外加横向磁场对高速GMAW焊缝成形的影响

对于高速熔化极气体保护焊接（GMAW）过程,当焊接速度超过临界值后,会出现驼峰焊道,焊缝成形变差.研究证明,熔池中动量很大的后向液体流是产生驼峰焊道的主要原因.研发了外加横向磁场发生装置,通过产生的电磁力来抑制后向液体流的动量,从而抑制驼峰焊道的形成.应用特斯拉计测试和考察了工件上磁感应强度大小及分布的影响因素.通过开展焊接工艺试验分析了不同强度的外加磁场作用下的焊缝成形规律.结果表明,外加横向磁场能明显调控熔池流态,有效抑制驼峰焊道和咬边等缺陷,显著改善焊缝成形,提高临界焊接速度.     

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.     

High speed fusion weld bead defects

Abstract

A comprehensive survey of high speed weld bead defects is presented with strong emphasis on the formation of humping and undercutting in autogenous and non-autogenous fusion welding processes. Blowhole and overlap weld defects are also discussed. Although experimental results from previous studies are informative, they do not always reveal the physical mechanisms responsible for the formation of these high speed weld bead defects. In addition, these experimental results do not reveal the complex relationships between welding process parameters and the onset of high speed weld bead defects. Various phenomenological models of humping and undercutting have been proposed that were based on observations of events in different regions within the weld pool or the final weld bead profile. The ability of these models to predict the onset of humping or undercutting has not been satisfactorily demonstrated. Furthermore, the proposed formation mechanisms of these high speed weld bead defects are still being questioned. Recent welding techniques and processes have, however, been shown to be very effective in suppressing humping and undercutting by slowing the backward flow of molten metal in the weld pool. This backward flow of molten weld metal may be the principal physical phenomenon responsible for the formation of humping and undercutting during high speed fusion welding.     

高速GMAW驼峰焊道形成过程的数值分析

基于高速气体金属电弧焊(GMAW)驼峰焊道形成过程的实验观测结果,充分考虑熔池中后向液体流的动量和热焓,在熔池表面变形方程中加入后向液体流的动能项,并将熔滴热焓分布在整个熔池表面层,建立了高速GMAW驼峰焊道形成过程的数值分析模型.模拟了一定焊接条件下的驼峰焊道形成过程及其三维形状与尺寸,与实测结果进行了对比,证明本文模型能够较好地模拟高速GMAW过程,可定量分析驼峰焊道形成过程.     

高速GMAW驼峰形成过程的数值分析

文中通过数值模拟来研究常速、高速熔化极气体保护焊的温度场和流场,并利用高速摄影观察熔池流动,分析了驼峰形成过程.结果表明,常速焊接熔池纵截面同时存在逆时针向内和顺时针向外两种流动方式,但随着焊接速度的提高,熔池纵截面仅存在逆时针向内单一流动方式.高速焊接时,较大动量的后向液体流和足够大的表面张力促进液态金属在熔池尾部不断堆积、变大.沿焊接方向,熔池受到不均匀的表面张力法向力作用而收缩,这是驼峰形成的两个重要因素.任何能降低表面张力的措施,都能抑制驼峰的形成.     

Influence of backward flowing molten jet on humping bead formation during high-speed GMA welding

Considering the inflttence of backward flowing molten jet observed by experiments, a new pool surface deformation formula and droplets heat content model are used to investigate the humping formation mechanism during high-speed gas metal arc (GMA) welding. Three-dimensional geometry of the humping bead is numerically simulated only if some extra force and heat acted at the rear part of weld pool are taken into account in the model. It has proved that both the momentum and heat content of backward flowing molten jet must be appropriately treated to quantitatively analyze the physical mechanism of the humping phenomenon.     

抑制高速GMAW驼峰焊道的外加磁场数值分析

当熔化极气体保护焊的焊接速度高于一定临界值时,会出现驼峰焊道成形缺陷.为防止驼峰焊道的出现,通过外加磁场与熔池中的焊接电流相互作用,产生指向熔池前方的电磁力,抑制熔池中后向液体流的动量从而抑制驼峰的产生.通过建立焊前工件上外加磁场的三维模型,计算了工件上的外加电磁场分布.提出热-磁耦合分析方法,实现焊接过程中熔池内外加电磁场的数值计算.结果表明,高速焊过程中,外加磁场主要以横向磁场分布在熔池区;焊丝与磁极间的距离会显著改变熔池内外加横向磁场的分布.     

