Development and preliminary study on the ultrasonic assisted GMAW method

The ultrasonic assisted GMAW (U-GMAW)method is proposed to achieve a more stable welding process and better weld quality. The U-GMA W system is developed, which consists of power supplies, ultrasonic vibration system and specially de-signed welding torch. The U-GMAW process and conventional GMA W process are compared through bend-on-plate welding.The weld beads are continuous and well protected, while the weld surface appearances by GMA W and U-GMA W are apparently different. The metal transfer mode changes from globular transfer to short-circuiting transfer after ultrasonic wave is applied onto the arc.     

Visualization of gas metal arc welding on globular to spray transition current

The transfer modes in gas metal arc welding have important effects on welding quality. However, present study of metal transfer modes is not yet fully understood. In this study, welding arcs was visualised using the optical emission spectroscopy technique. The carbon steel wire electrode was used for welding with 80% Ar?+?20% CO₂ shielding gas. The results showed that the globular to spray transition current was 330–350?A. During globular to spray transition, argon,CO₂ and Fe plasma tended to gradually change from localising near the arc axis to a two-layer structure having 11,000?K in high-temperature region away from the arc axis and around 7000?K in low-temperature region near the arc axis.     

双丝间接电弧氩弧焊的熔滴过渡

采用氙灯背光高速摄像系统及示波器对双丝间接电弧氩气保护焊的熔滴过渡及其对应的电压、电流波形进行了研究.结果表明,双丝间接电弧氩弧焊焊接电流与电弧电压的不同匹配选择,熔滴具有短路过渡、大滴过渡、混合过渡、射滴过渡、射流过渡等不同过渡形式.随着焊接电流的增大熔滴尺寸减小,熔滴细化,随电弧电压的增大,熔滴尺寸减小.熔滴过渡形式与电压、电流的波形之间有很好的对应关系.     

Determining the boundaries of globular-to-spray transfer in robotic GMAW

Robotic gas metal arc welding （GMAW） experiments were conducted using an ERTOS-1 electrode with Ar ＋ 10% CO2 shielding gas, and the welding current and arc voltage signals were collected by a data acquisition system. The boundaries between globular transfer and spray transfer in terms of the welding current and arc voltage were determined according to the waveform of electric signals and the Fourier transform results of arc voltage. The optimum welding parameters for the two transfer modes were obtained, which laid a foundation for the numerical simulation and control of GMAW process.     

药芯焊丝CO2焊熔滴过渡现象的观察与分析

药芯焊丝CO2气体保护焊熔滴行为对药芯焊丝工艺性有直接的影响.采用焊接过程的高速摄影技术和汉诺威焊接质量分析系统对药芯焊丝的熔滴过渡形态进行观察分析.证实随着焊接参数的变化,药芯焊丝可能形成排斥过渡、表面张力过渡和细熔滴过渡.在排斥过渡时,由于大熔滴在焊丝端部较长时间的停留,出现明显的熔滴自身的爆炸飞溅,气体的强烈逸出飞溅等现象,表面张力过渡是介于大熔滴的排斥过渡与细熔滴过渡二者之间的一种过渡形式.细熔滴过渡时,焊接过程稳定、飞溅小、焊缝成形良好、生产效率较高,是药芯焊丝理想的过渡形式.在细熔滴的过渡的条件下形成的渣柱对熔滴的过渡起着导向作用.     

Hybrid laser-arc welding of advanced high-strength steel

This study investigated the synergetic effect between laser beam and electrical arc during hybrid welding by using a spectral diagnostic technique. The synergetic effect increased the energy density in the keyhole and deepened the weld penetration, resulting in a lower plasma electron temperature. The metal transfer mode was a globular one at a small offset distance while a spray mode was achieved with an increase in the offset distance. The decrease in the arc voltage and arc current due to the synergetic effect caused this transition from spray to globular modes. Globular transfer mode destabilized the molten pool and keyhole with the large droplet impingement, leading to the formation of porosity in the corresponding weld bead. The presence of porosity was on-line detected by identifying serious fluctuations in the Fe I electron temperature signals based on the fact that the instability of the molten pool and keyhole is strongly related to the signals coming from the plasma.     

保护气体对金红石型药芯焊丝电弧行为影响分析

采用高速摄像装置及汉诺威弧焊分析仪分析了金红石型药芯焊丝在100% CO₂及80% Ar+20% CO₂气体保护焊时的熔滴过渡模式及电弧形态.结果表明,100% CO₂气体保护焊时小、中、大参数均出现排斥过渡特征,随电弧电压与焊接电流增加,熔滴尺寸减小,过渡频率增加,出现滴状过渡,波形呈锯齿状;80% Ar+20% CO₂气体保护焊时以滴状过渡为主,大参数时出现射滴过渡,波形近似直线.前者渣柱仅出现于熔滴形成长大的初期,后者在熔滴过渡全过程均有渣柱存在,且对熔滴过渡有一定的导向与稳定作用.这与电弧形态不同,熔滴与渣柱受电弧热作用的效果不同有关.     

