Effection Of Angular Misalignment On Heat Generation And Life Of High-speed Spindle System

The spindle is a key part in the high-speed CNC machine tool,and driven by the motor directly.Due to the omission of the intermediate transfer process,the spindle can be used at very high-speed condition.The fatigue life,wear and heat generation of bearing can affect the service life of the spindle system.Generally,the spindle is supported by multiple bearing,and its structural characteristics lead to the mutual influence and constraint between bearings and bearings or between bearings and spindle in terms of load and deformation.In order to evaluating work performance of bearing reasonably,it is necessary to analyze the bearing from the perspective of the whole spindle-bearing system.Therefore,based on the high speed spindle-bearing system,the problems of bearing fatigue and heat generation are studied in the following parts:(1)A numerical analysis model of spindle-bearings system capable of including any number of ACBBs was proposed in this paper.The shear effect was considered,and the spindle was modeled as Timoshenko's beam.In addition,the bearing was modeled by quasistatic method,and the centrifugal and the gyroscopic moment for angular contact ball bearing were especially taken into account,and the effect of axial preload and angular misalignment caused by the installation on the spindle-bearing was also considered.Moreover,A fast and reliable calculation strategy was developed to solve system modeld.(2)In order to ensure the maching accurary,suitable axial preload applied to ball bearing is necessary to increase bearing stiffness and suppress the spindle-bearing system vibration.In addition,for spindle-bearing system,the bearing angular misalignment is a inevitable phenomenon in practice application due to inaccurate mounting.Taking the two bearingsspindle system and three bearings-spindle system as the objective respectively,the effect of axial preload and angular misalignment on the ball-raceway contact forces and fatigue life of bearing in the spindle-bearing system were evaluated under the complex working conditions.The results showed that the influence of preload and angular displacement on the contact load and fatigue life of bearings in the system is related to the mounting position and arrangement of bearings.The multi-bearing bearing shaft is beneficial to improve the stiffness of the spindle,achieve high precision operation and improve system life.(3)The allowable error range of angular misalignment caused by the installation has been sprcified in the bearing manual,however,the angular misalignment distribution meeting the requirements will affect the fatigue life dispersion of angular contact ball bearing in multiple bearings-spindle system.The angular misalignment is assumed to meet the normal distribution,based on monte carlo sampling method,angular misalignment samples of bearings can be obtained,Taking the variable preload multiple bearings-spindle system as the objective,the contact forces for each bearing in multiple bearings-spindle system considering these angular misalignment samples are evaluated for the high speed lightly loaded and low speed highly loaded conditions by the presented system model.The fatigue life is assumed to follow the lognormal distribution,and the probability density distribution can be determined.The results showed that the angular misalignment has a significant influence on the contact and motion parameters of the ball of the bearing from the perspective of the whole spindlebearing system.There was a complex coupling relationship between these parameters,which leads to a significant difference in the lognormal fatigue life distribution of bearings.(4)The heat generation model was established,and taking the variable preload multiple bearings-spindle system as the objective,the effect of the angular misalignment of bearing outer-ring and spindle speed on the heat generation are evaluated for the high speed lightly loaded conditions.The results showed that the friction caused by the grease viscosity is the main heat source of the bearing,and the spindle speed has a significant influence on the total heat production of the bearing.In addition,the heat generation is affected by many factors,thus the bearing heat problem should be analyzed from the perspective of spindle-bearing system.