MIG welding of S235JR steel with the addition of gaseous sulphur hexafluoride SF6 to argon

The results of investigations of MIG welding of S235JR steel with G4Si1 wire with the addition of gaseous sulphur hexafluoride SF₆ in the concentration of 1.6–6.4% to argon are presented. The aim of the investigations is to investigate the effect of sulphur hexafluoride SF6 on the parameters of droplet metal transfer and the formation of the welded joint in automatic MIG welding in argon.     

Effect of gaseous sulphur hexafluoride SF6 on the process of MIG welding of AlMg4.5Mn0.7 aluminium alloy

The results of investigations of the process of MIG welding of AlMg4.5Mn0.7 aluminium alloy with the addition of sulphur hexafluoride SF₆ to argon at a concentration of 1.6–6.4% are presented. The aim of the investigations was to increase the productivity of arc welding and to improve the quality of welded joints and also the droplet transfer characteristics.     

Effects of shielding gas composition on arc characteristics and droplet transfer in tandem narrow gap GMA welding

The effects of shielding gas composition in tandem narrow gap gas metal arc welding were studied. The shielding gas included argon, carbon dioxide and helium. The arc characteristics and droplet transfer process were analysed. The results show that in the same welding parameters, the trail wire welding current is higher than the lead wire welding current. With the increase of carbon dioxide content, the welding currents of two wires decrease, and the trail wire droplet transfer mode transforms from spray transfer to projected transfer. With the increase of helium content, the welding currents increase and the lead wire droplet transfer mode transforms from projected transfer to spray transfer. The weld width is the largest when the shielding gas mixture is 80%Ar10%CO₂10%He.     

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.     

400MPa级超细晶粒钢电弧焊焊接接头组织与性能

采用普通电弧焊方法（手工电弧焊、二氧化碳气体保护焊、埋弧焊）对400MPa级超细晶粒钢进行焊接,并对不同工艺条件下的焊接接头的组织与性能进行了分析。结果表明,400MPa级超细晶粒钢电弧焊焊接接头热影响区存在着明显的晶粒长大现象;手工电弧焊和埋弧焊焊接接头性能明显下降,而二筘化碳气体保护焊焊接接头性能下降不明显。根据试验结果,实际生产中可以利用二氧化碳气体保护焊方法焊接400MPa级超细晶粒钢。     

低功率YAG激光-MAG电弧复合焊接不锈钢

以0Cr18Ni9Ti不锈钢钢板为试验材料,研究了低功率脉冲YAG激光-脉冲MAG电弧复合热源和单脉冲MAG焊接不锈钢.结果表明,低功率脉冲YAG激光-脉冲MAG电弧复合热源同样具有大功率激光-电弧复合焊接才有的增加熔深、提高焊接速度、稳定焊接过程等优点;低功率脉冲YAG激光的加入改变了电弧形态,电弧根部被吸引和压缩现象显著,提高了能量利用率;与单脉冲MAG堆焊相比,在相同焊接速度下复合焊最大能增加熔深1.3倍,在相同熔深下复合焊的焊接速度可以提高50%;复合焊焊缝的晶粒较单MAG焊缝中的晶粒细小,其焊缝抗拉强度比单MAG的好,断裂属于延性断裂.     

环保焊枪吸烟对小电流CO2气体保护电弧焊的影响

采用环保焊枪进行了小电流二氧化碳气体保护电弧焊平焊位置焊接,通过分析焊接过程中电弧形貌、电流电压和熔滴过渡方式变化以及焊缝成形、焊缝金属拉伸力学性能和X射线探伤结果,评估了吸烟功率变化时的吸烟效果以及吸烟行为对于焊接过程和焊缝质量的影响规律. 结果表明,使用环保焊枪可以显著降低小电流二氧化碳气体保护电弧焊时飘散在周围空间中的焊接烟尘. 吸烟过程虽然使得短路过渡熔滴频率略有增加,悬挂熔滴和电弧的稳定性略为变差,但对焊缝成形和焊接缺陷都无影响,焊缝金属屈服强度略有减小,抗拉强度略有增加.     

Microstructures and properties of laser/arc hybrid welds and autogenous laser welds in pipeline steels

Abstract

Lasers are capable of producing welds with deep penetration, low distortion and faster travel speeds, compared to arc welding. More recently, laser/arc hybrid welding processes have also been generating interest for industrial fabrication. In this paper, six carbon–manganese, mainly pipeline, steels were welded using both autogenous Nd:YAG laser welding, and Nd:YAG laser/MAG hybrid welding. The improvements in weld microstructures and weld metal toughness that are possible when using the hybrid process are described and illustrated. Laser/arc hybrid welding is shown to be a process that can generate good quality welds in commercially available pipeline steels. It also has the potential to complete girth welds in these steels with significantly fewer welding passes than are currently required for arc welded pipelines, reducing the joint completion time.     

