CHEMICAL MILLING OF NARROW CLOSE TOLERANCE SLOTS IN ALUMINUM AND STAINLESS STEEL.
MCDONNELL AIRCRAFT CORP ST LOUIS MO
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Five types of maskants and three etchant solutions were evaluated for the purpose of producing precision slots in stainless steel and aluminum. The screen printing maskants tested were Nelco Silk Screen Stop-Off Lacquer R-5018 and Meaker Stop-Off Lacquer. The photosensitive maskants tested were Kodak Photo Resist, Kodak Metal Etch Resist, and Kodak Photo Lacquer. Combinations of the different photosensitive maskants were also tested. The 321 stainless steel panels were milled with steel chem-mill etchants per PS 20022.2 and the 7178-T6 Aluminum panels were milled with either HCl solution or an alkaline etchant solution per PS 20023. The hydrogen ion normality was kept within a specified normality range during the steel chem-milling. The cutting rate of the etchant solution varried depending on the hydrogen ion concentration, the spraying conditions, and the maskant configuration. The only suitable maskant tested on steel was Kodak Photo Resist over Kodak Metal Etch Resist. The meaker and Nelco maskants were tested for chem-milling aluminum. Both maskants were suitable for milling the larger slot widths. The cutting rate varied depending on etchant solution and maskant configuration. Author