铝合金电阻点焊的熔核形成过程

点焊过程中熔核形成过程对焊接结构的强度和耐用性具有非常重要的影响.文中采用高速摄像技术研究了焊接电流和电极压力对铝合金电阻点焊形核过程的影响.结果表明,铝合金电阻点焊熔核首先在工件/工件接触面中心处形成,然后沿着水平方向生长,同时垂直方向也有少量的生长,一直扩展到电极头端面直径.熔核尺寸在点焊前80 ms时迅速长大,120 ms后基本保持不变,表明过长的焊接时间是没有必要的.随着电极力的增加,工件会经历较大的塑性变形,导致没有熔核形成.因此常规点焊时,不应采用过高的电极压力.     

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.     

镀锌钢板电阻点焊的多元非线性回归模型

为了研究用于家用轿车车身制造的镀锌钢板电阻点焊工艺,采用多元非线性回归正交组合的方法设计试验.试验将电阻点焊熔核形状参数和焊接接头抗剪强度作为考察指标,将焊接电流、电极压力、通电时间、预热电流四个参数,以及各参数之间的交互作用作为影响指标的考察因素,得到可预测熔核形状和焊接接头力学性能的四元二次回归数学模型,并通过方差分析对模型进行优化.结果表明,优化的回归数学模型可实现焊接接头熔核成形及力学性能较为准确的预测.在模型的基础上研究各参数及各交互作用对焊点质量的影响规律,从而可实现电阻点焊工艺参数的优化设计.     

汽车用DP800双相钢电阻点焊温度场数值模拟研究

采用SORPAS专用电阻焊有限元软件,对1.4 mm的DP800双相钢电阻点焊温度场进行了模拟,并将熔核形貌模拟结果与实验结果进行对比。结果表明,在参考工艺下,通电加热阶段电极和焊件峰值均升高,工件温度升高速度明显高于电极,通电过程结束时电极峰值温度达最高值566℃,焊件峰值温度达2120℃;随着焊接电流的增加,热循环曲线逐渐上移,加热速度和最高温度逐渐升高,高温停留时间延长;随着焊接时间的增加,加热速度没有明显变化,最高温度逐渐升高,高温停留时间延长;在没有飞溅的条件下模拟熔核形貌与实验结果基本吻合,但在大电流条件下由于飞溅的产生,造成模拟熔核尺寸大于实际结果。     

轨道车辆不锈钢车体电阻点焊缺陷产生及预防工艺

结合生产实际情况,介绍了不锈钢电阻点焊基本原理、冷作硬化不锈钢板电阻点焊的工艺特性、轨道车辆不锈钢车体电阻点焊常见缺陷类型,如:焊核直径不符合要求、缩孔、飞溅、未熔合、熔透率不达标、过烧、焊点外观不良等。分析缺陷产生的原因并制定预防措施,如焊接电流、电极压力、通电时间、工件装配及电极形状材质等影响因素。通过相应的工艺手段,提升焊点质量,保障产品的焊接和商品化质量。     

变电极力对管板单面电阻点焊形核的影响

根据管板单面电阻点焊结构特点,建立了轴对称有限元模型.通过结构、热电场的全耦合,分析了恒定电极力作用下,管板单面点焊的形核过程和特点,其焊接过程结构件的大变形导致形成的焊点质量不可靠.利用伺服焊枪通电过程中可实时改变电极力的特性,研究焊接过程中力的变化对焊点形状的影响规律.结果表明,单面电阻点焊焊接通电过程中改变电极力,在同等焊接工艺参数的情况下可增大焊接件间的连接宽度,减小焊接变形,提高焊点质量,为管板焊接在车身上广泛安全的应用提供理论依据.     