脉冲频率对三丝间接电弧焊稳定性的影响

三丝间接电弧焊是一种新的焊接方法,焊接过程中工件不连接电源,主丝连接焊接电源正极,两边丝分别连接两焊接电源的负极,电弧建立在主丝与两边丝之间.焊丝熔化后主丝与边丝导电距离的变化以及焊丝形成的多条熔滴过渡路径均对建立稳定的焊接过程提出了挑战.文中通过调控脉冲频率,分析了脉冲频率对电弧特性、熔滴过渡路径以及焊接电压和焊接电...     

窄坡口MAG焊摆动宽度对电弧行为特性的影响

以窄坡口焊枪摆动数学模型和焊丝熔化模型为基础,建立窄坡口MAG焊枪摆动系统的电弧长度数学模型。进行射流过渡和短路过渡条件下不同焊枪摆动宽度的焊接试验。通过高速摄像系统得到电弧和熔滴图像,分析焊枪摆动宽度对电弧和熔滴过渡的影响。利用建立的数学模型模拟电流、电压和弧长随时间变化的规律,对焊枪摆动宽度为3 mm时的短路过渡焊接试验中的电弧和熔滴现象进行理论解释。研究发现,在侧间距(焊丝到侧壁的距离)为0~0.5 mm时,电弧燃烧稳定,熔滴过渡平稳,焊缝质量良好。     

The measurement of metal droplet temperature in GMA welding by infrared two-colour pyrometry

The temperature of metal droplets is essential for clarifying the phenomenon of metal droplet transfer and the melting behaviour of wire; also, it governs the emission of fumes. On the other hand, in situ measurement of the temperature of a metal droplet formed at the tip of a wire during welding was difficult. Hence, this temperature was obtained in many experiences of measurements by such a way that several numbers of metal droplets were collected in a calorimeter to measure the amount of heat content of metal droplet and the heat was converted to temperature. With this way, however, the reliability of the measurement is not necessarily high because the heat loss of the metal droplet during the time when detaching from the wire tip and entering into the calorimeter has to be estimated properly. In this research, two-colour pyrometry has been conducted to obtain the temperature of metal droplets, in which metal droplets have been photographed by a high-speed camera during arc welding, two wavelengths (950 and 980 nm) of light in the infrared range have been selected from the thermal radiation light emitted from the metal droplet at the instant of arc extinguishment by using an imaging spectroscope, and the temperature has been obtained from the intensity ratio of the two waves of light. Consequently, in CO₂ arc welding, it has been revealed that the constricted arc causes high-heat input density locally at the arc root portion of a metal droplet and thereby the arc root portion exhibits a higher temperature. By contrast, in MAG (80% Ar–20% CO₂) arc welding, it has been disclosed that because the arc covers metal droplets, the temperature distribution in a metal droplet is relatively uniform and the average temperature is lower than in CO₂ arc welding.     

Effect of REM addition of wire on CO2 gas shielded arc phenomenon

Carbon dioxide (CO₂) gas shielded arc welding is the main arc welding method, but it generates a large amount of spatter during welding. The root cause of spatter lies in the fact that the droplet undergoes repeated irregular shaking. To solve this problem, spatter generation modes were clarified and the effects of polarity and rare earth metal (REM) addition of the wire on CO₂ gas shielded arc welding were investigated. As a result, when welding is performed with an electrode negative (DCEN) polarity using REM added wire, it was found that a conical arc plasma is formed, and the droplet which is transferred from the wire tip to the molten pool is fine and continuous, in what is termed ‘spray transfer’. Thus, spatter generation was reduced to 10% of amount of the conventional CO₂ gas shielded arc welding (from 0.058 to 0.005g/s).     

Energy parameters in a mathematical model of a dynamic welding arc

Summary

This paper describes a method for experimental determination of the dynamic characteristics of an arc sensor in GMA (MIG/MAG) welding in droplet transfer mode. The method basically involves a vibration device being used to excite sinusoidal waveforms of the torch height as well as data processing by means of an FIR digital low-pass filter and dispersive Fourier transformation (DFT). The experimental results show that the sensitivities of the arc sensor are much greater than in DC open arc welding. The response of the welding current to torch height variation is maximised at around 3 Hz. Although the response continues up to a higher level when the frequency exceeds around 5–6 Hz, the SN ratio is poorer than that at 3 Hz. The response of the welding current shows a phase lag relative to the torch height variation. The response of the welding voltage, however, shows a phase advance relative to the torch height variation, and the response increases with an increasing variation frequency of the torch height, but its SM ratio is much poorer than that of the welding current.

