The influence of assist gas on the mechanism of material ejection and removal during laser percussion drilling

This paper elucidates the effects of different gases on the dominant mechanisms of the material ejection and removal and the cooling rate during laser percussion drilling. In particular, work was conducted for the reactive O-2 and inert Ar assist gases, in terms of their effects on (a) the behaviour and characteristics of spatter, (b) the recast layer characteristics and (c) the material ejection spark distribution for the drilling of Nimonic 263 alloy sheets using a Nd-doped yttrium aluminium garnet laser. It was shown that using O-2 assist gas, the material ejection was characterized with increased liquid particle ejection, coupled with volatile burning, possibly similar to that of nucleation-induced explosions, while the employment of Ar assist gas influenced the material ejection to be dominated by bulk radial liquid ejection.