| Summary: | 碩士 === 國立中正大學 === 機械工程學系暨研究所 === 103 === A technique based on Operational modal analysis (OMA) in determining the optimal spindle speed to achieve higher material removing rate (MRR) for machine tools in machining is proposed. With several accelerometers attached respectively on the spindle and the work table of a machine tool, the natural frequency and its corresponding damping ratio of this machine tool during machining are identified using OMA and PolyMAX. In particular, the OMA technique is conducted based on displacement transmissibility measurement and singular value decomposition (SVD), which reduces the possibility in wrongly identifying natural frequencies due to presence of harmonics in machining. After identifying the natural frequencies, the corresponding damping ratio is then determined using traditional PolyMAX estimation algorithm. The identified results are compared with those from traditional impact testing technique. The differences in the identified results between two methods, i.e. OMA and impact testing, are attributed to the cutting impedance involved only in the OMA. With the identified natural frequency and damping ratio, the stability diagram which depicts the machining stability in terms of spindle speed and stiffness ratio can then be created. Experiments are presented to validate the optimal spindle speed chosen from the stability diagram. Results show that the MRR increases with a better surface roughness using the optimal spindle speed.
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