| Research Abstract |
To understand the effect of cutting speed on chip removal process and for the quest of ultimate cutting speed attainable in high speed machining, a feasibility study is proposed based on molecular dynamics (MD) computer simulation.
Fot the simulation of steady-state chip removal, translational boundary method, by which the cutting distance can be extended infinitely in theory, is proposed. In this method, to limit the calculation area, boundary layr moves at cutting speed with the cutting edge. In practical calculation, new atoms are continuously inserted into the calculation area, in which the cutting edge is fixed, and thrown away as they leave the calculation area.
By the introduction of a kind of "scaling" in distribution of kinetic energy of atoms in the model, thermal conductivity, which is mainly affected by electron conduction, of metal can be adjusted as practical one. Using this scaling, cutting temperature in microcutting of metal can be reasonably analyzed.
MD simulation of high speed microcutting of copper using diamond cutting edge show that the physical limitation of cutting speed is about 1,800 m/s. This ultimate speed is depends on the cohesive energy of the workmaterial to be machined. As the work surface melts under the cutting speed larger than 1,000 m/s, practical limitation of cutting speed is considered to be about 800 m/s. The results of MD simulation also show that an optimum cutting speed is predicted at about 200 m/s in microcutting of copper. At this cutting speed, minimum cutting force and best surface integrity are obtained. The ultimate and optimum cutting speed may be governed by thermal properties, especialy by thermal conductivity, of the worlmaterial to be machined.
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