The authors propose a new coolant named"micro bubble coolant" which includes micro bubbles (20 - 50μm in diameter). In a previous study, it was clarified that tool life was improved by applying this new coolant to various types machining applications, such as boring, turning, and grinding. This paper deals with the purification effects of the micro bubble coolant. Experiments indicated that bacteria that cause putrefaction of conventional water soluble coolant are eliminated by generating micro bubbles in the coolant. It was also demonstrated that the micro bubble coolant isolates minute machined chips and machine oil from the coolant.

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This paper deals with the relationship between tool wear properties and nitrogen impurities in diamond tools. It is very important to analyze nitrogen impurities at the tool edge, which is directly engaged in cutting. FT-IR microscopy, which is suitable for this analysis, is employed to analyze nitrogen impurities at the tool edge. The relationships between nitrogen impurities and tool life of synthetic diamond tools (Type Ib and Type IIa) for copper precision cutting are discussed. The results showed that nitrogen impurities significantly affect chipping and crater wear. Tools that contain larger amounts of nitrogen impurities show less chipping. On the other hand, crater wear volume corresponds to the quantity of nitrogen impurities in synthetic diamond tools and is affected by heat conduction.

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This paper discusses the influence of the lubricant applying effect (LAE) of cutting fluid on cutting of the super-alloy Inconel 718 plate. The LAE has been already recognized in such ductile metals as pure aluminum, pure copper, α-brass, mild steel, and stainless steel SUS304 by the authors. However, the LAE mechanism of Inconel 718 cutting has not been examined in detail. The LAE experiment for Inconel 718 plate cutting was conducted to determine the generating conditions and mechanism. The experimental results demonstrated that the LAE plays an important role in lubrication of the Inconel 718 cutting as well as ductile metal cutting. Applying materials to the precut surface of the plate can greatly improve machinability due to the reduction in friction between the lamella of the chip. However, range of cutting conditions in generating the effects was much smaller than the others in ductile metal cutting.

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To obtain knowledge useful to predict the tool life due to breakage, a series of slotting experiments was performed at various feed rates for medium carbon steel using coated carbide square end-mills 0.5 mm in diameter. The main results obtained were as follows. (1) There is a possibility of obtaining an optimum feed rate for the maximum slotting distance. (2) Lower feed rate causes chatter but higher feed rate rarely causes chatter. (3) Minor's law based on the S-N curve of bending rotating fatigue tests was not applicable because the cumulative damage deviated widely. (4) Newly defined cumulative damage seems to be useful to some extent to predict tool life by monitoring cutting force.

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