Dynamic Characteristics And Structural Optimization Of Gas Bearing-rotor System Under Fluid-solid Coupling

The processing quality of parts in high-speed milling depends largely on the dynamic characteristics of the spindle and the smoothness of the system.Under high-speed operation,there is a strong coupling between the gas film flow field of the electric spindle supported by the gas bearing and the rotor.In order to meet the development needs of high-speed precision machining,the coupling analysis of high-speed gas bearing-rotor systems under different load excitations and various working conditions is particularly important.Taking the gas bearing-rotor system as the research object,the high-speed'bearing-rotor system supported by the static pressure gas bearing is carried out in the milling process of the gas film flow field and the rotor displacement dynamic response,the rotor axis trajectory and the flow field pressure change.Based on the fluid-structure coupling method,the rotor axis trajectory and dynamic characteristic coefficient change laws at different speeds are analyzed.The CFD numerical modeling of the model and the derivation of the N-S equation are used to analyze the axis trajectory and frequency spectrum of the bearing-rotor system,combined with the dynamic characteristic coefficient of the bearing.The results show that the rotor fluctuation range and axis trajectory are greatly affected by the speed.When the system rotates at 20000r/min,obvious eddy phenomenon occurs,the axis trajectory begins to diverge,the rotor reaches the resonance frequency,and the stability of the bearing becomes worse.The three-dimensional modeling method of CFD numerical calculation,partition and local densification are used to study the change trend of the dynamic characteristic coefficient and the distribution law of the flow field of the whole bearing rotor system under different stepping loads.Compared with the steady-state stepping force,the transient stepping force under preload can significantly reduce the rotor overshoot,the rotor's stabilization time is also shortened.The reason is that under the transient stepping load,before 10ms,the load has made the rotor system flow field and solid field reach a coupling balance.At this time,the gas film has a certainringidity,and the system also has a certain load resistance.Based on the small orifice throttling gas bearing,the bearing capacity and stiffness are taken as the optimization objectives to optimize the structural parameters of the bearing,such as the circumferential position of the orifice,the hole diameter and the number of holes.The results show that the bearing capacity and stiffness of the aerostatic bearing with small orifice are increased by 60%and 15%,respectively.The fluid structure coupling simulation of the bearing rotor system supported by the gas bearing with two throttling forms of torus and pinhole throttling is carried out.The numerical analysis results show that the bearing capacity of the bearing rotor system supported by pinhole throttling is significantly improved.A gas bearing-rotor system characteristic test experimental platform was built,and the gas bearing-rotor system was tested under different working conditions.Firstly,the non-contact loading method is used to obtain the rotor displacement change rule under the static and different rotating speeds of the electric spindle,and the results are compared with the simulation results;secondly,the milling test is performed on the processed sample to obtain the law of the transient change of the milling force.