Measurement of dynamic resistance in resistance spot welding

The conventional methods of determining the dynamic resistance were mostly done by measuring the voltage and current at secondary side of transformer in resistance welding machines, in which the measuring set-up normally interferes with the movement of electrode, and the measuring precision is influenced by inductive noise caused by the high welding current. In this study, the dynamic resistance is determined by measuring the voltage at primary side and current at secondary side. This increases the accuracy of measurement because of higher signal-noise ratio, and allows to apply to in-process system without any wires connected to electrodes.     

Experimental study on electrode displacement fluctuation characteristics during resistance spot welding

Abstract

Electrode displacement has been used to monitor resistance spot weld quality for long, but the fluctuation of the electrode displacement has not been well studied. This paper analysed the mechanism of the displacement fluctuation by collecting the welding current and electrode displacement during welding process and extracted the incremental pulse expansion of the electrode displacement, which was named as the displacement fluctuation peak. Through metallurgical experiments, the relationship of the displacement fluctuation peak with the weld nugget growth during resistance spot welding process was analysed. The whole process can be divided into four successive stages, and five characteristic points of the displacement fluctuation peak curve were selected to online predict the weld quality. The variation in the displacement fluctuation peak curve under different welding currents was studied, and the results showed that the displacement fluctuation characteristics can be used to effectively evaluate the weld quality.     

热镀锌钢板连续点焊时电极损耗对焊接质量的影响

镀锌钢板电阻点焊时由于锌层的影响电极损耗非常严重.以厚0.8 mm家电用热镀纯锌钢板DX51D+Z为研究对象,探究在正交试验优化焊接参数后,热镀锌钢连续点焊时焊接接头质量变化的规律和电极损耗的特点.结果表明,当采用I=11 kA、P=2 500 N、T=13 cyc的点焊工艺参数组合可获得力学性能最佳的点焊接头;连续点焊试验初期(150点前)焊点力学强度稳定且焊点成形较好,焊接后期(150～300点)接头力学强度波动大,焊接状况不稳定;电极损耗至失效是接头质量急剧下降的主要原因,电极失效形式为头部塑性变形、端面坑蚀和Cu-Zn合金化,在本试验条件下,Cr-Zr-Cu电极焊互150点后显现不稳定现象,电极寿命约280点;失效电极端面的Cu-Zn合金层约65 μm.     

电阻点焊过程中动态电阻的变化规律

动态电阻变化是电阻点焊过程中的重要内容．了解不同材料在焊接中动态电阻的变化规律,可以预测点焊接头的形成过程,建立熔核形状与动态曲线的关系,实现对焊点质量的监测,目前．已对低碳钢,镀锌钢板、不锈钢、铝合金和镍合金等材料点焊时的动态电阻变化规律进行了研究。     

不锈钢电阻点焊过程中的动态电阻变化规律分析

对利用自动数据采集技术获取的不锈钢点焊过程中的动态电阻信息进行系统研究.结果表明,不锈钢点焊过程中动态电阻能够灵敏且有规律地反映点焊工艺参数的变化,蕴含着丰富的点焊质量信息.焊接过程中动态电阻变化与熔核生长过程具有明显的对应关系,动态电阻曲线的拐点时间及终点值等特征量分别与熔核出现时间和最终熔核尺寸有很强的相关性.点焊过程喷溅会导致动态电阻骤降,其动态电阻变化率曲线在相应位置出现尖峰,为喷溅的自动识别提供了依据.     

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.     

A mathematical model of rough surface contact characterization in spot welding

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电极点蚀形貌对铝合金电阻点焊的影响

采用有限元分析和物理模拟相结合的方法,研究了环形和孔形两种电极点蚀形貌对铝合金AA5182电阻点焊的影响.结果表明,环形点蚀使两试件间接触半径增大,电流幅值基本不变而峰值略外移,所得熔核直径略有增大;孔形点蚀使试件间接触半径增大更为显著,电流密度降低,且由于此时界面中部没有电流流过,材料不能熔化,只能形成环形熔核.孔形点蚀使点焊接头强度大大降低,其对接头强度的不利影响远大于环形点蚀.     