带状电极MAG焊工艺熔滴过渡分析

采用氙灯背光高速摄像系统对带状电极MAG焊的熔滴过渡进行了研究.试验发现,随焊接工艺参数的增大,钢带端部熔化变得均匀,由多个熔滴并存转变为只产生一个熔滴.熔滴在长大过程中沿钢带端部移动,过渡位置不定.随焊接参数由小到大变化,熔滴依次呈现短路过渡、大滴过渡、射滴过渡、射流过渡和旋转射流过渡等形式.结果表明,射滴过渡是带状电极MAG焊熔滴过渡的主要方式;电流、电压波形与熔滴过渡形式之间有很好的对应关系;由于其特殊的电极形状和熔滴过渡特点,带状电极MAG焊适合大电流高速焊,可以提高焊接效率.     

焊条典型熔滴过渡形态的判读

粗熔滴短路过渡,渣壁过渡,爆炸过渡和喷射过渡是焊条的基本过渡形态.过去一直采用光电示波器记录的电弧电压、焊接电流波形图,定性地描述熔滴过渡的一般特征,不可能进行精确的定量分析.通过对汉诺威弧焊质量分析仪获取的焊条四种典型熔滴过渡形态的电弧电压、焊接电流概率密度分布图的特征和短路时间t1、燃弧时间t2、加权燃弧时间t3和过渡周期tC的数据进行统计分析,可精确地描述焊条熔滴过渡形态的电弧物理特征,并能够判别焊条熔滴过渡形态.为焊条熔滴过渡形态的判定提供了一种新方法.     

Metal transfer instability in gas metal arc welding

Abstract

This work presents a simplified model of metal transfer in gas metal arc welding. The model incorporates key features of metal transfer including the change in droplet diameters as welding moves from the globular into the spray metal transfer region, and the increase in welding voltage that is observed to occur as the pendant droplet grows. The model predicts that an instability arises in the globular metal transfer region, which leads to deterministic chaos and complex limit cycles with many droplet sizes. The instability also causes deterministic chaos with a characteristic gap in droplet diameters at the transition to spray mode metal transfer. The model explains observed features of metal transfer in some detail, including the existence and location of preferred bands of droplet sizes. Whether the instability is present or not defines the boundary between chaotic globular metal transfer and the stable drop spray transfer mode. The identification of deterministic chaos in gas metal arc welding metal transfer opens the way for new approaches to welding control.     

Modelling of the short-circuiting transfer process in GMA welding. A numerical model for metal transfer phenomena in GMA welding

During gas metal arc (GMA) welding, such as MAG welding, the welding wire serves as a welding system electrode. The electrode wire is melted by arc heat to form a metal drop on the wire tip. Under the effects of forces such as gravity and electromagnetic force, the metal drop detaches from the wire and transfers to the base metal. Despite welding wire being continuously supplied, molten metal is intermittently transferred to the base metal. For this reason, various factors affecting the progression of GMA welding, such as the arc length and shape alongside the heat source and so-called arc initiation position, fluctuate in time and space. That is to say, metal transfer phenomena control arc stability and are moreover closely related to welding quality itself as well as to operability factors such as generation of spatter and welding defects. To clarify the corresponding mechanisms, it is necessary to undertake theoretical investigations in conjunction with observations by high-speed imaging.     

Steps toward a new classification of metal transfer in gas metal arc welding

This paper is reviewing the metal transfer according to the progress made in the welding sources and techniques development. It critically analysis the actual classification of the metal transfer in GMA welding, describing the relevant phenomenon and proposing improvements, to make the understanding and the work easier in the field of arc welding. Basic concepts are overviewed and defined or re-defined: fundamental transfer modes, natural vs. controlled transfer mode, variants vs. variances, mixed vs. combined modes, drop spray transfer. The new classification is simpler, without loosing the logic of numbering, both from fundamental point of view (the physics of the transfer) and the technological one (the increasing of the values of the welding parameters). It is extremely important for all the specialists involved in study, design or industrial applications of the arc welding technologies to have know–how about the metal transfer and its implications on the process and weld parameters.     

Wire melting phenomena in gas metal arc welding

Abstract

The wire melting rate in gas metal arc welding using constant voltage power supplies is well described by a parabolic model that considers the effects of electrical resistance and arc heating. However, tests performed with constant current power supplies indicate that the melting rate can deviate from this model when welding current is close to the globular–spray transition value. Although the causes of this anomaly have not yet been well established, most authors consider them to be related to variations in liquid metal temperature close to the metal transfer mode transition current. The present work evaluates the effect of welding parameters on the wire melting rate when a constant current power supply is used. A numerical model that considers the contribution of both Joule and arc heating was developed to calculate the temperature distribution in the wire and its melting rate. The model was used to assess the changes in either arc heating or metal vaporisation that might explain the melting irregularities. High speed cinematography was used to analyse metal transfer in the current range associated with the melting irregularities.     

