基于动态电阻曲线的电阻点焊熔核形核特征分析

在低碳钢电阻点焊过程中,利用实时传感技术对熔核形核动态过程的电极电压与焊接电流信号进行实时检测,通过对检测信号的计算得到反映熔核形核演变的动态电阻曲线,并以此为依据研究了电阻点焊熔核形核与生长过程的动态特征。结果表明,根据动态电阻曲线可将熔核形核过程划分为三个阶段,即初始阶段、生长阶段和稳定阶段,在不同阶段,熔核表现出不同的形核特征。焊接电流、焊接时间的变化导致提供的焊接能量不同,熔核形核过程产生不同的动态变化,并形成不同的熔核质量特征,均可在动态电阻曲线中得到体现。     

TiO2粉末介质介入铝合金电阻点焊熔核形核电阻特征分析

以TiO2粉末作为添加介质进行铝合金电阻点焊. 焊接过程中利用实时传感技术对电阻点焊熔核形核过程的电极电压与焊接电流信号进行实时检测,通过对检测信号的计算和分析得到熔核形核动态电阻曲线,研究TiO2粉末介质对熔核形核与生长过程电阻特征的影响. 结果表明,随着TiO2粉末介质的介入,熔核形核动态过程发生变化,表现出不同的动态电阻特征. 由动态电阻曲线提取的接触电阻、终了电阻和形核电阻热效应3个特征值均能反映TiO2粉末介质对熔核形核质量特征的影响,且终了电阻、形核电阻热与焊点最大承载力高度线性相关,可作为检测熔核形核质量的依据.     

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.     

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。     

交流电阻点焊中电极位移波动特征的分析

利用改进的交流电阻点焊监控系统采集电极位移和焊接电流,经分析认为电极位移曲线上的波动是由50 Hz的交流电阻热脉冲引起的.利用电阻点焊中的洋葱环现象分析了电极位移波动特征的机理,认识到电极位移在熔核形成前以热膨胀为主,在熔核形成后以相变膨胀为主,并且都具有波动特征.利用焊接电流曲线提供的晶闸管触发角和导通角依次计算功率因数角、动态电阻和动态电阻热.通过位移波动周波峰值与动态电阻热的对比分析,发现位移波动周波峰值在点焊过程中对热膨胀与相变膨胀有较强的敏感性,能用来反应熔核形成过程的不同阶段.     

铝合金电阻点焊的形核特点

在铝合金的电阻点焊过程中，由于接触电阻具有随机性和分布不连续的特征，而且铝合金材料本身具有优良的导电、导热能力，这使得其点焊的形核过程具有独特的特点。文中采用数值模拟与试验研究相结合的方法对铝合金点焊形核过程进行了分析研究。研究结果表明，铝合金点焊的形核过程与低碳钢等材料的形核过程显著不同，它可以分为以下三个阶段：随机形核阶段、扩展融合阶段和熔核增厚阶段。文中详细介绍了每个阶段的特点和规律。特别是在工频交流焊接的情况下，前两个阶段一般在第一个半波内就已经完成，因此第一个半波对铝合金点焊的焊接质量起着决定性作用。结合这些特点和规律对铝合金点焊的控制提出了一些有价值的建议。     

电阻点焊熔核形核信息的声发射信号表征

以结构负载压电传感的方式,研究借助声发射信号表征电阻点焊铝合金过程的熔核形核信息,包括焊接过程的声发射信号表征和熔核质量信息的声发射信号表征.结果表明,电阻点焊不论是稳定形核还是非稳定形核均可以用声发射信号来表征熔核形核的不同物理阶段.熔核形核的飞溅、开裂等特征事件也可以利用电阻点焊过程声发射信号的形核声发射特征参数来予以界定.声发射特征参数与熔核形核尺寸、焊点拉剪载荷具有较好的相关性.可以使用焊接过程中的声发射特征参数作为检测或预测熔核形核尺寸和焊点拉剪载荷的依据之一.     

