Real-time monitoring of immobilized oxide defects on bead surface in welding of high-strength galvanized steel

Welding is widely used for joining steel components in the automobile industry. With the use of high-quality materials, welding defects began to become increasingly complex. Immobilized oxide is one of the recent complex defects. Immobilized oxide defects generated in gas metal arc welding (GMAW) of high-strength steel and high-strength galvanized steel result in unpainted part on the surface of welding beads. Thus, it is necessary to be eliminated by using grinding and peening. However, it is difficult to find where oxides generate and how oxides generate in order to eliminate it. Few studies have explored the mechanism of immobilized oxide formation in other fields so far. In this study, the generation patterns of oxide defects were confirmed. Further, an oxide defect monitoring system for GMAW was developed by using an infrared camera and image processing equipment. The chemical properties of the immobilized oxide were verified by performing energy dispersive spectroscopy (EDS). The oxide appeared to be brighter in the infrared image, and then, image processing was conducted to determine the boundary of oxide defects. The processed images were laid over the original images, and the oxide defect area was displayed on the monitoring panel. Patterns of oxide defect generation were confirmed when it was combined with the following molten pool area moving in the opposite direction of the welding direction in our results. The developed monitoring system can be easily applied to the automatic welding process in the automobile industry.