High speed tandem TIG welding of ferritic stainless steel plate

Weld humping and undercut are the most common appearance defects in high speed welding. A high speed tandem TIG welding process was developed to suppress the formation of these appearance defects and to improve the productivity of TIG welding. In this paper, the mechanical properties and microstructure of joints obtained from tandem and single TIG welding were tested and compared. The results show that the sound weld appearance can be obtained by tandem TIG welding at the welding speed of 3 m/min for 1.5 mm thick 409L stainless steel plate. The mechanical properties of the tandem TIG welded joint are in the similar level with single TIG welded joint. The analysis of the tandem TIG welding process indicates that the assistant arc with a push angle can prevent the liquid metal flowing backward to the trailing region of weld pool and the premature solidification of thin liquid layer in the gouging region.     

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.     

Effects of torch configuration and welding current on weld bead formation in high speed tandem pulsed gas metal arc welding of steel sheets

Abstract

Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed gas metal arc (GMA) welding. In order to increase the maximum welding speed, effects of the inclination angle, interwire distance and welding current ratio between the leading wire and trailing wire on bead formation in high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5° to 13° , which provides an appropriate component of arc force in the welding direction. The irregular flow is also related to the distance between the leading wire and the trailing wire, and the flow becomes regular when the distance is in the range 9–12 mm. Moreover, the stabilisation of the bulge of the weld pool between the two wires, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow towards the rear part of the weld pool, are essential to increase the maximum welding speed. These conditions can be obtained by adjusting the ratio of the leading arc current to the trailing arc current. A maximum welding speed as high as 4–4·5 m min^?1 is achieved by setting the current ratio to a value ranging from 0·31 to 0·5.     

Effect of droplet heat content distribution on humping formation in high speed GMAW

The momentum of strong backward flowing melt jet and the thermal action from transferred droplets are two dominating factors affecting the formation of humping bead in high speed gas metal arc welding (GMAW). Appropriate describing the influence of the distribution mode of droplet heat content in the weld pool is essential to understand the physical mechanism of humping bead formation. Based on the experimental results, four kinds of droplet heat content distribution modes are proposed and employed to calcu...     

EXPERIMENTAL INVESTIGATION ON FORMING PROCESS OF HUMPING BEAD IN HIGH SPEEDMAG ARC WELDING

开展了高速活性气体保护( MAG)电弧焊接工艺实验, 确定出了不同焊接电流条件下形成驼峰焊道时的临界焊接速度、相邻驼峰之间的距离以及同一驼峰焊道“波峰”和“谷底”的断面形貌. 基于高速MAG电弧焊熔池的视觉检测图像, 分析了驼峰焊道的产生机理, 并利用上坡焊和下坡焊实验进行了验证. 同时, 也分析了保护气体成分对高速MAG电弧焊焊缝成形的影响.     

焊接速度和焊接电流对竖向高速GMAW驼峰焊缝的影响

运用自主研发的爬壁机器人研究焊接速度和焊接电流对竖向高速熔化极气体保护焊(gas metal arc welding,GMAW)驼峰焊缝的影响. 结果表明,焊接速度或焊接电流超过某一临界值时,竖向高速GMAW会形成驼峰焊缝,且熔池中由电弧压力、熔滴冲击力和重力作用下产生的动量很大的后向液体流是竖向高速GMAW形成驼峰焊缝的主要原因. 同时,焊接速度和焊接电流显著影响驼峰焊缝形貌. 当焊接电流不变时,随焊接速度提高,驼峰焊缝的驼峰间距和驼峰高度先稳定减小,后缓慢减小,而焊缝宽度则稳定减小;当焊接速度不变时,随焊接电流增加,驼峰焊缝的驼峰间距先增加后减小,驼峰高度则是先增加后不变,而焊缝宽度则稳定增加. 此外,焊接速度过小或焊接电流过大均会造成金属液下淌.     

Influence of welding parameters on distribution of wire feeding elements in CO2 laser GMA hybrid welding

Abstract

The effect of welding parameters on the distribution of wire feeding elements has been investigated during CO₂ laser and pulsed gas metal arc hybrid welding process. The molten metal flow on the pool surface and inside of the samples was observed by a high speed video camera and an in situ X-ray transmission imaging system respectively. The results indicate that the fluid flow towards the inside of keyhole, namely inward flow, improves the homogeneity of weld metal. The distribution of alloying elements is more homogeneous in leading laser compared with leading arc, since both of the drag force of the plasma jet and momentum of droplet promote the inward flow in leading laser. Almost homogeneous distribution of alloying elements can be attained if the oxygen content in the shielding gas is more than 2%, since the Marangoni flow direction changes from outward to inward with increasing the oxygen content.     