热成形钢板和微合金钢板的电阻点焊质量对比分析

从熔核尺寸、动态电阻曲线和工艺窗口等方面,对热成形超高强钢板和微合金钢板的电阻点焊质量进行了对比分析。结果表明:在焊接时间仅为80 ms,热成形钢就已形成熔核,而微合金钢点焊熔核在180 ms才开始形成。热成形钢点焊的熔核生长速度比微合金钢快,并且出现飞溅的时间也早。热成形钢点焊工艺窗口的焊接电流宽度仅为1.2kA,易发生飞溅,焊接稳定性差。     

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.     

非等厚两板铝合金电阻点焊熔核偏移过程研究

在非等厚板材的电阻点焊中,熔核的偏移对点焊质量有很大的影响.本文通过MATLAB建立非等厚两层板铝合金二维轴对称热传导模型,对厚度组合为1.0 mm/2.0 mm的5052铝合金电阻点焊温度场进行了模拟,得出熔核在非等厚板中的形核过程和偏移的本质原因,并利用高速摄影试验验证了模型的准确性.结果表明:在点焊初期,薄板侧的高温区大于厚板侧高温区;随着焊接时间的增加,高温区逐渐偏向厚板,并最终形成一个偏向厚板侧的熔核.这是由于在点焊熔核形成前,散热作用的强弱是影响高温区域偏移的主导因素.熔核开始形成后,析热作用的强弱成为主导熔核偏移的因素,熔核向具有大电阻、散热少的厚板一侧偏移.因此,熔核偏移主要是由焊接区在加热过程中焊件析热和散热不均所致.     

Research on equivalent heating mechanism in resistance spot welding

The resistance spot welding quality is always one of the key subjects for studying, to which many welding scholars at home and abroad devote themselves. It has not been solved satisfactorily at present. The complexity of spot welding process, invisibility of nugget formation and singleness of control method decide that stabilizing quality is a rather difficult task. The limitations of describing how the nugget grows up based on single-sensor information source are analyzed. A control method based on multi-information fusion for the purpose of equivalent heating of each weld nugget during spot welding is put forward. The experiment results show that nugget size fluctuations are within 8.3%-20% under constant current control, and are within 6.3%-11.1% under information fusion control.     

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。     

A cooperative control strategy of resistance spot welding process by combining the constant current control with the DRC method

The modeling control method based on the dynamic resistance characteristics of good nuggets, that is the DRC method, is an improvement on the dynamic resistance threshold method for the quality control of resistance spot welding. But there is still a control blind area in the initial four cycles. For this reason, the quality of every weld nugget could not be fully ensured. Thus a new fuzzy cooperative control method is put forward. It uses a multi-information time-control mechanism by combining the constant current control technology with the DRC method in a relay way. This whole-process control strategy has led to a good control effect and produced the dual-identicul results in the weld nugget quality and the welding time.     

非等厚异种钢电阻点焊熔核成形的多元非线性回归模型

利用多元非线性回归正交组合的方法进行试验设计,分析两种厚度不一的异种钢板电阻点焊工艺.试验将表征非等厚异种钢材料电阻点焊熔核形状的熔核直径、熔核偏移,作为考察指标,将焊接脉冲电流、电极压力、焊接时间、热处理脉冲电流4个工艺参数,以及各参数之间的交互作用作为影响指标的因素,得到可预测熔核形状参数的回归数学模型.结果表明,优化的回归数学模型可实现该类非等厚异种钢电阻点焊接头熔核成形的较为有效的预测.在模型的基础上分析各工艺参数及各交互作用对焊点质量的影响规律,可进而对该类材料电阻点焊工艺参数进行优化设计.     

Braze‐welding of electrical conductors to concentric plugs

In resistance spot welding of thin sheet–thick sheet–thick sheet joint, when the sheet thickness ratio is large (sheet thickness ratio = total thickness of sheet joint/thickness of the thin sheet positioned on the outside of the joint), how to stably secure the nugget between the thin sheet and the adjoining thick sheet is a key issue. If the sheet thickness ratio is so large, nugget formation between the thin sheet and thick sheet is extremely difficult. In order to control of the nugget (position of formation, shape, etc. of the nugget) during welding for three sheets joint with a high sheet thickness ratio, optimum welding process was investigated. The developed ‘two-step force, two-step current’ welding process was suitable for high sheet thickness ratio joint and relaxed the constraints on the sheet thickness ratio. In Step 1 (first part of welding period) of the welding process, a nugget is reliably formed between the thin sheet and thick sheet by applying conditions of low electrode force, short welding time, and high current. In the subsequent Step 2 (second part of welding period), a nugget is formed between the two thick sheets by applying high welding force and a long welding time. In the weld results of a three sheet joint (0.7+2.3+2.3 mm; sheet thickness ratio: 7.6) using mild steel GA (0.7 mm) as the thin sheet and 780 MPa high strength GA (2.3 mm) in the two thick sheets, ‘two-step force, two-step current’ spot welding process showed the wide available welding current range.     

