Friction and cutting forces in cryogenic machining of Ti-6Al-4V

Conventional cutting fluid serves both as a coolant and lubricant. In cryogenic machining, liquid nitrogen (LN2) is recognized as an effective coolant due to its low temperature; however, its lubrication properties are not well known. The focus of this study was to investigate how the friction between the chip and the tool is affected by focused jetting LN2 to the cutting point in machining Ti-6Al-4V. Results of cutting force measurements indicated that the cold strengthening of titanium material increased the cutting force in cryogenic machining, but lower friction reduced the feed force. A mathematical model was developed to convert the measured 3D forces in oblique cutting into the normal and frictional force components on the tool rake face, and then to calculate the effective friction coefficient. It was found that the friction coefficient on the tool-chip interface was considerably reduced in cryogenic machining. Increased shear angle and decreased thickness of the secondary deformation zone, findings from a chip microstructure study, offer further evidence that friction is reduced. (C) 2001 Elsevier Science Ltd. All rights reserved.