Electrode life of aluminium resistance spot welding in automotive applications: a survey

Short electrode life has been one of the crucial issues for aluminium resistance spot welding in high-volume automobile manufacturing. A fair amount of heat may be generated at the electrode/workpiece interface because of the high electrical contact resistance of the aluminium oxide layers. Correspondingly, rapid electrode degradation is observed due to severe Cu–Al alloying, pitting and cavity during welding. This issue has not yet been fully addressed. This survey focuses on the current studies of understanding and development of electrode life improvement specifically on those that extend electrode life via optimising the electrical contact resistance at the interface, including altering the surface conditions of the workpiece, weld parameters development and weld equipment selections, and new electrode designs, and etc.     

Numerical study of electrode geometry effects on resistance spot welding

Abstract

This work numerically investigates the geometrical effects of the electrode containing a coolant hole on transport variables during resistance spot welding. The model accounts for transient magneto-fluid mechanics, heat and species transport, bulk resistance in workpiece, and film and constriction resistances at contact interfaces. The computed results show that electrode cooling due to the coolant hole influences transport processes during not only freezing and cooling periods but also heating and melting periods. Electrode cooling can be interpreted by thermal resistance, depending on the shapes of the electrode and coolant hole within the growing thermal diffusion layer. Major factors affecting electrode cooling are different in distinct time stages. In most cases, enhanced electrode cooling due to the coolant hole decreases the electrode temperature and nugget growth rate. A decrease in the electrode face radius strongly increases nugget growth rate and workpiece temperature and decreases electrode temperature, whereas its effect on cooling rate is insignificant. The optimum design and sensitivity analysis of the electrode shapes subject to required cooling rate, nugget growth rate and welding time are revealed.     

窄间隙MAG焊侧壁熔深信息的获取与同步化

窄间隙焊中坡口侧壁熔深是反映焊接质量的重要参数,针对侧壁熔深信息难以直接获取的问题,提出一种窄间隙MAG焊熔深信息离线获取,并实现与其他焊接数据采集信息同步的方法。首先设计了一个划线装置,实现在工件上标记开始数据采集到结束数据采集的位置,其次通过平行焊接方向、在工件最大熔深位置处对工件进行切割、打磨、腐蚀,获取整体熔合线变化曲线,并采用人机交互的图像处理算法对熔合线进行边缘提取和函数拟合,实现侧壁熔深信息获取及与其他数据信息的同步,为进一步的熔深建模和控制研究奠定基础。     

Alternative current flux zoned tungsten inert gas welding process for aluminium alloys

Abstract

A new variant of activating flux tungsten inert gas (TIG) welding process called flux zoned TIG (FZ-TIG) welding is proposed to weld aluminium alloys based on the mechanism of activating flux constricting welding arc. This process can not only increase weld penetration but also obtain perfect weld surface appearance simultaneously. An alternative current FZ-TIG welding is made using SiO₂ as the side region material and flux FZ108 developed by the authors with uniform design method as the central region coat material. The weld penetration can reach above three times that of the conventional alternative current TIG welding. All the weld shape, weld microstructure and weld mechanical properties are fine. Except for argon shielding gas flowrate, other welding parameters, including welding current, welding speed, central coat width, central coat content and solvent, have great effect on the weld penetration of alternative current FZ-TIG welding for aluminium alloys.     

窄间隙埋弧焊在厚壁加氢反应器中的应用

介绍了窄间隙焊的特点,对坡口形式的确定、埋弧焊剂的筛选、焊接工艺参数的选择进行了详细分析。生产实践证明,窄间隙焊接工艺经济可靠且能保证焊接质量。     

Predicting electron beam welding conditions in the manufacture of multi-seam structures

The problem of producing multi-seam components by electron beam welding is investigated. It is shown that if the variation of temperature after welding the first joints is not taken into account and subsequent welded joints are produced in the same conditions, the depth of penetration increases. This has been confirmed by experimental results. To ensure the same depth of penetration in producing several welded joints in the same component, the second and subsequent welded joints should be produced in the corrected conditions after equalizing the temperature throughout the entire volume of the component. A method is proposed for calculating the electron beam welding conditions of consecutively produced welded joints and the holding time of the component to ensure equalization of temperature.     

