Comparison of tool–chip stress distributions in nano-machining of monocrystalline silicon and copper

• The stress distributions along the tool–chip interfaces in nano-machining of copper and silicon are obtained using the MD simulation approach.
• The contact length of tool–chip interface is shorter for silicon nano-machining due to α-to-β phase transformation.
• The normal and friction stress distributions along the tool–chip interface in silicon nano-machining show significant fluctuations.
• No existing friction models for machining are suitable for describing the friction stress distribution in nano-machining.

Tool–chip interface is a critical zone for machining processes, and the interaction between work material and tool governs chip formation and affects cutting performances. To investigate the tool–chip stress distribution and friction phenomena in nano-machining of monocrystalline silicon and copper materials, a molecular dynamics simulation approach is adopted. The Tersoff potential function is employed to model the interatomic force among silicon atoms, and an EAM potential function is used to model the interatomic force between copper atoms. Twelve cases of 3D orthogonal machining with various cutting conditions are simulated. The stress distributions along the tool–chip interface in copper and silicon machining are investigated and compared at various cutting speeds (10–400 m/s) and with two tool rake angles (−15° and −30°). Also the effect of depth of cut on the friction behaviors in silicon machining is investigated at three levels of depth of cut. The results show that the main deformation mechanism of silicon machining is the amorphous phase transformation, while the machining process of copper is dominated by the plastic deformation involving the generation and propagation of dislocations. Under the same machining parameters, the contact lengths of tool–chip interface are close for the cases of silicon and copper machining at the initial stage, but they are constantly longer for copper machining beyond the initial stage. Along the tool–chip interface, the normal and friction stress distributions are more complex in silicon machining than those in copper machining, and the material flow near tool edge could be downwards instead of upwards. The patterns of stress distributions in copper machining are not influenced significantly by the cutting speed and tool rake angle, but those in silicon machining show significant variations and thus are less conclusive. The results also indicate that the well-established friction models for conventional machining may not work for nano-machining.