Experimental Measurement and FEM Modeling of the Dynamic Characteristics of the Milling Spindle with Different Bearing Preload

This study was aimed to identify the influence of the bearing preload on the dynamic characteristics of a spindle tool through the experimental approach. Generally, the bearing preload can be changed by adjusting the spacer clearance between front and rear bearings in spindle. The modal characteristics of the spindles with different preloads were then assessed through the vibration tests. Current experimental measurements show that the dynamic stiffness and damping ratio associated with the dominating modes of the spindles vary negatively with the increasing of the spacer clearance. The axial preload corresponding to different spacer clearance were estimated, revealing a nonlinear relationship between them. Besides, the effects of the bearing preload was also investigated by fmite element modeling approach, in which the bearing preload and contact stiffness of spindles with different preloads were calculated based on the Hertz contact theory. Results obtained of the experiments of the milling machine show that the lower preloaded spindle behaves lower resonant frequency and higher dynamic stiffness when compared to the spindles with higher preloads.