The effect of metal transfer stability (spattering) on fume generation,morphology and composition in short-circuit MAG welding

The main objective of this work was to evaluate the hypothesis that the greater transfer stability leads also to less volume of fumes. Using an Ar + 25%CO₂ blend as shielding gas and maintaining constant the average current, wire feed speed and welding speed, bead-on-plate welds were carried out with plain carbon steel solid wire. The welding voltage was scanned to progressively vary the transfer stability. Using two conditions of low stability and one with high stability, fume generation was evaluated by means of the AWS F1.2:2006 standard. The influence of these conditions on fume morphology and composition was also verified. A condition with greater transfer stability does not generate less fume quantity, despite the fact that this condition produces fewer spatters. Other factors such as short-circuit current, arcing time, droplet diameters and arc length are the likely governing factors, but in an interrelated way. Metal transfer stability does not influence either the composition or the size/morphology of fume particulates.     

脉动送丝MIG焊的熔滴过渡及焊缝成形分析

文中在等速送丝MIG焊基础上,搭建了脉动送丝MIG焊系统,利用焊接电流电压信号采集系统以及高速摄像等设备对焊接过程进行检测,研究了脉动送丝对MIG焊熔滴过渡及焊缝成形的影响.结果表明试验发现,脉动送丝条件下熔滴所受轴向机械力是影响熔滴过渡形式的关键因素.在相同的脉动送丝频率下,脉动送丝速度基值与峰值时熔滴过渡形式有所差异;随着脉动送丝频率的改变,熔滴过渡形式也会发生变化;相比于等速送丝,脉动送丝条件下形成的焊缝熔宽更宽,且随着脉动送丝频率的增加,熔宽逐渐增大.     

Influence of GMAW-P current waveforms on heat input and weld bead shape

Abstract

Manufacturers use different, proprietary pulse current programming algorithms in their synergic 'one knob control' pulsed gas metal arc welding (GMAW-P) power supplies. Since the different pulse waveforms produced by these supplies can produce somewhat different welding characteristics, inconsistent results can be obtained when transferring welding procedures between different GMAW-P power supplies. A primary objective of this work was to characterise the differences in welding heat input and weld bead shape that could be produced by the pulsed current waveforms from four different commercial supplies. To eliminate the affects of subtle differences in electrical characteristics and to ensure that the exact shape of all waveforms was fully known, the comparison was also done by simulating the waveforms generated by three of the four power supplies on the fourth supply, which was equipped with waveform programming capability. Then, the four waveforms were used to create 'bead on plate' welds over a range of wire feed speed settings, and corresponding heat inputs were calculated from current and voltage samples recorded by a computer data acquisition system during welding. Welds were also done at the same wire feed speed setting using a constant voltage supply. All welds were then cross-sectioned for penetration and dilution measurements. In general, all of the waveforms produced good metal transfer and weld quality. However, the heat input and beads shapes varied noticeably. The heat inputs for the four pulse waveforms and constant voltage welds differed by as much as 150 J mm^?1 (17% of the maximum heat input) at the highest wire feed speed of 212 mm s^?1. The weld penetration differed by 1 mm (22% of the maximum penetration) at a wire feed speed of 169 mm s^?1 and the dilution differed a maximum value of 6.5% dilution (22% of the maximum dilution) at a wire feed speed of 169 mm s^?1 .     

水下湿法焊接短路电流控制的探索

通过改变焊接回路的电压反馈比例获得脉冲电压,利用给定电压调节短路电流,用80C196KC单片机的HSO 1口产生脉冲波形控制送丝步进电机,形成脉动送丝方式。在单片机控制下,脉冲电压、脉动送丝与短路电位三位一体同步调控。系统除了具有电压、电流波形均匀工整,短路过渡频率受控,水下焊缝成形较为美观等特点外,在一定送丝频率下,短路时峰值电流明显降低,焊接过程十分稳定。     