Identification of acoustic emission signal in aluminum alloys spot welding based on fractal theory

The acoustic emission signal of aluminum alloys spot welding includes the information of forming nugget and is one of the important parameters in the quality control. Due to the nonlinearity of the signals, classic Euclidean geometry can not be applied to depict exactly. The fractal theory is implemented to quantitatively describe the characteristics of the acoustic emission signals. The experiment and calculation results show that the box counting dimension of acoustic emission signal, between 1 and 2, are distinctive from different nugget areas in AC spot welding. It is proved that box counting dimension is an effective characteristic parameter to evaluate spot welding quality. In addition, fractal theory can also be applied in other spot welding parameters, such as voltage, current, electrode force and so on, for the purpose of recognizing the spot welding quality.     

双相钢点焊熔核界面撕裂失效模式参数控制

采用改进响应面试验分析方法对影响1.4 mm双相钢DP600点焊接头界面撕裂失效模式的工艺参数进行研究.结果表明,焊接电流、焊接时间以及保持压力是影响双相钢焊点界面撕裂失效模式的关键参数,合适的焊接工艺参数有助于提升熔核直径比,并且降低其对焊接参数的敏感度.以焊接工艺的鲁棒性为优化目标,获得了控制焊点界面撕裂失效模式的...     

Numerical and experimental study of nugget size growth in resistance spot welding of austenitic stainless steels

A 2D axisymmetric electro-thermo-mechanical finite element (FE) model is developed to study the effect of welding time and current intensity on nugget size in resistance spot welding process of AISI type 304L austenitic stainless steel sheets using ANSYS commercial software package. In order to improve the accuracy, temperature-dependent properties of materials are taken into account during the simulation. The diameter and thickness of computed weld nuggets are compared with experimental results. The FE predicted weld nugget growth and nugget size agree well with experimental results. The effects of welding time and current intensity on nugget growth are also studied. Generally, increasing welding time and current is accompanied by an increase in the fusion zone size with a decreasing slope. However if expulsion occurs, nugget size reduces due to melt spattering. Except for an initial nugget formation stage, welding time has minor effect on nugget size in comparison with welding current.     

Enhancing nugget size and weldable current range of ultra-high-strength steel using multi-pulse resistance spot welding

ABSTRACT

This paper presents an innovative approach that uses a pulse-profile to improve the welding quality of CP1180 steel in resistance spot welding process. Three pulses with two cooling times were used in the developed multi-pulse welding (MPW) schedule. The experimental results show that the first pulse increases the contact area between the sheets to improve the current flow pattern. The second pulse was designed to extend the sheet-to-sheet contact area and corona bond for preventing rapid nugget growth. Using these designs, the nugget size was maximised through the third pulse. The maximum nugget size using the designed MPW schedule was 18.5% greater than that of the single-pulse welding schedule and the weldable current range was extended by 130%.     

铝合金点焊的多场耦合建模与动态过程数值模拟(英文)

基于铝合金点焊的热、机、电及相变原理,建立热电力耦合场的轴对称有限元数值仿真模型,实现对焊接区温度场、电场、应力应变的动态模拟。发现了焊接电流变化激发的铝合金动态电阻"瞬态逆向虚变效应",揭示了过程热电耦合瞬态与稳态差异性作用机理,阐释了焊接电流增加而瞬态电阻骤降的反常现象。基于铝合金点焊稳态仿真与实验结果修正了动态电阻数值计算模型。AA5182的计算与实验结果表明,考虑动态电阻"瞬态逆向虚变效应"的动态仿真模型能够精确描述焊接电流调整过程中的电参数动态变化和铝合金焊点熔核的生长过程。