On-Line Process Control Used in the Laser Welding of Metal Sheet Lightweight Structural Panels

Abstract Lightweight Structural Panels (LPS) made out of multilayer thin metal sheets are innovative materials which allow high structural performances combined with low weight and low material cost. Among the possible configurations a new option defined Cellular and Stratified lamination (C&S) makes use of a double corrugated core joined to external skins which leads to isotropic performance. Double corrugation creates a grid of bumps which have to be welded to the external flat skins. Nd:YAG laser spot welding was selected to reduce distortion. Since C&S structural performance is affected by spot weld strength, a process control based on plasma emission during laser processing was developed. The system described in the paper allows continuous monitoring of the weld quality, highlights the unrecoverable defecs, and modulates laser parameters in order to compensate efficiency decay and assure product quality.