| CNC machine tool,as the key equipment of modern processing industry,has received more and more attention.The status of high-grade numerical control machine tool was highlighted in Made in China 2025.With the development of CNC machine tools in terms of high speed and high precision,it is a long-term and important work to reduce the machine tool error and enhance its precision.It has been proved that 40%?70%of the machining errors are caused by thermal deformation.Therefore,it is of great significance to study the thermal characteristics of the feed drive system of machining center and to model its thermal error.In this paper,taking the Y-axis feed drive system of vertical machining center as the research object,the thermal characteristics of Y-axis feed drive system of vertical machining center were analyzed and thermal error modeling was carried out based on the experimental method and simulation method.First,the experimental platform was set according to the work plan.The experiments for thermal characteristics were conducted and the temperature and thermal errors distribution field were obtained.Then,the finite element model was established to analyze the thermal characteristics of the Y-axis feed system.Finally,according to the experimental data,the thermal error model based on the nonlinear data fitting and based on RBF neural network were established respectively.The main research contents include:(1)The temperature rise and thermal error testing platform was built and the thermal characteristics of Y-axis feed drive system of vertical machining center were experimentally analyzed.Firstly,an experimental platform of Y-axis feed system was built to observe the temperature rise and thermal error of Y-axis feed system.The temperature rise and thermal errors of the Y-axis feed system at different positions,feed velocities and ambient temperatures were obtained through the thermal characteristics experiment,and the influences of the feed velocities and ambient temperatures on the Y-axis feed system were investigated.The experimental data provided a reference for the validity verification of the subsequent finite element simulation model,and a support for thermal error modeling(2)The thermal characteristics of Y-axis feed drive system of vertical machining center were analyzed based on finite element method.Firstly,based on the heat transfer theory,the calorific value and thermal boundary conditions of the heat source were calculated,and the finite element model was established.Then,the steady-state temperature field and transient temperature field distribution of the Y-axis feed system were analyzed by finite element simulation,and the steady-state thermal deformation distribution of the Y-axis feed system was obtained by using the thermo-structural coupling analysis.Next,by comparing with the experimental results under the same condition,the validity of the finite element model was verified.Also,based on the finite element model,the influences of feed velocity and ambient temperature on the Y-axis feed system were further explored.Finally,the size and structure of the rear bearing housing was optimized by the response surface optimization method,which reduced the temperature and thermal deformation,and improved the thermal characteristics of the Y-axis feed system.(3)The thermal error of Y-axis feed drive system of vertical machining center was modeled by means of nonlinear data fitting and neural network.The temperature rise-position-thermal error model based on nonlinear data fitting and the RBF neural network were proposed respectively,and the models were verified correspondingly.By comparing the accuracy of the two models,the thermal error model based on RBF neural network was proved to have better thermal error prediction accuracyThis study is of great significance for analyzing the thermal characteristics of vertical machining center's feed drive system,which helps in reducing the thermal error of machine tool and improving the precision of machine tool. |
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