精密工学会誌

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The machining of difficult-to-machine materials, such as hardened steel, titanium alloys, inconel, and stainless steel, is usually associated with low productivity, high cost, poor surface quality, and short tool life. Therefore, improving the machinability of difficult-to-machine materials is essential. In this study, the development of a built-up layer (BUL) under certain cutting conditions was promoted to protect the tool surface and extend the tool life when machining hardened steel S45C (H-S45C) with an uncoated WC-Co tool. The dimensions, microstructure, and chemical compositions distributions of the BUL were accurately measured. The tool wear and roughness of the machined surface were also determined to evaluate the usefulness of the BUL. From the results, it was shown that the BUL, composed of an elongated microstructure of H-S45C, acts as a protecting layer on the tool surface, decreasing the tool wear and extending the tool life; Further, the relationship between the formation of the BUL and the surface roughness was also experimentally verified. It was confirmed that the BUL formed during the machining of H-S45C helped maintain the quality of the finished surface, and the adhesion on the nose helped decrease the variations in the surface roughness of the finished surface.

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Due to its piezoelectric properties, the zinc oxide (ZnO) thin film is used for Micro Electro Mechanical Systems (MEMS) sensors and actuators. In order to reduce the fabrication costs and to improve the reliability of MEMS devices, a low temperature process is desired. ZnO layer is deposited on the oxidized chrome (CrO) buffer layer that is deposited on silicon substrates. Both ZnO and CrO layers are deposited by RF magnetron sputtering at room temperature. The crystalline properties of ZnO are measured with an X-ray diffraction (XRD), a scanning electron microscopy (SEM) and an atomic force microscope (AFM). The results show that varying the O₂/Ar flow ratio during the deposition of CrO layer may improve the crystalline properties of ZnO. Piezoelectrically actuated cantilevers with the ZnO thin film are fabricated and tip deflection of the cantilever is measured. The piezoelectric strain constant of ZnO thin film is calculated from the tip deflection. The results show that the piezoelectric strain constant increases and saturates with the thickness of ZnO layer. The obtained piezoelectric strain constant of ZnO thin film is 3.7 pC/N which is 74% of the bulk ZnO.

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Lost motion is the center of major disturbance to the contouring accuracy of NC machine tools as conventional compensation often causes over-compensation resulting in undesirable slits in reversal motion. This paper describes a model of the table drive system of a ball screw with loss of elastic energy brought by ball wedging in the nut. A simplified compensation method for that lost motion is derived from the model. The performance has been evaluated by ball bar measurement in a test machine under various conditions including the table position, movable load and feedrate. The ball bar measurement on a large double column machining center shows the generality of the proposed method.

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