Quality monitoring technology for laser welding

The possibilities of laser welding quality monitoring by evaluating the plasma which appears on the surface of the metal is considered in this paper. As one of the results, it is found that the size of the laser induced plasma changes at a period of ms order. It also becomes clear that there is a linear correlation between both of the signal levels of the charge voltage caused by the laser induced plasma and plasma radiation, and the penetration depth of laser welding on the workpiece. Also, since this charge voltage changes when a humping bead occurs, it is promised that those welding instabilities which occur at low power densities can be detected by the plasma charge voltage monitoring method.