射滴过渡频率增加了3～4倍。当瞬时电流进入熄弧阶段时，熔滴过渡形式转变为短路过渡。随着送丝速度的增加，短路过渡频率从29 Hz减少至20 Hz。     

焊缝金属硅锰质量比对小电流焊接不锈钢药芯焊丝熔滴过渡及电弧稳定性的影响

采用自制熔滴收集装置、高速摄影仪、电弧焊质量分析仪研究了在电流小于100A条件下焊接时焊缝金属中硅锰质量比对E308LT0-1不锈钢药芯焊丝熔滴过渡及电弧稳定性的影响。结果表明:随着焊缝金属中硅锰质量比的增大,焊接过程中大尺寸熔滴占比先降后增,小尺寸熔滴占比先增后降,当硅锰质量比为0.311时,小尺寸熔滴占比最大,大尺寸熔滴占比几乎最小;不锈钢药芯焊丝的熔滴过渡形式主要为非轴向短路过渡,当硅锰质量比为0.311时,熔滴过渡最平稳,飞溅程度最低,电弧稳定性最好。     

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.     

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.     

Droplet transfer model for laser-enhanced GMAW

Laser-enhanced gas metal arc welding (GMAW) is a recent modification of conventional GMAW. It applies a low power laser to the droplet to obtain an auxiliary detaching force to help the detachment and achieve controlled metal transfer. As a primary parameter that affects the process and weld quality, the size of the droplet needs to be monitored and controlled. However, its direct measurement requires a high-speed camera and is not preferred in a manufacturing site because of its high cost and complicated system structure. Soft-sensing method was thus proposed as an alternative to obtain it in real time. Laser power intensity, wire feed speed and welding voltage were identified as the major parameters that determine the droplet size and were thus selected as the auxiliary variables to estimate the primary parameters: size and transfer rate of the droplet. Least squares (LS) regression equation, back-propagation neural network (BPNN), particle swarm optimization-based back-propagation neural network, and three swarm cooperative particle swarm optimization-based back-propagation neural network (TSCPSO-BPNN) models were established from the collected data. Simulation results were analyzed and compared among these models. It was found that the selected auxiliary variables were closely related to the primary variables. Droplet size and transfer rate estimates made based on the TSCPSO-BPNN model are similar to those based on LS regression equation. After dimension reduction, the LS equation can be simpler than TSCPSO-BPNN model while the accuracy is sufficient and meets the requirement for future control. The estimation by LS method could thus be utilized in the control of the laser-enhanced GMAW.     

超声辅助MIG焊接中超声作用特性研究

超声辅助熔化极惰性气体保护(Ultrasonic assisted metal inert gas,U-MIG)焊是一种新型熔化极焊接方法,利用外加声场将相应声学效果引入焊接熔池达到改善接头性能的目的。通过试验系统化研究超声对电弧形态、熔滴过渡以及接头宏观形貌的作用规律,主要目标是更好地理解超声在不同焊接条件下的作用特点。对高速摄像采集的电弧数据进行处理,结果发现随电弧电压增加,超声对电弧的压缩效果也逐渐增大;而随送丝速度增加,焊接电流增大,电弧压缩效果减弱。针对熔滴受力特点分析,可以看出超声作用后熔滴会受到一个促进熔滴过渡的附加力作用。在焊接电流为200 A时,该附加力达到最大,约为2.8×10-3 N,继续增大焊接电流,该附加力逐渐降低。对比不同送丝速度时焊缝宏观形貌,结果显示为了获得更高的焊接效率不能无限提高送丝速度,存在一个最佳的参数匹配值。结合平面驻波理论分析,随温度增加,声辐射力逐渐减弱,这在一定程度上也会削弱附加力作用效果。利用熔池薄膜模型探讨电弧、熔滴过渡以及熔池振荡三者之间的关系,超声对电弧形态、熔滴过渡的影响均可改变熔池的振荡特性,这间接表现为接头形貌的改变。通过试验与理论分析,为U-MIG焊接方法进一步发展与应用打下坚实基础。     

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.     

Monitoring of liquid droplets in laser-enhanced GMAW

In the laser-enhanced gas metal arc welding (GMAW) process developed recently, droplets of melted metal can be detached from the wire under relatively low currents with the assistance of an auxiliary force provided by a laser. The stability of the arc and the quality of the resultant welds are improved. To compete with the gas tungsten arc welding of the much lower productivity in joining precision, the size of the droplet can be pre-defined and be controlled to meet the requirements from different applications. For this purpose, image processing algorithms are developed to measure the size of a growing droplet during the laser-enhanced GMAW process. The relatively low contrast, strong illumination and reflection caused by the laser, and strong radiation from the arc make an automatic processing of the image challenging. Images are analyzed to understand its characteristics and design the image processing and recognition algorithms accordingly. In particular, a model-based method is used to filter out non-droplet edge points and a second order equation in the polar coordinate system is introduced to model the droplet. Experimental results verified the effectiveness of the developed algorithms.     

一种熔滴过渡特征信息提取和分析的新方法

利用同步采集系统采集了脉冲熔化极氩弧焊(P-MGAW)熔滴过渡过程的电信息和光谱信息。在反映熔滴过渡特征方面,光谱信息变化最为显著,信号强度变化占总强度的47.5％。电弧光谱信息中具有焊丝端头熔化、熔滴长大、缩颈和分离等过程的明显特征。采用Daubechies和Symlets离散小波分别分析了P-MGAW熔滴过渡过程的电信息和光谱信息后发现:电信息和光谱信息在高频细节分量中包含完全对应的熔滴分离特征信息,同时还含有熔滴过渡过程的其他细节特征。     

Welding polarity effects on weld spatters and bead geometry of hyperbaric dry GMAW

Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding(GMAW) experiments with direct current electrode positive(DCEP) and direct current electrode negative(DCEN) operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows: an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.     

脉冲MIG焊建模仿真分析及弧长控制

针对脉冲MIG焊过程中的电弧稳定性问题,建立基于尖端不稳定熔滴过渡理论的焊丝熔化动态电弧模型,并对焊接过程中的电弧电压、电弧长度及熔滴过渡尺寸进行仿真,得到与实际焊接相似的电弧电压波形,分析脉冲电流下熔滴过渡频率及影响电弧稳定性的因素,且进行弧长稳定控制的仿真研究,在此基础上运用快速原型技术建立铝合金脉冲MIG焊控制系统,采用电弧电压反馈对铝合金脉冲MIG焊过程进行送丝调节的弧长控制试验。研究表明:所建立的铝合金脉冲MIG焊焊丝熔化动态电弧模型很好反映了实际焊接过程,揭示出脉冲MIG焊焊接过程中熔滴过渡时间间隔具有一定的不确定性和电弧长度的不稳定性,通过电弧电压反馈控制可显著改善铝合金脉冲MIG焊过程电弧系统的稳定性。     

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。