Study On The Key Technology Of High Speed Motorized Spindle For Grinding

The motorized spindle was designed and the prototype was manufactured cooperated with Wuxi Machine Tool Factory. The spindle adopts the popular structure such as built-in motor, cycling-water cooling, ceramic ball bearing support , preload applied by springs and oil/air lubrication. In order to improve the spindle dynamic characteristics and optimize its structure, firstly, the dynamic characteristics of the high speed angular-contact ceramic ball bearing were studied and compared with that of the steel ball bearing with the rotational speed ranging from 0 to 150,000 r/min. According to rolling bearing analysis theory, the bearing dynamic equations were established and were solved by numeric method, and the analyzing software was also developed. The result shows that the bearing dynamic characteristics changing nonlinearly mainly depend on the rotational speed and ball material property at high speed. The axial displacement of the bearing inner ring initially decreases and then significantly increases when the rotational speed grows higher. The stiffness value, also, initially drops and then rises considerably. The ceramic ball bearing gains significant advantages over the steel ball bearing in high speed applications.Then, the dynamic characteristics of the high-speed motorized spindle rotor-bearing system were studied, while considering the rotational speed effect on bearing radial stiffness. Based on the transfer matrix method, the calculating software was developed with which the critical speed characteristics of the spindle were studied in terms of several factors including axial pre-load and grinding tool specifications. The result shows that the rotational speed effect on bearing stiffness influences the critical speed significantly. The critical speeds increase slightly with pre-load increasing. The first critical speed decreases at a large rate when grinding tool extending-length and mass increase, whereas the second critical speed is not so subject to the grinding tool length and mass as the first one.Finally, the three test rigs were developed, one for bearing stiffness measuring, one for two-phase fluid lubrication and the third for three-phase fluid lubrication test. Furthermore, the experimental method was discussed, also.