Cavitation Bubble Dynamics in Ultrasonic-Assisted Grinding with a Large-Load Longitudinal-Flexural Amplitude Transformer

Ultrasonic-assisted grinding (UAG) exhibits distinctive advantages in machining high-performance hard and brittle difficult-to-machine materials, where material removal is typically achieved through the synergistic action of abrasive grains, micro-jets and shock waves on the material surface. To effectively regulate the intensity of the cavitation effect, for the large-load amplitude transformer applied in UAG, numerical simulations were conducted to analyze the radiated sound field induced by the transverse and flexural vibration of the grinding wheel, thus characterizing the movement laws of cavitation bubbles during its vibration process. Simulation results show that the acoustic pressure amplitude radiated from the wheel circumferential surface reaches 1.4 MPa, far higher than the Blake cavitation threshold of 0.106 MPa. Based on the Keller–Miksis oscillator model, a cavitation bubble dynamics model incorporating the translational motion was established for the large-load grinding wheel in the UAG environment. Quantitative analysis shows that cavitation bubble oscillation is jointly regulated by multiple process parameters: the radial expansion amplitude reaches its maximum of 18.96 μm at a frequency of 20 kHz. When the acoustic pressure amplitude increased from 0.3 MPa to 0.5 MPa, the cavitation bubble expansion amplitude increased by 176%. The cavitation bubble expansion amplitude reaches its maximum and the cavitation effect is the most intense at a grinding pressure of 0.2 MPa and a grinding wheel rotational speed of 1000 r/min. The analysis results not only provide a theoretical reference for process parameter optimization from the perspective of cavitation effect in the UAG tool system, but also offer a fundamental basis for revealing the synergistic action mechanism of abrasive grains, micro-jets and shock waves, as well as for the precise regulation of cavitation intensity in UAG of hard and brittle materials.