Static And Dynamic Characteristics Analysis On The Spindle System Of NC Lathe

The spindle system as a very important component of lathe is directly involved in the lathe turning,and its static and dynamic characteristics have a great influence on the cutting stability and machining accuracy.Studies of bearing stiffness and effect parameters are relatively lack.Spindle system lacks comparative research on methods.Although the traditional theoretical model contains most of the factors,it is still relatively isolated among the factors,without taking into account the coupling of the interaction between them.Based on the deficiencies in the current study on spindle system of NC lathe,the paper has finished following research work in according to certain type of NC lathe.(1)The static analysis model is established through the cylindrical roller bearing inner ring balance equation.Based on the analytical mechanics theory and Hertz contact theory,the paper establishes the contact stiffness model of cylindrical roller bearing,through the interaction of roller and ring,has established the balance equation of the roller and bearing inner ring and derived the four degrees of freedom dynamic equation of cylindrical roller bearing,and derives the dynamic stiffness model.By iteration method,double row cylindrical roller bearing static load distribution decays to both sides by the center line of the half angle of contact and outside of half angle is 0,the geometric parameters(the roller number,radial clearance)and physical parameters(load)affect the static load distribution by the half angle of contact and maximum contact load;Dynamic load fluctuates over time periodically,the load-bearing area is half sine form approximately,the outside of load-bearing area is 0.Radial clearance,the roller number and the load have a greater influence on the dynamic load distribution.Rational speed has less effect on the dynamic load distribution.Double row cylindrical roller bearing radial static stiffness is nonlinear,load and roller number can improve the static stiffness,radial clearance can reduce the static stiffness,The odd even pressure and single double row also have some influence on it;Dynamic stiffness fluctuates over time and presents periodicity,and the low peak appears between two adjacent high peaks concomitantly,and two peaks appears respectively in the contact zone where odd and even number rollers present symmetrical arrangement.Geometrical and physical parameters have influence on dynamic stiffness,and load,roller number and radial clearance have a greater influence on the mean and volatility of bearing dynamic stiffness,and rational speed has less effect.Moreover roller number and rational speed determines the fluctuation frequency of bearing dynamic stiffness,and roller number and radial clearance have a significant effect on mutation point and mutation peak of dynamic stiffness.(2)Based on the empirical formula multi-parameter axial static model of angular contact bearing is established under the axial load.Through the establishment of mathematical model influence of multiple parameters on radial clearance of angle contact ball bearing,the paper establishes five degrees of freedom inner ring balance equation according to the bearing deformation geometry relationship,and derives the dynamic stiffness model of the angular contact ball bearing.Through MATLAB simulation,load of angular contact ball bearing distributes uniformly along the circumference under axial force,and axial load,the ball number,and contact angle affect the static load distribution directly.Axial static stiffness of angular contact ball bearing is also nonlinear,the initial radial clearance,load and ball number are helpful to improve bearing static stiffness,and channel curvature radius coefficient can reduce its value.(3)Considering the effect of shear deformation,the paper uses finite element method to establish spindle system model of NC lathe and reflects the stiffness characteristics of the roller bearing in dynamic equations.Based on the finite element method and transfer matrix method,the paper uses SAMCEF and MATLAB software to calculate the natural frequency,critical speed and natural modes of spindle system.The paper also accomplishes harmonic analysis,transient dynamic analysis on the basis of the spindle system stiffness analysis.Results of the finite element method and transfer matrix method are equal within tolerance limits,and the critical speed is much greater than the operating speed.Thus the spindle does not resonate.Resonance occurs in the natural frequency from the spindle displacement response curve and amplitude-frequency characteristic curve of key locations.The basic trend of the spindle bearing position transient response curves is that displacement decreases rapidly after increasing slowly.Track of spindle center is a peripheral area,and the edge fluctuates.The paper obtains dynamic strength distribution of spindle in energized position.it presents the trend that the middle strength is maximum,both sides gradually reduced.In summary,the theoretical model of spindle system established is effective.