铝合金电阻点焊过程的有限元模拟

建立了铝合金电阻点焊过程的有限元分析模型，采用基于显微接触理论的接触电阻模型模拟点焊过程中试件与试件界面上的接触电阻。计算获得了焊接过程中电极／试件和试件／试件接触界面上接触半径的变化，以及试件间界面上压应力、电流密度和温度的分布。试验考察了熔核的形成和长大过程。比较表明，计算与试验测量结果符合很好，证实了所采用的接触电阻模型在铝合金电阻点焊模拟中的正确性和适用性。     

New technology for measuring resistance of electrical contact and estimating welding quality

Incomplete penetration is a common defect in the welding gap of large size (welding area is over 100 mm²) electrical contact, which leads to an instability of welding quality. Nevertheless, there was limited research dealing with non-destructive quality inspection of electrical contact. In this research, the resistance of CJ400 electrical contact was measured with the device medium frequency inverter resistance spot welding (MFI-RSW) machine. Multipulse measuring method was designed and proved efficient to reach a higher accuracy by restraining the influence of the contact resistance between electrodes and electrical contact. Moreover, the error of resistance caused by temperature rising in the measuring process is also eliminated effectively. Therefore, more accurate resistance of electrical contact could be extracted compared to the method of single pulse measuring. Then, the relationship between resistance and welding quality was studied and a new quality inspection method was proposed.     

热镀锌高强钢电阻点焊的点蚀对熔核形成的影响

热镀锌高强钢由于高强度特性以及良好的抗腐蚀性,可满足汽车轻量化与安全性需要,在车身制造中逐渐得到广泛应用.但热镀锌高强钢点焊的电极磨损严重,点蚀磨损特征变化明显,对熔核形成产生较大影响.建立点焊过程的点蚀有限元模型,采用数值分析与试验方法研究点蚀对熔核形成影响.结果表明,点蚀的产生与发展增加了工件之间的实际接触面积,使电流密度降低,熔核直径减小;同边缘位置点蚀相比,电极中心位置点蚀由于对熔核区域的电流分流作用,更加不利于熔核的形成.随着点蚀面积的增大,形成环状熔核几率增加.     

Numerical simulation of spot welding for galvanised sheet steels

Abstract

Galvanised sheet steels are now widely used to be the substrate for body in white (BIW) construction in the automotive industry. Weldability of galvanised sheet steels much worsened compared to spot welding of low carbon steels. The present paper develops a 2D axisymmetric model and employs an incremental coupled thermal–electrical–mechanical analysis to predict the nugget development during resistance spot welding (RSW) of galvanised sheet steels. Temperature dependent contact resistance for faying surfaces was determined to take into account of the influence of zinc coat for spot welding galvanised sheet steels. The effect of dynamic contact radii on temperature distribution was studied and compared with results under constant contact area assumption. The predicted nugget shape and size agreed well with the experimental data. Higher current and longer welding time should be applied for galvanised sheet steels compared to low carbon steel spot welding. The proposed model can be applied to predict weld quality and choose optimal welding conditions for spot welding galvanised sheet steels.     

球形电极电阻点焊过程的热力耦合分析

基于有限元理论建立了球形电极电阻点焊过程的电热力耦合模型，以ANSYS软件为平台分析了点焊的预压以及熔核的形成、长大及断电冷却过程。模拟得到了焊接过程中温度场、应力应变场的分布以及接触面积的变化，经过试验验证了所建电热力耦合模型的正确性。     

基于稳定分布的铝合金点焊接触电阻

接触电阻是电阻点焊熔核形成与数值模拟的重要参数,决定着点焊质量.采用电阻点焊接触电阻的计算模型与统计分析相结合的方法,通过模型计算工件/工件、工件/电极之间的接触电阻,并将其作为统计抽样检验的数据,研究接触电阻的分布规律.文中采用稳定分布去拟合工件间的接触电阻,并利用非参数统计Dn方法对拟合曲线进行检验.结果表明,所建立的计算模型正确,同时选用的稳定分布函数能更好的拟合工件间的接触点电阻,它们对研究电阻点焊有着重要的理论意义和实用价值.     

