Development of a High-speed Spindle System with a Preload Adjusting Mechanism

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Ball bearings are usually used for spindle systems under preloading. This is an important factor affecting static and dynamic behaviors of machine tools during cutting operations. However, an excessive preload causes a sudden rise of bearing temperature and bearing seizure at high-speed operations. Therefore, the preload on bearings should be adjusted according to the cutting conditions.In this research, a new spindle system was developed by installing a preload adjusting mechanism using piezo-electric and hydraulic actuators. A new type of oil-air lubrication system was also developed by applying piezoelectric nozzles to the oil-air mixing equipment. The performance of the developed spindle system was evaluated through the impulse-force response test and cutting test. The results obtained through the tests are summarized below. (1) The quality of lubrication was improved by using the piezoelectric oil-air mixing equipment instead of the conventional type. (2) The temperature rise of bearings during high speed operations is effectively suppressed by adjusting a preload at low level, and the occurrence of bearing seizure is also suppressed. (3) The static and the dynamic behaviors of the spindle system are improved by adjusting a preload at high level. (4) By increasing a preload, the occurrence of chatter vibration is effectively suppressed. (5) Higher static and dynamic stiffness are obtained by using the piezo-electric actuators instead of the hydraulic actuators.The developed new spindle system can be applied not only heavy duty cutting operations but also high-speed cutting operations.