Research On The Design And Manufacturing Of High-speed Ceramic Motorized Spindle

High performance spindle system is one of the key function units of NC machine tools. Motorized spindle is the main form of high-speed spindle system, which integrates many key technologies such as high-speed precision bearings, high-speed motor and driving, oil-air lubrication and cooling, precision manufacturing and assembling, and some other related supporting technologies. In this research, a high speed ceramic motorized spindle equipped with high-performance structural ceramic shaft and bearings is designed and developed. Because of engineering ceramics’ extraordinary physical properties such as high hardness, low thermal expansion, light weight, abrasion resistant and good chemical and thermal stability, it can reduce the high-speed rotational centrifugal force and inertia force and increase the stiffness and rotation accuracy of spindle-bearing system greatly, so as to accommodate very well the high-speed and precision requirements of spindle system. In addition, it can reduce friction and decrease the temperature response, accordingly effectively reduce the energy consumption and save resources. Development of ceramic motorized spindle can improve the performance and quality of the spindle system and NC machine tool significantly.In this paper, in order to improve the performance of ceramic motorized spindle and achieve its application in NC machine tools, the following key technologies of ceramic motorized spindle in process of design and manufacturing are researched.(1) Innovative high speed ceramic motorized spindle with a bearing without inner rings is designed and manufactured. The bearings are a kind of hot isostatically pressed silicon nitride (HIPSN) fully-ceramic ball bearings, whose rotor shaft is made from yttria partially stabilized zirconia (Y-PSZ), on which the outer race is designed. Ceramic ball bearings’kinematics, dynamics, failure mechanism and life prediction and other basic theoretical problems are researched. Internal structure parameters of ceramic bearings and the overall structure of ceramic motorized spindle are designed and optimized. It achieves an assembly of high-speed ceramic motorized spindle with high precision.(2) The ceramic material is used in the motor rotor shaft of spindle. Through creating motor model of the ceramic spindle, primary design parameters of ceramic spindle motor are optimized. Direct torque control system of ceramic motorized spindle based on PMAC is designed and researched. The theoretical analysis and simulation research on it are finished. (3) The near-net size sintered process of ceramic parts is researched. High-strength and high toughness ceramic spindle blank parts are sintered successfully. The grinding mechanism, grinding force, grinding surface quality control methods and the corresponding process parameters optimization of ceramic grinding are studied. The high-precision machining technologies of ceramic balls, ceramic rings and ceramic shafts are achieved. The surface roughness of ceramic bearing race is less than0.05μm. The machining accuracy of ceramic spindle shafts and ceramic bearing rings reach grade P4of the testing standard for precision of bearing components.(4) Performance test and analysis of the developed ceramic motorized spindle are finished. The test results show that the maximum speed achieves30000r/min, the maximum power achieves15kW, radial runout of shaft is less than μm, in the condition of best lubrication and appropriate preload, radial rigidity of the ceramic spindle system achieves322N/μm, no-load vibration is less than0.8mm/s, no-load temperature rise is less than10℃. Ceramic motorized spindle has been applied in NC machine tools successfully.This study not only provides the theoretical basis and technical support for design and development of ceramic motorized spindle without inner rings on high-speed NC machine tools, but also obtains original achievements with independent intellectual property rights on basic theories and key technologies of structural design and optimization of ceramic spindle, design and processing of ceramic parts, spindle motor design and drive control, and so on., accordingly promotes the application and development of high-speed ceramic motorized spindle in NC machine tools.