The element transfer behavior of gas pool coupled activating TIG welding

This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as the inner layer gas to protect the tungsten electrode and the molten pool metal. Pure O_2,N_2 or mixture of them are used as the outer layer gas to increase the weld penetration and improve the low temperature toughness of weld metal. Through analyzing the interaction between outer gas and arc and the distributions and existing forms of oxygen and nitrogen elements,the transfer behaviors of nitrogen and oxygen from arc to pool were investigated. The results show that,the interaction between the outer gas and arc plasma makes the arc slightly constrict. The incoming oxygen enriches on the molten pool surface and exists in the form of iron oxide,chromium oxide,manganese oxide and silicon oxygen compounds. The incoming nitrogen evenly distributes in the molten pool and exists in the form of nitrogen atom.     

The humping phenomenon during high speed gas metal arc welding

Abstract

A commonly observed welding defect that characteristically occurs at high welding speeds is the periodic undulation of the weld bead profile, also known as humping. The occurrence of humping limits the range of usable welding speeds in most fusion welding processes and prevents further increases in productivity in a welding operation. At the present time, the physical mechanisms responsible for humping are not well understood. Thus, it is difficult to know how to suppress humping in order to achieve higher welding speeds. The objectives of this study were to identify and experimentally validate the physical mechanisms responsible for the humping phenomenon during high speed gas metal arc (GMA) welding of plain carbon steel. A LaserStrobe video imaging system was used to obtain video images of typical sequences of events during the formation of a hump. Based on these recorded video images, the strong momentum of the backward flow of molten metal in the weld pool that typically occurred during high speed welding was identified as the major factor responsible for the initiation of humping. Experiments with different process variables affecting the backward flow of molten weld metal were used to validate this hypothesis. These process variables included welding speed, welding position and shielding gas composition. The use of downhill welding positions and reactive shielding gases was found to suppress humping and to allow higher welding speeds by reducing the momentum of the backward flow of molten metal in the weld pool. This would suggest that any process variables or welding techniques that can dissipate or reduce the momentum of the backward flow of molten metal in the weld pool will facilitate higher welding speeds and productivity.     

Nitrogen absorption phenomenon of GTA welding with nitrogen-mixed shielding gases: effect of plasma characteristics on nitrogen content in GTA welded metal

In order to clarify the nitrogen absorption mechanism in gas tungsten arc welding, the measurement of the weld metal nitrogen content under nitrogen mixture shielding gases, and the numerical analysis of plasma heat source characteristics in nitrogen dissociation phenomenon were conducted. The nitrogen content of weld metal produced by He arc reduces to approximately a half relative to that by Ar arc in the shielding gas condition of less than about 1% mixture ratio. Additionally, it is assumed that a decline in the plasma temperature in the vicinity of the molten pools due to the generation of metal vapour, accompanied by a reduction in atom-like nitrogen content, cause intense impact on the reduction mechanism of weld metal nitrogen content in a He arc.     

Influence of molten metal flow on undercutting formation in GMAW

Molten metal flow on weld pool surface in gas metal arc welding process is investigated using a vision-based sensing system and an interpolation algorithm. Bead formation is investigated by analysing flow patterns and its driving forces of weld pool under different welding speed, welding current and shielding gas. Results show that if longitudinal to transverse velocity ratio exceeds 2.0 in the front of weld pool, outward molten metal mainly driven by arc force cannot reach the widest section of the weld pool. Meanwhile, the transverse spreading of molten metal is still hindered in the middle of weld pool as it turns to be inward flow dominated by Marangoni force. These phenomena impede molten metal supply to weld toes which causes undercutting defect. Scaling analysis shows that the predicted undercutting defect agrees well with that resulted from experiments.     

Study of wind-toughness of metal arc welding with reference to multi-pass weld metal quality

The maximum cause to make mechanical toughness of a weld metal reduce in process management is known to be a mixture of nitrogen including in the atmosphere by breaking the shield condition. Mixture of the atmosphere is prevented by blowing the shielding gas such as carbon dioxide, argon, and this mixture to the arc and the molten pool in gas metal arc welding, but it is easily affected by wind. Therefore, it has been recommended conventionally that wind velocity should be controlled to less than 2.0 m/s. But it is thought that this recommendation value is unsuitable to produce multi-pass weld metal with high mechanical and porosity toughness properties because this was provided from examination results by only consideration of porosity toughness of single-pass weld metal but non-consideration mechanical toughness. In this paper, the shielding condition is evaluated not only chemical analysis and mechanical properties of multi-pass weld metal in some velocity wind environment but also visualizing varied shielding gas behaviour by the Schlieren method. As a result, it is necessary to control the wind velocity to less than 0.5 m/s to produce multi-pass weld metal with good properties. And the calculated velocity of shielding gas should be controlled to more than twice the wind velocity.     

