Study On Thermal Performance And Dynamic And Static Characteristics Of The Aerostatic Spindle

The aerostatic spindle is the core component of ultra-precision machine tool,which directly affects machining accuracy.Typically,aerostatic spindle is driven directly by a motor.When the spindle is running,due to the shear friction loss of the aerostatic bearing film and the loss of the motor,the spindle will generate thermal errors which affect the machining accuracy.Sometimes even thermal expansion of the bearing structure can cause the bearing to fail.Therefore,thermal characteristics of the aerostatic spindle is studied.In addition,the effects of temperature rise on dynamic and static characteristics of spindle are studied.It has important theoretical and practical value for improving the thermal stability of aerostatic spindle system.In this thesis,the aerostatic spindle of lathe is the research object.The internal heat sources of the spindle system is analysed,and the heat output of the bearing and motor and the transfer coefficient are calculated.The heat transfer method between the components of the spindle system was analyzed,and the heat transfer coefficient between the components of spindle system and the air and cooling water was calculated.The steady state thermal-structural model is established in finite element software.The effect of cooling water flow rate on the temperature distribution and thermal deformation of the spindle system is analyzed.And the influence of inlet air temperature on the spindle core is analyzed.Then the transient thermal-structural model is established to study the temperature variation of the spindle system with time and obtain the thermal equilibrium time.And the axial deformation of the spindle core changes with time is analyzed.The FLUENT software is used to simulate the bearing film pressure distribution of the spindle system.The effects of film thickness,gas supply pressure and eccentricity on the bearing capacity,stiffness and gas consumption of thrust bearings and radial bearings are studied.Then,the influence of temperature rise on the bearing capacity and stiffness of the thrust bearing and the front and rear radial bearings is analyzed and compared.The dynamic characteristics of the spindle core are analyzed by the finite element software.The spring element is used to simulate the stiffness of the film,and the modal analysis of the spindle rotor is carried out.The free mode and working mode of the spindle rotor are obtained.The critical speed of the spindle rotor is calculated,and the influence of temperature rise on the natural frequency of the spindle core is analysed.By measuring the temperature variation with time and the amount of thermal deformation at a specific point of the spindle system,and comparing with the simulation results,the correctness of the established thermal-structural coupling model and the validity of the thermal analysis simulation results are verified.At the same time,the modal test of the main shaft is carried out by the hammer stroke method,and the natural frequency is obtained.The correctness and effectiveness of the simulation results of the spindle dynamic characteristics are verified.