Analysis And Optimization Design Of Electric Spindle Based On Stiffness Calculation Of Ball Bearing

Electric spindle technology has been developed along with the development and demands of modern manufacturing technology such as high-speed grinding and high-speed CNC machine tools. As the power and speed of electric spindles growing higher and higher, the electric spindles with high speed are used more and more widely in many machine tools. The working speed of an electric spindle usually approximates its first critical speed, which makes it necessary to analyze the dynamic performance of an electric spindle such as natural frequency and critical speed.On the basis of analyzing the internal static and dynamic behavior and stiffness with theories and methods about ball bearing, a parameterized finite element model of the bearing-rotor system is established on ANSYS. Choosing the static stiffness as optimization goal, the structure of electric spindle is optimized. According to the optimization results, the structure of the electric spindle becomes more compact, and the critical speed is increased as well. Therefore the vibration characters of spindle, especially those within the first critical speed are improved.The geometric relationship, contact stress and deformation and load distribution of ball bearings are introduced based on Hertzian contact theory. Taking angular contact ball bearing as research object, stress and deformation under radial, axial, axial preload and the combined load are analyzed. Then, the static stiffness is calculated. Taking centrifugal force, gyroscopic moments and internal friction into consideration, the internal dynamic states and dynamic stiffness of high-speed angular contact ball bearings are analytial calculated.Based on the stiffness calculation results of ball bearings, a parameterized finite element model of the bearing-rotor system is established on ANSYS. Choosing the static stiffness of electric spindle as the optimization goal, support span and motor installation location are optimized. Modal analysis of the electric spindle system before and after optimization is carried out, by doing so, the static stiffness increases by 7.81%. Then, the first three natural frequencies and modes of vibration are compared, the result shows the first nature frequency increases by 1.93% . A three-dimension modal analysis of electric spindle is carried out too, which makes the first five vibrational modes more intuitively.