B340LA低合金高强钢电阻点焊工艺试验优化与分析

在1.0 mm厚B340LA低合金高强钢电阻点焊工艺窗口范围内,以峰值拉剪力、失效能耗和熔核大小为考核指标,利用正交试验方法系统地研究了通电时间、焊接电流和电极压力等工艺参数对焊点质量的影响。结果表明,影响焊点质量的主次顺序为通电时间焊接电流电极压力,优选工艺参数组合为:通电时间8 cyc、焊接电流8.3kA和电极压力0.35kN,并试验验证了优选工艺参数组合条件下的点焊接头质量较高,飞溅较少。     

电阻点焊动态信号实时监测及焊接质量预测

利用现代传感技术和计算机监测技术,建立电阻点焊电信号和机械信号实时监测系统,实现对点焊过程中焊接电流、电极间电压、动态电阻和动态电极压力的实时监测。根据动态电阻和动态电极压力的变化规律,通过相关分析,提取表征焊接质量的动态电阻特征值和动态电极压力特征值。利用多元线性回归分析建立点焊质量预测模型,选用设定的焊接电流、电极压力、焊接时间、动态电阻特征值和动态电极压力特征值作为输入变量,表征点焊质量的熔核直径作为输出变量。试验结果表明,建立的点焊质量预测模型可较准确地预测点焊熔核直径,最大预测偏差不超过0.4 mm。     

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.     

基于ANSYS汽车用镁合金电阻点焊熔核形成过程温度场计算机数值模拟研究

采用ANSYS有限元分析软件,对1.2 mm厚的AZ31镁合金双层板电阻点焊过程温度场进行了计算机模拟,分析了焊接工艺参数对焊接温度场的影响。结果表明,在通电加热过程中接触界面中心温度最高,随着到中心距离的增加温度逐渐降低;随着加热时间延长,接触界面中心温度迅速升高,接触界面心部与边缘温度梯度增大;随着焊接电流和焊接时间的增加,工件界面处峰值温度逐渐升高,但增幅呈递减的趋势,高温区域逐渐扩大,熔核直径和熔透率几乎呈线性增加;随着电极压力的增加,工件界面处峰值温度降低,高温区域缩小,熔核尺寸和熔透率均减小。     

Development of single-side resistance spot welding technology applying in-process welding current and electrode force controls

An indirect resistance spot welding process with single-side electrode access was developed for automotive applications. The variable controls of electrode force and welding current during welding were studied in order to achieve the promotion of weld nugget formation and the suppression of expulsion without sacrificing the productivity and design flexibility of automobiles. The welding experiments were performed on lapped test coupons of 0.7-mm-thick cold-rolled sheet with tensile strength of 270 N/mm² and 1.6-mm-thick cold-rolled sheet with tensile strength of 980 N/mm² using a resistance spot welding system consisting a servo-motor-controlled welding gun and an inverter DC power supply. Welding experiments verified that the occurrence of expulsion and formation of molten nugget were significantly influenced by the heat generation and melting process at an initial period during welding and manageable by applying the variable patterns of electrode force and welding current. When welding was performed under the large shunting condition simply with the constant force and current pattern of 400 N in electrode force, the appropriate current range was less than 1 kA. On the other hand, it extended to 2.6 kA when performed with the variable force and current pattern of 800 N in force and 4 kA in current at the first stage and 400 N in force at the second stage, confirming the fact that the variable pattern successfully suppressed the expulsion and promoted the nugget formation. Numerical simulations were conducted to compare the difference in welding phenomena between the constant force and current pattern and the variable force and current pattern and clarified that the effect of variable force and current pattern on the promotion of nugget formation and the suppression of expulsion.     

电阻点焊应变式压力传感器弹性体的设计及应用

针对电阻点焊压力的在线监测,根据电阻点焊电极受力分析结果,提出通过缩短压力传感器与电极间的安装距离、减少受力不平衡带来的测量误差的方法。设计可直接安装在下电极及其电极握杆之间的应变式压力传感器,并对其弹性体进行设计计算。测试结果表明,该传感器能够实时测量电阻点焊过程中的电极压力,及时响应点焊熔核形成过程压力的瞬时变化,可间接预测熔核大小、监测焊接过程中的飞溅。     

