Electromagnetic Characteristic of Twin-wire Indirect Arc Welding

Traditional welding methods are limited in low heat input to workpiece and high welding wire melting rate. Twin-wire indirect arc（TWIA） welding is a new welding method characterized by high melting rate and low heat input. This method uses two wires one connected to the negative electrode and another to the positive electrode of a direct-current（DC） power source. The workpiece is an independent, non-connected unit. A three dimensional finite element model of TWIA is devised. Electric and magnetic fields are calculated and their influence upon TWIA behavior and the welding process is discussed. The results show that with a 100 A welding current, the maximum temperature reached is 17 758 K, arc voltage is 14.646 V while maximum current density was 61 A/mm2 with a maximum Lorene force of 84.5 ~tN. The above mentioned arc parameters near the cathode and anode regions are far higher than those in the arc column region. The Lorene force is the key reason for plasma velocity direction deviated and charged particles flowed in the channel formed by the cathode, anode and upper part of arc column regions. This led to most of the energy being supplied to the polar and upper part of arc column regions. The interaction between electric and magnetic fields is a major determinant in shaping TWIA as well as heat input on the workpiece. This is a first study of electromagnetic characteristics and their influences in the TWIA welding process, and it is significant in both a theoretical and practical sense.

Numerical simulation of applied electromagnetic field and electromagnetic force in all-position welding

All-position welding is an important technology in energy sources, chemical, shipbuilding and other industries. When welding current is larger than 200 A, the molten metal tends to flow down due to the force of gravity. In order to ＂push＂ the molten metal into the weld, a new kind of U-frame excitation model, which could produce electromagnetic force to balance the gravity of the molten pool, was designed. The related parameters of the excitation model were simulated by Maxwell 3D, and the relationships between the parameters and the magnetic induction intensity were analyzed. Finally, the electromagnetic force in the molten pool was calculated, and the appropriate parameters of the U-frame excitation model were determined. The results of the simulation verify the feasibility of the all-position welding excitation model.

Numerical Simulation of Electromagnetic Force in Double-Sided Arc Welding Process

Up till now, most of the researchers believe that there are four kinds of forces in the weld pool convection, they aresurface tension, electromagnetic force, buoyancy and gas shear stress. So electromagnetic force is very important,especially when large current is applied. In most of previous models, the electromagnetic force is calculated analytically,in which only the axial component of current is considered. Actually the radial component of current has thesame effect, and may be advanced in some locations. In double-sided arc welding process, instead of the earthclamp, another torch is placed on the opposite side; the current will go from one torch, through the weld zone,to another torch. In this case, the current is more concentrated in the weld zone; the electromagnetic force willhave significant effect compared with conventional welding process. In this paper, a new method of numericalcalculation for electromagnetic force is developed, in which both axial and radial components are considered. And asan example, the distribution of electromagnetic force in double-sided arc welding is calculated. It demonstrates thatthis new method could give more accurate simulation of electromagnetic force, and is close to the actual process.

Scaling Relationships for Input Energy in Electromagnetic Welding of Similar and Dissimilar Metals

In Electromagnetic Welding (EMW) process, the capacitive energy is the source of input energy. The tool that is used for welding comprises of an electromagnetic coil. The job piece to be welded is placed in close proximity with the coil. The welding is achieved by impact, when the colliding job pieces are accelerated towards each other by the Lorentz force. The electromagnetic and mechanical properties/ parameters of the equipment, tool and the job govern the overall welding process. We have described a procedure to calculate the capacitive input energies for jobs of different sizes. Data is given for welding of strips of aluminium, copper and S.S. in similar and dissimilar combinations. Since the EMW technique is used in limited applications, this type of data is not available. We have validated our model with some data available in the literature. It is hoped that, this information will help the designer, to select and standardize the system and process parameters.

Distribution of Electromagnetic Force of Square Working Coil for High-Speed Magnetic Pulse Welding Using FEM

