On-line quality monitoring in plasma-arc welding

Detection and analysis of the arc signals of plasma-arc keyhole welding is a promising approach for quality monitoring due to its higher productivity and lower costs. However, the development of on-line inspection techniques and feedback control is still in its infancy. In this paper, the weld voltage and current were simultaneously acquired at high speed and investigated with the aid of computers. It is shown that the overall AC power of the arc signals, especially the low frequency part (0–100 Hz) of the arc signal power spectra, varies greatly with the variation of the status of the weld pool. Two algorithms that are able to detect the behavior of the weld keyhole were developed. The experimental results indicate that the algorithms are a usable, practical method in the penetration quality monitoring of plasma-arc welding.