激光-电弧复合焊接咬边缺陷分析及抑制方法

为了提高激光-电弧复合焊接的可靠性,对复合焊接咬边缺陷成形机理及抑制方法进行了研究.结果表明,激光能够提高复合焊接的临界咬边速度,最高可达电弧焊接的5倍.在激光-电弧相互作用下,复合焊接存在两种抑制咬边的机理.一种是改变焊趾处固、液、气三相的表面张力状况,形成指向熔池外部的合力.另一种是通过提高熔池内温度梯度和热输入来增加熔池内由内向外的流动速度和时间,使熔化金属能够流向并填充焊趾,这种抑制机理作用更为显著.试验确定了复合焊接临界咬边速度的经验公式和电弧电压的合理调节范围.     

氮氧联合过渡对GPCA-TIG焊焊缝的影响

针对外层引入氮氧混合气体的气体熔池耦合活性TIG焊,通过改变焊枪内外喷嘴的相对位置,分别研究了外层气体与熔池表面的耦合程度不同时焊缝成形、焊缝中氮氧含量及焊缝组织性能的变化规律.结果表明,氮氧联合过渡时气体熔池耦合活性TIG焊焊缝窄而深;低温冲击韧性高于母材及传统TIG焊的7.5%以上,而抗拉强度和屈服强度均略低于母材;焊缝组织晶粒细小,奥氏体上沿晶界分布着少量铁素体.气体熔池耦合活性TIG焊焊缝中的氮氧含量可以通过调节焊枪内外喷嘴的相对位置进行微量控制.     

Pulsed flash welding strips of nickel alloys

Summary

Type 329J1 duplex stainless steel was welded by gas tungsten arc welding in argon‐nitrogen mixed gas atmospheres. The tensile properties and microstructures of the weld metals were examined. The nitrogen content increases and the ferrite content decreases with increasing nitrogen partial pressure of the atmosphere. The ferrite content linearly decreases with an increasing nitrogen content. The tensile strength and elongation of the weld metal produced in the argon atmosphere are much lower than those of the base metal, but they increase with an increasing nitrogen content and approximate those of the base metal at around 0.4 mass% nitrogen content. The fractographs suggest that only the base metal and high‐nitrogen weld metal clearly show dimple patterns. The tensile‐tested base metal and high‐nitrogen weld metal have complex crack paths, whereas the other weld metals have relatively straight paths. The tensile properties of the weld metal are affected by the ferrite content and chromium nitride.     

渣金间辅助外电场提高焊接工艺稳定性分析

为探索焊接过程实现高稳定性工艺的潜在途径,最大限度地减少重要钢结构制造中焊缝咬边及成形缺陷带来的焊后返修工作,提出并试验了一种利用埋弧焊渣金间随焊施加辅助外电场对渣金电导载流进行导流,进而提高焊接工艺稳定性的方法,并应用焊接电信号分析仪对弧压信号进行了采集统计分析.结果表明,以钨电极作阴极利用电场在渣金熔体内部形成稳定的电导载流,可使熔渣电导性能得以改善,并引导电子进入电弧阴极中心以增强电弧的集聚程度.同时外电场作用也使渣金内部的带电粒子形成有序运动并在界面结合成低表面能的活性氧化物,又可改善液态熔渣在焊缝金属表面的润湿铺展性能.实施辅助电场引入的这些有益作用使焊缝形状、表面光洁度、尤其是焊缝边缘平直均匀性得到较好地改观,焊接过程工艺稳定性得以进一步提高.     

Effect of welding current and speed on occurrence of humping bead in high-speed GMAW

The developed mathematical model of humping formation mechanism in high-speed gas metal arc welding (GMAW) is used to analyze the effects of welding current and welding speed on the occurrence of humping bead. It considers both the momentum and heat content of backward flowing molten jet inside weld pool. Three-dimensional geometry of weld pool, the spacing between two adjacent humps and hump height along humping weld bead are calculated under different levels of welding current and welding speed. It shows that wire feeding rate, power intensity and the moment of backward flowing molten jet are the major factors on humping bead formation.     

Neural network modeling for weld shape process of P-GMAW

Weld shape control is a fundamental issue in automatic welding. In this paper, a double side visual system is established for pulsed gas metal arc welding （ P-GMAW） , and both topside and backside weld pool images can be captured and stored continuously in real time. By analyzing the weld shape regulation with the molten metal volume, some topside weld pool characterized parameters （WPCPs） are proposed for determining penetration in butt welding of thin mild steel. Moreover, some BP network models are established to predict backside Weld pool width with welding parameters and WPCPs as inputs.     

Control of nitrogen content and porosity in gas tungsten arc welding of high nitrogen steel

Abstract

In welding of high nitrogen steel (HNS), it is essential to control the nitrogen content and porosity in the weld metal. In this paper, the influence of shielding gas composition and heat input on the nitrogen content and porosity in the weld metal of HNS was investigated by gas tungsten arc welding. The experimental results indicate that the weld nitrogen content increases as N₂ in the shielding gas is increased in the same heat input of welding. The weld nitrogen content decreases with increasing the heat input for pure argon used as a shielding gas, whereas it increases with increasing the heat input for the shielding gas including some nitrogen. The nitrogen pore can be avoided when the nitrogen content in the shielding gas is <4% in the heat input range of 528–2340 J mm^–1.     

