Abstract: The thermal characteristics of the newly designed XK717 CNC milling machine were analyzed using the finite element method. The results were compared with those of the XK510 CNC milling machine (a mature product). Based on the comparison, the weak components in the thermal characteristics of the XK717 CNC milling machine were identified, thus indicating the direction for improving the overall thermal characteristics of the XK717 CNC milling machine. Keywords: Thermal characteristics; Finite element method; CNC milling machine In machining, the process system generates a temperature field under the influence of various heat sources (frictional heat, cutting heat, ambient temperature, thermal radiation, etc.), causing thermal deformation of the machine tool, cutting tool, workpiece, and fixture. This affects the relative displacement between the workpiece and the cutting tool, resulting in machining errors and consequently affecting the machining accuracy of the parts. According to a survey by Professor J. Peclenik of the University of Birmingham, UK, in precision machining, manufacturing errors caused by thermal deformation account for 40% to 70% of the total manufacturing errors. Therefore, how to reduce thermal deformation and improve machining accuracy is a very challenging and important problem in machine tool design. At present, many scholars have studied the thermal deformation of machine tools through experiments and theoretical analysis. For example, Zhejiang University has studied the problem of elastic thermal contact using the finite element method, developed the finite element system, and applied it to the structural optimization of the TKA6916 CNC floor milling and boring machine, achieving certain results [1]. Okuyama et al. measured the relative thermal displacement of the grinding wheel spindle and the worktable during the operation of the surface grinding machine through experiments, and used the finite element method to conduct theoretical research on the thermal deformation of the grinding machine. The results showed that the theoretical and experimental conclusions were consistent [2]. Moriwaki et al. studied the influence of thermal deformation caused by changes in ambient temperature on the machining center through experiments and the finite element method [3]. This paper will analyze the overall thermal characteristics of the newly designed XK717 CNC milling machine using the finite element method, and compare it with the analysis results of the XK510 CNC milling machine (a mature product). Based on the comparison results, the weak parts of the thermal characteristics of the XK717 CNC milling machine will be identified, thus pointing out the direction for improving the thermal characteristics of the CNC milling machine. 1 Considering the complex structure of the XK717 CNC milling machine, the overall finite element model was simplified for ease of analysis. A 20-node solid element SOL ID95 mesh was used, and the overall finite element model is shown in Figure 1. 2. Analysis Conditions: The XK717 CNC milling machine's spindle system uses 7020C bearings in the front support, installed in pairs with the opening facing downwards. The middle support also uses 7020C bearings in pairs with the opening facing upwards, with a design preload of 500 N. The rear support uses 7018C bearings, installed in pairs back-to-back, with a design preload of 200 N. The bearing arrangement is shown in Figure 2. For a typical milling process, a 40 mm diameter end mill (high-speed steel) with Z = 6 teeth is used to machine carbon steel. The milling depth ap = 20 mm and the milling width ae = 2 mm. The feed per tooth is a[sub]f[/sub] = 0.01 mm, the rotation speed is 3500 r/min, and the energy distribution on the worktable along the X direction is assumed to be as shown in Figure 3. It is also assumed that the total energy absorbed by the worktable is 10% of the cutting energy. Based on these conditions, the boundary conditions for thermal analysis can be calculated. The specific calculation method is shown in reference [4]. The material properties of each part of the machine tool are shown in Table 1. 3 Results Analysis Figure 4 is the temperature field cloud diagram of the XK717 CNC milling machine when the spindle speed is 3500 r/min. It can be seen from the figure that the part with higher temperature of the milling machine is the front support of the spindle; the average temperature values ​​of the front, middle and rear supports are 62.13 ℃, 57.44 ℃ and 45.35 ℃, respectively. Figure 5 is the XK717 The thermal deformation cloud diagram of the whole machine of CNC milling machine shows that the thermal deformation of the front part of the spindle box is more serious, while the average thermal deformation of the front end face of the spindle, which mainly affects the machining accuracy, is 0.143 mm. [align=center] [/align] Figure 6 and Figure 7 are the temperature field and thermal deformation field cloud diagrams of XK510 CNC milling machine under the same simulation conditions. The average temperature values ​​of the front, middle and rear supports are 52.7℃, 52.71℃ and 36.5℃, respectively, while the average thermal deformation of the front end face of the spindle is 0.062 mm. By comparison, it can be seen that the bearing temperature rise of XK717 CNC milling machine is higher than that of XK510 CNC milling machine, and the thermal deformation of the front end face of the spindle is more than twice as large. This is mainly because: [align=center] [/align] (1) XK717 CNC milling machine has more bearings, 2 each in the front, middle and rear, for a total of 6, while XK510 The milling machine has only 4 supports: two front supports and one each for the middle and rear supports; (2) The XK717 milling machine is a large CNC milling machine with a spindle diameter of about 0.1 m, while the XK510 milling machine has a diameter of only 0.065 m. This indicates that the bearing size of the newly designed XK717 CNC milling machine is much larger than that of the original milling machine when selecting bearings. The above two reasons directly affect the heat generation of the CNC milling machine bearings, which in turn affects the temperature rise of the bearings and the thermal deformation of the spindle. Since the XK510 CNC milling machine is a mature product, its machining accuracy has always been relatively high during use. However, the analysis results show that the thermal deformation accuracy of the newly designed XK717 CNC milling machine is significantly lower than that of the XK510 CNC milling machine. Therefore, it is necessary to take some measures for the XK717 CNC milling machine to reduce the thermal deformation of the machine tool. From the result cloud diagram, it can be seen that the spindle and spindle box components are the key factors affecting the thermal deformation of the spindle. 4 In conclusion, through the overall thermal characteristics analysis of the newly developed XK717 CNC milling machine and the comparison with the results of the XK510 CNC milling machine, the results show that the thermal deformation accuracy of the XK717 CNC milling machine is not as good as that of the original milling machine, and the reasons for this are analyzed. Moreover, it can be seen from the result cloud diagram that the spindle and spindle box components of the XK717 CNC milling machine are the components with the most severe temperature and thermal deformation. Therefore, corresponding measures should be taken to improve the thermal characteristics of the spindle and spindle box components.