Molecular Dynamics Analysis of Microcutting Process

为了了解微细切屑去除过程，并追求极高的加工精度，在最先进的实验切削机床和金刚石刀具上，对未切屑厚度小于1 nm的铜和铝进行了精密控制的微细切削实验。切屑形貌的观察表明，即使在纳米级未切屑厚度下，也可以去除稳定的剪切带切屑。从切屑的厚度、片层间距和折叠间距随着未切割切屑厚度的增加而不断减小的事实来看，纳米切屑去除过程的机理似乎与常规切割的机理相同。利用分子动力学（MD）计算机模拟方法，对亚纳米级未切屑厚度下金属切削中的微切屑去除过程进行了分析和研究。比较表明，相当合理的切屑形态之间的相关性和尺寸效应的切削力和比能量从MD模拟和微观切削实验。结果表明，MD模拟可以作为分析微切削切屑和表面生成过程的有效工具。对微切削实验和MD模拟结果的分析表明，从最小切屑厚度的角度看，金属微切削的最终加工精度可达1 nm。最小切屑厚度是指在机床理想工作状态下，切削刃从工件表面上去除的最小未切屑厚度。

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.