Lifetime Analysis of Motorized Spindle Bearings Based on Dynamic Model

The traditional probabilistic-based lifetime evaluation methods for motorized spindles ignore the effects of load dynamic and structural difference. Therefore, we propose a dynamic model-based lifetime estimation method that combines these effects to improve the estimation results for motorized spindles, especially at the design stage. Given that bearing lifetime dramatically influences the reliability of motorized spindles, this paper also designs a shaft-bearing-toolholder based on a dynamic model to estimate the lifetime of bearing group. The proposed dynamic model closely resembles the actual structure of spindles and indicates the stiffness of bearings and contact surface conditional on the nonlinearity of inputting radial and axial forces. The stiffness model is verified by performing an experiment and a finite element analysis. The load applied to bearings is accurately calculated using the dynamic model. Afterward, the load is introduced to a well-known bearing lifetime model, and the lifetime of each bearing and bearing group is calculated. The bearing lifetime results obtained under preload, clamping force and cutting force conditions are then discussed.