International Journal of Electrical Machining
Online ISSN : 2188-5117
Print ISSN : 1341-7908
ISSN-L : 1341-7908
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Paper
  • Akihiro GOTO, Minoru DOHI, Hiroshi FUJIWARA
    Type: PAper
    2019 Volume 24 Pages 1-6
    Published: 2019
    Released: January 15, 2020
    JOURNALS FREE ACCESS

    In this study, the transfer of insulating material from an electrode to a workpiece with discharge pulses was investigated. A method of transferring a conductive material has already been developed. However, for an insulating material, it is necessary to transform it into conductive electrode to allow discharge. In this report, zinc was used to bind the insulating material in order to form the electrode, and the zinc also works as a medium to transfer the insulating material during discharges. for the transfer of the insulating material as well as the binder of the electrode. It was expected that heat generated by discharges vaporizes all zinc elements and only the insulating material would remain on the surface of the workpiece. In fact, however, it was difficult to remove those zinc elements and a large amount of zinc remained in the layer. In this report, a method of reducing the elements of zinc from the layer was investigated.

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  • Atsutoshi Hirao, Takayuki Tani, Hiromitsu Gotoh, Naotake Mohri
    Type: Paper
    2019 Volume 24 Pages 7-12
    Published: 2019
    Released: January 15, 2020
    JOURNALS FREE ACCESS

    In this study, we propose a new micropin forming method in which the forming plate can be stationary while the rotating electrode moves towards the forming plate. As the processing area in this method is large, a higher removal rate is possible compared with the WEDG micropin forming method. Forming by this method is done easily by a micropin with a diameter less than 50 μm under low electrical discharge conditions. In this study, the aim was to obtain the desired electrode diameter by means of scanning electrical discharge machining. The electrode diameter narrowed rapidly with increasing machining time, and it was difficult to control the micropin diameter by controlling only the machining time. Therefore, the micropin forming was performed by controlling the indicator scanning length during machining. The results depend highly on the ratio of consumption of the forming plate and electrode. The relationship between the electrode diameter and scanning length—obtained from the experimental values and theoretical ratio from the consumption theory—was investigated. Micropins with a maximum diameter of 150 μm were obtained. The experimental values were found to be in good agreement with the theoretical values. Because the wear ratio was changed by the miniaturization of the electrode, there was a difference bet ween the theoretical and experimental values.

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  • Yoshihito HAGIHARA, Masaaki SANO, Akira OKADA
    Type: PAper
    2019 Volume 24 Pages 13-20
    Published: 2019
    Released: January 15, 2020
    JOURNALS FREE ACCESS

    In order to improve the thermal fatigue strength of EDMed molding dies, thermal fatigue tests of the treated surfaces by large-area electron beam (EB) under various conditions and gas nitriding were conducted. The thermal fatigue characteristics of the treated surface were evaluated by surface roughness measurement, microscopic observation, and X-ray residual stress measurement. These results indicate that the EB treatment has more dominant influence on the residual stress than pre-processing, such as EDM and milling, and the residual stress of EB treated surface is released in the early stage of the thermal fatigue test. Moreover, the gas nitriding treatment can inhibit the heat crack generation and its propagation on the surface in the thermal fatigue test.

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  • Yasuhiro Okamoto, Motoki Ota, Akira Okada
    Type: PAper
    2019 Volume 24 Pages 21-26
    Published: 2019
    Released: January 15, 2020
    JOURNALS FREE ACCESS

    Gallium nitride (GaN) is attractive material for blue light emitting diodes and high-frequency and highpower semiconductors. In general, GaN is sliced by using a wire saw method, although this cutting method has some problems such as thick damaged layer on sliced surface and environmental issue. On the other hand, laser slicing method has the possibility to reduce the kerf loss and the damaged layer compared with the wire saw method. In addition, high quality GaN with low damaged layer can be expected by using an ultrashort pulsed laser irradiation. Therefore, ultrashort pulsed laser was focused inside GaN, and the possibility of its separation by internal modified layer formation was experimentally investigated. GaN is partly decomposed into gallium and nitrogen by ultrashort pulsed laser irradiation, and thin internal modified layer is created by the combination of brittle fracture and decomposition of GaN. The continuous internal modified layer can be obtained by 10 ps pulsed laser irradiation, and GaN can be separated by its internal modified layer.

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  • Togo Shinonaga, Mitsuhiro Kimura, Motohiro Inoue, Akira Okada
    Type: Paper
    2019 Volume 24 Pages 27-32
    Published: 2019
    Released: January 15, 2020
    JOURNALS FREE ACCESS

    Zirconia has been widely applied for cutting tools and biomaterials, since it has superior mechanical properties such as high fracture toughness, bending strength and biocompatibility in ceramics. In order to maintain its surface functions for long-term, further improvement of wear resistance for zirconia has been required. In this study, improvement of wear resistance for zirconia is proposed by large-area electron beam (EB) irradiation. Experimental results show that mean width in roughness curve of zirconia surface increases with increasing the energy density of EB, although the maximum height in surface roughness is almost same as the ground surface. In friction and wear test, coefficient of friction reduces with increasing the energy deinsity of EB since ball material smoothly slides on the EB irradiated zirconia surface. Furthermore, it is made clear that wear resistance of zirconia significantly improves by the EB irradiation under appropriate energy density.

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  • Guodong Li, Wataru Natsu, Zuyuan Yu
    Type: Paper
    2019 Volume 24 Pages 33-38
    Published: 2019
    Released: January 15, 2020
    JOURNALS FREE ACCESS

    In the EDM process of drilling deep blind micro-hole with an aspect ratio larger than 10, machining speed decreases significantly in the last stage of machining due to frequent retreat of the micro tool. Up to now, reasons for the speed decrease were mostly thought to be gradual deterioration of the machining environment in the inter-electrode area, mainly caused by debris accumulation and concentration in the narrow gap area. However, it is difficult to confirm the state of the gap area in micro scale by direct observation. Therefore, an affirmed explanation for the speed decrease in micro EDM drilling has not been reported. In this research, in order to analyze the behaviors of bubble, debris and discharge characteristic in the inter-electrode area and the reason for speed decrease, direct observation of the gap area was carried out with an originally designed sandwich workpiece and a high-speed camera. The characteristics of discharge, bubble behavior and change of discharge area have been investigated and discussed in different hole depths.

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