Optical sensor to monitor and control temperature and build height of the laser direct-casting process

A nonintrusive optical sensor system is applied to real-time process control of the recently developed laser direct-casting process, in which a stream of metal powder is introduced into the beam of a high-power (500-W) cw laser to fabricate complex three-dimensional structures. The sensor system allows two critical parameters, temperature and build height, associated with this process to be monitored and controlled continuously. We achieved a height-sensing resolution of +/-0.25 mm and temperature control with a resolution of +/-10 degrees C at a typical working temperature of 1500 degrees C with an evident improvement in process quality, especially for complex workpieces comprising relatively high, thin walls at which the conductive heat transfer varies substantially as the process proceeds. (C) 1998 Optical Society of America OCIS codes: 140.3390, 060.2370, 120.6780.