Study On The Static-dynamic-thermal Characteristics Of Spindle Of Machine Tool And Its Effects On Deformation

As the core component of machine tools, the performance of the spindle is the key factor which restricts the improvment on machining efficiency and accuracy. The contact deformation and contact stiffness of the spindle are affected by preload, initial deformation conditions, they will be changed according to with the changing of the rotating speed and frictional heat. It is obvious that the stiffness is the key parameter to determine the dynamic characteristics of the spindle unit. Therefore, the deformation is an important factor throughout the above characteristics. The deformation for the main thread and the stiffness for the bridge to study on the coupled static characteristics, dynamic characteristics, thermal properties and its effects on deformation is a significant subject for theory and engineering. In this paper, based on the interference contact theory, heat transfer theory, rolling friction theory and rotor dynamics, taking the mechanical spindle as the object and reducing the deformation and improving the dynamic characteristics as the goal, the modeling theories method of preload- contact load- rotation speed- temperature gradient-stiffness and natural frequency of the spindle is established, analyzed and verified by experiments. The creative results are obtained as follows:Based on Hertz contact theories, the proposed dynamic analysis model of the bearing is established, the relationship among preload, the contact load, the contact angle, the friction torque and frictional heat, the radial and axial displacement, the radial and axial stiffness of the bearing under static and high-speed operation is discussed.The tribology and heat transfer theories are applied for the establishment of the heat transfer model. The effect of the speed, preload, kinematic viscosity and other parameters on the friction torque is analyzed, and the Impedance and equation of heat transfer are derivated.Based on the interference theory, the coupled deformation model of bearing and spindle with the preloaded interference deformation, the thermal deformation and the centrifugal force under high-speed operation is estabished, and the effect of the coupled factors on the deformation of the inner and outer channel, the contact load on the stiffness is discussed. And a simplified heat balance equation is established, the effect of the thermal deformation to the bearing clearance is studied, as well as the changing of ball and channel.The double rotor dynamics model of a mechanical spindle unit is established and analysed by rotor dynamics theory and the overall matrix transfer method. Bearing span’s effect on the the first natural frequency of spindle is obtained. Meanwhile, the relationships of preload and the stiffness, the temperature gradient and the contact stiffness are introduced in the transfer matrix to correct the coupled dual rotor dynamics model with static and dynamic thermal characteristics, which is used to analyze the effect of the preload and temperature variation on dynamic characteristics of the spindle.The deformation law of the belt spindle, considering the combined effects of thermal deformation, bending moment and torque, is analyzed based on the mechanics of materials and elasticity. Three running phases of belts spindle have been analyzed and modeled: start-up phase with leaping change because of changing of force and bending moment, accelerating stage with axis deflection, constant speed stage with axis regression.The experiment platforms for testing static and dynamic, thermal characteristics of spindles are built. Some experiments have been processed, including thermal characteristics testing, experiments about motion track of belts spindle under the combined effects of bending moment-torque-thermal deformation, the effects from thermal deformations to the stiffness and natural frequency of the spindle, and so on. All these experiments illustrate that the rationality and validity of the above-mentioned theories, methodologies and models.This dissertation reveals the coupling effect of the static, dynamic characteristics and thermal characteristics, and it’s effcet on the spindle’s comprehensive characteristics including deformation law, the results are of great value in theory and engineering.