Ultrafine bubbles (UFBs) are microbubbles with a diameter < 1 μm, which are used in a number of applications, including cleaning, sterilization, and water purification. The use of coolants containing UFBs in grinding has been reported to improve performance and machining accuracy. In conventional methods, however, UFB concentrations are relatively low. In this study, we developed a high-concentration UFB generator based on a rotary shear system, and investigated the effects of production conditions on UFB concentration and particle size distribution. Furthermore, we prepared UFB coolant using the developed generator, evaluated its characteristics, and conducted grinding experiments on carbon steel to evaluate the effects of the UFB coolant on grinding performance. The effects of the generation conditions on the UFB concentration were investigated, and the results showed that there is an appropriate range for the gas concentration and that the value of the shear force applied to the liquid containing the gas contributes to achieving a higher concentration. Characterization and grinding experiments with UFB coolant revealed that the grinding ratio improved without impairing the performance of the coolant.

In the finish grinding of parts with a narrow wall surface, it is difficult to secure a good machined surface using a coarse and small-diameter mounted grinding wheel because the number of active abrasive grains on the wheel is small. In this study, an ultrasonic helical scan grinding method was developed in which a rotating grinding wheel was ultrasonically vibrated in the direction of the grinding wheel axis, with the grinding wheel axis tilted in the feed direction. In this grinding method, the interference between abrasive grain trajectories increased due to the ultrasonic vibration of the abrasive grains, thus increasing the density of grinding marks. The results of a grinding experiment with high-speed tool steel using a PA120 grinding wheel with a diameter of 3.8 mm showed that ultrasonic helical scan grinding improved the ground surface properties and reduced the grinding resistance compared with conventional grinding, ultrasonic grinding, and helical scan grinding.