Theoretical Study On Variable Preload Of Motorized Spindle Based On HT17-24000-30 Grinding Machine

As the key component of CNC machine tools,the motorized spindle directly affects the machining accuracy and stability of the machine tool.The bearing preloading technology is the key technology of the motorized spindle and has an important impact on the performance motorized spindle.In actual production,due to the single preloading method of the bearing and the lack of theoretical basis of the bearing preloading,the motorized spindle usually only meets the single performance requirements of high-speed machine tools.In order to achieve the low-speed heavy cutting and high-speed light cutting function requirements of the high-speed machine tool low-speed heavy cutting and high-speed light cutting function,to achieve a high-efficiency spindle system,a variable bearing preloading technology is needed to determine the preload required for the machine tool spindle under different working conditions,and the preload should be applied to the bearing by a modulating preload application.In this paper,the HT17-24000-30 variable preloading motorized spindle was taken as the research object.By establishing the quasi-static model of the rolling bearing with thermal displacement,the bearing preload of the high speed machine tool spindle under different preloading modes was analyzed.Secondly,the finite element model of motorized spindle temperature field was established.The coupling relationship between bearing preload and bearing temperature rise and thermal displacement under different axial preload and speed conditions were studied.The coupling relationship between bearing preload and bearing temperature rise and thermal displacement under different axial preload and speed conditions was studied.Then the dynamic stiffness of the rolling bearing considering the bearing thermal displacement,different rotating speed and preloading force was calculated,and the finite element model of the motorized spindle rotor system was established based on the stiffness variation.The effects of bearing preload and speed with the dynamic characteristics of the motorized spindle system were studied by modal analysis.Finally,the HT17-24000-30 variable preloading motorized spindle was tested for temperature rise and vibration under different preload and speed.The influence of pre-tightening force on the temperature and vibration of the motorized spindle is obtained,and a method for determining the optimal preload is proposed.Through research,it is found that as the rotational speed and preload increase,the bearing temperature rise and thermal displacement increase significantly.And in the positioning preload mode,the radial expansion of the inner ring increases due to the increase of bearing thermal displacement and rotational speed.This will lead to a significant increase in the actual preload of the bearing.At the same time,it is found that increasing the bearing stiffness can improve the dynamic special effects of the motorized spindle system,and as the bearing thermal displacement increases,the radial stiffness of the bearing increases,thereby increasing the natural frequency of the motorized spindle system.The test results showed that in the low speed range,the change of the axial preload had no significant effect on the spindle vibration and bearing temperature;In the medium speed range,as the axial preload force increases,the spindle vibration is significantly weakened,and the bearing temperature was significantly reduced.In the high speed range,as the axial preload force increases,the spindle vibration was greatly reduced,and the bearing temperature was greatly increased.The error between the temperature field test results and the simulation results carried out in this paper was within 10%,which can better reflect the action law of bearing preload.The speed range was divided into three sections:high speed,medium speed and low speed.Considering the requirements of bearing stiffness and temperature rise under different working conditions,different preloading weights W1 and W2 were introduced in different speed ranges.Thus,got a optimum preload of the bearing corresponding to the speed and external load.