基于粗糙集的窄间隙MAG焊焊缝偏差建模方法

针对旋转电弧窄间隙MAG多层单道焊焊缝跟踪需要,提出一种基于粗糙集的焊缝偏差智能建模方法.首先设计工件模仿多层单道焊的坡口状态,并采集不同偏差下的试验数据,然后根据电弧长度变化的Matab仿真和试验数据变化规律将一个旋转周期内的电流划分为12个区间,提取各区间电流平均值和左右区间差值来建立决策表.通过对决策表离散化、约简,最终获得“IF…THEN”形式的知识模型.结果表明,对模型验证并与神经网络对比,二者预测能力相当,精度满足焊缝跟踪需要,而粗糙集模型的可理解性大大提高且能进一步从数据中发掘焊缝偏差与焊接电信号潜在的规律,为电弧控制器设计做准备.     

Research on droplet transfer in oscillating arc narrow gap GMA welding

In this paper, the droplet transfer in oscillating arc narrow gap gas metal arc （ GMA ） welding was studied. According to the experimental results, the oscillating arc has effect on the droplet transfer mode. The droplet transfer frequency in narrow gap groove is higher than that in bead-on-plate welding. Because of the change of arc location in narrow gap groove, the droplet transfer in oscillating arc narrow gap changes regularly. The droplet transfer frequency near groove sidewall is higher than that at the middle of narrow gap groove.     

钢轨窄间隙弧焊焊枪自动纠偏系统

将窄间隙电弧焊接方法用于无缝线路钢轨焊缝的焊接,为满足焊缝两侧壁能够同时熔合,轨底窄间隙焊接采用开环控制的焊枪摆动焊接方式,导致摆动过程中焊丝端部位置出现累积误差.为消除焊枪摆动的累积误差,针对已有工艺特点,采用双视觉传感的焊枪摆动控制方法,通过采集熔池区图像,实时计算焊丝端部的摆动偏差和摆角偏差,并对焊枪摆动进行反馈...     

Analysis of keyhole geometry in plasma arc welding

The key problem for numerical simulation of plasma arc welding （PAW） process is to develop a suitable and adaptive volumetric heat source mode which reflects the physical characteristics of keyhole PAW. To this end, the keyhole geometry under different PAW process conditions must be predicted. In this paper, a mathematical model for determining the keyhole shape is developed with considering the mass and momentum conservation of the in-keyhole plasma jet as well as the pressure equilibrium at the plasma jet/liquid metal boundary. A suitable heat source model related to the keyhole shape is applied to the calculation of PAW weld dimensions. The predicted results are in good agreement with the experimental ones.     

Development of narrow gap multi-layer welding process using oscillation laser beam

The oscillation laser beam is considered to be effective as a heat source of narrow gap multi-layer welding because oscillation laser welding can control the penetration shape and prevent the lack of fusion. In this study, in order to establish a narrow gap welding process by oscillation laser beam, butt welding experiments of 50 mm thickness carbon steel plate were performed. By the appropriate control of the heat input area using the in-process sensor for recognizing the groove shape, narrow gap welding of a thick plate with groove which was cut by gas cutting was achieved. Properties of the welded joint had been confirmed by nondestructive testing, tensile test and side bend test. A two-dimensional numerical calculation model for welding deformation was developed. This calculation model was used for investigation of the optimal groove angle. The results of calculations were in quantitative agreement with the experimental results. Microstructure of the weld zone had multiple thermal histories. According to the hardness test results, maximum hardness of the heat affected zone of the upper layer has been lowered than that of the lower layer.     

三种窄间隙焊接技术的特性比较与应用选择

窄间隙技术是弧焊技术中向更高生产率、更高质量、更低焊接生产成本大幅度进步的最有效技术。针对现有窄间隙技术应用中存在的认识误区,分别列出窄间隙埋弧焊、窄间隙热丝脉冲钨极氩弧焊、窄间隙气体保护焊3种成熟技术的各自技术优势以及技术局限性。在此基础上提出生产应用选择的指导原则:同时要求具有高的焊接生产率、高的接头质量、低的焊接成本时,优先选用窄间隙气体保护焊技术;仅仅只考虑接头质量和力学性能,不考虑焊接生产率和成本时可选用窄间隙热丝脉冲钨极氩弧焊技术;平焊位置作业,只考虑过程的稳定性和焊接质量,不考虑工艺技术的简便性、接头的残余应力大小和焊接成本时,可选择窄间隙埋弧焊。     

窄间隙埋弧焊坡口形式和尺寸

根据焊件的壁厚、材质、机加工能力、焊件制造工艺流程,设计对应的窄间隙埋弧焊坡口形式及尺寸,其主要目的是在保证焊缝质量、方便施焊的前提下,尽量减少焊接填充量,提高生产效率,降低生产成本.     

