Molecular dynamics simulation of nano-milling on copper

Miniaturised ultra-precision components are in great demand in micro/nano electro-mechanical systems, whose surface features are generally intricate and of nanometric dimensions. Since milling has high machining accuracy, simplicity, environment-friendliness and capability of generating complex and ultra-precision features, nano-milling has been considered a promising technique for efficient fabrications of components with nanometric features. However, the critical challenge is that the fundamental material removal mechanisms for nano-milling are still unclear, due to the difficulties in nano-scale experiments.This thesis has conducted a systematic investigation into the nano-milling of single crystal copper with the aid of molecular dynamics analysis. The following are the main findings and conclusions:1. The Morse potential with compensation scaling can be used to reliably describe Cu-Cu interactions with both simulation accuracy and efficiency. A suitable integration time step for the simulation of copper, comprehensively determined by the algorithm constraint and bond-distance dynamics, has been identified to be within the range of 4 fs to 12 fs.2. Single crystal copper is sensitive to the rotational speed of a nano-milling tool. The resultant threshold cutting speed should be 2,062 m/s.3. The crystallographic orientation effect of single crystal copper has been identified through nano-scratching. The material coefficient has been found to vary with cutting directions.4. A chip removal criterion has been established according to the contact length of the macro-scale.5. Stress waves have been found to propagate along the directions in 45 degree with the feeding direction of nano-milling and they can influence the minimum mid-wall thickness in a multi-grooving process.6. The quality of both single- and multi-grooving processes has been investigated by analysing the residual shear stresses around the grooves, shear strain rate variation and stress wave propagation. The study reveals that the machining mechanisms of end milling and peripheral milling at the nano-scale are fairly similar. The depth of cut is critical to the groove quality from a single-milling path. Due to the minimisation of the surface energy, the groove geometry cannot be perfect, and the geometry distortion can spread to a depth of seven atomic layers. 7. It has been discovered that both the depth of cut and mid-wall thickness play a significant role in multiple grooving. The minimum mid-wall thickness in sequential grooving is determined by the highest residual shear stress inside the workpiece. For simultaneous grooving, strain rate and highest shear stress play important roles in Method-B (with opposite rotational orientations) and Method-A (with the same rotational orientation), respectively. 8. Dimensional analyses are preformed to generalise the simulation results, and dimensionless nano-milling charts are then constructed to guide the selection of nano-milling parameters based on grooving efficiency and quality