压电致动器辅助电阻点焊工艺实现及飞溅控制

电阻点焊是一种多物理场耦合且封闭不可见的金属成形过程，焊接过程中电流大且通电时间短，电极力与熔核区热熔化程度匹配不当，极易造成飞溅问题，影响表面成形并降低焊点强度. 针对此问题，文中提出了一种压电致动器辅助电阻点焊的方法，利用压电致动器自身响应时间短、输出推力大的特点，将压电致动器辅助压力施加于焊接过程，实现电阻点焊过程中宏观静压力与压电致动器辅助快速动态可编程压力调节. 结果表明，压电致动器在电阻点焊气缸宏观预紧力下可实现可控的压力输出，不同频率的振动可辅助加载于原始压力波形之上，在保持焊接参数不变的情况下，压电致动器的振动输入可有效改善熔核区热分布，实现对焊接飞溅的抑制并增大熔核直径，综合提升接头性能.     

Influencing factors on nugget formation during multipoint welding by single-side resistance spot welding

ABSTRACT

Recently, weight reduction and improvement of crashworthiness of auto bodies have become important issues. At the same time, stiffness of auto bodies is also needed to ensure a smooth ride. Using hollow parts, such as bended pipes and hydroformed parts, is one of the solutions to the demand for both rigidity and light weight.

To weld hollow parts and sheet panels together, welding methods which allow us to access from one side are required. Single-side resistance spot welding (single-side RSW) process is one of those, and has recently been attracting attention.

However, because of the long current path and small electrode force, it is difficult to concentrate the electric current in the welding spot compared with conventional direct resistance spot welding (direct RSW). Furthermore, in multipoint welding, shunt current will occur easily, and the nugget formation will be inhibited.

To obtain a guideline for making sound nuggets, influencing factors for shunt current were investigated. In addition, a numerical study was carried out to discuss the difference between direct RSW and single-side RSW.

According to the CAE analysis, the shunt current of single-side RSW will be higher rate than direct RSW. The rate of shunt current was influenced by the electrical resistance of its current path. For this reason, with shorter distance between welding points, or with lower electrical resistance of material, it is difficult to get large nuggets. By enhancing the electrical resistance of shunt current path, shunt current could be reduced and a larger nugget would be obtained.     

热补偿电阻点焊铝合金接头的性能

采用热补偿电阻点焊的方法焊接铝合金A5052板,分析了焊接电流、焊接时间及电极压力等焊接参数对熔核尺寸与接头抗剪强度的影响,并分析了接头抗正拉强度与焊接电流的关系.铝合金的热补偿电阻点焊接头抗剪力及熔核直径随焊接时间延长而增大,随电板压力的增大而减小.当焊接电流为12kA时,接头拉剪力达到最大值,约5.5 kN.试验结...     

Study on parameters optimization in resistance spot welding of stainless steel with rectangular electrodes

By means of the quadratic regression orthogonal combination design, a mathematical model of the relationship between the quality of spot welds and the welding parameters, including welding current, welding time and electrode force, is established.The influences of welding parameters on long-axis dimension of the nugget and shearing resistance of spot welds are studied and the welding parameters are optimized. The results show that the regression equation obtained can realize the accurate prediction of long-axis dimension of the nugget and shearing resistance of spot welds.     

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.     

The small-scale resistance spot welding of refractory alloy 50Mo-50Re thin sheet

This paper is a review of the recent studies of small-scale resistance spot welding (SSRSW) of a refractory alloy 50Mo-50Re thin sheet (0.127 mm thick). The effects of seven important welding parameters—hold time, electrode material, electrode shape, ramp time, weld current, electrode force, and weld time—were studied systematically in an attempt to optimize the welding quality. The diameter of a weld nugget was found to be only 30–40% of the electrode diameter in SSRSW. This was due to the relatively low electrode force used in SSRSW compared with the high electrode force employed in large-scale resistance spot welding (LSRSW) where the diameter of the nugget was almost 100% of the electrode diameter. Large pores often found in the nugget during SSRSW could result from shrinkage during solidification due to fast cooling or fromdue to agglomeration of residual volatile elements absorbed during powder metallurgy processing of the material.