Research On Vibration Characteristics Of Motorized Spindle Based On Thermal Displacement And Bearing Interference

With the wide application of high-speed machining technology in equipment manufacturing industry,high-speed CNC machine tools have become the key equipment of industrial manufacturing 4.0.High-performance motorized spindle is one of the core components of high-end CNC machine tools,which has an important impact on the machining accuracy and stability of machine tools.The rotation heat of angular contact ball bearings causes the deformation of the ring channel,which changes the fit amount of bearings,and then changes the dynamics of bearings and rotor systems.Determining the interference of the bearing inner ring to eliminate the influence of thermal displacement and centrifugal displacement has become an urgent problem to be solved in the design and development of the motorized spindle.The main research work of this paper includes:Firstly,the loss model of motorized spindle is established to accurately calculate various losses under different working conditions.The Siumlink module is used to establish the motor model considering iron loss and the frequency conversion drive model of motorized spindle.Considering the current harmonic effect,the iron loss calculation model with modified empirical coefficient is established to calculate the iron loss,copper loss and mechanical loss under multiple working conditions.Then,according to the calculated loss,the internal heat generation is determined and the heat transfer coefficient of each boundary condition is calculated.The temperature field analysis model of motorized spindle is established by using finite element analysis software,and the internal temperature distribution under different working conditions is obtained.Based on bearing fit theory and Harris theory,the influence model of temperature and centrifugal force on fit amount is established,and the two kinds change law of initial fit quantity is studied.Based on Hertz contact theory and quasi-statics theory of bearing,a bearing stiffness solution model is established.The thermal displacement,centrifugal displacement and bearing interference amount are coupled into the model,and the influence of different fit and speed on stiffness dynamic parameters is analyzed.The pseudo-dynamic model of bearing is established to analyze the influence of bearing interference,bearing structural parameters and dynamic characteristics,and to determine the best interference of bearing.Finally,the experimental platform of comprehensive performance of motorized spindle is built,and the related experiments of motorized spindle are carried out.The related results obtained from the experiments are compared with the simulation results,so as to verify the accuracy of the established loss,temperature field and dynamic model.The results show that the energy loss model of motorized spindle established in this paper can effectively reduce the higher harmonics in current and improve the accuracy of current waveform.Iron loss accounts for the largest proportion of motorized spindle loss and mechanical loss is the smallest.The fundamental loss accounts for the largest proportion of the total loss.The established loss model of motorized spindle can well simulate the running state of motorized spindle.The temperature distribution inside the motorized spindle is uneven,with the highest temperature at the rolling body and the lowest at the stator.With the increase of speed,the temperature of each component of the motorized spindle increases nonlinearly.The thermal displacement caused by the temperature rise of the bearing increases the interference of the inner ring,while the centrifugal displacement decreases the interference of the inner ring.When the two are considered comprehensively,the change of inner ring interference decreases inversely with the rotating speed and increases directly with the initial interference.With the increase of interference,the radial stiffness of bearing is improved,the axial stiffness is reduced,the contact load between inner and outer rings is increased,and the contact angle of outer ring is reduced.The interference of bearing can be appropriately increased to enhance the stiffness of bearing and improve the dynamic characteristics.After comprehensive consideration of various factors,a set of optimal interference of bearing inner ring under different speeds is put forward.In this paper,through the analysis of the dynamic characteristics of motorized spindle bearings and the whole motorized spindle,the relevant laws of its dynamic parameters are obtained,which provides theoretical basis for the optimal design of motorized spindle.