Investigations of the gas flow of conic-cylindrical and supersonic nozzles in a laser cut kerf

Abstract

In the laser cutting process the gas flow is of main importance for exhausting molten and evaporized material from the cut kerf. The present paper investigates the gas flow of conventionally used conic-cylindrical nozzles and newly designed supersonic nozzles in a cut kerf. A quantitative description of pressure gradients and velocity profiles of the flow field is given as a result of numerical simulation. The calculations are compared with experimental Schlieren photographs. For both nozzle types the dependence of the flow field on the variation of the nozzle adjustment and the nozzle stand-off distance is investigated. In case of the conic- cylindrical nozzle the non-linear pressure and velocity distribution inside the kerf indicates both the shock formation caused by expansion to ambient pressure and the detaching of the flow field. The important result for the supersonic nozzle is the independence of the flow field from the nozzle stand-off distance which leads to an unchanged cut quality. Therefore the supersonic nozzle is of special interest for 3D laser cutting and cutting of thick materials.