Study On Monocrystal Silicon Nanometric Cutting By Molecular Dynamics Simulation

In ultra-precision machining, especially nanometric cutting process, chip removal takes place in a limited region containing only a few atoms or atomic layers. So some phenomena including chip removal, machined surface formation and so on, differ from those of general cutting process. It is extremely difficult to observe and measure various microscopic phenomena occurring in nanometric cutting through experiments, nor can the conventional theory based on continuum mechanics explain these phenomena. Molecular dynamics (MD) approach is a very effective tool for prediction and analysis of ultra-precision machining in theory, which provides a shortcut from micro phenomena to macro characteristics.By setting the non-rigid tool and the Debye model as the conversion between kinetic energy and temperature, the cutting model of monocrystalline silicon is established. The cutting processes are simulated with the help of MD approach. Nanometric cutting mechanism is analyzed from the viewpoint of instantaneous distribution of atoms, cutting force, potential energy between silicon atoms and cutting temperature. It is found that the deformed atoms at anteroinferior of cutting edge are formed and propagated, which causes the machined surface metamorphic layers by combining the broken bonds. Some silicon atoms are deformed and piled up in front of the tool because of the tool's extrusion and cut, which generates the chips. A few silicon atoms near the tool nose occur dislocation. The atoms at different locations on tool are analyzed and found that the highest temperature occurs on the flank and the biggest cutting force generates on the rake. The tool temperature fluctuates around a certain value.The effects of cutting thickness, cutting speed and cutting edge radius on cutting mechanism are studied in response to simulation results of different cutting conditions from the viewpoint of theory. From the results of MDS, it is shown that when the cutting thickness rises in nanometric cutting process, cutting force, potential energy between silicon atoms and cutting temperature will increase. Then, when cutting speed adds, both potential energy between silicon atoms and cutting temperature will increase. The cutting force will reduce. Cutting force, potential energy between silicon atoms and cutting temperature will increase with the increasing of cutting edge radius. The Morse potential and the Tersoff potential are used for the atoms interaction between silicon and carbon to study the effect of different potentials on the simulation results.The cutting processes are simulated about the monocrystalline silicon with point defects. It is found that with the rising of ratio of point defects in monocrystalline silicon, cutting force and potential energy between silicon atoms reduce. Although the temperature of workpiece rises, the temperature of tool has no obvious changes.