Research On Thermal Characteristics And Thermal Error Modeling Of Precision CNC Gear Hobbing Machine

In the machining error of the machine tool,the thermal error of the machine tool accounts for 40%-70%,which seriously limits the improvement of the machining accuracy of the machine tool.The CNC gear hobbing machine is an efficient and economical gear making process.With the upgrade of the CNC system and the improvement of its own transmission accuracy,the gear hobbing accuracy is constantly improving,so the influence of thermal error on the machining accuracy cannot be ignored.This paper takes a laboratory-modified precision CNC gear hobbing machine as the research object,and carries out the analysis and research on the thermal characteristics of the machine tool.The thermal-structure coupling simulation is used to analyze the changes of temperature and thermal deformation of the machine tool,and then the thermal error experiment of the machine tool is carried out.Fuzzy clustering and analysis of correlation are used to optimize the temperature variables required for thermal error modeling to obtain thermal key points.The thermal error model of the gear hobbing machine is established by the Bayesian network,which provides a theoretical basis for compensation of thermal error of CNC hobbing machine.The main contents and conclusions of the research are as follows.(1)It is an analysis of the structural characteristics of the gear hobbing machine and the generation of heat sources.Starting from the principle of gear hobbing machine,the processing method of the hobbing machine and the characteristics of the cutting force are analyzed,and the decomposition of the cutting force is obtained.Based on the relevant theory of heat transfer,the thermal characteristics of the gear hobbing machine are studied.Next,cutting heat,bearing heat,motor heat,and convective heat transfer between the machine tool and the external environment during machining are analyzed,and the calculation methods of the heat source intensity and convective heat transfer coefficient of each part of the machine tool are expounded.This analysis can be used as a precondition for thermal-structural coupled simulation of machine tool.(2)The three-dimensional model of the tool holder and part of the bed of machine tool of the CNC gear hobbing machine is established,which reasonably simplifies the structure model of the gear hobbing machine.The steady-state and transient thermal-structure coupling simulation of the temperature and thermal displacement of the CNC gear hobbing machine during the machining process is carried out by using the finite element software.According to the simulation results,the motor rotor with the highest temperature is 42.1?,and the area with the largest deformation is 85.6?m.At the same time,the temperature field and deformation of the tool holder,hob spindle,sliding bearing,etc.are also analyzed,and the characteristics of their changes are also analyzed.Among them,the maximum deformation of the hob spindle is 46.9?m,and the range of the position close to the hob is37?m-41?m.This thermal deformation will eventually be converted into machining errors.Therefore,the thermal simulation analysis of the machine tool is carried out,and at the same time,it provides a reference for the thermal error modeling.(3)Using fuzzy clustering to optimize the initial selection of 9 temperature variables for modeling the thermal error of the machine tool,and then by comparing the correlation between the thermal error of the hob spindle and the temperature variable,4 thermal key points are obtained by screening.Through clustering and correlation analysis,not only the collinearity between temperature variables is reduced,but also the complexity of thermal error modeling of machine tools is reduced.(4)The temperature rise of the temperature measuring point of the hobbing machine and the thermal error data of the hob spindle X direction(radial)were collected experimentally,and the thermal error model of the CNC hobbing machine was established by using the Bayesian network.Comparing the results of the thermal error model with the experimental data,the maximum error of the two are 2.6?m and 3?m,respectively.The maximum error of the prediction of the updated model is 2.9?m,indicating that the thermal error model can effectively reflect the thermal error of the CNC gear hobbing machine with high prediction accuracy,which makes the compensation of thermal error of CNC gear hobbing machine evidence-based.