| As the development of the manufacturing industry, the requirement of heavy CNC machine tool and the demand of machining accuracy are increasingly high. Due to the large dimension of heavy CNC machine tool, the asymmetrical heat expansion phenomenon of different parts of machine tool is serious under the effect of environment and the interior factors of machine tools, which causes the larger shift between workpiece and tool tip point location. So the machining accuracy is influenced seriously. In this paper, temperature field and the thermal error of the heavy CNC horizontal lathe spindle system is studied. Then the finite element method is used to study the temperature distribution and thermal deformation of the machine tool, the simulation result is compared with experimental result to analyze the thermal error characteristics. What’s more, the experimental measured data is used to optimize the temperature measuring point and establish thermal error model. Finally, thermal error compensation software based on the Siemens 840 D system is developed to compensate the thermal error, and the experiment is implemented to verify the effect of compensation. The main work is summarized as follows:1. A three-dimensional model of the spindle system of heavy horizontal lathe is established under reasonable simplification method and then finite element grids are generated. Heat producer of machine tool and boundary conditions of heat convection is analyzed on the basis of profoud understanding of heat transfer law and finite element method. Heat flux and heat transfer coefficient is calculated according to experience and theoretical formula of heat transfer law to establish the finite element model, which is used to simulate the change rule of temperature field and expansion of the spindle system based on ANSYS-workbench. Meanwhile, the influence of the bearing preloaded force on the temperature rise and expansion of the spindle is analyzed by the simulation.2. In view of the heavy horizontal lathe structure characteristics, the experiment is designed according to the temperature field distribution of simulation result to detect the temperature and thermal error data of the spindle system of heavy horizontal lathe. Respectively to detect the processing status, no-load constant speed status and no-load variable speed status of machine tool to analyze the thermal error under different working conditions. The experimental results is compared with the finite element results to prove the validity of the simulation method.3. Fuzzy cluster method is used to optimize the temperature measurement points combined with the partial correlation analysis method, after optimization, four thermal sensitive points of the thirteen temperature measuring points is selected for the thermal error modeling of the spindle, the validity of the optimization is verified by multiple linear regression model.4. The multiple linear regression, BP neural network and Elman neural network are used to establish the thermal error model respectively. The matching and prediction effect of different models are compared, which lays a foundation for the thermal error compensation.What’s more, the temperature measuring points optimizaion and thermal error modeling system is designed by MATLAB, which facilitates the thermal error modeling work.5. The thermal error compensation method based on the thermal compensation function of Siemens 840 D system is researched, then the thermal error compensation software is developed by using C# language. The software can be seamlessly integrated into the Siemens 840 D system, and the compensation value is calculated by the thermal error model through collects the temperature data of the machine tool. The compensation value is passed to the numerical control system via the software to implement the compensation. The experiment result shows that the compensation method has good effect. |
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