DEVELOPMENT OF 600m/s SUPER HIGH-SPEED AND NANOMETER ORDER ULTRA PRECISION MACHINE TOOL

本研究的目的是在韧性材料加工中，通过超高速加工，使加工影响层深度最小化，并从整体上提高表面精度。韧性材料在其大部分断裂强度范围内表现为塑性。然而，当加工速度超过其静态塑性波传播速率时，它们变得“脆”。这种行为导致加工过程中塑性流动/变形和加工硬化的显著减少，从而可能改善总表面完整性，即使它伴随着裂纹产生的可能性。在这样的动机下，一个超高速机床安装超细进给系统，以防止裂纹的产生开发。在该机床上，采用空气静压轴承的砂轮轴和工件轴分别以300 m/s的速度旋转，可实现600 m/s的相对磨削速度。对纯铝和铝合金进行了磨削试验。结果，在低于静态传播速率的加工速度下产生大量的塑性流动，而塑性流动几乎不存在于超过静态传播速率的加工速度下，并且澄清了静态塑性传播速率是与去除机制不同的断裂点。为了从理论上支持实验结果的有效性，还对实验中使用的类似材料进行了分子动力学模拟。结果还证实了在超过静态塑性波传播速率的速度下的磨削机理与普通磨削过程完全不同。因此，这项研究证实了超高速和超精密加工的韧性材料的有效性。

This study aims to minimize the depth of the work-affected layer and totally improve the surface accuracy in the ductile material machining by applying the super high-speed machining over the speed of the materials' static plastic wave propagation rate. The ductile materials behave plastically throughout most of its fracture strength range. However, they become "brittle" as machining speed exceeds its static plastic wave propagation rate. This behavior leads to a significant reduction in plastic flow/deformation and work hardening during the machining process, so as possibly to improve the total surface integrity, even though it is accompanied with the possibility of crack generation. Under such motivations, a super high-speed machine tool mounted an ultra fine infeed system to prevent crack generation was developed. In the machine tool, by the rotation of grinding wheel shaft and workpiece shaft which adopted the air static pressure bearing at 300m/s, respectively, the 600m/s relative grinding speed can be achieved. Several grinding experiments were conducted on pure aluminum and aluminum alloy. As a result, a big amount of plastic flow is developed at the machining speed below the static propagation rate, whereas plastic flow hardly resides at the machining speed beyond the static propagation rate, and it is clarified that the static plastic propagation rate is a breaking point from where the removal mechanism is different. In order to theoretically support the validity of the experimental results, several molecular dynamics simulations were also conducted on similar materials used in the experiments. As a result, it is also verified that the grinding mechanism at the speed which exceeds the static plastic wave propagation rate is completely different from that of the ordinary grinding process. Consequentially, this study confirmed the effectiveness of super high-speed and ultra precision machining of ductile materials.