Friction And Dynamic Characteristic Study Of Rotor Bearing System Of Motorized Spindle Under Oil-air Lubrication

As a key component of CNC machine tool,the thermal characteristics of the bearing and the dynamic characteristics of the spindle system directly affect the machining accuracy and reliability of mechanical equipment.At present,the theoretical research and experimental analysis of the bearing friction performance and the vibration characteristics of the spindle system caused by lubrication and preloading are insufficient.Taking the rotor bearing system of highspeed motorized spindle as the research object,this paper studies the friction and wear characteristics of point contact pair,fluid solid coupling heat transfer analysis of bearing and dynamic behavior of rotor bearing system under different working conditions by combining theoretical analysis and experimental research.The results are as follows:(1)Experimental study on friction characteristics of point contact pair under different working conditions.The tribological properties of GCr15 ball/GCr15 disk material were studied by ball disk friction test method.The results show that compared with grease lubrication and oil lubrication,oil-air lubrication can effectively reduce the bearing temperature rise,and the friction coefficient is the smallest.Under oil-air lubrication,the friction coefficient increases and then decreases with the increase of load,and the speed and air supply pressure have little effect on the friction coefficient;The width and depth of wear mark under oil-air lubrication are the best;With the increase of rotating speed,the wear mark depth increases gradually,while with the increase of load,the wear mark depth increases first and then decreases.Therefore,the antifriction and antiwear performance of point contact pair under oil-air lubrication is relatively good.The minimum bearing friction torque measured by the bearing friction torque test platform is 0.95 N·mm,and the peak value of bearing friction torque mainly occurs near the rotation frequency.The friction coefficients of bearings under grease lubrication,oil lubrication and oil-air lubrication are calculated as 0.0024,0.0016 and 0.0015 respectively,which provides a basis for the selection of dynamic model parameters of rotor bearing system.(2)Study on fluid solid coupling heat transfer characteristics of motorized spindle bearing under oil-air lubrication.Based on the theory of elastohydrodynamic lubrication,numerical analysis model of oil-air two-phase flow heat transfer in bearing cavity is established to analyze the influence of different working conditions on bearing temperature field.The results show that the increase of rotating speed leads to the increase of heat generation,and the increase of air inlet speed significantly reduces the bearing temperature rise.When a single nozzle is used,the bearing temperature gradually increases from the inlet area to both sides,and reaches the highest on the opposite side of the inlet;when multiple nozzles are uniformly distributed,the temperature distribution tends to be consistent,and the effect is better when the number of nozzles is 2.With the increase of nozzle diameter,the oil-air velocity decreases,and sufficient heat exchange can be carried out in the bearing cavity to take away more heat and reduce the temperature rise.The validity of the numerical model is verified by the performance test of B7008 bearing,which provides a basis for the selection of the optimal parameters of the oil-air lubrication system of high-speed bearing.(3)Study on dynamic characteristics of motorized spindle rotor bearing system under bearing friction.A mathematical model considering the effect of friction is established for the rotor bearing system of motorized spindle,the Runge-Kutta method is used to solve the nonlinear dynamic response of the rotor bearing system of motorized spindle,and the influence of different lubrication methods on the amplitude of the system is analyzed.The results show that the amplitude of the spindle system increases with the increase of the rotating speed,and the amplitude increases slowly in the range of low rotating speed,and faster in the range of high rotating speed;The amplitude of spindle system under oil-air lubrication is less than that under oil and grease lubrication.The research shows that under different lubrication modes,the friction coefficient and system amplitude under oil-air lubrication are the smallest.(4)Study on nonlinear dynamic characteristics of motorized spindle rotor bearing dynamic system considering mass eccentricity.The nonlinear dynamic model of rotor bearing system supported by rolling bearing is established,the nonlinear dynamic response of the system is obtained by numerical integration method,and the effects of speed,stiffness and preload on the dynamic response of the system are analyzed.The results show that the increase of rotating speed makes the system appear alternately between periodic motion and chaotic motion,and the amplitude of the system increases.Properly increasing the preload can make the system in periodic motion and reduce the amplitude of the system.The numerical results are compared with the experimental results to verify the reliability of the model.Based on Melnikov method,the mathematical expression of possible chaos in motorized spindle rotor bearing system is given,and the corresponding chaotic threshold is calculated from the actual parameters.The value of control parameters can be determined according to the edge of chaos,so as to avoid the blindness of control parameter selection.It has important theoretical and practical guiding significance for mastering the mechanism of chaotic motion and chaos control of motorized spindle rotor bearing system.