Modelling and testing of the dynamic support stiffness of assembled bearings in motorized spindles

The dynamic support stiffness (DSS) of assembled bearings in high-speed motorized spindles (HSMSs) is the main factor affecting the rotor’s operating stiffness which, in turn, directly affects the machining accuracy of HSMSs. This paper establishes a thermo-mechanical coupled quasi-static model of the DSS of assembled bearings, providing a theoretical model for analysing the combined effects of preloading method, assembly form, thermal expansion and external load. An experimental method is designed to quantitatively measure the DSS of assembled bearings in HSMSs. By combining the modelling with experimental measurements, the effects of radial force and speed on the radial and axial DSS of the assembled bearings in an HSMS are investigated. The results show that the radial DSS of the front and rear bearings increases with radial force and decreases with speed; while the axial DSS of the front bearings decreases with radial force and speed, and the axial stiffness of the rear bearings is less affected by the radial force and speed under the condition of constant-pressure preload. The proposed experimental device can accurately measure the DSS of assembled bearings at speeds of up to 30000 r/min. This study provides a new theoretical model and experimental method for the estimation and quantitative measurement of DSS in assembled bearings in HSMSs.