A Study on Oil/Air Lubrication and Preload of a High Frequency Fully Ceramic Motor Spindle

Trend of the high speed and high efficiency machining has pushed the continuous demand of higher spindle speed and power for the machining center application. However, the extremely high speed will produce significant centrifugal force. Conventional steel spindles are not appropriate for high speed operation because of their high rotational inertia and low damping ratio. Moreover, heat generation and dynamic loading caused by high speed rotation have been obstacles for increasing the speed limit in many conventional steel spindles applications. In this study, a high frequency fully ceramic motor spindle equipped with fully ceramic ball bearings without inner rings and ceramic spindle shaft is designed for higher speed, rigidity, precision and longer operating life. Furthermore, the performance of the ceramic motor spindle under different preloads and oil/air lubrication parameters is investigated. The optimum lubrication conditions that create the smallest temperature rise are obtained by the applying of the Taguchi method. Specifically, the effects of preload on the temperature rise and the static rigidity of the ceramic motor spindle are studied. The results provide a useful tool in designing a high speed ceramic motor spindle with a small increase in temperature and sufficient static rigidity.