Design Of Air Turbine Spindle With Surface Restriction Compensated Gas Bearing And Study Of Its Static And Dynamic Characteristics

The aerostatic spindle is the core component of the ultra-precision machine tool,and its performance is one of the key influencing factors of the machining capability of the machine tool.Ultra-precision aerostatic spindles are mostly supported by orifice throttling bearings and driven by motors in recent years.There are problems such as low load capacity and stiffness,motor heating,etc.,which limit the processing capacity of the spindle.For high-speed machining in which angular positioning or high speed stability is not required such as ultra-precision turning or micro-milling,the performance of the aerostatic spindle could be improved by adopting surface restriction gas bearings and air turbines.In this paper,based on the structure scheme design of the air turbine spindle with surface restriction compensated gas bearing,the CFD simulation method is used to analyze the aerodynamic performance of the air turbine and the dynamic and static performance of the surface restriction thrust bearing,and the effectiveness of the bearing CFD simulation model is verified through experiments.It provides a theoretical basis for the structure design of the spindle.The overall structure of the spindle is designed according to the determined performance index,and the surface restriction bearing and air turbine are designed in detail.The multiple reference frame model in Fluent is used to simulate the aerodynamic performance of the air turbine.The flow field distribution and mechanical characteristic curve of the turbine are obtained,and the influence of the supply pressure,nozzle diameter and blade tip clearance on the aerodynamic performance of the turbine is analyzed.According to the simulation results,the influence of air turbine parameters on its working efficiency is studied.The efficiency of the designed air turbine is evaluated by comparison with existing products.Based on the establishment of CFD simulation model of surface restriction thrust bearing,the influence of bearing parameters on its static performance is studied.The single factor variation method is used to analyze the influence of the parameters of the triangular section and rectangular section throttle groove bearing on their performance,and the orthogonal experimental design is used to study the order of influence of the geometrical parameters of the rectangular cross-section throttle groove bearing on the bearing load capacity.The static characteristics and flow field dynamic characteristics of surface restriction bearings and several other common throttling bearings are compared and analyzed.And the similarities and differences of bearings with different throttle methods in bearing load capacity,stiffness and flow field vortex are studied.The perturbation method combined with dynamic mesh technology is used to analyze the relationship between the dynamic stiffness and damping coefficient of the surface throttle thrust bearing and the disturbance frequency.On the basis of determining the manufacturing process of the spindle,the prototype of the air turbine spindle is trial-produced.The bearing load capacity and stiffness of the thrust bearing of the spindle are tested and compared with the simulation results to verify the effectiveness of the CFD simulation model of the surface restriction thrust bearing.