High quality welding of stainless steel with 10 kW high power fibre laser

Abstract

The objectives of this research are to investigate penetration characteristics, to clarify welding phenomena and to develop high quality welding procedures in bead on plate welding of type 304 austenitic stainless steel plates with a 10 kW fibre laser beam. The penetration depth reached 18 mm at the maximum at 5 mm s^?1. At 50 mm s^?1 or lower welding speeds, however, porosity was generated at any fibre laser spot diameter. On the other hand, at 100 mm s^?1 or higher welding speeds, underfilling and humping weld beads were formed under the conventionally and tightly focused conditions respectively. The generation of spatters was influenced mainly by a strong shear force of a laser induced plume and was greatly reduced by controlling direction of the plume blowing out of a keyhole inlet. The humping formation was dependent upon several dynamic or static factors, such as melt volume above the surface, strong melt flow to the rear molten pool on the top surface, solidification rate and narrow molten pool width and corresponding high surface tension. Its suppression was effective by producing a wider weld bead width under the defocused laser beam conditions or reduction of melt volume out of keyhole inlet under the full penetration welding conditions. Concerning porosity, X-ray transmission in situ observation images demonstrated that pores were formed not only from the tip of the keyhole but also at the middle part because of high power density. The keyhole behaviour was stabilised using a nitrogen shielding gas, resulting in porosity prevention. Consequently, to produce high quality welds in 10 kW high power fibre laser welding, the reduction procedures of welding defects were required on the basis of understanding their formation mechanism, and 10 kW fibre laser power could produce sound deeply penetrated welds of 18 mm depth in a nitrogen shielding gas.     

Modelling of bead hump formation in high speed gas metal arc welding

Without any presupposed mechanism, a unified three-dimensional model is developed to predict the formation of humping bead in high speed gas metal arc welding, which considers the three phase coupling of solid, liquid and gas and the effect of shear stress exerting on weld pool surface caused by arc plasma. A strong backward fluid flow in weld pool is identified as the major factor for bead hump formation. The generation of thin liquid transition zone and its premature solidification are two conditions responsible for the occurrence of humped weld. In case of low inner contact angle between the liquid metal and workpiece surface, the bead hump is still generated. With increasing welding current, the bead hump can be suppressed.     

电弧弧长对激光-电弧复合焊飞溅和底部驼峰的影响

由于热源形式的特殊性,激光-电弧复合焊接过程中激光和电弧间易发生相互干扰,产生飞溅和底部驼峰等缺陷。以590 MPa级船用高强钢为研究对象,研究了电弧弧长对激光-电弧复合焊飞溅和焊缝底部驼峰的影响。为了深入研究激光-电弧复合焊飞溅和底部驼峰的产生机理,利用高速摄像设备对熔滴过渡行为和焊缝底部熔池进行了观察。结果表明,适当缩短电弧弧长可以降低激光和电弧间的相互干扰,提高复合焊接过程的稳定性,进而降低飞溅产生的倾向。底部驼峰是小孔熔透性差和底部熔池流动不连续所引起的。缩短电弧弧长可以对底部驼峰的产生起到抑制作用,这是因为缩短电弧弧长可以降低等离子体对激光的吸收,提高激光的能量利用率,增加小孔熔透性和稳定性。 创新点： 研究了电弧弧长对激光-电弧复合焊飞溅和底部驼峰的影响,采用高速摄像方法对底部熔池流动进行了观察,进一步明确了激光-电弧复合焊接焊缝底部驼峰的产生原因。     

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.     

Effect of rotating arc process on molten pool control in horizontal welding

This paper describes the effect of rotating arc process on molten pool control in narrow gap horizontal welding. From energy strategy and force strategy, technical advantages of rotating arc process in molten pool control are explored. On the one hand, because of the decrease of temperature and holding time in weld centre, rotating arc process limits the tendency of molten pool sagging with the arc rotating frequency no more than 10 Hz, which is indicated from the simulation results of heat distribution characteristics. On the other hand, rotating arc process induces the flow of molten metal in the weld width direction by the periodical effect of arc force and droplets impingement, which is observed by the high speed photography system. This oscillation propels the molten metal at lower side against the effect of gravity to flow to the upper side, which is beneficial for the molten pool formation of horizontal welding.     

Experimental determination of the critical welding speed in high speed MAG welding

In high speed MAG welding process, some weld formation defects may be encountered. To get good weld quality, the critical welding speed beyond which humping or undercutting weld bead can occur must be known for different conditions. In this research, high speed MAG welding tests were carried out to check out the effects of different factors on the critical welding speed. Through observing the weld bead profiles and the macrographs of the transverse sections of MAG welds, the occurrence tendency of humping weld was analyzed, and the values of critical welding speed were determined under different levels of welding current or voltage, and the effect of shielding gas compositions on the critical welding speed was also investigated.