Anti-Spatter Composite Coating for Laser Drilling of NIMONIC 263 Alloy

摘要

Spatter is one of the inherent defects commonly associated with holes produced with laser drilling. The present work reports a method of spatter prevention, workable for a wide range of laser process parameters. It is based on the application of a thin layer of anti-spatter composite coating (ASCC), containing a mixture of ceramic filler particles embedded in a silicone elastomer matrix, on the workpiece surface prior laser drilling. Experiments were performed using a 400 W Nd:YAG laser for the drilling of through holes in NIMONIC 263 alloy sheets of 2.6 mm thick. The work shows that the ASCC effectively prevents the deposition of spatter such that closely spaced holes are produced whilst maintaining the as-received surface characteristics of the NIMONIC 263 alloy for all the assist gases (i.e. O_2, air, N_2 and Ar) tested. The ASCC can be easily peeled off after drilling. Contact angle analysis has proved that the molten NIMONIC 263 material does not wet the ASCC surface, which is mainly due to the low surface tension of the silicone elastomer matrix. As a result, the incorporation of the composite coating effectively changes the wetting characteristics of the workpiece surface. Fundamentally, the ASCC provides a physical 'constriction' (i.e. ASCC hole) around the to-be drilled substrate hole. Due to this constriction, the free space on the NIMONIC 263 substrate surface is eliminated and thus continuum spatter ejection (out of the drilling site) is achieved by the high-pressure forces from the assist gas jet and recoil pressure. This is confirmed by high-speed photographic studies, which showed that the ejection angle of the substrate material is altered to be vertically inclined towards the laser beam.