Microstructural analysis of the anode in gas metal arc welding (GMAW)

The nature of the applied shielding gas has a strong influence on arc stability and transfer metal mode of the welding process. In particular, increase of the percentage of carbon dioxide in argon induces the increase of the transition current value from the globular to spray metal transfer mode. This work shows that these effects are linked to the chemical and microstructural modifications of the anode tip during the gas metal arc welding process. The microstructure of the anode is investigated for various experimental conditions. Transition between the two transfer modes is linked to the existence and disappearance of a rather insulating oxide “gangue” at the wire extremity whose nature depends of the shielding gas. Chemical reactions at high temperature such as oxidation–reduction reactions between shielding gas and melted metal govern the transition of the spray-arc to globular transfer mode.     

碱性药芯焊丝熔滴过渡特性及工艺性分析

利用高速摄像和汉诺威弧焊分析仪,在富氩气体保护条件下,在不同的焊接参数下对3种碱性药芯焊丝样品进行了测试和分析. 结果表明,较小焊接参数时,熔滴过渡形式为粗熔滴排斥过渡,电弧稳定性差,飞溅大;随着焊接参数的增大,熔滴过渡逐渐转变为细熔滴过渡,过渡过程趋于稳定. 熔滴受到较大的排斥力以及熔体的表面张力大是造成大颗粒飞溅的主要原因,较长的渣柱对熔滴过渡具有导向作用,细化熔滴和形成稳定、较长的渣柱是改善碱性药芯焊丝工艺性的重要途径.     

Characterization of GMAW arc instability phenomena related to low oxidation potential shielding gases

Characterizing instability phenomena in arc welding may be a complex task, since they depend on a number of interrelated factors. Such phenomena may manifest themselves in various ways, acting on the characteristics of the arc, the metal transfer, the amount of splatter and fumes formed, the arc format, the geometry of the bead and other aspects of welding. The literature on the subject reports diverse forms of instability associated with arc welding with solid wire and gas shielding (GMAW). This work aimed to define the instability phenomena associated with the GMAW process in welding with gases with a low oxidation potential. To do so, the welding current and voltages were monitored and metal transfer was filmed at high speed. The welding tests were carried out on plates of common carbon steel with a source operating at a constant current and an electrode with positive polarity. By synchronizing the filming with the welding current and voltage signals, the results showed that, during the periods of highest voltage, the transfer tended to be globular repulsive, as opposed to spray transfer during the lowest voltage periods. The synchronization of the electrical signals with the optical sensor indicates that, during periods of unstable operation, the arc is more luminous. It also showed that more fumes were generated during these periods.     

焊接电弧光谱信息模式识别软件的开发

采用模式识别方法,用Visual Basic开发了一套熔滴过渡光谱信号模式识别软件系统.根据熔滴过渡与光谱信号的对应关系,以及光谱信号波形的几何特征,抽取了多个关键性的特征参数.基于统计模式识别的Bayes决策理论,建立了相应的识别函数和最小距离法分类器.判别结果表明,利用该系统能够较好地对MIG,MAG和CO2焊熔滴过渡类型进行自动识别,为实现熔化极气体保护焊熔滴过渡自动控制奠定了基础.     

保护气体成分对双丝旁路耦合电弧GMAW旁路熔滴过渡形式的影响

双丝旁路耦合电弧GMAW的旁路焊枪选择了正极性接法即焊丝接电源负极,旁路熔滴仅依靠重力向熔池过渡,旁路熔滴尺寸较大且过渡过程并不稳定.针对这一问题,采用已建立的双丝旁路耦合电弧焊接过程信号控制与高速摄像采集系统,采集了纯氩气保护时旁路熔滴过渡形式,并分析了旁路熔滴尺寸较大且过渡过程不稳定的原因.在此基础上,采用80% Ar+20% CO₂为保护气体进行了焊接试验.结果表明,焊接过程中,保护气体中的O元素在旁路熔滴表面形成了氧化膜,旁路电弧在旁路熔滴表面的氧化膜上稳定燃烧,从而使电磁收缩力重新作用在旁路熔滴上并促进旁路熔滴向熔池过渡,因此焊接过程中旁路熔滴尺寸明显减小,熔滴过渡过程更加稳定.     

电弧电压变化量分析熔滴过渡特征的研究

利用焊接过程中熔滴还没有发生短路瞬间的电弧电压变化量△U，可以区分药芯焊丝气体保护焊(FCAW)熔滴过渡特征．绘制了一定焊接条件下的金属过渡模式图，为最终确定FCAW的最佳工艺参数(焊接电流、电弧电压等)提供指导，可实施长时间在践监控熔滴过渡过程。