Grain size effects on nanocutting behaviour modelling based on molecular dynamics simulations

Grain size is one of the most critical factors affecting the mechanical and thermal properties of metallic materials. In this study the effect of the grain size of a workpiece made of pure Aluminium on the nanocutting process has been investigated via means of Molecular Dynamics simulations. The polycrystalline workpiece has been generated starting from a Face-Centred Cubic block of Aluminium atoms which was melted and subsequently quenched under various cooling rates in order to control the average grain size. The case of a monocrystalline workpiece has been considered as well. The generated workpieces were ground by a diamond abrasive. Simulations have been repeated in order to eliminate any statistical errors. The obtained results suggest that the average grain size of the workpiece significantly influences almost every aspect related to the nanocutting process. More specifically, it has been found that the cutting forces increase and the friction coefficient decreases with the grain size. Very small grain sizes lead to lower thermal conductivity and consequently high temperature at the cutting region. Finally, it has been shown that the high residual stresses at the grain boundaries can be relieved as the tool passes on top of the workpiece; this phenomenon resembles heat treatment. In summary, the nanocutting behaviour of polycrystalline materials depends on the average grain size and significantly differs from the case of monocrystalline materials. This should be taken into account in future numerical models of nanocutting processes