Magnetic pulse welding process, one of high speed welding processes, uses electromagnetic force from discharged current through a working coil which develops a repulsive force between the induced currents flowing parallel and in the opposite direction in the pipe to be welded. For achieving the successful weldment and using this process, the design of working coil is the most important factor, because working coil has to generate a high-intensity magnetic field on the surface of the workpiece during the process. Therefore, the objective of this study is to analyze the distribution of electromagnetic force of square working coil for magnetic pulse welding. For this, FE-model has been developed to analyze the distribution of electromagnetic force;after that, distribution of electromagnetic force, results of numerical analysis and experimental results for verifying the developed FE-model were compared. A 3-dimensional electromagnetic FE-model has been developed using a general commercial computer program, ANSYS/EMAG code. The shape and material of square working coil were decided through literature surveys. For the experiment, an MPW equipment W-MPW manufactured by WELDMATE Co., Ltd. was employed;also the materials were the Al 1070, SM45C for Al and Steel square pipe and rod respectively. After the experiment, leakage test was used to verify the weldability. Also weld joints were observed on longitudinal cross-section by microscope. The electromagnetic force generated was the greatest one at the center adjacent to square working coil, decreasing as moving into the edge. As the result of Al/Steel welding experiment, weldment of square Al pipe was not completed at the corner of weldment. These results are similar to the output data from developed electromagnetic FE-model where electromagnetic force decreases as moving into the corners of square working coil.

Effect of the Welding Parameters on the Structural and Mechanical Properties of Aluminium and Copper Sheet Joints by Electromagnetic Pulse Welding

Aluminium-copper hybrid parts, as a substitution to copper parts, result in weight and cost reduction, and are relevant in applications related to the electronic, heating and cooling sector. However, aluminium to copper joined by thermal welding processes presents challenges in terms of achieving good joint quality. This is attributed to their dissimilar mechanical and thermal properties which result in large stress gradients during heating. This study investigated joining of aluminium to copper sheets by electromagnetic pulse welding, which is a solid-state process that uses electromagnetic forces for joining of dissimilar materials. Hybrid sheet welds were obtained for all parameters conditions, selected according to a Taguchi L18 design. The structural and mechanical characteristics were examined and related to the welding parameters by means of a Pareto analysis and response graphs. The welded zone started with a wavy interface with interfacial layers and defects and evolved to a flat interface without interfacial layers. The maximum transferable force depended on the minimum specimen thickness and the strength of the hybrid sheet weld. In case of aluminium sheet thickness reduction, the maximum transferable force was linearly correlated with the aluminium sheet thickness. High quality joints were obtained for no aluminium sheet thickness reduction and for a sheet weld strength which was at least as high as that of the base material. The most effective way to increase the transferable force was to lower the initial gap and to increase the free length, which resulted in no aluminium sheet thickness reduction. Alternatively, the use of a rounded spacer decreased the effect of the aluminium sheet thickness on the transferable force. An increase in weld width was achieved for an increase in capacitor charging energy and gap, whereas an increase in weld length was obtained for a decrease in gap. An increase in weld width did not necessarily result in an increase in the transferable force. In the regarded cases, a hybrid sheet with narrow weld width could therefore have higher quality.

铜-铝电磁脉冲焊接界面形成过程的原子扩散行为

电磁脉冲焊接技术以高压脉冲放电驱使异种金属可靠连接而备受关注,但其界面结合机制尚不明确.该文搭建了铜-铝电磁脉冲焊接综合试验平台,捕获了焊接的动力学过程,得到碰撞点速度与碰撞角度的变化规律.在此基础上,构建了基于分子动力学模拟的电磁脉冲焊接典型界面(平直界面与涡旋界面)形成过程的对应模型,探究了焊接中的原子扩散行为,并根据模拟结果计算了典型结合界面的扩散层厚度,同时采用透射电子显微镜分析了结合界面的微观结构.研究结果表明,剧烈碰撞驱使界面材料塑性变形,界面材料塑性形变形成冶金结合和机械咬合是铜-铝电磁脉冲焊接界面的结合机制,且涡旋界面处的原子扩散厚度大于平直界面.该文可为深入理解电磁脉冲焊接机理和调控焊接效果提供科学依据.

Inconel-52M焊丝高频脉冲TIG电弧及熔池流动行为研究

基于高速摄像机和图像处理技术,分析了脉冲频率(0~60 kHz)对焊接电弧和Inconel-52M镍合金焊丝熔池流动行为的影响及其作用规律.结果表明,在常规低频脉冲电流上复合高频脉冲电流会使电弧形态显著收缩,随着高频脉冲频率的增加,电弧弧根尺寸逐渐减小.与常规低频脉冲焊相比,高频脉冲电弧的整体面积减小,核心区面积及其占比增加,电弧能量集中度和温度(能量)得到提高.在高频脉电流的作用下,电弧轴向压强和径向电磁力增大,最大可分别提高18.0%和8.1%.电弧轴向电磁压强增大导致熔池流动性增强,使焊缝液态金属流动更充分,从而易形成大焊缝宽度和低润湿角的焊缝形貌.

