Hc. Man et al., Analysis of the dynamic characteristics of gas flow inside a laser cut kerf under high cut-assist gas pressure, J PHYS D, 32(13), 1999, pp. 1469-1477
The behaviour of the cut-assist gas jet inside a simulating laser cut kerf
for a supersonic and a conical nozzle tip were studied by a shadowgraphic t
echnique under conditions of inlet stagnation pressure from 3 to 7 bar. The
effects of the stand-off distance, kerf width, material thickness and the
inlet stagnation pressure upon the dynamic characteristics and momentum thr
ust of the gas flow inside the cut kerf were investigated. It was found tha
t under a gas pressure of 7 bar, the gas jet from a conical nozzle tip expa
nds radially and the jet momentum deteriorates rapidly inside the kerf. The
behaviour of the jet is strongly influenced by the stand-off distance and
thickness of the workpiece. On the other hand, the gas jet from a supersoni
c nozzle inside the cut kerf has tidy boundary and uniform distribution of
pressure and thrust. The sensitivity to the stand-off distance and the work
piece thickness of the supersonic nozzle are much less as compared with the
conical nozzle. With the supersonic nozzle, a dress free clean cut on 5 mm
stainless steel can be achieved at an inert cut-assist gas pressure as low
as 5 bar instead of the normal operating range of 10 bar or above for the
conical nozzle.