Papers by Author: Shigeki Okuyama

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: Micro V-groove cutting of cobalt-free tungsten carbide using two types of V-shaped diamond tools is performed using mist of zinc dialkyl-dithiophosphate (ZnDDP) as lubricant. The two types of tool tested are 1) mono-crystalline diamond and 2) poly-crystalline diamond made of approximately 30 nm-sized diamond crystals. The geometry of the V-groove-cutting process is theoretically investigated and the relationship between V-groove angle, original rake angle, and effective rake angle is clarified. Through the cutting experiments, the effects of diamond types and rake angle on tool-wear characteristics are explained. When rake angle is set at zero degrees, tool chipping frequently occurs for both types of diamond tools even when ZnDDP is supplied. However, when rake angle is set at -30 degrees for poly-crystalline diamond, tool wear is minimized.

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: This paper proposes a new grinding-fluid-supply system for improving the grinding performance of a CBN wheel. The system generates cavitations in the fluid flow, which is expected to provide higher cooling and superior grinding-chip removal capability. The system is applied to one-pass surface grinding of steel plates, and residual stress and surface roughness are evaluated. The system has a major effect on improving surface roughness, but has a minor effect on reducing the residual stress under shallow-cut grinding conditions. The effects appear greater under the heavier grinding conditions.

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.

Abstract: A grain-arranged diamond wheel was developed and grinding performance of the wheel against aluminum alloys and titanium alloy, Ti6Al4V, has been investigated using various kinds of grinding fluid. Mirror finishing of aluminum alloys was successfully performed without grinding burn when emulsion-type grinding fluid with an extreme-pressure additive was used. When oil base lubricants or a fatty acid was supplied using a MQL supply unit, fine finishing could not be done. Mesh size of the grinding wheel had only a minor effect on surface roughness. When Ti6Al4V was ground by the developed wheel, an adhesion of work material on diamond grains occurred causing the finished surface to deteriorate.

Abstract: In order to realize environmental-friendly machine tools, a linear-motor-driven table supported by constant-flow hydrostatic water bearings is developed. The table system is free from environmental pollution because the system needs no oil. For simplicity, a single-sided bearing system is chosen for the table-slide. To obtain a high sustaining force, preload is applied to the bearings using the attractive force of an iron core linear-motor’s magnets. The preload is effective in both the vertical and horizontal directions by inclined motor magnets. Miniature gear-pumps supply flow to the bearings without pump pulsation, and the bearings consume very small amounts of water and electric power. The measured table sustaining force was 3.0kN and static stiffness was 0.3kN/m under a flow rate Q=0.92mL/s per bearing and ideal bearing clearance h=16m.

Abstract: Diamond tools wear easily under cutting tungsten carbide. To clarify the wear mechanism, the authors composed a temperature-measurement system of a cutting point using a dual-colorinfrared pyrometer and performed planing experiments. Infrared rays, emitted from the contact point between a mono-crystal-diamond tool and a cobalt-free tungsten carbide, are transmitted though the diamond tool and an optical fiber and then they are detected by the pyrometer. Before the planing experiments, rubbing experiments were performed using a mono-crystal-diamond stick and a tungsten-carbide disk. The effects of gas environments and rubbing conditions on contact-point temperature, friction coefficient, and diamond wear were experimentally investigated. Planing experiments of the tungsten carbide using mono-crystal-diamond tool, were performed. The effects of planing conditions and gas environments on cutting-point temperature and tool wear were investigated. Through the experiments the following results were obtained. Rubbing and cutting point temperature is the highest in Argon gas followed by Nitrogen gas and is the lowest in Air. Diamond-tool wear is the greatest in Argon gas, less in Nitrogen gas, and the least in Air. The reason for this is that a chemically or physically absorbed layer of oxygen or nitrogen on tungsten carbide acts as a lubricant at the contact point. Cutting-point temperature was in proportion to cutting speed. The temperature under cutting speed at 90m/min and cutting depth at 1.0μm in Air was approximately 170degrees Celsius.

Abstract: A grain-arranged diamond wheel is developed and grinding performance of the wheel against industrial pure aluminum, one of the most hard-to-grinding materials, is investigated. The developed wheel efficiently ground pure aluminum without adhesion even when general-purpose grinding fluid, Type A3-1, was used. Moreover, wheel wear was not observed during the experiment, and grinding energy was extremely low. By using the developed wheel, a mirror surface can be easily obtained by one-pass surface grinding with very low table speed.