Research On Key Technology Of Enbironmentally Friendly Watet Based Dynamic For CNC Machine Tool Spindle

Motorized spindle is the core component of high-speed and high-precision CNC machine tool,and it is also the key component of high-end machine tool which combines bearing and motor.Its comprehensive performance is restricted by the bearing capacity,stability and rotation error of bearing.In order to meet the major application requirements of high-speed grinding CNC machine tools in China,this paper focuses on several key scientific issues such as lubrication medium,load-bearing performance,stability and rotation accuracy of high-speed water-based hydrodynamic bearingA new type of water-based lubricant with controllable viscosity and stable lubricity was developed by using water as base fluid,green hydroxypropyl methyl cellulose,sodium carboxymethyl starch,propylene glycol and triethanolamine oleate as water-based additives.It is found that the wear depth and wear width of the water-based lubricant are greatly reduced when the mass percentage of graphene oxide nanoflakes is 0.5%compared with that of water.Both numerical calculation and finite element simulation show that the bearing capacity and stability are effectively improved,while the temperature rise of the lubricant is not high and the performance is good.According to the requirements of high-speed,precision and stable operation of motorized spindle,the numerical analysis software of water-based hydrodynamic bearing is developed by using the theory of fluid lubrication.The load-bearing performance of hydrodynamic bearing is calculated and analyzed under different arrangement areas of surface texture,micro pit diameter,micro pit depth and area ratio.The influence of spindle deflection and machining error on the load-bearing performance of water-based hydrodynamic bearing is revealed.The analysis shows that reasonable arrangement of surface texture can effectively improve the bearing capacity of hydrodynamic bearing,and effective measures to prevent spindle deflection can reduce the decline of bearing capacity,Thus,the processing accuracy,roundness and cylindricity error are reduced and the bearing capacity is improved.The Reynolds equation is improved by using Poiseuille's law,and the dynamic characteristic mathematical model of hydrodynamic bearing with active fluid supply is established.The dynamic characteristic coefficient,critical mass and critical velocity of hydrodynamic bearing are calculated.Compared with ordinary hydrodynamic bearing,the critical velocity of hydrodynamic bearing increases exponentially and the dynamic characteristic coefficient changes little.The numerical analysis shows that the increase of cross stiffness,which is unfavorable to the stability,can be restrained by arranging the pressurization holes,and the stability of the hydrodynamic bearing can be effectively improved,so that the hydrodynamic bearing can operate stably at a higher speed.Based on the Reynolds equation,the dynamic kinematics model of the hydrodynamic bearing spindle system is established,and the trajectory of the axis motion is simulated and analyzed.It is found that there is a stable region in the range of the axis motion of the hydrodynamic bearing.In the stable region,the spindle can return to the original equilibrium position after being disturbed,but outside the stable region,the spindle can not return to the original equilibrium position after being disturbed.In order to verify the feasibility of numerical simulation,the experimental platform of motorized spindle supported by water-based hydrodynamic bearing is built,and the measurement and control system developed by Ni is used to complete the non-contact measurement of spindle rotation accuracy.The real-time measurement of the radial rotation error of the spindle is realized under different liquid supply pressure,bearing clearance and bearing speed.Through experimental analysis,it is found that the hydraulic pressure,bearing clearance and bearing speed can affect the rotation accuracy of motorized spindle.The higher the bearing speed is,the closer the spindle rotation center is to the geometric center of the bearing bush,and the higher the rotation accuracy is.By comparison,the maximum difference between the measured results and the simulation prediction results is 0.3 ?m,and the average relative error is 13%,which verifies the correctness of the simulation prediction model and proves that the simulation method of water-based hydrodynamic bearing can realize the accurate prediction of the rotation accuracy of motorized spindle.