Friction on Tool/Chip Interface in Nanometric Machining of Copper

Tool/chip interface on tool rake face is also called the first shear zone in machining processes. The interaction between tool rake face and formed chip greatly affects chip morphology, cutting forces, and other phenomena observed in machining. However, the interaction at nanometric scale has not been addressed by the large body of existing literature on nano-machining. In this study, we adopt the molecular dynamic (MD) simulation approach to model the orthogonal machining of monocryatlline copper by a diamond tool at nanometric scale. Two levels of machining speed, namely, 100m/s and 400m/s, are adopted, and the depth of cut is fixed at 2nm. The tool has a negative rake angle, −30°. Morse potential and EAM potential energy functions are employed to model the interaction pairs of copper/carbon and copper/copper atoms, respectively. The simulation results reveal that not only the cutting force components, but also the ratio of the tangential force along tool movement direction versus the thrust force increases with the increase of cutting speed. More importantly, we investigate the stress distributions along tool/chip interface, and discover that the patterns are overall steady regardless of the change of machining speed or the progress position of cutting tool movement. Compared the simulation results with five dominant friction models for macro machining, none of the five models are suitable to fit the friction distribution patterns obtained in nanometric machining. However, the sliding model with constant friction coefficient seems to be effective in approximating one portion of the friction patterns.