Thermal-Structure Coupling Analysis And Experimental Study On Spindle-Bearing System Of Grinding Wheel Of Surface Grinder

The high precision of the machine tool spindle system is mainly affected by the pre-tightness of the spindle bearings and the stability of the thermal characteristics.The key to improve the machining accuracy of CNC machine is to analyze the temperature rising and thermal deformation of machine tool spindle system at work,and it can improve the performance of CNC machine effectively.Bearing friction heat in spindle system is the main internal heat source,the heating of the bearing friction makes the different temperature rising at the various parts of the spindle system,and the temperature rising causes the thermal expansion of part,which leads to the thermal displacement of the spindle.In order to study the variation of the temperature with time between the parts of the machine tool spindle system and its own thermal deformation characteristics,in this paper,the MGK7120 × 6 high precision surface grinding machine tool as the research object,the temperature field and thermal deformation of the spindle-bearing system of the grinding wheel are simulated,and the temperature measurement test of the spindle system is carried out to verify the correctness of the simulation of temperature field.The main work of this paper is as follows:(1)Based on the theory of thermal characteristics of rolling bearing,the causes of friction and friction torque of bearing are introduced in detail in this paper.Based on the theory of heat transfer,the three basic heat transfer modes between different materials with different thermal conductivity are theoretically explained and analyzed,and the four methods of heat transfer analysis are summarized.(2)Based on the theory of the heat conduction and boundary condition of temperature field,the simulation of steady temperature field and transient temperature field of the spindle-bearing system are carried out.According to the simulation results of the steady temperature field,the temperature distribution law of along the centerline of the spindle is obtained,and changing the speed of the spindle,the temperature variation of the bearing parts at different speeds is obtained.According to the simulation results of the transient temperature field,the changing rule of temperature with time of bearing roller and the raceway of the outer and inner rings is obtained,furthermore,when the time t=600s,1800 s,3600s and 4800 s,the temperature distribution curve of the spindle along the axis direction are obtained.(3)Based on the Hertz elastic contact theory,the calculation formula of the stress and deformation of the rolling bearing is deduced.Based on the theory of the thermal-structural coupling analysis,the thermal-structural coupling simulation of the spindle-bearing system is carried out on the basis of the simulation of the temperature field.The simulation results show that the thermal stress distribution on the surface of the bearing roller is elliptical,which is similar to that of the Hertz elastic contact stress.The path of the inner and outer circle of the bearing is established,and the thermal displacement of the outer and inner rings of the bearing is calculated in three directions: radial,tangential and axial,furthermore,the variation of the thermal displacement of the inner and outer rings of the bearing in three directions is obtained.Finally,the path of the spindle along the center line is established,and the variation law of the thermal displacement and thermal stress of principal axis in the three directions of the radial direction,tangential direction and axial direction is obtained.(4)According to the simulation results of the spindle-bearing system in the temperature field,the temperature of the spindle-bearing system is verified by the temperature measurement of the MGK7120 × 6 high precision surface grinding machine tool.The relationship between the speed and the heat balance time was obtained by changing the spindle speed and repeating the test.