再认识电阻焊接头及其性能

在解决生产过程中铝合金点焊质量难题时,发现铝合金电阻焊接头中存在一个疏松区,从而将电阻焊接头从外向内分为塑性环、承力致密区和疏松区;试验检查和分析了这3个区域的力学性能,以及焊接参数（电极直径、焊接时间、焊接电流和电极压力）对它们的影响。     

Some Tribological Influences on the Electrode-Worksheet Interface During Resistance Spot Welding of Aluminum Alloys

In this study, the effect of worksheet surface characteristics on the electrical contact resistance of electrode-worksheet interface during resistance spot welding of aluminum alloy (AA5182) was discussed. The electrical contact resistance was influenced by both the oxide layer and surface roughness of the worksheet. However, the effect of oxide layer was more dominant, and the effect of surface roughness was likely to be linked with the damaging of oxide layer and not the contact area. The oxide layer on AA5182 was non-uniform with Mg-rich small spots dispersed on the surface. Grinding and scratching the worksheet surface was effective in reducing the oxide layer thickness and, hence, reduced the electrical contact resistance. It was observed that the surfaces with higher electrical contact resistances at this interface showed faster pitting rate of electrode. The study also suggested that the static electrical contact resistance measured before resistance spot welding could be useful for predicting materials likely behavior during the actual resistance spot welding process of AA5182.     

电器触点的焊接技术

综述了电器触点加工中所采用的连续自动焊、精密点焊、复合焊等多种焊接技术的适用范围及发展趋向。     

矩形端面电极电阻点焊温度场数值模拟

基于ANSYS有限元分析软件,对电极端面为矩形的电阻点焊温度场进行数值模拟研究.在综合考虑模拟精度和具体工艺条件的基础上,对物理模型进行适当的简化处理,建立了矩形端面电极电阻点焊温度场1/4三维有限元分析模型,接触电阻采用电阻率的形式进行处理.结果表明,在焊接初期电极压力在电极端面边缘形成较大的应力分布,使得最高温度分布在电极边缘区域,随着焊接时间增加,接触电阻减小,最高温度向内部转移形成熔核,此时与传统点焊情况相似.     

管板单边电阻点焊过程预压接触分析

通过建立轴对称有限元模型,对管板单边电阻点焊预压过程中电极与板以及板与管间接触行为进行了研究,系统分析了预压阶段接触区域范围及接触压力分布的影响因素.研究发现,管板焊接过程预压阶段的接触压力分布与传统点焊过程预压阶段接触压力分布有很大的不同.在电极和板以及板和管之间均形成环状接触区,可能导致焊后形成环状熔核;预压过程中,电极和板间接触区不受压力变化影响,板和管间接触区则受压力影响明显;接触区域大小和电极端面直径、管板厚度等因素均有关系.试验表明,所建模型的模拟结果与实际是相吻合的,为今后管板电阻点焊工艺参数优化及车身轻量化中管板厚度比优化提供有效依据.     

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.     

基于有限元法的电阻点焊电极热输入机理

为了探明点焊过程中通过电极散失热量的过程和机理,展开了对电阻点焊电极热输入机理问题的分析和研究,基于有限元法(FEM)提出并建立了电极热输入计算模型,并根据模拟仿真策略对电极瞬态热输入的成分和大小进行了分析和探讨,最后通过试验验证了分析的结论.结果表明,点焊过程中散入到电极的热可分为电阻热和传导热两部分,电阻热流的变化规律与焊接电流一致,而传导热流则在电极输入热中占主导地位.此工作有助于电极散热和焊接质量控制等方面的研究.     

Comparative study of small scale and ‘large scale’ resistance spot welding

Abstract

An incrementally coupled electrical–thermal–mechanical model is developed to simulate small scale resistance spot welding (SSRSW) using the finite element method. This numerical model is then employed to study the differences between SSRSW and ‘large scale’ resistance spot welding (LSRSW). The variations in contact area, current distribution, and temperature profile at the workpiece/workpiece interfaces are compared. The computation shows that the difference in electrode force could be the essential reason for other differences between SSRSW and LSRSW. Compared with LSRSW, a much lower electrode force (pressure) applied in SSRSW results in a relatively small contact area and hence a much higher current density, which in turn leads to a greater heating rate and higher temperature at the workpiece/workpiece interface. This small contact area also results in a relatively small nugget diameter in SSRSW, which is only about 30% of the electrode tip diameter. In contrast, the nugget diameter in LSRSW is comparable to the electrode tip diameter. The predicted nugget diameters in both SSRSW and LSRSW of mild steel sheets compare well with experimental results.     

