Theoretical And Experimental Investigations On Thermal Characteristics Of The Feed System For CNC Machine Tools

Due to the need for high efficiency and high precision machining equipment in modern industry,CNC machine tools are developing towards high speed,high precision,large displacement and high load.However,high speed and high load make the feed system produce a lot of heat,resulting in thermal deformation of processing system for machine tool,causing thermal error of workpiece in processing,and reducing the machining precision.Therefore,the research on the thermal characteristics of CNC machine tool feed system has important theoretical and practical value.In this paper,the feed system was choosed as the research object.Combining theoretical research,numerical calculation and experiment,the distribution characteristics of heat source,temperature and thermal deformation of feed system were analyzed,and the heat transfer mechanism of feed system was expounded.The specific contents are as follows.(1)According to the fundamental law of heat conduction and Newton’s law of cool,the three-dimensional heat conduction differential equation was deduced and the boundary conditions,the heat source system and finite element method for the heat conduction differential equation was given.According to formula of thermal expansion coefficient and three basic equations of elastic mechanics,the differential equation for solving the displacement was deduced.(2)Taking the X feed shaft of numerical control lathe as an example,the experiment system was established.Platinum thermistor sensor was selected to detect the temperature of the two supporting bearings.The infrared thermal imager was used to detect the surface temperature of the guide rail and the screw intermittently.The thermal error of the feed system was measured by the laser interferometer,and the torque current of the servo motor was obtained through the FOCAS1 library function.Then,the comprehensive description of thermal characteristics for feed system was achieved.(3)The finite element model of the CNC machine tool feed system was established and the "moving heat source" load mode was applied in the finite element calculation.By combining finite element analysis and dichotomy,heat generation rate of each heat source was calculated,and the total heat generation rate caculated by finite element analysis was basically consistent with the total heat generation rate extracted from the experimental data.The validity of the finite element model and the calculation method was verified.(4)According to the results of finite element analysis,the temperature field and thermal error of feed system were analyzed.The distribution of temperature field and thermal error of ball screw and guide rail is obtained.The heat transfer of each part of the feed system and its variation with time are analyzed,and the main factors affecting the temperature field of the ball screw and guide rail were deduced.