A modeling approach for analysis and improvement of spindle-drawbar-bearing assembly dynamics

With the increase in the use of high speed machining (HSM), the need to predict spindle-bearing performance at high speeds is strategically critical to the implementation of HSM. In this research, considering the effects of drawbar on the dynamic behavior of the milling motorized spindle-bearing system, a double-rotor model of spindle-drawbar-bearing assembly has been established by utilizing the whole transfer matrix method (WTMM) and a nonlinear rolling bearing dynamic model including the centrifugal force and gyroscopic effects. The critical speeds and the dynamic stiffness of the spindle have been systematically studied. The effects of bearing axial preload, bearing specifications, bearing span and the inner diameter of motor rotor on the dynamic characteristics of the spindle are analyzed, and the spindle is designed by using the optimum selecting method. The results show that the drawbar is a sensitive part to affect the spindle dynamic behavior, and the effect of drawbar on the dynamic characteristics of the spindle system should be considered carefully. The axial preload and inner diameter of motor rotor have a bigger influence on the dynamic characteristics of the spindle than bearing span and rear bearing specification. The proposed model has been verified experimentally by measuring the dynamic stiffness at the spindle nose, and the simulated results are compared well against the experimental measurement. The results indicate that the double-rotor model is suitable for the prediction of dynamics of the spindle-drawbar-bearing assembly.