Research On Service Performance Prediction Of Spindle Bearings Under Variable Condition Preload

High speed,high precision and high reliability spindles are the demand of the extreme development of high-speed machining equipment,and the thermal deformation of the shaft caused by the temperature rise of the bearing under service conditions directly affects the machining accuracy and service life of the spindle.The intelligent development of the spindle requires that the spindle has good dynamic performance and thermal characteristics under the variable conditions of low speed and heavy load,medium speed and medium load,and high speed and light load.The preload is the key to affect the stiffness,life,temperature rise and other service performance of bearings.At present,the preloading method and preload provided by the spindle manufacturer only ensure the bearing to have good service performance under a single working condition.This paper proposes a method to control the temperature rise of the spindle bearing at different speeds by actively adjusting the preload and to ensure other good service performance,which has the characteristics of flexible application,low cost and small change of spindle structure.Aiming at this method,the improvement of analytical algorithm for contact parameters of high-speed angular contact ball bearing,the contact state and service performance of the bearing under variable conditions,the thermal mechanical coupling modeling and preload optimization are studied as follows.(1)The analytical method of contact state parameters of high speed angular contact ball bearing is researched based on improved Newton-Raphson algorithm.A quasi-static model of high-speed angular contact ball bearing is established based on Hertz contact theory.Aiming at the problems of the traditional Newton-Raphson algorithm in solving the contact parameters of high-speed angular contact ball bearings,such as the difficulty of determining the initial value and the difficulty of convergence in the iterative process,the intermediate variables are introduced in the numerical solution process to reduce the number of unknowns and step-by-step solution is carred out to make the selection of the initial values of the nonlinear equations more clear.The iterative correction factor is introduced into the improved Newton-Raphson algorithm,and the genetic search strategy is used to optimize the iterative correction factor,which improves the accuracy of the solution and shortens the convergence time.Through the matrix transformation,the solution process of Jacobian matrix is simplified.Compared with the traditional algorithm,the improved Newton-Raphson algorithm is simpler and more efficient.The effects of raceway ovalization,outer ring inclination and preloading mechanism on the nonlinear variation of contact parameters of high speed angular contact ball bearings are analyzed by using the improved algorithm.(2)The bearing contact state and service performance under variable operating conditions is researched.In order to further improve the prediction accuracy and robustness of bearing mechanical model,a unified mechanical model of the bearing is constructed according to the force characteristics of balls and inner raceway in contact and non-contact states.The influence law of radial force,preload and speed on the change of the number of balls in contact with the inner raceway is revealed.The mathematical description of bearing stiffness and life is established,and the change law of bearing dynamic stiffness and life under the change of contact state is explored.Based on the kinematic characteristics between the ball and raceway,the mechanism of bearing friction heat generation is analyzed,and the analytic equation of bearing local friction heat generation is established,heat generation of the bearing under different working conditions is quantified.The results show that the larger radial force,the smaller preload and the higher speed make part of balls separate from the inner raceway.With the increase of preload,the number of contact balls increases,which lends to a sudden change in the bearing radial stiffness,and the bearing life increases first and then decreases.The increase of preload and speed results in the increase of bearing heat generation.Therefore,the appropriate preload can make the bearing obtain good service performance.(3)The bearing thermal-mechanical coupling modeling under the influence of multiple factors is research on.In view of the coupling characteristics of thermal and mechanical properties of the bearing under operating conditions,based on the quasi statics theory,the centrifugal effect and thermal effect are considered to establish the thermal-mechanical coupling correction model of the fixed position preload bearing under the influence of multiple factors.The thermal network model is used to solve the temperature field of the bearing,the dynamic parameters of the bearing is identified.The coupling relationship between the bearing structure size,contact parameters and temperature rise is explored,and the influence of various factors such as preload and speed on the temperature rise of the bearing is revealed.The temperature rise test results of the bearing under fixed position preload show that the proposed model has good accuracy and reliability,and the temperature field of the bearing under different working conditions can be effectively obtained by the method in the article(4)Optimization of bearing preload is researched.In practice,the spindle needs to meet the processing requirements of low-speed heavy-duty,high-speed light-load and other multi-working conditions.However,the pre-set preload of the spindle bearing cannot meet the comprehensive requirements of bearing service performance under variable working conditions.To sovle this problem,the optimization strategy of bearing preload with stiffness,life and temperature rise as constraints at different speeds is proposed.In order to ensure the stiffness,life and temperature rise data of the bearing at different speeds are equivalent and in the same order,all kinds of data are normalized.The normalized data of the bearing stiffness,life and temperature rise are fitted into the curve using polynomial fitting and power function fitting methods.Based on the multi-objective optimization theory,the optimization model of preload is established according to the efficiency coefficient method.The adjustable preload loading device and bearing preload and temperature rise test platform are designed.Simulation and experimental results show that the optimized preload can not only meet the comprehensive requirements of bearing stiffness and life at different speeds,but also ensure that the temperature rise of the bearing is within the appropriate range.The proposed method provides theoretical guidance for the preload optimization of spindle bearing under variable conditions,and provides an idea for the subsequent study of spindle bearing temperature rise control,which has reference significance.