窄间隙埋弧焊的发展

分析了窄间隙埋弧焊的技术难点,应用现状及其发展.现在高效率、低耗能环保型自动化焊接方法越来越受到关注,窄间隙埋弧焊在焊接厚壁容器和厚板时的高效率、低成本、高质量使它应用越来越广泛.     

回火焊道焊接技术中焊接接头几何尺寸影响因素的分析

试验针对核电压力容器用钢SA508-3钢进行,采用TGS-56焊丝和TIG焊,在100 mm厚SA508-3钢板进行单道次堆焊,通过对焊缝断面的宏观金相观察,分析不同焊接工艺参数对回火焊道焊接技术中焊接接头几何尺寸的影响.结果表明.回火焊道焊接技术的实现与焊接电流和送丝速度关系明显,焊接电流对热影响区深度d尺寸影响较大,送丝速度主要起改变焊道余高(b)的作用,焊接电流越小或送丝速度越大,b+h(焊缝熔深)与d的差值越小,越利于回火焊道焊接技术的实现;焊接速度对焊接接头各几何尺寸影响均较大,焊接速度变化不能明显地改变b+h与d的差值.     

窄间隙焊技术在核电建设中的应用

窄间隙焊接是将常规的焊接工艺与窄间隙坡口结合在一起,通过专门的装置和控制技术而集成的一种新型焊接技术.介绍了常用的窄间隙焊接技术的优劣和应用现状,重点介绍了窄间隙焊接技术在核电站焊接上的应用,主要包括压力容器、核电站主设备和核电站主管道的焊接.展望了窄间隙焊技术在核电站建设中应用的前景和发展趋势,尤其是窄间隙焊机的国产...     

厚壁管窄间隙全位置焊接测壁熔透技术研究

从焊前准备、钨极摆动轨迹分析、区段分析、送丝行为分析等几方面介绍厚壁管窄间隙全位置焊接侧壁熔透技术特点,其研究成果对全位置焊接机的制造和调试具有普遍指导意义。     

Rotating arc horizontal narrow gap welding of high strength quenched and tempered steel

Rotating arc horizontal narrow gap welding of quenched & tempered ( Q&T) steel was innovatively performed for solving the bottleneck that the molten pool sagged due to the gravity. The shapely multilayer single pass horizontal joint could be obtained by using the rotating arc welding process. The cold crack was not observed in the joint without controlling the heat input and selecting the consumables intentionally. Mkrostructure of the joint could be divided into three zones:base metal zone ( BMZ) , heat-affected zone (HAZ) and weld zone ( WZ). Because of the characteristic of the rotating arc horizontal welding process, the defects in the joints were slag inclusion formed at the inUrlayer of lower side wall. The tensile strength and hardness of HAZ and WZ were larger than those of BMZ. The impact toughness in WZ, HAZ and BM at 0℃ is equal to 115, 212 and 236 J, respectively.     

窄间隙MAG立焊动态过程模拟及热物理特性

窄间隙MAG焊(NG-MAG)过程中电弧摆动和分时熔合技术是保证侧壁熔合良好的关键. 通过对摆动电弧移动过程中速度大小和方向不断变化规律的分析,在经典双椭球热源模型的基础上采用坐标变换法建立了NG-MAG立焊摆动电弧动态热源模型. 温度场模拟结果表明,NG-MAG立焊热循环曲线呈"多峰"现象,焊缝表面成形似"积木"而截面成形似"哑铃",与试验结果基本吻合. 分析认为"多峰"现象主要由电弧热源逐次逼近而后远离所致,而"积木"和"哑铃"的成形特点与移动过程中电弧速度(热输入)的周期变化及焊接熔池的动态变化高度相关,上述热特点对后续进行NG-MAG立焊组织演化研究提供技术支持.     

钛合金电子束焊缝熔凝区形状的人工神经网络模型

通过采用人工神经网络方法对TC4钛合金电子束焊缝熔凝区形状尺寸进行预测研究.在大量工艺试验的基础上,采集网络训练样本,并对训练样本和测试样本进行标准化,通过确定合适的人工神经网络模型、网络结构、网络算法以及网络训练次数,建立了从聚焦电流、电子束流和焊接速度到焊缝熔深、熔宽、正面焊缝宽度、深宽比、焊缝余高、钉头半角的BP网络映射模型.结果表明,网络的最大输出相对误差不超过5%,说明该网络具有较强的映射能力,能满足预测要求.