Ultrasonic cavitation in machining

Abstract

This project involves research on the material removal mechanisms of ultrasonic cavitation in machining. Ultrasonic cavitation in machining (UCM) is a non-contact machining process in which the forces created from the rupture of cavitation bubbles in abrasive slurry serves as the main material removal mechanism. The objective is to experiment and investigate the material removal mechanisms involved and determining the suitability of UCM in improving surface finish. This has been done by conducting a series of experiments with both machining fluid with and without micro abrasive particles. The first experiment was conducted on a grade 5 Ti-64 alloy using a 40kHz ultrasonic set up and two material removal mechanisms were identified under pure cavitation condition. The first mechanism was due to the shockwaves generated from the collapse of cavitation bubble while the second mechanism is due to the forces created from the re-entrant micro jets. The addition of abrasives dampens the effects of cavitation erosion and causes material removal of smaller scale on the workpiece surface. At the same time, addition of abrasives increases heterogeneous cavitation in the machining fluid. A second experiment was then conducted on SUS304 steel samples machined by wire electrical discharged machining (WEDM) using a same set up. By using slurries containing different abrasive sizes and concentrations as the machining fluid, it was found that the average surface roughness Ra was reduced from about 2.5 μm to about 1.7 μm after 20 minutes of processing time. This improvement of surface roughness is attributed to the removal of thermal recast layer due to WEDM.