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1730493 
Journal Article 
Laser cleaning of metal surfaces 
Walters, CT; Campbell, BE; Hull, RJ 
1998 
Unk 
Proceedings of SPIE
ISSN: 0277-786X
EISSN: 1996-756X 
PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS (SPIE) 
3343 
859-865 
WOS:000076793000091 
There is a critical need to replace ozone-depleting substances and hazardous chemicals that, in the past, have been used routinely in aerospace maintenance operations such as precision cleaning of metal surfaces. Lasers now offer the potential for removal of many organic materials from metals without the use of any solvent or aqueous cleaning agents. This paper presents quantitative results of laser-cleaning process-development research with a pulsed Nd:YAG laser and several common metals and organic contaminants. Metal coupons of Stainless Steel 304, Aluminum 5052, and Titanium were contaminated with known amounts of organic oils and greases at contamination levels in the 5 to 200 mu g/cm(2) range. A fiber-optic-delivered 1064-nm pulsed laser beam (20-Hz repetition rate) was scanned over the coupons with different overlap and pulse fluence conditions. Measurements of mass loss revealed that all levels of initial contamination could be removed to final cleanliness levels less than 3 mu g/cm,(2) at which point the mass loss measurements became uncertain. Pulse fluence thresholds for initial cleaning effects and practical cleaning rates for several metal and contaminant combinations are reported. From the totality of the results, an overall picture of the contaminant removal mechanism is emerging. For semi-transparent films, it is conjectured that a thermo-mechanical effect occurs wherein the laser energy is absorbed predominantly in the metal substrate which expands on the nanosecond time scale. This rapid expansion, in combination with some material evaporation at the film/metal interface, is believed to eject the contaminant film directly into aerosol droplets/particles which can be swept away and collected for recycle or cost-effective disposal in a compact form. Evidence for this mechanism will be presented. 
laser cleaning; laser removal of organic films; precision cleaning of metals; pulsed laser applications; solvent replacement