钛型气保护药芯焊丝焊接参数的选择与应用

分析了气保护药芯焊丝熔滴过渡形态类型和主导力,探讨了焊接参数与熔滴过渡形态的关系及焊接参数的选择原则与工程应用。结果表明,该类焊丝熔滴过渡的基本形态是非轴向排斥滴状过渡。在正常范围内,焊接电流不改变熔滴过渡形态,但偏低的电弧电压能导致熔滴过渡形态改变;焊接电流和电弧电压的合理匹配是获得满意工艺性的决定因素。焊丝焊接参数选择的“合于使用”原则,强调适合于施工现场使用的焊接参数特征。焊丝的工程应用表明,大电流、强规范（含高的电弧电压）是该类焊丝主流过渡形态的技术参数特征,短路过渡不应成为该工艺的主要过渡形态。     

自保护药芯焊丝全位置焊接电弧稳定性分析与评价

采用高速摄像仪和汉诺威弧焊质量分析仪对三种市售X70管线用自保护药芯焊丝全位置焊接的熔滴过渡及电弧稳定性进行观察分析.结果表明,全位置焊接电弧稳定性为1号焊丝最好,3号居中,2号最差;电流变异系数比标准差更能准确地反映电弧稳定性;单凭平均短路时间不能作为判定电弧稳定性的依据,必须结合短路时间频次分布图才有意义;短路过渡时电弧电压概率密度分布为双驼峰形状,双驼峰处曲线的概率密度分布及整条曲线的收敛情况可作为评定电弧稳定性的重要参考依据.     

激光对脉冲MIG焊熔滴过渡的改善作用

采用脉冲熔化极惰性气体保护焊（MIG）的方法焊接304不锈钢,在试验中利用电信号采集系统和高速摄像进行同步采集,研究熔滴过渡情况. 结果表明,送丝速度调节适当时,可以实现一脉一滴的射滴过渡形式. 送丝速度偏大时,焊接过程中会夹杂部分瞬时短路过渡,短路时间小于1 ms,影响焊接过程的稳定性. 当采用激光-脉冲MIG复合焊时,对瞬时短路现象有改善作用. 在一定范围内,激光功率增加,瞬时短路过渡出现的次数减少,改善作用增强. 当激光功率达到一定阈值时可完全消除瞬时短路现象,实现一脉一滴的过渡形式,焊接过程稳定. 即激光的加入提升了焊接品质与焊接效率.     

转向架用SMA490BW耐候钢超射流过渡焊接工艺试验

采用超射流过渡焊接工艺模式,分别对转向架用SMA490BW钢对接接头和T型接头的底层焊道进行焊接工艺参数优化试验,并研究焊接接头的微观组织和力学性能。结果表明:在其他焊接工艺条件不变的情况下,当对接接头底层焊道的电流290 A、电压27.8 V、焊速9.4 mm/s和钝边0.5 mm时,T型接头底层焊道的电流280 A、电压27.2 V、焊速6 mm/s和坡口角度50°时,可获得较为理想的焊缝成形。与传统的脉冲MAG焊接工艺相比,超射流过渡MAG焊接工艺的熔深能力更大,焊接接头的屈服强度、抗拉强度和延伸率有所提高,符合焊接工艺评定试验标准的要求。     

一种基于亚射流的PMIG焊电弧电压控制方法

针对熔化极脉冲氩弧焊(PMIG焊)主要采用恒流控制和等速送丝的焊接方式,提出了一种基于亚射流的PMIG焊电弧电压控制方法;其控制原理是对每个脉冲周期的平均电弧电压进行检测,当平均电弧电压在亚射流区域内,则完全依靠其在亚射流区域内固有的自身调节能力进行调节,当平均电弧电压超出亚射流区域后,在其它焊接参数不变的条件下,通过改变基值时间来改变脉冲周期内的平均电流值,从而改变焊丝熔化速度,提高电弧调节能力和抗扰动能力.结果表明,采用该控制方法可以显著改善焊接电弧的动态响应特性,有效抑制电弧电压的扰动,焊缝成形均匀一致.     

