Dynamic Analysis Of High Speed Electric Spindle Ball Bearings-rotor System

In the early 1980 s, the advanced manufacturing technology first appeared. Gradually, the advanced manufacturing technology, which cross, fuse and integrate all the various aspects, had replaced the mechanical manufacturing technology. The advanced technology which includes machinery, electronics, energy, information and materials, is used in the whole process of the products manufacturing. The design and manufacture of the products are seen as the center, while the electromechanical integration as the main body. The information technology is also integrated into the manufacturing technology now. Electric spindle technology is the base of advanced manufacturing technology, which is one of the core components of the high-speed machining center. Electric spindle technology is benefit to significantly improve the machining efficiency and precision. The working speed of machine tool spindle is very high, which is nearly closed to the critical speed of the system or the limit speed of bearing. The limiting speed of bearings is designed to meet the performance requirements for electric spindle. Under the high speeds of the system, the revolution speed has a strong impact on the dynamic performance of machine tool spindle. Therefore, the requirements of the dynamic performances analysis are putted forward to the system of high speed. This paper mainly analyzed the system’s inherent frequency, critical speed and unbalance response. Finally, the achievement of the paper will benefit the structure design of the motorized spindle and be contributed to improve the performance of electric spindle.The research objective of the thesis is to study the internal dynamic performance of the high-speed angular contact ball bearing and the dynamic performance analysis of the system at high speeds. The paper uses the finite element method(FEM) to divide spindle rotor unit and then analyzes the questions by mathematical modeling, MATLAB programming, numerical analysis and dynamic analysis method.This thesis aims at studying the basic structure and working principle of the angular contact ball bearing and finishing the analysis of the bearing’s mechanical properties, under static load or low speed condition. Then the thesis research the geometrical structure of high speed motorized spindle’s bearings and establish the mathematical model of the bearing. On the basis of the initial data getting from the static analysis, the internal dynamic equations to high speed bearing are solved successfully. Through the analysis to bearing’s internal ball rolling element, we find that the gyroscopic moment and the centrifugal force have a very obvious effect on the performance of the bearing. With the increase of rotational speed, the influence is growing exponentially. Great changes have taken place in the contact angle and the contact stress between the inner-raceway and outer-raceway. Finally, the stiffness of bearing is reduced as well as the total rigidity of the system. Under the condition of high speed rotor system, the influence of the bearing internal dynamics state is not ignored. Those factors affect the system natural frequency, critical speed and unbalance response. The effect of pre-load on the system’s inherent frequency, critical speed and unbalance response of the end-shaft is obvious, too. A certain degree of increase for the pre-load could be of benefit to the system dynamic performance, but it is not valid to the bigger the better for the pre-load, because too big pre-load maybe lower the bearing life. It is a great improvement of the system dynamic performance to reduce the quality of the rotor end-shaft parts and decrease extending length. Finally, the suggestions are putted forward to optimize and improve the electric spindle design.