On-Line Monitoring For Electrode Invalidation During Spot Welding Of Zinc Coated Steel

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...