铝合金脉冲MIG焊机研制

铝合金在高速列车制造中,占有很重要的地位。铝合金因其独特的时有特殊的要求。本文研制的脉冲ＭＩＧ焊机,主电路采用大功率晶体管作为主控元件,从铝合金ＭＩＧ焊特点出发,采用电流脉冲技术控制铝合金ＭＩＧ焊熔滴过渡行为,在整个焊接电流范围内,均得到小滴流过渡,电弧挺度好,熔滴过渡均匀。脉冲参数采用一元化调节,操作方便,只要给定送比脉冲参数由焊机内部自动产生,实现了自适应控制。铝合金ＭＩＧ焊在不同的状态有不同     

脉冲CO2气保焊的工艺研究

在晶体管脉冲 CO_2焊研究的基础上,提出了利用双电源产生脉冲电流进行CO_2气保焊的方法,确定了两种焊丝直径下能使电弧稳定的脉冲参数变化范围,阐述了主要脉冲电流参数对电弧稳定性、熔滴过渡和飞溅的影响。研究表明:与常规 CO_2气保焊相比,在平均电流为200～300A 时,利用这种方法焊接可以在很大程度上减少飞溅,并能改善焊缝成型。     

Interchangeable metal transfer phenomenon in GMA welding: Features,mechanisms, classification

Metal transfer modes in arc welding processes have previously been classified as Natural or Controlled Metal Transfer. Modern laboratory techniques have helped to establish a new transfer classification mode in GMAW of carbon steels, which has been termed Interchangeable Metal Transfer. In order to characterize the new mode, a series of specimens was welded at different combinations of welding current (wire feed speed), arc voltage and gas composition. Laser backlighting techniques and high speed filming were employed to study metal transfer. The video was synchronized with the welding current and arc voltage signals to aid the understanding of the transfer behaviour. The results showed that this new interchangeable metal transfer class is distinguished from the Natural or Controlled Metal Transfer class because of its unique characteristic of periodical changes in the transfer mode induced by changes in welding parameters (a self-sustained behaviour). The characteristic feature of the interchangeable metal transfer class was shown to comprise of two or more natural transfer modes occurring in a regular repetitive sequence. The metal transfer sequence occurs without interference from the operator or the adaptive control system of the power source. Phenomenological explanations based on arc physics are given to justify the main governing factors for the particular metal transfer characteristics.     

铝合金薄板脉冲MIG焊低热输入工艺

利用数字化焊接电源在AA6061铝合金板上进行了单脉冲,双脉冲和梯形波三种脉冲熔化极焊接工艺的平板堆焊试验.分别通过改变基值时间、焊接速度两种方式来探讨焊接工艺参数对铝合金薄板脉冲MIG焊输入能量及显微组织的影响机理.结果表明,提高焊接速度和通过调节低能量脉冲群的脉冲个数与调节低能量脉冲群的脉冲基值时间来增大基值时间均可以降低热输入,且通过增大基值时间来降低热输入的方式能够细化焊缝组织中的晶粒尺寸,而增大焊接速度则可以提高焊接接头的硬度.     

Controlled bridge transfer (CBT) gas metal arc process for steel sheets joining

In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short-circuit current to a low level just before the re-arcing. The reduction in spatter requires an improvement in the accuracy of predicting the re-arcing by stabilizing the metal transfer and improving the robustness of the accuracy against disturbances. The controlled bridge transfer (CBT) process optimizes the accuracy of predicting the re-arcing in real time in response to the metal transfer, realizes spatter reduction and stable arc in non-pulsed GMAW. Traditionally, GMAW is carried out using electrode positive polarity. However, this polarity is not sufficient for welding extra-thin steel sheets, specifically those thinner than 1.0 mm. With electrode negative (EN) CBT process, although slight arc voltage fluctuation occurs caused by the behaviour of cathode spots on the tip of the wire during EN polarity GMAW, instantaneous voltage uses command computation to improve the transient response against the disturbance. Consequently, a stable arc can be obtained without increasing the number of short circuits in a unit time to obtain spatter-free welds.     

