| Research Abstract |
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.
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