Thermo-mechanical coupling model and dynamical characteristics of machining spindle-bearing system

To investigate the varying dynamical characteristics of CNC machine tool's spindle system at high rotating speed, a thermo-mechanical coupling model of spindle-bearing system is established, which consists of a spindle shaft model and a bearing model. The spindle shaft model is generated by the finite element method considering the effects of centrifugal forces, gyroscopic moments and softening of bearing stiffness. Taking the effects of the radial deformation of bearing inner and outer rings and the change of bearing preload caused by the initial assembly interference between the spindle and bearings, the centrifugal forces and rising temperature into account, the bearing model is improved based on the nonlinear Jones' bearing model. The simulations show that the induced centrifugal expansion of inner ring and thermal expansion of inner and outer rings will strengthen the bearing stiffness while the thermally induced preload lowers the bearing stiffness for the 'back to back' bearing arrangement. In addition, the centrifugal effect of the spindle impacts the dynamical characteristics more obviously than the softening of bearing stiffness.