铝合金电阻点焊熔核形核过程动态特征研究

发布时间：2018-10-30 15:08

【摘要】：电阻点焊过程伴随着电、声、热等多种能量释放,与熔核形核生长密切相关。本文面向铝合金材料,以研究电阻点焊过程熔核形核生长为目的,利用实时传感技术对电阻点焊熔核形核动态过程的电极电压、电极电流和结构负载声发射信号进行了同步检测,研究了电阻点焊熔核形核的生长过程、熔核质量识别、焊接飞溅及电极损耗对熔核形核特征的影响,以及Ti O_2粉末介质介入对熔核形核生长过程的影响。此外还基于ANSYS计算平台建立了相应的数值模型,研究了熔核形核生长过程的传热特征与电势变化。研究结果表明,根据动态电阻曲线可将熔核形核生长过程划分为初始阶段、生长阶段和稳定阶段,不同阶段表现出不同的形核特征。随着输出焊接能量的不同,熔核形核动态过程产生的变化可在动态电阻曲线中得到体现。与熔核形核相关的电信号特征参数与熔核尺寸、焊点承载力表现出良好的相关性,为通过实时检测熔核形核动态信号分析、识别熔核质量提供了依据。根据动态电阻和结构负载声发射同步信号分析发现,熔核形核过程的飞溅常发生在熔核稳定阶段的中后期。随着电极在点焊中的损耗加剧,熔核形核动态电阻变异值变化显著,并影响熔核形核质量。可利用电阻点焊过程动态电阻变异值来评估电极损耗的程度,为电极损耗的实时监测提供了理论依据。Ti O_2粉末介质介入改变了待焊工件表面的接触状态,显著提高形核初始阶段动态电阻,得到尺寸更大、承载能力更强的熔核。利用ANSYS通过有限元分析发现,电阻点焊过程温度随熔核形核生长过程不断变化,不同焊接工艺下熔核形核过程温度变化并不相同。Ti O_2粉末介质介入能提高熔核形核过程电极间的电压,从而提高接触电阻和熔核形核过程的动态电阻,使形核电阻热效应增加;还能提高熔核形核过程的温度梯度,使熔核直径与焊点承载能力得到显著提高。
[Abstract]:The process of resistance spot welding is closely related to the nucleation growth with the release of many kinds of energy, such as electricity, sound and heat. In this paper, for the purpose of studying the nucleation and nucleation growth of resistance spot welding process, the electrode voltage of dynamic nucleation process of resistance spot welding is studied by using real-time sensing technology. The current of electrode and the acoustic emission signal of structural load were detected synchronously. The effects of nucleation process, quality identification, splashing and electrode loss on the nucleation characteristics of resistance spot welding were studied. And the influence of Ti O _ 2 powder medium on nucleation and growth process. In addition, the corresponding numerical model is established based on the ANSYS calculation platform, and the heat transfer characteristics and electric potential changes during the nucleation process are studied. The results show that according to the dynamic resistance curve, the nucleation growth process can be divided into three stages: initial stage, growth stage and stable stage, and different stages show different nucleation characteristics. With the variation of the output welding energy, the dynamic process of nucleation can be reflected in the dynamic resistance curve. The electrical signal characteristic parameters related to the nucleation and the size of the nugget and the bearing capacity of the solder joint show a good correlation, which provides a basis for the identification of the quality of the nugget by analyzing the dynamic signals of the nucleation in real time. According to the dynamic resistance and structural load acoustic emission synchronous signal analysis, it is found that the spatter of nucleation often occurs in the middle and late stage of the nucleation stabilization stage. With the increase of electrode loss in spot welding, the variation of dynamic resistance of nugget nucleation varies significantly and affects the quality of nugget nucleation. The dynamic resistance variation value in resistance spot welding process can be used to evaluate the degree of electrode loss, which provides a theoretical basis for the real-time monitoring of electrode loss. The contact state of workpiece surface is changed by the intervention of Ti O 2 powder medium. The dynamic resistance at the initial stage of nucleation can be improved significantly, and the nucleation with larger size and stronger bearing capacity can be obtained. By using ANSYS finite element analysis, it is found that the temperature of the resistance spot welding process changes with the nucleation process. The temperature change of nucleation and nucleation process is different in different welding processes. Ti O\ -2 powder medium can increase the voltage between electrodes in the nucleation process and thus increase the contact resistance and the dynamic resistance of the nucleation process. The thermal effect of nucleation resistance is increased; The temperature gradient of the nucleation process can also be increased, and the nugget diameter and the bearing capacity of solder joint can be improved significantly.
【学位授予单位】：重庆理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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