## 3 The Results of the Numerical Experiment  
### Residual Stress Analysis  
Figure 2 shows the evolution of the stress field in which laser fuses are deposited and are thin-walled; Figure 2a-e are cloud maps of the stress field distribution of the cladding layer at the end of the layer 1 to layer 5 scan. From these pictures, when the number of forming layers is low, it is due to the low substrate temperature. After each layer of sedimentation, there is a large residual stress, and as the number of sediments increases, the substrate is fully warmed up and the residual stress generated by the front layer is released when the back layer is deposited. Thus, with an increase of cladding layers, the stress decreases and the distribution becomes more uniform. Figure 3 shows the cloud maps of stress field distribution at different times during milling; 0 s in the figure is the stress field cloud map after the additive manufacturing cools for 900 s. As seen in Figure 3a, there are significant differences in stress states in different regions; the residual stresses in the central region are relatively stable and basically consistent, and the stress fluctuations are large in the two regions of the start and end points of the laser heat source. The maximum residual stress is concentrated at the intersection of the cladding layer and the substrate. These results are due mainly to the thermal end effect [22]. As seen in Figure 3b-f, as milling progresses, the Von Mises values of the thin-walled pieces are significantly reduced, and at the same time, the distribution of residual stress in thin-walled parts is changed. At the initial moment, the sedimentary layer as a whole is in a pull stress state; as the cutting process progresses, and with the gradual removal of sedimentary surface materials, the pull stress that remains on the surface of the sediment layer caused by the additive manufacturing process decreases or even becomes pressure stress. Figure 2: Stress field cloud diagram during thin-walled part forming: (**a**) the first floor ends; (**b**) the two floor ends; (**c**) the three floor ends; (**d**) the four floor ends; (**e**) the five floor ends. For studying the distribution of residual stress better, this study selects five paths from the bottom up at equal intervals in the cutting stability area of the machining surface and selects 20 nodes at equal intervals in each path. Residual stress values are collected for each node based on the path selected, and the collected residual stresses are calculated and averaged to obtain the residual stress for each path. As shown in Figure 4, with the other parameter conditions unchanged, the milling speed \(v_{\mathrm{c}}\) is set to 140 m/min and the radial cutting depth \(a_{\mathrm{e}}\) is set to 0.3 mm; then, the difference between the residual stress of the milling surface and the original forming surface is determined. It can be found that the maximum pull stress of the original face reaches 396 MPa, with the minimum being 234 MPa. After milling, the maximum pull stress is 205 MPa, and the minimum is 145 MPa; compared with the original surface residual pull stress, this represents a decrease of about 47% on average, showing a great reduction. At the same time, it can be found that after milling, the standard deviation of residual stresses throughout the surface is reduced; this can be explained by the fact that residual stress distribution is more uniform after milling and its anisotropy improves considerably. Figure 4: Residual stress on milled surface and residual stress on original forming surface. Figure 3: Stress cloud at different times during the milling process: (a) 0 s; (b) 0.037 s; (c) 0.074 s; (d) 0.111 s; (e) 0.148 s; (f) 0.185 s.  
Cutting temperature is an important variable to be monitored during milling. Figure 5 shows the comparison of the peak temperature of the tool tip during the processing of forged parts and additive manufacturing Ti6 Al4V titanium alloy at different milling speeds.