Effects of rolling bearing configuration on stiffness of machine tool spindle

Rolling bearings are widely used in the complex mechanical systems as important components. With the advancement in the manufacturing technology, the requirements of high-performance machining tool became essential. A bearing is one of the most important components of spindle, and it is a crucial factor in determining the overall quality. The configuration of bearings of spindle is the key problem during high-performance spindle design, which influences the performance of spindle, especially stiffness. This paper aims to develop a method to analyze various spindle stiffnesses with different configurations of bearing to support the optimization of spindle. Firstly, a quasi-static model is established to solve stiffness matrix of bearing, and then a spindle-bearing system mathematical model is established. Secondly, the stiffness matrix of bearing is added into the whole system to form an integrated spindle-bearings model. Finally, the spindle stiffness with different bearing configurations are analyzed. The results indicate that the number of bearings influences the spindle radial stiffness and bearing direction affects the spindle axial stiffness. Once the number and direction are specified, reasonable pre-load method, shorter overhang, and proper span can greatly improve the spindle dynamic characteristics. In addition, an experimental spindle is designed and fabricated to test various axial stiffnesses with different bearing configurations, and stiffness characteristics of commonly used bearing configurations are summarized from the experimental results and provide useful guide for the spindle design.