Influence of centrifugal expansion on bearing stiffness in motorised spindles at high speeds
摘要
Given the high-speed operating conditions of motorised spindles, centrifugal expansion influences the bearing stiffness of the spindles. According to the principles of elastic mechanics, a centrifugal-expansion model that considers speed and interference was developed for bearings and spindles. This model couples centrifugal expansion with the quasi-static bearing model by adjusting the boundary condition of the outer diameter of the bearing’s inner ring from 0 to the contact force Qi between the rolling elements and the inner ring. The optimised centrifugal-expansion model accounting for speed, interference, and contact force Qi was developed, resulting in an improved bearing model that considers centrifugal expansion. This model was applied to a specially designed motorised spindle and a stiffness test device to study the impact of centrifugal expansion on bearing stiffness under both fixed-position preload and constant-pressure preload conditions. The results indicated that neglecting the contact force Qi led to an overestimation of centrifugal expansion, while neglecting centrifugal expansion resulted in an underestimation of bearing stiffness. Both the bearing stiffness and centrifugal expansion results obtained through coupled iteration agreed well with the experimental data. The experimental results revealed that bearing stiffness was more sensitive to speed under constant-pressure preload than under fixed-position preload, while fixed-position preload was more affected by temperature rise. The results show that the bearing model with coupled centrifugal expansion is more suitable for the analysis of the dynamic characteristics under high-speed conditions.