TRIP780高强钢的点焊工艺性能

对TRIP780高强钢进行一系列电阻点焊试验,对点焊部位进行金相分析、显微硬度分析、抗剪切试验和十字拉伸试验等分析手段.研究焊前预热、焊后回火、焊接时间等工艺因素时TRIP钢点焊焊点的优化效力.焊前预热工艺对焊点的组织和力学性能的影响较小,在合理范围内延长焊接时间能有效地提高焊点的抗剪切性能,焊后回火工艺能有效地改善焊...     

Empirical model of effects of pressure and temperature on electrical contact resistance of metals

Abstract

An important input property in the development of process models for resistance spot welding is electrical contact resistance. A model for the pressure and temperature dependence of electrical contact resistance was developed from established concepts of contact resistance. The key to developing the desired relationship is determining surface roughness characteristics, which is experimentally problematic. To overcome this difficulty the electrical resistance of contacting interfaces was measured as a function of the pressure applied across the interfaces. Using known information about the temperature dependence of bulk resistivity and mechanical properties, a curve fitting procedure was used to establish the desired relationship of contact resistance to pressure and temperature. This empirical model agrees well with experimental measurements in the regime of low applied pressure. At high pressures, predictions underestimate contact resistance, and this was attributed to strain hardening of asperities at the contacting interface. The model also predicts that the competing effects of bulk resistance and contact resistance will produce a peak in the variation of contact resistance with temperature. The model provides a suitable means for incorporating the pressure and temperature dependence of contact resistance into process models of the resistance spot welding process.     

管板单边电阻点焊形核过程有限元模拟

根据管板单边电阻点焊结构特点,建立了轴对称有限元模型.通过结构、热电场的全耦合,分析了焊接过程中接触面压力变化规律,单边焊熔核形成过程以及形核特点等.结果表明,单边点焊和传统点焊焊接过程有很大的不同.单边点焊焊接过程中工件变形严重,电极和板以及板和管子间接触状态变化复杂,熔核形成需要电流大、时间长,且最终形成环状熔核.与金相试验比较,管板单边焊熔核特征的计算结果与试验结果相符合,证实了所建模型的正确性和适用性.为研究单边点焊过程中焊接参数对熔核形成过程的影响规律及确定合理的管板焊接参数奠定了基础.     

Electrical-thermal interaction simulation for resistance spot welding nugget process of mild steel and stainless steel

A three-dimensional finite difference electrical-thermal model for resistance spot welding nugget process of mild steel and stainless steel is introduced. A simulation method of the interaction of electrical and thermal factors is presented. Meanwhile, calculation method of contact resistance and treatment method of heater structure is provided. The influence of the temperature dependent material properties and various cooling boundary conditions on welding process was also taken intoaccount in the model. A method for improving the mild steel and stainless steel joint was analyzed in numerical simulation process. Experimental verification shows that the model prediction agrees well with the practice. The model provides a usefultheoretic tool for the analysis of the process of resistance spot welding of mild steel and stainless steel.     

通过监测电极位移的模糊控制铝合金点焊

利用热弹塑性有限元来仿真研究铝合金的点焊过程,分析了焊接电流和电极挤压力对点焊质量的影响。研究了电极位移与焊接电流和挤压力间关系,证明电极位移表征了点焊质量,只要电极位移控制在一个合适的范围内,就能得到理想的点焊质量。在此基础上,提出监控电极位移,利用模糊控制方法,实时改变点焊的电流,从而控制点焊熔核尺寸,达到良好的点焊质量。由于模糊控制的引入,极大地扩大了点焊对挤压力等的适应能力,方便了点焊初始参数的选取。     

电容储能式逆变点焊机的研制

针对特殊结构和材料的焊接性能,指出目前的焊接问题主要是存在飞溅和接触电阻过大而带来的“打火”现象;提出了将高频脉冲电流用于电阻点焊,理论上可以彻底消除飞溅;采用电容储能焊技术可以消除“打火”现象。将电容储能焊与逆变技术相结合,成功研制了电容储能式逆变点焊机’试验表明该焊机完全满足桥带的焊接工艺要求,并且消除了焊接飞溅和“打火”现象。