Analysis Of Vibration Characteristics Of Ultra-high Speed Grinding Electric Spindle Under The Action Of Magneto-thermal

High-speed electric spindle is one of the key components of ultra-high-speed grinder,and its vibration characteristics directly affect the grinding accuracy of the machine tool.When the electric spindle is working,the internal temperature rise will cause changes in the material properties of the built-in motor windings and permanent magnets,which will change the electromagnetic losses and affect the temperature field of the electric spindle.The unbalanced electromagnetic force produced by thermal deformation will aggravate the electromagnetic vibration of the electric spindle,and further affect the machining accuracy of the electric spindle.Therefore,it is of great significance to study the vibration characteristics of the electro-spindle under the action of magneto-thermal coupling.This article takes the ultra-high-speed grinding electric spindle as the research object,first considers the temperature characteristics of the built-in motor material,and uses the two-way coupling method for magneto-caloric analysis,thereby improving the accuracy of the temperature field analysis of the electric spindle.Then the influence of the temperature field on the thickness of the air gap is analyzed,and the unbalanced electromagnetic force of the permanent magnet of the rotor is obtained,and then the vibration characteristics of the rotor-bearing system of the electric spindle under the action of the unbalanced electromagnetic force are studied.The main research contents of the thesis are as follows:(1)The theoretical calculation method is used to calculate the heat source loss and thermal boundary conditions of the grinding electric spindle in this paper.The temperature characteristics of the built-in motor materials are studied,and the resistivity of the winding copper wires and permanent magnets is calculated.Use ANSYS Workbench and Maxwell to establish the magnetic and thermal bidirectional coupling analysis model of the electric spindle,and obtain the temperature field distribution of the built-in motor winding,permanent magnet and stator respectively.(2)Through experiments,the temperature rise of the winding end,front and rear bearing outer ring,front end cover,rear end cover,and shell are measured respectively,and the temperature change curve of each part with time is obtained.It can be obtained by comparing the temperature of the winding end of the built-in motor obtained by unidirectional coupling analysis,bidirectional coupling analysis and experimental measurement,and the results obtained by bidirectional coupling analysis are closer to the experimental values.On this basis,the temperature of the outer ring of the front and rear bearings,the front end cover,the rear end cover and the shell obtained from the fifth two-way coupling analysis are compared and analyzed with the corresponding experimental values,which further proves the magnetic-thermal coupling finite element of the grinding electric spindle system The validity of the model.(3)Establish the thermal-structure coupling model of the electric spindle,use the temperature field of the electric spindle obtained by the magnetic-thermal bidirectional coupling analysis as the heat source load,analyze the change of the thickness of the air gap between the stator and rotor of the built-in motor,and obtain the deformation of the permanent magnet of the rotor relative to the stator the amount.Based on the thermal deformation of the permanent magnets of the rotor,a Maxwell 3D electromagnetic field analysis model is established,and the unbalanced electromagnetic force caused by the thermal deformation of the permanent magnets of the rotor is studied.(4)Calculate the stiffness of the bearing at different temperatures,and use ANSYS Workbench to perform a simulation analysis of the restrained modal and harmonious response of the rotor-bearing system,and obtain the first six-order mode shape and natural frequency of the rotor-bearing system at different temperatures..The modal test analysis of the rotor-bearing system is carried out at different temperatures to further verify the accuracy of the finite element model of the rotor-bearing system.Then,considering the magnetic-thermal coupling effect of the electric spindle system,the vibration response at the front end of the spindle,the front bearing,the permanent magnet and the back end of the spindle are respectively studied.