Laser welding closed-loop power control

A closed-loop control system is developed to maintain an even seam width on the root side of a laser weld by continually controlling the output laser power of a 1500 W CO, laser. Quality control is done by a photodiode monitoring the root-side light emission from the process. The control system is successfully demonstrated to work in the bead-on-plate configuration on 2 mm sheets, both at constant speeds and at speeds ranging from 0.32 to more than 0.72 m/min in one welding trial. The power control system is able to deal with sheets of variable thickness in one welding trial, with the following thickness changes made as partly lap welds: 1.25 to 1.25 mm, 0.5 to 2 mm, and 1.25 to 2 mm. Sheets of 0.5 mm lap joined to 2 mm sheets displayed even root seams along the entire seam, except at the immediate edges of thickness change. (C) 2003 Laser Institute of America.