Research On Complex Dynamic Characteristics And Comprehensive Testing Technology Of High-speed Motorized Spindle System

High-speed motorized spindle(HSMS)system is the most important functional component in high-end computer numerical control(CNC)machine tools and the carrier to realize high-speed and ultra-high-speed cutting.The complex dynamic characteristics of the HSMS directly affects the machining quality of the workpiece and its own service life.However,the test methods and techniques for the key indicators of its operation quality have yet to be overcome.In this paper,the comprehensive testing technology of complex dynamic characteristics of HSMS was studied,and a novel HSMS and its system were developed independently according to the needs.On the basis of the establishment of the experimental platform,the deficiencies and urgent needs of theoretical analysis and experimental methods for its dynamic support stiffness and bearing friction loss,which are two important dynamic characteristics,were emphatically studied.In addition,the experimental loading methods of the HSMS were studied,which improved the comprehensive performance test technology of the HSMS.The main work is as follows:The experimental methods and testing techniques for the performance and operation quality of HSMS were studied,including an experimental scheme was proposed for the detection of comprehensive performance indexes such as output characteristics,electromagnetic characteristics,dynamic support stiffness,temperature rise characteristics and rotation characteristics of the HSMS.In order to test the comprehensive performance of the HSMS,an advanced HSMS and its supporting subsystem were developed independently.Two novel loading methods were proposed for the problem of dynamic loading of HSMSs.Finally,an experimental platform for the HSMS system and its comprehensive performance test system was built,which provided an experimental basis for subsequent research.Based on the quasi-static model of the ball bearing,the numerical simulation of the internal dynamic state of the bearing was completed.On the basis of solving the basic dynamic parameters of each rolling element,the solution method of the dynamic support stiffness of the assembled bearing in the HSMS was studied.The influence of radial force on the radial/axial/angular stiffness of the bearing was discussed.A contact loading device with a cylinder as an actuator and a rolling bearing as a separator was developed,and the experimental data analysis method was studied to realize the measurement of bearing dynamic support stiffness under high-speed.Finally,through the combination of the theoretical model and experimental detection,the influence of rotational speed and radial force on the dynamic support stiffness of the bearing was analyzed.Aiming at the problem that the HSMS produces severe heat under high-speed conditions,theoretical models of bearings friction loss were established.Two direct and quantitative methods were studied to measure the frictional loss of bearings: the free-deceleration method and the energy-balance method.The experimental results show that the viscous resistance loss is a major component of bearing friction loss even under the condition of oil-air lubrication.A comparison of the theoretical calculations and the experimental results was used for deriving the empirical formula of lubricant volume percentage in the bearing cavity with respect to the lubricant flow,gas pressure,rotating speed and pitch diameter,which characterizes the influence of oil-air lubrication parameters on bearing friction loss.The optimal lubricant flow was determined,the effectiveness of a novel preload online adjusting device was verified and the importance of the viscosity-temperature relationship of the lubricant and the thermomechanical coupling factor on bearing friction loss was revealed through experiments.The research results are of great significance for the prediction,measurement and reduction of friction loss of high-speed bearings.Aiming at the problem of dynamic torque loading during high-speed rotation of HSMS,based on the rheological behavior of the magnetorheological fluid,a novel high-speed dynamic loading system for an HSMS was designed,fabricated and tested.The working principles and structure of this loading system are described.The torque model of the loader was derived based on the constitutive equation and simulation calculation of magnetic induction intensity through 2D static electromagnetic field analysis by Maxwell software.In addition,the torque-current relationship under different speeds was measured through experiments,and we found nonlinear relationships between the viscosity and shear stress of the magnetorheological fluid with the shear rate.The Herschel–Bulkley model was corrected by fitting for the experimental results.The loading torque,calculated by the modified model,conformed with the experimental results.This lays the foundation for the design of a high-speed transmission device based on the magnetorheological shear principle.Finally,the loading performances of the loading system such as torque stability,temperature stability and reusability were experimentally studied,which verified the feasibility and correctness of the loading system.It provides a novel method to test the dynamic performance of HSMSs under load.To solve the problem of dynamic diameter/axial loading of HSMS,a flexible loading system based on high pressure water jet was designed,manufactured and tested.A jet's impact force model was derived based on the continuous momentum equation.Through finite element simulation of the fluid and calibration tests of the jet's impact force,the relationships between target distance,injection pressure,flow rate,nozzle diameter,target diameter,rotational speed and impact force were obtained,which realized the quantitative loading of HSMS.In addition,the dynamic performances of the HSMS loaded with high-pressure water jet were tested.The experimental results show that 1)high-pressure water jets can provide stable long-term loading for the HSMSs,and 2)loading increases the temperature,power consumption and vibration of HSMSs and no-load test can not reflect the true working condition of the HSMS.It provides a reliable experimental method for the study about the operation quality of HSMS.