The processing of herringbone grooves is required in the small hydrodynamic bearings used for hard disk drive units that are used in cellular phones and other portable information devices, which involves a complex shape, microdimensions, and a high degree of accuracy. In this study, we developed a coining process for herringbone grooves, which is effective in improving accuracy, productivity, and cost performance. We investigated the fabrication of micro-end mills for cutting of a coining punch for herringbone grooves, which is made of hardened die steel (60HRC). We fabricated a cBN micro-end mill with a diameter of 100μm, and clarified its effectiveness in cutting hardened die steel.

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This study was performed to examine the axial vibration system inside magnetic grinding method processed by vibrating work piece square tube by fixation of magnetic pole in the inside. <?> Using two types of magnetic abrasive, i.e., electrolytic iron powder and SUS304 magnetic pin mixing magnetic abrasive, the inside magnetic abrasives machining experiment in making brass square tube to be a work piece <?> was carried out, and polishing quality was determined. The results indicated that the machined surface roughness was finished from 0.044μm Ra to 0.021μm Ra when the SUS304 magnetic pin mixing magnetic abrasive was used. A smoother surface was obtained with the SUS304 magnetic pin mixing magnetic abrasive in comparison to the electrolytic iron powder mixing magnetic abrasive. The effects on polishing quality in the square tube corner of the electrolytic iron powder and SUS304 magnetic pin mixing magnetic abrasives were examined experimentally.

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The helical scan grinding method has been developed to improve a finishing surface with highly efficient grinding. A straight or mounted wheel is fed at an angle (helix angle) related to the direction of grinding velocity that can be realized easily on an NC grinding machine. This method has a feature that provides the use of a wheel with coarse grains in finish grinding, leading to highly efficient finishing. In this study, the better ground surface of silicon nitride ceramics (Si₃N₄) was observed using the straight diamond wheel (SD170) feeding at an angle compared with conventional grinding. This surface roughness was similar to that in the case of conventional grinding using fine diamond grains (SD600). Moreover, the beneficial effects of this method were seen under various grinding conditions, such as feed rate or depth of cut.

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