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In precision laser cutting, the generation of dross can be reduced by using a high-pressure assist gas flow. However, our previous work made it clear that, for a conventional convergent nozzle, the pressure of assist gas on a workpiece is reduced to less than half of the cylinder gas pressure because of the generation of Mach Shock Disk. Furthermore, the removal of material from the micro-kerf becomes difficult since the fluidity of molten material is low in the narrow kerf. Therefore, nozzle shapes were investigated to improve the removal of material from the micro-kerf, and their effect on the fine cutting of a thin metal plate using a pulsed Nd: YAG laser was also discussed. The height of dross could be reduced by using a Laval throat nozzle with an initial expansion zone compared with that for a straight throat nozzle. The pressure on the workpiece was greater, and the straightness of the assist gas flow was excellent when the Laval throat nozzle with the initial expansion zone was used. Moreover, it was confirmed that the molten material could be effectively removed from the micro-kerf even at a middle cylinder gas pressure of around 600 kPa. Therefore, the Laval throat nozzle with the initial expansion zone can be used for fine cutting owing to its reduction of dross.

Effect of Nozzle Shape on Micro-Cutting Performance of Thin Metal Sheet by Pulsed Nd: YAG Laser