Papers by Author: Go Okahata

Abstract: There is a compelling need for development of a surface grinding machine for 450mm diameter silicon-wafers. The authors have developed a new surface grinding machine for the large scale silicon-wafers. The machine has a rotary work table equipped with a constant-flow hydrostatic water bearing. The table system has to attain high static stiffness to achieve higher loop stiffness. This paper investigates static performances of the rotary table by numerical computation. The obtained results are compared with the experimental ones. Accordingly, it is verified that the developed rotary table has sufficient static performances for the large scale silicon-wafer grinding machine.

Abstract: Precision machine tools using hydrostatic water bearings are superior to those using hydrostatic oil bearings in terms of environmental protection, worker’s safety, and cost. As for hydrostatic water bearings, a constant-flow type is more suitable than a constant-pressure type. However, the hydrostatic water bearings applied for machine tools are few cases, and there are only a few reports concerning the constant-flow bearings. In this study, sustaining force of the constant-flow hydrostatic water bearing pad is computed numerically by using ANSYS FLUENT. Then the solutions evaluated by the simple analytical models, which were proposed previously, are examined by comparing them with the numerical result. Additionally, an improved analytical model is proposed.

Abstract: Rubbing tests between a diamond stick and a tungsten carbide plate and planing experiments of cobalt-free tungsten carbide using a mono-crystalline diamond tool are conducted, and the effect of lubricants on tool wear is investigated. Five kinds of lubricants such as: sulfur-base extreme-pressure additive; dimethyl-silicone; oleic acid; zinc dialkyldithiophosphate (ZnDDP); and chemical solution type coolant (FGC950) are chosen for the lubricants. Through the rubbing experiments, diamond stick wear is the greatest when using dimethyl-silicone, followed by FGC950 and it is the least using ZnDDP. On the other hand, tool edge chipping is the greatest when using FGC950, followed by sulfur-base extreme-pressure additive and it is the least using ZnDDP. Through the planing experiments, tool chipping is dominant in diamond-tool wastage in comparison with abrasive wear. Tool life is the longest when using ZnDDP and obtained surface roughness is 0.022 mm Ra after 177 m planing.

Abstract: A linear-motor-driven table supported by hydrostatic-water bearings had been developed. The table slider is supported by a single-sided recess type bearing system and preloaded by attractive force using a linear-motor magnet. Since eccentric excitation force is applied to the table slider due to the change of attractive force according to the magnet track position of the linear-motor, pitching motion of the table occurs. This paper investigates the effect of air volume contained in a water-supply tube on the pitching motion. Larger air volume results in lower natural pitching frequency of the table slider, lower logarithmic decrement of the pitching motion and larger pitching angle. When the natural pitching frequency corresponds to the frequency of the eccentric excitation force during table feed, pitching angle grows by resonation.