Effect of tool geometry in nanometric cutting: a molecular dynamics simulation approach

Abstract

To investigate the effect of tool geometry in nanometric cutting, molecular dynamics (MD) simulations of nanometric cutting were carried out with tools of different edge radii relative to depth of cut. Simulation studies were carried out by varying the tool edge radius, r (3.62– 21.72 nm) and depths of cut, d (0.362–2.172 nm) by maintaining the d r ration constant (0.1, 0.2 and 0.3). Variations of the cutting and thrust forces, the force ratio, the specific energy, and the sub-surface deformation with the tool geometry and depths of cut were investigated and found to have a significant influence on them. The results were also found to be in reasonably good agreement with the experimental and simulation results reported in the literature. Unlike in conventional cutting where the depth of cut is significant compared to the edge radius (or, the edge radius is negligible), in nanometric cutting this is generally not the case due to small depths of cut and minimum possible edge radius that can be produced on a single crystal diamond tool by the best manufacturing practice (20–70 nm). It also appears that the high negative rake angle and/or large edge radius (relative to the depth of cut) of the tool used in practice for finishing of advanced materials such as silicon wafers in nanometric cutting provides a high hydrostatic pressure underneath the tool required for the formation of a small plastic deformation zone immediately beneath the tool instead of initiating brittle fracture. A material removal mechanism was proposed that would cover the range from conventional machining to grinding, to ultraprecision machining, and finally to the indentation-sliding as a cognate transition for material removal operation. Indentation-sliding model appears to be more appropriate when considering machining brittle materials with tools of large edge radius relative to the depth of cut or large negative rake tools. Similarly, for grinding of ductile materials, the appropriate model would be using either tools of large edge radii relative to the depth of cut or large negative rake tools.