Thermally induced preload and stiffness calculation for machine tool spindle bearing

To investigate the influence of thermal displacement due to non-uniform temperature rising in machine tool spindle system under bearing preload and dynamic stiffness, a thermo-mechanical coupling model is established. The factors to influence bearing friction loss are analyzed and thermal load and boundary conditions of machine tool spindle system are calculated. And the instantaneous temperature distribution and thermal deformation of machine tool spindle are solved by FEM. According to the bearing load-displacement equation, thermal induced preload is acquired, and the radial stiffness of bearing is evaluated by improved Jones' quasi-statics model. The laws and main influence factors of thermally induced preload are tested and analyzed. The theoretical and experimental results indicate that thermal displacements of spindle, baffle, bearing housing and bearing strengthen preload and bearing stiffness of the rigidly preloaded bearing; the increasing initial preload, rotating speed and environmental temperature extend the changing preload amplitude; bearing preload and stiffness are highly sensitive to local cooling which changes thermal displacement.