Hidetaka Miyake

Accretion of titanium carbide by electrical discharge machining with powder suspended in working fluid

Abstract A surface modification method by electrical discharge machining (EDM) with a green compact electrode has been studied to make thick TiC or WC layer. Titanium alloy powder or tungsten powder is supplied from the green compact electrode and adheres on a workpiece by the heat caused by discharge. To avoid the production process of the green compact electrode, a surface modification method by EDM with powder suspended in working fluid is proposed in this paper. After considering flow of working fluid in EDM process, the use of a thin electrode and a rotating disk electrode are expected to keep powder concentration high in the gap between a workpiece and an electrode and to accrete powder material on the workpiece. The accretion machining is tried under various electrical conditions. Titanium powder is suspended in working oil like kerosene. TiC layer grows a thickness of 150 μm with a hardness of 1600 Hv on carbon steel with an electrode of 1 mm in diameter. When a disk placed near a plate rotates in viscous fluid, the disk drags the fluid into the gap between the disk and the plate. Therefore, the powder concentration in the gap between a workpiece and a rotational disk electrode can be kept high. A wider area of the accretion can be obtained by using the rotational electrode with a gear shape.

Multi-Wire Electrical Discharge Slicing for Silicon Carbide Part 2: Improvement on Manufacturing Wafers by Forty-Wire EDS

In this paper, a machining energy control slicing method for cylindrical shaped ingots and forty-wire electrical discharge slicing (EDS) technology are investigated. Our recent study in [4], ten-wire EDS was applied to 100 mm-square polycrystalline SiC material. Applying this technology to ingot slicing, an appropriate process technology for cylindrical shaped SiC materials which are the same as an actual ingot is required. The slicing of cylindrical shaped SiC using conventional multi-wire EDS causes the increase of sori, or wire break with unstable machining process since wasteful machining power is not controlled as a function of machining length. To resolve this problem, we applied the machining energy control method which varies machining power with machining position. Using proposed method, ten-simultaneous slicing of cylindrical shaped SiC material is obtained with 80 μm/min in machining speed. The sori of machined surface is 34 μm, and TV5 is 28 μm as a result. Moreover, forty-wire EDS technology is applied to SiC slicing for improving wafer productivity. We successfully verified forty-simultaneous slicing of 100 mm-square poly-crystal SiC material without wire break. The sliced 39 thin plates are obtained 385 μm in average thickness, and 16 μm in maximum thickness variation.

Development of a 5-DOF Controlled, Wide-Bandwidth, High-Precision Maglev Actuator for Micro Electrical Discharge Machining

This paper describes a five degrees of freedom (5-DOF) controlled, wide-bandwidth, high-precision maglev local actuator to maintain a suitable distance between an electrode and the workpiece for micro electrical discharge machining (EDM). The actuator is sufficiently compact to be attached to conventional electrical discharge machines. The maglev actuator possesses a positioning resolution of the order of sub-micrometer and micro-radian, a bandwidth greater than 100 Hz in the 5-DOF directions, and a positioning stroke of 2 mm in the thrust direction. The maglev actuator can be levitated stably and positioned precisely, even under electrical discharge conditions. The use of the maglev actuator could increase the machining speed for Phi 1 mm holes by 21.8%, compared with the conventional EDM.

Characteristics of a Schottky Barrier Diode and the SiC Wafers Sliced by Wire Electrical Discharge Machining

The multi-wire electrical discharge slicing (multi-wire EDS), which is a brand-new method for fabricating wafers, is expected to considerably reduce the production cost of SiC wafers by decreasing in the width of kerf and kerf loss. We evaluated, for the first time, the influences of a wire electrical discharge machining (WEDM) on the SiC wafers based on experiments using WEDM equipped with a power supply of EDS. Although the analyses by transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) revealed that the WEDM influenced layer consists of a contamination layer including several kinds of metals and a layer having crystal defects was certainly formed near the wafer surfaces, the width of the influenced layers was only 3μm, and the layer could be easily removed by the grinding process. Furthermore, characteristics of Schottky barrier diodes (SBDs) fabricated with removing the influenced layer formed by WEDM are comparable to those fabricated with using conventional wafers.

High-Speed and High-Accuracy EDM of Micro Holes by Using a 5-DOF Controlled Maglev Local Actuator

The objective of this study is to realize high-speed and high-accuracy electrical discharge machining (EDM) of micro holes using a combination of a conventional EDM machine and a maglev local actuator. In this paper, the conventional EDM machine and the wide-bandwidth, high-precision, 5-DOF controlled maglev local actuator are combined and cooperatively controlled. Then to accelerate the debris ejection from the machined holes, the driving methods of the axial jump and radial vibration of the electrode are discussed. The experimental results show that the maglev local actuator can adjust the gap between the electrode and a workpiece speedily, and the machining speed is improved by 434.2%, compared with conventional EDM machine. Moreover, by the jump and the circular motion of the electrode, the debris ejection can be accelerated, the abnormal electrical discharge can be avoided, and the machining speed also is improved by 580.3%.