异种有色金属电磁脉冲焊接研究现状及发展趋势

电磁脉冲焊接技术由电磁脉冲成形技术演化而来,通过电磁力驱动被焊接金属发生高速碰撞,实现碰撞界面的冶金结合进而获得焊接接头,作为一种固相连接技术,尤其适用于性能差异显著的异种材料焊接。随着国内外研究者对电磁脉冲焊接技术的深入研究,发现该技术在铝与镁、铝与铜、铝与钛、铝与镍钛等异种有色金属焊接领域的应用前景日益广阔。然而,目前缺乏对异种有色金属电磁脉冲焊接研究现状及发展趋势的综述研究,未能明确该技术在异种有色金属焊接中存在的问题和发展方向。因此,本文详细探讨了异种有色金属电磁脉冲焊接接头的微观结构特征、元素分布规律及显微组织特性,并阐述了接头形成机理,主要包括碰撞界面结合模型和缺陷形成机制。研究发现,不同异种有色金属组合的焊接界面结构明显不同,电磁脉冲焊接接头的力学性能优化需要通过进一步揭示焊接界面结构的形成机制来实现,电磁脉冲焊接技术难以对电学性能差、厚度大以及强度高的材料进行高质量焊接,需要加强相关辅助焊接技术、辅助装备的研究开发。最后对电磁脉冲焊接技术在异种有色金属的焊接过程中存在的问题及未来发展方向进行了展望,提出了未来该技术的研究发展方向,为电磁脉冲焊接技术的相关研究奠定了基础。

不同搭接形式下铜/钢电磁脉冲焊接界面分析

由于铜/钢的物化参数相差较大,熔钎焊时存在接头脆性、应力集中等问题,本研究借助新型电磁脉冲焊接技术,通过设计锥度或台阶形式的搭接方法,获得了铜/钢焊接接头,并借助界面微观SEM、EDS观察及显微硬度测试,分析不同搭接形式下的接头连接特征。结果表明:直接搭接时界面波形较差,有少量孔隙;台阶搭接时界面波形较大,但是,波形界面存在前后漩涡,且有“熔合区”;锥度搭接时界面为近似均波连接特征。当采用锥度结构设计时,波状界面的扩散区宽度为5μm,两种材料结合相对紧密。界面塑性变形、元素扩散程度决定界面硬度分布,采用锥度搭接设计时金属粒子流能够飞出界面,产生的塑性变形相对较小,其硬度过渡平缓,有利于冶金结合。

隧道一体式热熔垫片电磁焊施工技术及应用

隧道防水层传统施工工艺普遍存在热熔垫片安装难度大、防水板与热熔垫片焊接质量差等施工难题,在二衬混凝土浇筑过程中,防水板易脱落,二衬背后易形成脱空,甚至发生脱落的防水板切割二衬的情况,且施工效率低,造成了较大的质量隐患。基于以上原因,依托彭水隧道防水层施工,积极开展热熔垫片安装、防水板焊接施工技术攻关,优化了带丝网的热熔垫片与钢垫圈的一体式组合方式,改进了热熔垫片安装设备,同时引进了电磁焊机进行焊接作业,有效解决了传统施工工艺存在的质量通病,极大程度提高了防水层施工效率和施工质量。

Grain refinement and improved properties through electromagnetic stirring in Al alloy MIG welds

This paper described the effects of external excitatory parameters of current and frequency on the microstructure and mechanical properties of weld metal in MIG welding with longitudinal electromagnetic field. With a high speed video camera capturing the images of arc shape, the mechanism of arc rotation and how the periodic contraction and expansion of arc affected the movement of molten pool were investigated. The technique resulted in fine equiaxed grains in weld metal and optimum parameters of electromagnetic stirring were suggested based on the extent of refinement. Fine-grained weld metal exhibited better yield strength and significant improvement in elongation.

