Optical focus control system for laser welding and direct casting

A non-intrusive optical sensor system has been developed for focus control of laser welding. This detects the light generated by the process through t he laser delivery optics, and exploits the chromatic aberrations of these o ptics to detect any laser Focal error at the workpiece, This system works f or a wide range of materials and welding parameters, and example results ar e presented. The sensor has also been applied to laser 'direct casting', a profess in which 3-D structures are built by flowing metal powder into a fo cused laser beam. In this case, melt pool temperature is also important, an d so additional optics are incorporated into the sensor to provide a pyrome tric temperature measurement which is used to control the laser power. (C) 2001 Elsevier Science Ltd. All rights reserved.