Dynamic characteristics of gas jets from subsonic and supersonic nozzles for high pressure gas laser cutting

During laser cutting of stainless steels, titanium and aluminum alloys, a c oaxial and high pressure inert gas jet is used to improve the cut edge qual ity. The process normally consumes a large amount of inert gas and has a po or tolerance to variation in process parameters. This is solely because the gas nozzles are mostly of the conical and convergent type in which the gas jets are subsonic. Based on two dimensional steady state gas dynamic theor y, computer simulation and shadowgraphic techniques, the gas jet patterns f rom conical nozzles and the newly designed supersonic nozzles are analyzed. The distribution of pressure, momentum, gas density and existence of shock waves are predicted and mapped. Based on these characteristics, the effect of the gas jets upon the cut quality is explained. It is concluded that a supersonic gas jet offers the best how characteristics for high pressure la ser cutting. (C) 1999 Elsevier Science Ltd. All rights reserved.