Quality evaluation in resistance spot welding by analysing the weld fingerprint on metal bands by computer vision

This paper introduces a novel method for the quality evaluation of resistance spot welds. The evaluation is based on computer vision methods, which allow nondestructive on-line real-time processing. The input of the system is the image of a weld imprint on a metal band which covers the electrodes against wear and soiling. The shape and size of the structures within the imprint correlate with the nugget area and, therefore, allow an accurate estimation of the quality of the spot weld. The system segments the electrode imprint and computes the nugget area from the minimum and maximum axis of a fitted ellipse. This method does not need training samples to perform reliable quality estimation. Additionally, the used algorithms are easy to implement and efficient, which guarantees real-time ability. Since there is only a single low-cost camera needed, the hardware can be placed directly on the gun arm, which makes a fast evaluation possible.