Non-parametric effects on pore formation during resistance spot welding of magnesium alloy

The effects of faying surface condition, pre-existing pores in base material and cover plate on the pore formation during resistance spot welding of magnesium alloy were investigated. The results reveal that the hydrogen rejection and the pre-existing pores in base material have little effect on the pore formation, and that the larger pore formation is mainly caused by shrinkage strain during resistance spot welding of magnesium alloy.     

精密逆变电阻点焊的应用

首先介绍了精密逆变电阻点焊机系统，包括系统的组成，特点，然后介绍几种典型工件的焊接工艺，结果表明，这种焊机在精密零件 的电阻点焊中有其独持的工艺优势，有很好的推广应用价值。     

DZ-47触头电阻焊

触头是低压电器的执行元件,其焊接质量直接决定了整个电器的运行可靠性和使用寿命.使用电阻焊的方法对DZ-47电触头进行焊接,分析了焊接电流、焊接时间及电极力对触头剪切力的影响规律,并对焊接界面的组织形态及元素分布进行了研究.结果表明,在合理的工艺条件下,电阻焊焊接触头是可行的.此外,由于焊接过程中电磁力和电气触头结构设计的因素,即使在相同工艺参数下焊接的触头不同方向的界面扩散层厚度和元素扩散量都不相同.     

Degradation mechanism of electrode tip during resistance spot welding of aluminium alloy sheets

Abstract

This study investigated the electrode life and the electrode degradation characteristics during continuous resistance spot welding of aluminium alloy sheets. When a long welding time and dome radius type electrode were used, the electrode life was extended more than that when a short welding time and radius type electrode are used. The electrode tip is considered to degrade by the following mechanism: an Al–Cu alloy layer is formed at the electrode tip during continuous welding, and then it peels off from the electrode tip transferring to the surface of aluminium alloy sheet. Its peeling makes the electrode tip indented and finally the electrode tip flattens with increasing diameter of electrode tip. In order to eliminate the direct contact between electrode and worksheet, a special Cu foil insert device for resistance spot welding of aluminium alloy sheets was developed and an extremely long electrode life was achieved.     

点焊镀锌钢板时电极表面熔敷TiC涂层对电极失效的影响

利用SEM、EDx和XRD等方法分析了在点焊镀锌钢板时电极表面熔敷TiC涂层对电极失效的影响.结果表明:点焊镀锌钢板时电极的失效机制主要是电极和镀锌板之间局部焊接的断裂发生在电极表面而导致的电极磨损,以及电极和镀锌板表面的锌之间的合金化.表面涂敷TiC的CuCrZr电极的寿命(1 200点)是CuCrZr电极寿命(500点)的2.4倍,表面处理能提高电极寿命的主要原因是在点焊镀锌钢板时表面涂敷的TiC层能阻碍电极和镀锌板之间的局部焊接和阻碍电极和镀锌板表面的锌之间的合金化.     

低碳钢点焊动态过程的模型化控制

ＤＲＣ法点烛质量监控技术关键之一是恰当地设定和描述表示点焊熔核形成过程最优动态品质的给定动态电阻特性。本文在深入试验研究和理论分析的基础上，确立了标识最优动态品质动态电阻特性的总体模型及其特征参数，据此实现了低碳点焊热过程的模型化控制。     

电阻点焊中电极位移的测量方法分析

简述了电阻点焊中传统的电极位移测量方法,包括直接测量方法、上电极运动测量方法和长臂工装测量方法.通过有限元方法分析了焊钳在设定电极力和动态电极力作用下的变形,并分析了该变形对上电极运动测量方法和长臂工装测量方法的影响.结果表明,因动态电极力的影响,使焊钳发生变形以及下电极发生相对较大垂直位移和偏转角,从而使上电极运动测量方法和长臂工装测量方法均无法准确测量电极位移值.最后提出了梯形关系的电极位移测量方法.     

