Development of a New Ultra-precision Finishing Process Applying the Cavitation Phenomena in Ultrasonic Vibration

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This research proposes a new ultra-precision finishing process in which the motion of the abrasive is controlled by cavitation caused by ultrasonic vibration in distilled water mixed with abrasive. The abrasive accumulates onto the surface of the workpiece and shows microscopic vibration by cavitation based on the ultrasonic vibration. This must remove the material from the surface the workpiece. To realize the above-mentioned principle, an experimental setup, which consists of an ultrasonic oscillator, electrostrictive vibrator (l8kHz frequency, 400 W output), vibration amplifying horn, and tool, was developed. The tool made of SUS3O4 stainless steel was mounted onto the tip of the horn. The workpiece was set into a container with distilled water and the abrasive under the horn. The ultrasonic vibration was imparted vertically to the target surface of the workpiece. The machining characteristics were experimentally investigated using the developed setup. A C3604 brass plate (□20×5 mm) was used as a workpiece. The clearance between the horn tip and the target surface of the workpiece was varied from 0.5-2.0 mm. Machining characteristics identified from the experimental results were summarized as follows : (1) Although abrasive mixed into the distilled water helped to smooth the surface of workpiece, it prevented cavitation in the water. This resulted in a decrease of the machining efficiency. (2) The smaller the clearance between the tool tip and the target surface of the workpiece, the deeper was the machined depth because of the higher machining force by the enhanced cavitation. (3) Because of the concentration of the cavitation when the clearance was smaller, the machined geometry more closely followed the tool's geometry. This caused more effective machining at the center of the tool, generating a rougher surface at the center of the machining area than at the edge. (4) This process is applicable not only for micro-machining but also micro-edge finishing.