| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 102 === The ultrasonic assisted drilling has been verified to be able to significantly improve the cutting efficiency of high hard materials. High-frequency vibrations can be easily realized by electric power. But there are some security concerns such as electrical leakage in humid environment for application of dental handpiece. The aim of this thesis is to develop a pneumatic axial vibrator integrated with the existing air turbine cartridge. High pressure air is applied as the power source to create high frequency axial vibration.
Because of less power consumption, the self-excited vibration is chosen as the working principle of the developed pneumatic vibrator, and its excitation source draws on the cavity resonance phenomenon. The pressure relief and recovery mechanism is designed to continuously convert the gas pressure into the kinetic energy of vibration. Firstly through the theoretical analysis, the working principle and the influential parameters of the pneumatic vibrator are studied and evaluated. According to its derived embodiment design, the CFD simulation is carried out to comprehend and optimize the relationship between the design parameters and the vibration performance. Based on the optimized result, the prototypes are precisely developed. The developed prototypes are experimentally tested to verify the influence of load on their performance - vibration amplitude and frequency. Finally through the integration testing of the pneumatic vibrator and the air turbine cartridge, the ultrasonic assisted drilling performance is also confirmed.
The experimental results demonstrate that the cavity resonance effect is feasible to drive the pneumatic vibrator. Without axial load, the pneumatic vibrator can create an amplitude of 91 μm at the frequency of 674 Hz for the air pressure of 5.5 bar; and it can withstand a maximum load of 2035 mN by supplying an air pressure of 4 bar and achieve an amplitude of 93 μm at the frequency of 535Hz. The air turbine cartridge under a radial load of 500 mN can be assisted by the pneumatic vibrator to effectively enhance its cutting rate by 2.5 times that without axial vibration at the frequency of 341 Hz.
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