N和O元素引入对GPCA-TIG焊焊缝冲击韧性的影响

通过外层气体引入O和N元素,气体熔池耦合活性TIG焊(gas?pool?coupled?activating?TIG?welding)可以实现深熔深、高质量和连续焊接.?为了研究清楚O和N元素引入对焊缝冲击韧性的影响规律和机理,针对SUS304不锈钢分别测试了外层气体为O2,N2和O2?+?N2时的焊缝低温冲击韧性,并...     

Using brazing alloys for controlling the quality of resistance spot-welded joints in titanium alloys

Investigations were carried out into the special features of the process of electron beam welding (EBW) with the supply of nitrogen into the weld pool. The effect of the gas medium on the focusing of the electron beam and the depth of penetration is described. The dependence of the chemical composition of weld metal and of the mechanical properties of the welded joint on the amount of supplied nitrogen is determined. It is assumed that it is sufficient to alloy the welded joints in austenitic creep-resisting steels with nitrogen during EBW in order to increase the hot cracking resistance of the weld metal.     

气体熔池耦合活性TIG焊方法

提出了一种新型活性TIG焊方法——气体熔池耦合活性TIG焊,即GPCA-TIG焊.该焊接方法将气体分两层流动,内层气体采用惰性气体起到保护熔池的作用;外层气体则为含活性元素O的气体,将活性元素O引入熔池金属,达到增加熔深的目的.文中以SUS304不锈钢为焊接母材,研究了GPCA-TIG焊接法对焊接电弧及焊缝成形的作用,以及该方法主要工艺参数对焊缝熔深和深宽比的影响.结果表明,在相同参数下,与常规TIG焊方法相比,GPCA-TIG焊可不开坡口一次性焊透8 mm不锈钢板,焊接效率明显提高.同时采用该方法,可以有效避免钨极的氧化烧损.     

焊丝含氮量及焊接电流对高氮钢焊缝组织和性能影响

针对高氮奥氏体不锈钢焊接过程中由于N元素逸出引起气孔、导致力学性能恶化的问题,利用相图计算软件设计并制备了含氮量为0.35%和0.85%两种奥氏体不锈钢焊丝,系统地研究了氮含量和焊接电流对高氮钢焊缝气孔倾向性、微观组织以及力学性能的影响规律. 结果表明,高氮钢焊缝气孔倾向和力学性能与焊接电流、焊丝氮含量密切相关:随着焊接电流增加,氮含量0.35%的高氮钢焊缝抗拉强度和断后伸长率均增加,未出现气孔;而氮含量0.85%的高氮钢焊缝具有很高的气孔倾向,抗拉强度和断后伸长率变化不大,当焊接电流增大到一定值后,气孔倾向性明显降低.     

On process–structure–property interconnection in anti-phase synchronised twin-wire GMAW of low carbon steel

The paper investigates process–structure–property interconnection in anti-phase synchronised twin-wire gas metal arc welded low carbon steel samples wherein process variation is achieved by using similar and dissimilar currents and diameters at lead and trail wires. Scanning electron microscopy and microhardness measurements are used as characterisation techniques. The investigation offers new observations on heat generation and distribution in twin-wire welding that affect weld bead and microstructure formation due to changes in arc phenomenon and molten metal flow in weld pool. Use of dissimilar currents facilitates effective utilisation of heat. The two-stage arcing in twin-wire welding facilitates slow heating and cooling that leads to weld metal and heat affected zone softening. A combination of polygonal ferrite, pearlite and bainite with varying compositions is observed across the weldment. A higher current value and larger wire diameter at the lead wire leads to coarsening of the grains thereby reducing the hardness.     

熔融金属填充焊接工艺试验系统设计

为了解决目前弧焊工艺中热输入难以控制的问题,适应高效化生产的需求,提出了一种熔融金属填充焊接新工艺. 重点介绍了方法的试验系统构成原理及各组成部分的设计. 利用锡铅合金为试验材料,对系统进行堆焊验证试验. 试验证明系统能够很好的控制液流的温度和直径、焊接速度以及气体压力,实现对焊接过程中焊接热输入的精确控制. 结果表明,该装置能够实现熔融金属填充焊接工艺的试验要求,利用该系统得到的焊缝深宽比最大能够达到6.     

冷却速率对高氮钢焊缝组织和性能的影响

研究了水冷和空冷条件下高氮不锈钢焊缝金属微观组织和力学性能的变化规律,讨论了冷却速率对高氮不锈钢焊缝微观组织和力学性能的影响规律. 结果表明,冷却速率增加能够有效增加高氮钢焊缝金属中的氮含量,尤其对于含氮量0.85%的高氮含量焊丝,增氮效果更明显. 冷却速率增加对高氮钢焊缝金属抗拉强度提高程度取决于焊丝中的氮含量,对于低氮含量高氮钢焊丝,冷却速率增加能够显著提高焊缝金属抗拉强度,当焊丝中氮含量超过0.58%时,冷却速率增加对焊缝金属抗拉强度影响不大,最终接头强度达到850 MPa.