Assessing the Quality of Spot Welding Electrode Tips Using Image Processing Techniques

Spot welding is used extensively in the automotive industry. The quality of an individual welding spot is a major concern due to the heavy reliance on their use in the manufacture of cars. The main parameters that control the quality of a welding spot are current, voltage, welding force, welding time, and the quality of the welding electrodes. The condition of the welding electrodes plays a major part in determining the quality of a welding spot. For example, excessive wear can occur during the welding process and can cause weakening in the weld nuggets. As the number of welds increases, the electrode tip wears down and so the contact area between electrode tip and work piece increases. Hence the applied current should be increased in order to maintain the same current density so as to preserve the quality of the welding nuggets. In order to determine the quality of the welding electrodes, images of the electrode tips are captured and are processed using various imageprocessing algorithms. These algorithms can be used to measure the tip width and hence assess the quality of the electrodes. The quality of two types of spot welding electrode tips, dome and flat tips, is assessed using image processing and boundary representation techniques. For each tip type, a database of 250 images is used to test the performance of our algorithms. Also the quality of the tip for these 250 images is determined manually. An excellent agreement is found between these manual and automatic methods.