Dynamic Characteristic Analysis And Reliability Robust Design Of Electric Spindle

As one of the key parts of high grade NC machine tool,the performance of the electric spindle not only directly determines the surface quality of the workpiece,but also affects the production efficiency,stability and reliability of the machine tool.Generally,the electric spindle is mainly used for high-speed cutting,so there is a great demand for the angular contact bearing.As the rotating speed increases,the contact stress between the bearing ball and the raceway will also increase.When the rotating speed increases to a certain extent,the operating speed of the electric spindle is close to its natural frequency,it will generate resonance phenomenon.In particular,when the working speed is within a certain range,the front part of electric spindle is deformed due to the influence of cutting force.If the deformation exceeds a certain threshold,it will have a certain impact on the machining accuracy of the part.In addition,considering the bearing and the structure of the spindle size and material parameters in the process of manufacturing or processing has certain volatility,the random factors of motorized spindle caused certain effect on each failure modes,so it is necessary on the basis of the analysis of dynamic characteristics of motorized spindle,considering frequency reliability of motorized spindle bearing,strength reliability and stiffness reliability,combining with the results of the analysis to do the robust design.Its main work content is as follows:(1)Based on hertzian theory and outer raceway control theory,a quasi-static model of angular contact ball bearing is established to analyze its static and dynamic characteristics,focusing on the influence of bearing structure parameters,material parameters,working speed and preload force on its radial and axial stiffness.(2)Using motorized spindle of simplified parameterized modeling and importing it into Workbench.Using spring instead of bearing and carry the whole model on modal analysis and harmonious response analysis.Using the DOE module to simulate the influence of random factor in order to obtain the inherent frequency and stiffness of motorized spindle system.Finally,using the transfer matrix method to validate the result of the finite element.(3)Through simple screening of all random variables through local sensitivity values in the Workbench,the genetic BP neural network was used to fit the functional relationship between the natural frequency and spindle stiffness of the electric spindle system,bearing stiffness,spindle structure size and material parameters.By using the same method,the function relation between the maximum shear stress under the contact surface of bearing ball and the inner and outer ring raceway and bearing structure size and material parameters is fitted.Corresponding bearing strength,spindle natural frequency and spindle stiffness function are established and reliability sensitivity analysis is conducted.(4)Based on robust design theory,the mathematical optimization model was established,with the quality and reliability sensitivity of the electric spindle system as the objective,and the upper and lower limits of random variables,bearing strength reliability,natural frequency reliability of the electric spindle and the lower limits of the stiffness reliability of the spindle as the constraint conditions,conducting the optimization solution by MATLAB.This paper mainly uses the reliability knowledge to carry on the reliability robust design to the system regarding the motorized spindle three main failure forms,emphatically studies the bearing main structure parameter,the material parameter,the pre-tightening force and the work speed influence to the motorized spindle system.It has certain reference value to the motorized spindle design.