Performance of supercritical carbon dioxide sprays as coolants and lubricants in representative metalworking operations

Abstract This paper investigates the cooling and lubrication properties of supercritical carbon dioxide (scCO 2 ) sprays as potential substitutes for aqueous emulsions and straight oils used in the metalworking industry today. Sprays of rapidly expanding scCO 2 act to cool and lubricate machining and forming processes by delivering a mixture of dry ice and lubricant deep into the cutting/forming zone. In this work, experiments with turning, milling, drilling, thread cutting, and thread forming were performed with scCO 2 and other metalworking fluids (MWFs) to evaluate their relative performance with respect to tool wear and machining torque. Observations reveal that scCO 2 –MWFs are more effective in removing heat from the tool-workpiece interface than conventionally delivered (flood) aqueous MWFs as well as other gas-based MWF sprays. In addition, scCO 2 –MWFs delivered in lubricant-expanded phase, where scCO 2 is used to increase volume of lubricant in the spray field, are shown to provide better lubricity than straight oils and oil-in-air minimum quantity lubrication (MQL) sprays. As a result, scCO 2 –MWFs can reduce tool wear and improve machining productivity in a wide range of manufacturing operations leading to appreciable improvements in the economics of manufacturing. Also given that CO 2 is a recovered waste gas that is non-toxic, scCO 2 –MWFs can improve the environmental and worker health performance of manufacturing operations.

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