To clarify the effects of shielding gases on the arc sensor, experiments using four types of shielding gas - pure Ar, Ar + 10% CO₂, Ar + 20% CO₂, and CO₂ — were conducted. The results show that, contrary to those obtained in open arc welding, the responses in short-circuiting arc welding using pure Ar are higher than those using Ar and CO₂ mixed gases.

Simulations using an arc sensor model proposed by the authors are also run for short-circuiting arc welding and the results analysed. The analytical results based on this model show the theoretical and experimental results to be similar qualitatively but to disagree quantitatively. The theoretical results further show that not only the average short-circuit frequency, but also the rate of change of the short-circuit frequency induced by variation of the arc length strongly affect the sensitivities of the arc sensor.     

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.     

An analysis of butt joints in a railway viaduct

Summary

Undercut and/or humping are generated when the arc length in high-speed pulsed MAG welding is too high, and spatter is generated if it is too low. Refinement of the droplets from the wire and simultaneous maintenance of one droplet transfer per pulse avoid short-circuiting in a short arc and enable spatter and highspeed/high-efficiency welding to be rendered compatible with each other. The requirements are to maintain a stable droplet shape during one droplet transfer per pulse, to maximise the welding speed limit without spatter generation, and to develop a technology for arc length shortening at the limit of short-circuiting by wire droplet refinement as objectives basically centred on pulsed MAG welding. This paper describes an investigation of the factors controlling droplet transfer through a division being made into the driving force imparted to the droplets and the deformability of the weld metal receiving this force as well as a method of droplet refinement based on resolution of these aspects. Through the simple rectangular wave pulse of a high peak current being set for a short time using an inverter-type pulsed power source at a constant wire diameter to increase the electromagnetic pinch force, one droplet transfer per pulse is possible on condition that the droplet volume is reduced by around 30% as compared with that obtained using a conventional power source with a chopping transistor on the secondary side. To increase the droplet deformability, the wire composition can be changed to achieve one droplet transfer per pulse on condition that the droplet volume is reduced by 20%. These droplets also show the same surface tension as conventional droplets as well as a lower viscosity coefficient. Through a combination of a pulsed current waveform and improved wire properties, the droplet volume can be reduced to around one half that of conventional droplets. The critical speed of spatter- and defect-free welding is then increased as an improvement immediately applicable on an actual automotive mass production line.     

金属粉芯型药芯焊丝熔滴过渡及飞溅观察分析

采用高速摄影技术对金属粉芯型药芯焊丝的熔滴过渡及飞溅进行观察分析,总结了金属粉芯型药芯焊丝在试验参数下的熔滴过渡类型和特征以及飞溅类型和特征,阐述了熔滴过渡特征以及飞溅特征产生的原因．结果表明,采用100％CO2气体保护时,焊接过程中电弧电压波动较大,熔滴过渡不稳．以排斥过渡为主,少量细颗粒过渡和爆炸过渡,焊接飞溅大;采用5％CO2＋95％Ar保护时,熔滴过渡为单一射滴过渡,熔滴过渡平稳,电弧稳定,焊接飞溅小;金属粉芯型药芯焊丝飞溅形式主要包括：气泡放出型飞溅、缩颈飞溅、熔滴爆炸飞溅以及电弧力引起的飞溅．     

高频交变磁场对大电流GMAW熔滴过渡和飞溅率的影响

在熔化极气体保护焊过程中,采用大送丝速度,增大焊接电流和焊丝伸出长度是提高焊接熔敷率的直接途径.但当熔滴过渡转变为旋转射流过渡时,电弧不稳,飞溅增大,焊缝成形变差.施加不同频率的纵向交变磁场,对焊缝成形进行控制.采用高速摄像技术,拍摄焊接过程中的电弧形态和熔滴过渡,研究不同频率的磁场对熔滴过渡和焊接飞溅率的影响规律.结果表明,熔滴过渡形式不同,产生飞溅的机理不同;外加频率为1 000 Hz纵向交变磁场时,电弧的旋转半径减小,电弧的挺度增大,旋转射流过渡时电弧更稳定,焊接飞溅率降低,焊缝成形改善.     

Nd：YAG激光-脉冲MAG复合热源焊熔滴过渡分析

采用高速摄像技术拍摄熔滴形成、长大及脱落的过程,观测并分析激光加入对电弧焊熔滴过渡的影响.结果表明,发现激光改变了熔滴的空间飞行轨迹、过渡稳定性、熔滴过渡模式.并从熔滴受力角度建立了脉冲MAG焊接熔滴力学模型,分析了激光加入后熔滴受力状态的改变情况.分析发现复合激光后,脉冲MAG熔滴还受到额外两个力的作用,即激光小孔产...     

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.