Papers by Author: Yoshiyuki Uno

Abstract: Brittle materials, such as silicon, silicon carbide and sapphire have been conventionally sliced for wafers by a multi-wire saw method with slurry in industrial fields. Recently, the multi-wire saw method with a fixed diamond abrasive wire has been available as a commercial product at acceptable cost, and the high slicing performance is expected compared with the normal multi-wire saw method with slurry. However, there still remain some problems such as bad working environment with abrasives, cleaning cost of sliced wafers, crack generation on the sliced surface and a large kerf loss against a wafer thickness. On the other hand, the developed multi-wire EDM slicing method would accomplish the high performance slicing of silicon and silicon carbide with a narrow kerf width under a clean process environment. However, the thinner wire is challenging process with a normal round shape wire electrode. Therefore, the new wire electrode with track-shaped section was proposed in order to satisfy both the narrow kerf width and the high wire tension even in the case of thin wire electrode. In this study, the running control of wire electrode with a track-shaped section was experimentally investigated, and the possibility of proposed process was discussed.

Abstract: In a wire EDM using a thin wire electrode, better exclusion of debris from the machined kerf is important in order to maintain stable machining performance, since the area of spark generation is along a line and very small. When large amounts of debris stagnate in the gap, secondary discharges possibly occur and these discharges easily concentrate on the same location, which leads to unstable machining performance, wire breakage, low machining rate and a low shape accuracy. Conventionally, the exclusion of debris is carried out by jet flushing with an upper and lower nozzle. However, the flow field of machining fluid in the kerf due to the jet flushing and the effect of jet flushing conditions from the nozzles on debris exclusion have not yet been sufficiently examined. This study aims to clarify the flow field in the machined kerf by computational fluid dynamics (CFD) and to propose new jet flushing methods for smooth debris exclusion in the wire EDM. The effects of workpiece thickness and machined kerf length on the flow field of working fluid in the kerf under conventional jet flushing conditions are discussed. Then, jet flushing with a tilting nozzle is proposed in order to decrease the debris stagnation area near the wire electrode. As a result, by using the tilting nozzle, removal rate can be improved because of the smooth debris exclusion.

Abstract: A newly surface treatment method was proposed by the combination of the high-speed laser scanning with Galvano scanner and the single-mode pulsed fiber laser with Master Oscillator Power Amplifier, and various periodic structures could be formed by this technique. The surface roughness of irradiated area increased almost proportionally with increasing the number of laser scan, and it could be controlled by the number of scan. The repellency of surface could be increased by the laser irradiation compared to that of ground surface under nitrogen atmosphere condition, while the hydrophilic property of surface could be improved by the laser scanning under air atmosphere condition. Moreover, it was found that the corrosion resistance of the surface could be improved by laser irradiation.

Abstract: This paper deals with EDM characteristics of newly develops electrically conductive ceramics. Titanium boride (TiB2) is widely used as die and mold materials because of its high hardness, high-temperature resistance and so on. The EDM characteristics of the titanium boride, such as electrode wear rate, removal rate and surface roughness were investigated. Experimental results show that EDM with low electrode wear rate is possible when copper electrode is used with positive polarity. The removal rate becomes much higher when graphite electrode is used with negative polarity.

Abstract: A new surface finishing method by large-area electron beam irradiation (EB-polishing) for stainless steels for orthopedic surgical tool was proposed in our previous paper, and it was shown that high-efficient surface finishing was possible by the EB-polishing. In this report, the surface structure of EB-polished stainless steel is analyzed by TEM and EDX. Also, surface modification effects such as resistance to corrosion and blood repellency are evaluated. Then, the applicability of the EB-polishing as a new surface modification method of stainless steel for orthopedic surgical tool is discussed.