The Asymmetric Laplace Law for distribution of aluminum contact resistance in spot welding

This paper investigates the distribution of contact resistance of the aluminum alloy in the squeeze stage. A new method of measuring path＇ s resistance is proposed firstly. Contact resistances are calculated accurately by the systems of 5 linear equations and solutions show that three contact resistances are different. The probability density functions of contact resistance in workpiece/workpiece（ W/W） and upper electrode/workpiece（ E/W） show that the curve shape has steeper peak and heavier tail than that of the normal distribution. Non-parameter hypothesis test is performed and the result shows that R2 , R4 reject the normal distribution using chi-square and kolmogoroo statistic D method. Therefore, the Asymmetric Laplace distribution is fitted to empirical distributions and is applied to quantify the influence of random contact resistance. The result illustrates that AL distribution is very close to contact resistance of W/W and upper E/W and normal distribution has some deviation. The paper is helpful to research the initial nugget conditions, weldability and the transient multi-coupling field.     

数学化电阻点焊控制器

根据电阻点焊的控制要求,设计了基于微处理器技术的数字化点焊控制器。控制器基于PHILIPS的80C552单片机设计,具有焊接程序控制、焊接电流波形调制、故障诊断等功能;控制器提供了基于LCD显示与键盘输入的数字化参数设置界面对控制器的可靠性设计进行了分析,采取了硬件和软件的抗干扰措施。试验证明设计的点焊数字控制器具有良好的动态特性。     

Analysis of workpiece magnetisation on liquid nugget during resistance spot welding

This paper investigates the effect of workpiece magnetisation on the magnetic flux density and nugget shape during resistance spot welding (RSW) process. To this end, this paper analyses the magnetisation process of ferromagnetic workpieces. The magnetisation was calculated by the equivalent surface current. The effect of magnetisation on the nugget shape was studied for RSW of steel and a specially designed aluminium workpiece. The results show that the magnetisation of ferromagnetic workpieces will increase the dimensions of the weld nugget in the thickness direction. The magnetic flux density induced by workpiece magnetisation and that induced by welding current have the same order of magnitude (10^?1 T). This indicates that the magnetisation of ferromagnetic workpiece is an important source of magnetic force acting on liquid nugget. Therefore, it should not be ignored in studying the physics of RSW process, especially for the fluid flow in RSW of ferromagnetic materials.     

变电极力作用下的电阻点焊质量分析

热镀锌低碳钢板在车身内外板上获得了广泛应用.在传统的气动焊枪作用下,采用恒定的电极力焊接时,点焊质量不稳定.然而变电极力对镀锌钢板电阻点焊质量的影响很大.因此利用伺服焊枪能够精确控制电极力的特点,运用正交试验设计方法,深入分析了点焊过程中三个阶段电极力,即预压力、焊接力和锻压力对点焊质量的影响,得到了最优的变电极力参数.结果表明,点焊过程中的锻压力是影响点焊质量的重要因素,其次是焊接力,而预压力是最次要因素;最优的变电极力参数能够明显提高热镀锌低碳钢板的焊点拉剪力和熔核直径,这为基于电极力检测的点焊质量实时评价和电极力控制方面的研究奠定了基础.     

Estimation of current path area during small scale resistance spot welding of bulk metallic glass to stainless steel

Abstract

The current path area is a significant factor in estimating the temperature distribution via numerical modelling for resistance spot welding. This paper presents a method for the estimation of the current path area at the faying surface during small scale resistance spot welding between bulk metallic glass and stainless steel. Observation of cross-sections and fracture surfaces reveals the welding process at the faying surface for both dissimilar and similar welding. The equipotential surface that depends on the difference between the contact area of the electrode-to-sheet and sheet-to-sheet interfaces is estimated by numerical modelling. The current path area at the faying surface is estimated by measuring the electric potential between the sheets, taking into account the current distribution.