Spatter removal characteristics and spatter prevention during laser percussion drilling of aerospace alloys

The aerospace industry has been employing laser drilling to produce high qu antity closely spaced holes in turbine engine components for effusion cooli ng. However, laser drilled holes are inherently associated with the deposit ion of spatter as the ejected material resolidifies and adheres around the periphery of the holes. This article presents an investigation on the effec tiveness of an antispatter composite coating (ASCC) for the drilling of clo sely spaced array (2 mm hole pitch) holes in three aerospace materials (IN 100, Nimonic PK 33, and 263 alloys) with an optical fiber delivered 400 W N d:YAG laser. The ASCC, comprised of a mixture of ceramic filler particles e mbedded in a silicone elastomer matrix, was applied on the surfaces of the alloy substrates before laser percussion drilling. The work shows that the ASCC effectively prevents the spatter deposition such that laser drilled th rough holes are produced while maintaining the as-received surface characte ristic when using either O-2 or Ar assist gas. The spatter prevention mecha nism and the characteristic of the ASCC have been investigated. Contact ang le analysis revealed that the contact angles for the ASCC and one of alloys (Nimonic 263) were 118 degrees and 46 degrees, respectively. Such a differ ence was identified to be primarily due to the low surface tension of the s ilicone elastomer matrix. The thermal resistance of the ASCC was increased due to the embedding of the ceramic particles, which absorb a significant p roportion of the heat generated by the ejected molten material and prevente d the coating from being burned away. (C) 2001 Laser Institute of America.