Drilling time and hole quality in a laser drilling process depend greatly upon the selection of the type and pressure of the process gas. Process gas is commonly used for melt ejection, protection of optics and removal of plasma/vapor. This paper presents a detailed analysis of the gas type and gas pressure effects on the drilling speed and hole quality. O2, N2, Ar and compressed air were used in this investigation for Nd:YAG laser drilling of In718 alloy. It is shown that despite the lower penetration rate, the total volume of material removed is higher with oxygen assist gas due to oxide layer formation and plasma formation within the holes which increases the hole wall ablation, although drilling time with oxygen is longer than with other gases. Hole quality variations for holes under different gas type and pressure conditions are evaluated. One very interesting and significant findings was that the hole quality that achieved by laser drilling without assisting gas is better than that obtained when using argon, nitrogen or compressed air.
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