| The direct-drive A/C axis bi-rotary milling head(referred to as milling head)is the core component of the five-axis Computer Numerical Control(CNC)machine tool,which is mostly used to process large and complex surfaces,reflecting the level of high-end equipment manufacturing.There are many internal heat sources in the milling head,and the working conditions are affected by multiple heat sources,resulting in a non-uniform temperature field inside the head,which leads to the different temperature rise of each component.The complex thermal coupling relationship of the milling head and the limited cooling conditions make it a difficult problem to improve the machining accuracy.So it is especially important to study its thermal characteristics to suppress thermal errors.This paper takes the milling head developed by a company in Ningbo as the research object,and carries out steady-state thermal and transient thermal simulation analysis by combining with finite element simulation software;builds the temperature rise experiment to analyze the variation law between temperature and thermal error under working condition;establishes the numerical model of the optimal flow rate of cooling water and conducts the thermal error suppression experiment to verify the accuracy of the model.The basic structural components,basic parameters,and thermal error sources of the milling head are introduced.On this basis,the thermal performance of the milling head is analyzed with emphasis on the thermal state.Including the heat generation of each heat source and the convective heat transfer coefficient between the parts,laying the foundation for the finite element simulation to set the thermal boundary conditions.The theoretical model of thermal elasticity of the milling head is established,and the degree of influence of each heat source on the thermal displacement of the milling head is explored to provide a reference for the subsequent experimental arrangement and enterprise improvement of the structure.The finite element simulation analysis is based on the thermal performance of the pendulum milling head.Firstly,a 3D model of the pendulum angle milling head is established and simplified,material parameters and mesh division form are determined,and thermal boundary conditions are set to solve the steady-state thermal and transient thermal results.By interpreting the temperature field and thermal deformation field clouds,the causes of serious heating in each part and the factors leading to the large thermal displacement at the nose of the electric spindle are analyzed,and the variation law between thermal displacement and temperature is obtained.Based on the finite element and thermoelastic numerical analysis results to determine the temperature and displacement detection position,build the experimental platform,collect temperature and thermal displacement data and plot the figures.The results are analyzed and the thermal displacement and temperature reaching thermal equilibrium times are discussed.The accuracy of the finite element simulation is verified by comparing the experimental results with the simulation results.Thermal error suppression experiments are performed to meet the machining accuracy criteria.K-means++algorithm is used to preferably select the temperature-sensitive point,and the point is cooled in subsequent experiments.Two cooling strategies are proposed,and the best cooling strategy is selected through experiments.The cooling water flow rate has a significant effect on cooling,so the numerical model of the cooling water flow rate is established and the best flow rate of cooling water v_nis solved.To verify the accuracy of the model,different flow rates are set for thermal error experiments to provide a theoretical basis for enterprises to improve the cooling structure and select the parameters of cooling water flow rate. |
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