Analysis And Modeling Of Thermal Error In Linear Feed System Of CNC Machining Center

Numerical control machine tool as the main body of modern manufacturing processing,its processing precision and processing efficiency are the focus of people’s attention.The main factor affecting the machining accuracy and efficiency of NC machine tools is the machine tool error,and in the machine tool error,the proportion of thermal error is the largest,especially in some ultra-precision machining,even up to about 70%.The feed system is a key component of machine tool,and its thermal characteristics are directly related to the machining accuracy of NC machine tool.Therefore,it is of great significance to analyze the thermal characteristics of NC machine tool feed system and establish a thermal error model to reduce the influence of thermal errors on machining accuracy.In this thesis,the basic theoretical analysis of thermal characteristics of the feed system of CNC machine tools was carried out,the finite element model of the feed system was established,the finite element analysis of the temperature field and deformation field were carried out and the change law was explored,and then the experimental platform of the feed system of CNC machine tools was built and the thermal error experiment was carried out,the thermal error model was established and the accuracy of the thermal error model was verified through the experimental data measured by the thermal error experiment,and finally the thermal error model was used to compensate the thermal error of the feed system and verified the effect of the compensation through the actual processing experiment,and it provided a favorable basis for reducing thermal error and improving machining accuracy of machine tools.The main contents of this article include:(1)Based on the basic theory of thermal characteristics,the main causes of thermal errors in CNC machine tools were clarified,and three heat transfer modes in machine tools were analyzed,such as heat conduction,heat convection and heat radiation.The basic finite element theory of temperature field and deformation field were expounded,and the main influencing factors of temperature field and deformation field are determined.(2)The thermodynamic simulation of NC machine feed system was carried out.Firstly,the finite element model of the ball screw feed system was established,the main heat source in the feed system was analyzed,and the heat generation and thermal boundary conditions of the main heat source in the machine tool were determined based on the basic theory of energy transfer.Secondly,the simulation results of steady-state temperature field and transient temperature field were obtained by finite element simulation.The temperature variation trend was analyzed,and the deformation field was obtained by heat-structure coupling analysis.Finally,based on the finite element model,the influence of feed speed and ambient temperature on the feed system was further explored,which laid a theoretical foundation for the later thermal characteristics experiment.(3)A thermal error experimental platform of the feed system was established,temperature and positioning error measurement experiments were carried out,and the changes of temperature,temperature rise,positioning error and thermal error with time at different positions were analyzed,and the experimental data obtained through thermal error experiment could provide data support for the subsequent establishment of thermal error model.In order to explore the influence of feed speed on temperature and thermal deformation,experiments were carried out under the same conditions and different feed speeds,and the changing trend of temperature and thermal deformation with feed speed in the feed system was obtained.(4)In order to accurately predict thermal errors in feed system,a BP neural network method(Tent-SSA-BP)based on chaotic mapping and improved squirrel algorithm was proposed.The training data was derived from the experimental results of thermal errors of the feed system.The prediction accuracy of the proposed method was verified by experimental data.Finally,the thermal error compensation experiment of the feed system was carried out by using the Tent-SSA-BP thermal error model proposed in this thesis.The workpiece was drilled by using the actual processing method.The positioning accuracy of the holes before and after compensation was compared,and the accuracy of the model and the feasibility of the compensation method were verified again.