平板集磁器结构对涡流分布与集磁效果的影响规律

电磁脉冲焊接技术在异种金属连接领域展现出广阔的应用前景,集磁器是电磁脉冲焊接系统中的重要组件,可以增强焊接区域局部磁场,改善电磁力分布,提高电磁能量利用率。该文以与多匝线圈配合使用的平板集磁器为研究对象,探究平板集磁器结构与集磁效果的对应关系,分析集磁器缝隙面夹角α对涡流分布的影响规律,提出漏电流和有效电流,并基于电路-磁场耦合的仿真模型计算集磁器的电流幅值及其有效电流比例,采用不同结构特征(锐角、直角和钝角)的集磁器开展铜板与铝板的电磁脉冲焊接实验。结果表明:集磁器缝隙面涡流流向存在分叉现象,根据电流作用于焊接与否,可将其分为有效电流和漏电流两部分,集磁器的上孔直径通过影响有效电流比例改变集磁效果。随着上孔直径增大,集磁器感应产生的总电流降低,但集磁器缝隙面夹角α同时也下降,有效电流比例会提高,所以集磁效果先升后降;当α为锐角时,有利于提高集磁效果,且当α为45°时,集磁效果最佳。相同电压下,采用锐角集磁器所获得的焊接样品抗拉强度最高,直角集磁器次之,钝角集磁器最低。该文可为电磁脉冲焊接系统中集磁器的设计提供实验依据和科学支撑。

铝钢电磁脉冲焊接界面特性及金属粒子分布分析

为明确铝/钢电磁脉冲焊接过程金属粒子运动对界面连接性能的影响,基于金属粒子流形成机理,对界面形貌及抗剪强度进行分析.结果表明,金属粒子滞留界面造成铝局部熔化,钢粒子原位生成FeAl,形成未结合区;沿着焊接方向,分射流对铝板压入作用逐渐增大,形成冶金结合的界面,并伴有富铝金属间相,直缝区为FeAl+Fe_(2)Al_(5),小波区为Fe_(2)Al_(5)+FeAl_(3),大波区为FeAl+FeAl_(3);铝钢焊接界面过渡区由塑变铝压入钢形成,铝侧焊缝的外边缘存在钢粒子,而钢侧焊缝存在熔融铝携带钢粒子,主要为FeAl+Fe_(2)Al_(5)+FeAl_(3),且在焊缝内侧滞留了大量金属粒子,并以椭圆环的形式分布,在焊缝外侧,金属粒子滞落铝板表面造成凹坑,但在钢板表面为嵌入的片状铝;因此,在金属粒子滞留,并产生较多金属间化合物的位置成为剪切试验断裂源;通过波长公式调整搭接间隙,减少粒子滞留界面,椭圆焊缝断裂于铝材,提高了接头强度.创新点:基于金属粒子流形成机理,控制IMCs组织,微调铝钢界面波形以减少滞留粒子,提高接头强度.

铝钢电磁脉冲焊接接头中性盐雾腐蚀行为

为了获得铝钢电磁脉冲焊接接头中性盐雾介质的腐蚀过程及机理,对5%NaCl腐蚀后的焊接接头进行拉剪试验,并采用带能谱的扫描电子显微镜进行断口微观形貌分析.结果表明,铝钢电磁脉冲焊接接头中性盐雾腐蚀3天后的抗剪强度由原态74 MPa降为33 MPa,为原态的44.6%,腐蚀周期7天时,焊缝完全失效;在焊缝外围,粒子流击碎铝板表面氧化物生成粒状腐蚀物NaAlO2,焊缝上FeAl3破碎,露出铝被快速腐蚀为Al(OH)3;在铝板表面撞击产生凹坑和嵌入钢板表面片状铝的位置最先被腐蚀,NaCl液体堆积并在表层金属下流动腐蚀,且沿着腐蚀坑互连方向扩展,再向焊缝存在FeAl3相的连接区延伸;当氧化膜或焊缝被NaCl介质腐蚀抬起且破碎后,向着铝基体深层腐蚀,形成多而深的沟壑或凹坑,这成为接头快速失效的主要腐蚀机理.

大口径5A06铝合金带焊缝波纹管电磁成形工艺机理

针对大口径5A06铝合金带焊缝波纹管采用传统工艺成形困难的问题,开展了带焊缝波纹管电磁成形工艺机理的研究。基于有限元软件LS-DYNA R8建立了大口径5A06铝合金带焊缝波纹管电磁成形有限元模型。基于电磁成形过程中管件成形过程、所受电磁力分布和变形历史的分析揭示了带焊缝波纹管电磁成形工艺的成形机理。结果表明,在带焊缝波纹管电磁成形过程中,管件发生多次“碰撞—反弹”的周期性变化,焊缝处材料的变形略微早于母材;管件受到的电磁力沿厚度方向由内到外逐渐降低;碰撞效应引起管件的能量损耗与应力释放,管件反弹量随着碰撞后应力的重新分配逐渐减小,进而实现带焊缝波纹管的高精度成形。

