【作者】 李双双；

【导师】 李冬青；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2006， 硕士

【摘要】 在镀锌钢板点焊过程中,由于镀锌层的存在大大加速了电极的失效,而电极的失效严重影响到焊点的质量,使熔核直径减小,甚至出现未熔合的现象,最终导致成批焊点的不合格。由于目前尚缺少一种在线监测电极性能的手段,常通过破坏性抽检焊点强度来间接判断电极的性能。这不仅工艺繁琐,而且无法应用于实际的生产现场。因此,如何实现在线监测电极性能,以保证焊点质量,是一个亟待解决的难题。在对相关参数的采集中,为了提高采集精度、保证采集数据的实时性以及减少现场环境下各种干扰因素的影响,文中利用了运算速度快、资源丰富的C8051F020单片机作为核心控制芯片,设计出相应的采集系统,并在生产现场及实验室条件下进行了大量原始数据的采集,为课题的研究奠定了很好的实验基础。对采集的数据进行了综合处理,得到电流、电压及动态电阻等参数在点焊过程中的基本形态和整体变化趋势,通过对比发现:动态电阻由于综合了电压和电流的影响,对焊点质量的变化更敏感,并且在焊点数达到210点左右时,动态电阻发生了突然的下降,降幅高达25%左右。动态电阻的突变反映了焊点质量的恶化和电极的失效,为电极性能的在线监测提供了重要依据。对动态电阻突变前后的焊点拉剪强度、熔核直径和金相组织进行对比,结果表明:动态电阻发生突变后,焊点强度比原来降低37.8%;熔核直径比原来降低28.2%;从金相组织中也可看出熔核中存在未熔合的现象,由此证实了动态电阻的突降点就是点焊电极的失效点。最后,通过对电极本身进行金相组织分析、短路测试试验、扫描电镜等试验,得出烧损后的电极不仅端部直径大大增加、点蚀和坑蚀现象严重,而且存在大量的Cu-Zn合金,从而为利用采集参数的变化来判断电极是否失效提供了直接的依据。本文通过点焊中焊接电流、电网电压、电极间电压和动态电阻与电极烧损过程及烧损程度之间的联系,给出了点焊镀锌钢板时点焊电极的在线质量监测方法,这对保证焊点质量具有非常重要的工程实际应用价值。更多还原

【Abstract】 In resistance spot welding (RSW) process of zinc coated steel, the zinc layer accelerates the electrode degradation which has been shown to been dominant in determining the quality of the welds. Electrode wear results in a decrease in weld diameter and even stick-out welds leading to the disqualification in quality of groups by groups welding spots. At present, due to lack a way to monitor the electrode property on-line, often using the security of the welds to judge the electrode property, which not only result in lower production rates, but also cannot be applied in the practical production. Therefore, how to monitor the electrode property on-line and assure the quantity of welding spot, is a difficult problem to be solved.A collecting system was developed with a C8051F020 microcomputer as the controlling core, for the advantages of fast operation speed and rich resource of hardware, in order to enhance the collecting precision, assure the real time of collecting data and reduce the interference of various factors in welding environment. And a lot of experiments were carried out and a great deal of original data were collected both in the production field and in the laboratory, preparing for the research of the topic.The whole variety trend of such parameters as welding current, supply voltage and dynamic resistance etc in spot welding process are got through the comprehensive processing towards the data that collect, the contrast shows that dynamic resistance is more sensitive to the change of spot welding quantity, because of the comprehensive influence of welding current, supply voltage, and when the number of welding spot is about 210, the dynamic resistance will descend suddenly, the reduction is up to 25% around. The mutation of the dynamic resistance well reflects the depravation of the welding spot quantity and expiration of the electrodes, which provides the good basis for the on-line quality monitor.Through contrast the load of tensile shear, weld diameter and the metallographic structure in mutation fore-and-aft of the dynamic resistance. Result indicates: After the dynamic resistance mutation, intensity of the welding更多还原