Effect of Cutting Speed on Cutting Phenomena and Its Limitation in High Sped Machining

为了了解切削速度对切屑去除过程的影响，寻求高速加工所能达到的极限切削速度，提出了基于分子动力学(MD)计算机仿真的可行性研究，在稳态切屑去除仿真的基础上，提出了理论上可无限延长切屑距离的平移边界法。在这种方法中，为了限制计算区域，边界层以切割速度与切割边一起移动。在实际计算中，新原子不断地插入到计算区域中，刀刃固定在计算区域内，离开计算区域时被丢弃，通过在模型中引入一种原子动能分布的“标度”，可以将主要受电子传导影响的金属的导热系数调整为实际导热系数。利用该标度可以合理地分析金属微切削过程中的切削温度。利用金刚石刀具对铜进行高速微切削的MD模拟表明，切割速度的物理极限约为1800m/S，这一极限速度取决于待加工材料的结合能。当切割速度大于1000m/S时，工作面熔化时，实际切割速度极限约为800m/S。分子动力学模拟结果还表明，铜的微切削最佳切割速度为200m/S左右。在此切割速度下，可获得最小的切削力和最好的表面完整性。最终和最佳的切割速度可能取决于被加工材料的热物性，特别是导热系数。

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.