There have been many reports on the use of ultrafine bubbles (UFBs) mixed into grinding fluids to improve machining performance. However, the detailed properties and behavior of UFBs are not fully understood. In this study, we examined the effects of cations on the long-term stability and effects of UFBs. We confirmed that cations neutralized the charge of UFBs and increased their size as well as decreasing their density. Furthermore, this was effective for removal of biofilm, which is a breeding ground for bacteria that cause putrefaction of the grinding fluid. Both UFBs and biofilms are negatively charged, but in the presence of calcium ions, the charges are neutralized, and therefore they lose the electrostatic repulsion and UFBs are more likely to collapse near the biofilm. That is, the addition of metal cations to UFBs caused a higher biofilm detachment effect when the UFBs were crushed than when UFBs were used alone.

This study was performed to develop textured surfaces composed of many dimple patterns of a few μm in depth with short in-plane periods of several tens of μm using vibration-assisted cutting by microvibration with a triangular pyramid diamond indenter tool in the depth of cutting direction (perpendicular to the workpiece surface). The effectiveness of the developed textured surface for improving surface functionalities was also examined. Using the developed fabrication method for textured surfaces, burrs (plastic buildup) around each dimple pattern generated during texturing were removed by on-machine mirror cutting to obtain a plateau-structured surface consisting of flat areas and dimple patterns. Several textured surfaces with different area densities were fabricated on brass specimens to improve tribological properties, and their dry sliding properties were evaluated. The results showed that the textured surface with a high area density, produced by on-machine burr removal, was effective in reducing friction and wear, and in accelerating the running-in process.