Molecular Dynamics Analysis of Microcutting Process

为了了解微切屑去除过程，并追求极高的加工精度，在最先进的实验切割机和金刚石刀具上，对铜和铝在未切屑厚度降至1 nm的情况下进行了精心控制的微切削实验。对切屑形貌的观察表明，即使在纳米级的未切屑厚度下，也可以去除稳定的剪切带状切屑。从切屑厚度、片层间距和折叠间隔随着未切削切屑厚度的减小而不断减小的情况来看，纳米切屑去除过程的机理与常规切削过程相同。利用分子动力学（MD）计算机模拟技术，对亚纳米级未切削切屑厚度下金属切削中的微切屑去除过程进行了分析和理解。通过对比发现，MD模拟和微切削实验得出的切削力和比能的尺寸效应与切屑形貌之间存在相当合理的相关性。结果表明，MD模拟是分析微切削过程中切屑和表面生成过程的有效工具。对微切削实验结果和MD仿真结果的仔细分析表明，从最小切削厚度的角度来看，金属微切削的最终加工精度可以达到1 nm，最小切削厚度定义为机床在理想操作下切削刃处从工件表面去除的切屑的最小未切削厚度。

For understanding of micro-chip removal process and in quest of extreme machining accuracy attainable, a carefully controlled microcutting experiments of copper and alminum were carried out under the uncutchip thickness down to 1 nm on the-state-of the-art experimental cutting machine and diamond cutting tool. The observation of chip morphology shows that the stable shear-banded chip can be removed even at nanometric uncut chip thickness. Judging from the facts that the thickness, lamellar spacing and folding interval of chips continuously decrease with the uncut chip thickness, the mechanism of nanometric chip removal process seems to be same as that of conventional cutting. Using molecular dynamics (MD) computer simulation, an attempt is made to analyze and understand the micro-chip removal process in metal cutting under sub-nanometric uncut chip thickness. Comparison shows fairly reasonable corelation between the chip morphology and the size effect in the cutting force and specific energy obtained from both MD simulation and micro-cutting experiments. The results suggests that MD simulation can be an useful tool for the analysis of chip and surface generation process in microcutting. Careful analyses of the results of the microcutting experiments and MD simulation show that the ultimate machining accuracy of 1 nm can be expected in metal microcutting from the viewpoint of the minimum thickness of cut which is defined as the minimum uncut thickness of chip removed from work-surface at a cutting edge under an ideal operation of machine tool.