Effects of assist gas on the physical characteristics of spatter during laser percussion drilling of NIMONIC 263 alloy

The effects of different assist gases, O2, Ar, N2and compressed air, during laser percussion drilling are investigated with regard to the physical features, i.e., thickness and surface geometry, of the resulting spatter and its bonding strength. Laser drilling was conducted on NIMONIC 263 alloy sheets, 2.6 mm thick, using a fibre-optic delivered 400-W Nd:YAG laser. The work has revealed that the spatter generated with O2 assist gas is distinctly different from those produced with N2, Ar and compressed air. The influence of the assist gas type on the mechanism of material ejectionrremoval is reported. The spatter bonding strength has been found to be associated with the ‘inertness’ of the assist gas employed, in which a progressive increase was observed in the order of O2, compressed air, and N2and Ar. It appears that the spatter bonding strength is dependent on the assist gas type and the workpiece material composition. In addition, it was found that the overlapping of spatter between adjacent holes, in closely spaced array holes, possessed higher bonding strengths. Consequently, the removal of overlapped spatter produced with inert assist gases is difficult to achieve without causing undesired modification to the material surface and hole geometry. q2000 Elsevier Science B.V. All rights reserved.