This study was performed to develop small-diameter drilling technology for hard and brittle materials, with the aim of achieving high machining quality, high machining efficiency, and low machining costs. We investigated the tool shape and the coolant to resolve issues regarding machining resistance behavior and chip adhesion. We investigated the effects of a liquid coolant-produced by adding photocatalytic titanium dioxide powder to water-on suppressing chip adhesion by irradiation with ultraviolet light to induce a photocatalytic reaction. The results are discussed below. When the titanium dioxide suspension was irradiated with ultraviolet light, a photocatalytic reaction occurred, and it was confirmed that the titanium dioxide suspension became hydrophilic. When drilling was performed while irradiating this suspension with ultraviolet light, almost no adhesion was observed on the tool. The hydrophilic nature of the titanium dioxide suspension reduced the amount of adhesion and the thrust force.

This study was performed to address global environmental issues and oil resource depletion by utilizing bamboo as a sustainable raw material. Fine bamboo fibers with controlled shape are made from bamboo cylinders using a machining center to obtain high-performance products with complex shapes. Forced chatter vibrations during cutting of bamboo cylinders causes variability of fiber shape, leading to a reduction in the mechanical strength of the product. To suppress forced chatter vibrations, it is necessary to set an appropriate interrupted cutting frequency based on the natural frequency of the bamboo cylinder. However, anisotropic cross-section and changes in height alter the vibration modes and frequencies, thus complicating control. In this study, the natural frequency was estimated based on cutting sound, and guidelines are provided to suppress chatter vibrations for improved fiber shape and product quality.