MATHEMATICAL SIMULATION OF HEAT AND MASS TRANSFER IN PULSED ARC WELDING BY MELTING ELECTRODE

1.~nonTherearealargenumberofinvestigationswhichhavebeencarriedouttOdescribemathematicallythe"powersource--weldingarc"systeminweldingwithsyst6thaticshort--circuitingofthearcgapusingthemeanparametersofthecondihons.However,theydidnotreflectthetechnologicalstabilityoftheprocess,becauseadeviationofoneoftheseparameterswithinthelicitsofaseparatedricrocycleleadstoitsdisrUPtion.Inparticulax,whenweldingindifferentspatialpositions,thedeviationresultinginanincreaseofaspecificparameter,suchasthepeakshort-…     

脉冲TCGMAW电流占空比对熔滴过渡和焊缝成形的影响

基于建立的熔滴过渡高速摄像分析系统,对高速脉冲TCGMAW在脉冲电流占空比变化下的熔滴过渡过程进行观察分析,并就脉冲电流占空比变化对熔滴过渡和焊缝成形质量的影响进行了研究。试验结果表明,在所用焊接规范下,当脉冲电流占空比较小时,焊丝熔化速度不能与送丝速度匹配,熔滴过渡方式表现为短路过渡形式,焊缝成形较差,甚至出现断弧、焊不起来的情况;随着脉冲电流占空比的提高,焊丝熔化能量加大,熔滴过渡方式逐渐过渡到射滴过渡和射流过渡,电弧电压的波动范围变小,焊缝成形良好。     

Welding current prediction in GMAW and UGMAW processes using response surface methodology

Abstract

Among all process variables in gas metal arc welding (GMAW) process, welding current is the most influential variable affecting heat input and weld quality. Its dependence on other process variables in GMAW and universal gas metal arc welding (UGMAW) processes (which makes use of a specially designed torch to preheat the filler wire independently, before its emergence from the torch) has been investigated using four factor five level central composite rotatable design to develop relationship for predicting welding current, which enables to quantify the direct and interactive effects of four numeric factors, namely wire feedrate, open circuit voltage, welding speed and electrode stickout and one categorical factor preheat current. Mathematical models developed show that welding current increased linearly with increaseing wire feedrate and open circuit voltage, whereas it decreased with increasing electrode stickout and preheat current. Numerical optimisation was carried out, and the optimal solutions generated indicate that under the same input conditions higher deposition rates are achievable in UGMAW process.     

Effect of process parameters on the quality of aluminium alloy Al5Si deposits in wire and arc additive manufacturing using a cold metal transfer process

A 3D print device using a cold metal transfer arc welding station to melt a metallic filler wire is developed to build aluminium part by optimising the process parameters. First tests achieved using standard pre-recorded process parameters allow to study the effect of the travel speed and the average welding power on the geometrical characteristics of mono-layer deposits and on walls built by layers superposition. Finally, a parametric study of the effect of each process parameter controlling the shape of the arc current or voltage and the filler wire feeding is carried out in order to try to improve the geometrical regularity of the deposits, and to better understand the effect of each parameter on the melting of the filler wire, its transfer on the support plate, and the geometry of the formed bead.     

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.     

激光+双丝脉冲MIG/MAG复合焊系统及工艺开发

为了对激光+双丝脉冲MIG/MAG复合焊工艺及理论进行研究,构建了激光+双丝脉冲MIG/MAG复合焊系统,双电弧的电源各自独立,电源的脉冲控制方式为推挽式.利用该系统进行焊接工艺试验,在焊接过程中,同步采集双路焊接电流、电弧电压信号,并进行高速摄像.结果表明,所构建的激光+双丝脉冲MIG/MAG复合焊系统能够进行稳定焊接,焊缝成形美观,且加入激光后,激光对电压的影响较明显,电压信号的稳定性增强.