Spatter-free laser percussion drilling of closely spaced array holes

Spatter is one of the inherent defects commonly associated with holes produced with laser drilling. This work reports on a method of spatter prevention, workable for a wide range of process parameters. The method is based on the application of a specially developed anti-spatter composite coating (ASCC), containing a mixture of ceramic filler particles embedded in a silicone elastomer matrix, on the workpiece surface prior to laser percussion drilling. Experiments were conducted using a fibre-optic delivered 400 W Nd:YAG laser for the drilling of closely spaced through holes (2 mm hole pitch) in Nimonic 263 alloy sheets. The work revealed that the ASCC effectively prevented the deposition of spatter such that laser drilled holes were produced whilst maintaining the as-received surface characteristics of the Nimonic 263 alloy for all the assist gases tested (O2, air, N2 and Ar). The process characteristics and spatter prevention mechanism associated with the use of the ASCC have been investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, contact angle analysis and high-speed photographic imaging. Comparative studies were also made with the case of uncoated laser drilling.