A Comparison of Lubricants and Coatings for Cold Extruding Titanium

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Abstract
Investigations were conducted on a number of surface coatings and lubricants, both experimental and commercial, as part of an overall process development program on cold extrusion of solid and hollow titanium shapes. Materials were evaluated on the basis of surface finish and extrusion pressure in cold forward extrusion of unalloyed titanium billets 1 ½ in. in diameter to solid round bars 0.95 in. in diameter (60% reduction). A fluoride-phosphate chemical conversion coating proved to be most desirable from the standpoint of adherence, ease of application and cost. The effectiveness of the coating in reducing extrusion pressure and producing a good surface finish was dependent on the lubricant used. Various types and combinations of lubricants, including graphite, molybdenum disulfide, boron nitride, wax, soaps, polyalkylene glycol, and sulfochlorinated mineral oil were used in conjunction with the coating. The solid films, was and soaps were both alone and suspended in several resin carriers. Of the various classes of materials, the solid-film lubricants produced the best surface finishes on the extruded bars. From the standpoint of producing the best surface finish at the lowest extrusion pressure, the most effective lubricants were self-drying gum resin mixtures containing (a) 10% graphite and (b) 5% graphite + 5% MoS2. With the combination of the fluoride-phosphate coating and these lubricants, hollow shapes of unalloyed titanium with surface finishes of from 30 to 60 μin. were cold extruded at working pressures comparable with those for cold extruding similar steel shapes.

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