电磁感应矫平工艺的多物理场耦合仿真研究

电磁感应矫平方法具有效率高、易操作的特点,在薄板矫平工艺中有良好的应用前景.以船厂使用的固定式一字型线圈感应矫平工艺为例,基于COMSOL Multiphysics有限元仿真软件建立了三维电磁-热-力耦合感应矫平有限元模型.该模型输入AH36钢板随温度变化的物理性能,以对接焊件残余应力与焊接变形作为初始状态,采用顺序耦合的方法计算矫平过程中电磁场、温度场与结构场的变化,从而验证了温度场与电磁场在矫平过程的双向耦合关系,得到焊接件在矫平后的变形量.通过自行搭建的感应矫平实验平台测试矫平工艺中的温度变化与变形量,验证了该有限元模型的准确性与有效性.

乏燃料水池覆面板对接焊缝裂纹检测研究

核电站乏燃料水池覆面板焊缝与母材交界面处的裂纹会严重影响设备的运行安全。考虑焊缝的真实特性,提出采用交流电磁场检测(alternating current field measurement,ACFM)技术来检测焊缝裂纹,以提高裂纹检测的灵敏度。首先,采用COMSOL软件建立了焊缝裂纹检测模型,分析了焊缝裂纹区域的磁场特征信号;其次,在实验试件焊缝与母材交界面处预置与数值仿真一致的人工裂纹,进行焊缝裂纹ACFM实验;最后,制作了焊缝裂纹检测系统,并进行了其性能测试。仿真、实验和测试结果表明:ACFM方法能够有效识别焊缝与母材交界面处平行于焊缝方向的裂纹,而不能识别垂直于焊缝方向的裂纹;通过焊缝裂纹检测系统测试得到的裂纹检测长度的偏差小于探头检测实验的偏差,但两者比较接近,证明了焊缝裂纹检测系统设计的合理性。ACFM能够实现乏池覆面板对接焊缝裂纹的定量化检测,满足现场高灵敏度的使用要求。

基于磁致伸缩电磁超声导波的钢板焊缝缺陷检测

针对工业现场使用压电超声波检测焊缝缺陷时需使用耦合剂的问题,研究了通过无须耦合剂的基于磁致伸缩电磁超声对薄钢板焊缝中缺陷进行检测的方法,并且针对电磁超声换能效率低、信号微弱的问题,通过仿真优化了回折线圈结构参数,选择了三分裂回折线圈,并探究了导波频率对缺陷检测灵敏度的影响。仿真结果表明:相比于无分裂线圈,选择三分裂回折线圈后激励信号面内位移幅值提高了94.2%,随着导波频率增加,缺陷反射回波幅值表现出先增大再减小的变化规律。实验结果表明:S0模态Lamb波垂直入射焊缝时,焊缝本身产生的回波与缺陷信号相比相对较小,缺陷检测阈值达到1 mm,缺陷定位误差小于2 mm,证明了电磁超声导波具备检测焊缝中毫米级缺陷的能力。

电力电缆铝芯线与铜连接管的电磁焊接条件研究

目前,电磁焊接技术在电缆接头制作中的可行性和优越性已经得到国内外诸多学者的证实,然而关于电缆接头电磁焊接的焊接条件却鲜有研究。鉴于此,该文通过对70 mm^(2)铝绞线铜中间连接管电磁焊接进行了仿真模拟和实验研究。研究结果表明,集磁器中轴线上磁场大致呈“钟型”分布,工作区位置磁场最大,远离工作区的位置,磁场迅速减小,集磁器工作区径向不同位置,磁场分布较为均匀。对外管的形变过程进行了仿真、测量及理论推导,理论推导所得外管加速阶段速度曲线与仿真以及实测速度波形相近,理论计算碰撞速度与实测值偏差在10%以内,并且外管的碰撞速度与充电电压近似呈线性关系。电缆接头电阻随着充电电压的提升而减小,当充电电压为12 kV时,接头电阻为25.2μΩ,仅为要求值的60.8%;电缆接头强度随着充电电压的提升而提高,当充电电压大于12 kV时,铝绞线本体发生断裂,说明电磁焊接接头强度大于母材的强度。当充电电压为12 kV时,焊接接头切面观察到连续的波状界面,波峰约20μm,波长约70μm,已经达到焊接效果,此时实测碰撞速度为128.9 m/s,理论推导计算出的碰撞速度为134.7 m/s,与下限碰撞速度之间的偏差分别为5.6%和10.3%,因此可以较好地预测两种材料达到焊接条件所需的能量值,为今后的电磁焊接装置设计提供有效的参考。