Design of supersonic nozzle for laser cutting with high pressure gas

This paper presents the theoretical results of our investigation on the design of a supersonic nozzle tip for high pressure gas laser cutting. The design is based on the theories of gas dynamics and the aim is to convert the potential energy of high stagnation gas pressure into effective kinetic energy such that a high momentum gas jet with uniform and tidy boundary could be obtained. The designed supersonic nozzle consisted of four sections: stable, convergent, throat and divergent. Each of these sections are designed strictly based on gas dynamic theories. The behavior of the exit jet and the distance of normal shock under condition of stagnation gas pressure ranging from 4 to 16 bar were investigated by computer simulation. The behavior of the exit jet in boundaryless condition as well as in slots of controlled dimensions were observed by Shadowgraphy. The slots that simulate laser cut kerf in practice were created by assembling two sheets of clear perspex with controlled gap width in between. Compared with the commonly used subsonic and transonic nozzle tips, this design of supersonic nozzle tip for high pressure gas laser cutting can reduce the gas consumption rate and improve the working distance tolerance.