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The application of sub-zero coolants to machining highstrength, high-temperature alloys will, in certain applications increase metal removal rates up to 400%. These increases are not necessarily concurrent with cost reduction, because of the additional expense of sub-zero equipment, coolants and machine maintenance. The mechanical properties of the materials tested were not affected by subzero temperatures. Cost comparisons showed sub-zero coolants to be more economical in only one of the four tests when the machining of production parts was simulated. The results indicated that uninterrupted cutting operations on long cuts can be accomplished more efficiently with subzero coolants than with conventional coolants. Machining with sub-zero coolants is uneconomical on short runs and in interrupted cutting operations. The three sub-zero cooling methods evaluated were: (1) Application of CO2 mist at the cutting edge (-81F to -101F). (2) Flooding the workpiece and tool with ABCO 156 A Solvolene (-58F). (3) Freezing the workpiece in a cold chest (-110F) prior to machining. The machining operations performed were turning, milling, drilling, tapping and grinding. The materials used in the tests were: A-286, an austenitic stainless steel; L-605, a cobalt base alloy; R-235, a nickel base alloy; H-11, a hotwork die steel; Mo-0.5Ti, a molybdenum base alloy. Roomtemperature tests were performed with conventional coolants to establish tool geometry, tool material, feed and cutting speed for comparison with sub-zero machining tests. The results are presented in graphical form (Author)