## 3 The Results of the Numerical Experiment
### Residual Stress Analysis
As can be seen from the figure, at different milling speeds, the cutting peak temperature of additive manufacturing Ti6 Al4V titanium alloy is higher than that of forging Ti6 Al4V parts, and when the milling speed increases, the milling temperature increases accordingly. Under the same processing conditions, compared with the forging, the cutting peak temperature of the additive manufacturing Ti6 Al4V titanium alloy milling model is increased by about 26.2%. Figure 6 compares the residual stress changes of milling surfaces at different milling depths, with other parameters as constant and considering a milling depth of 0 mm as the size of the residual stress of the original face. Figure 6a presents a comparison of Mises stress; it shows that the maximum pull stress of the original face is 325 MPa after milling and the maximum tensile stress is 176 MPa. Where the milling depth is 0.1 mm, the residual stress drop is the largest, reduced by approximately 54%. By observing the influence of milling depth on surface residual stress, it can be found that the surface residual tensile stress increases as the depth of milling increases. As can be seen from Figure 6b-d, milling has a significant impact on surface \(X\) direction and \(Y\) direction stresses, with the largest decreases being 77% and 131%, respectively. The effect on \(Z\) direction stress is weak, with the biggest drop being about 47%. At the same time, the \(X\) direction, \(Y\) direction and \(Z\) direction stresses of the milling surfaces as a whole show the trend of gradually decreasing the pull stress as the milling depth increases towards the pressure stress. The initial temperature has a significant effect on the milling performance of titanium alloys. In the composite manufacturing process of adding and subtracting materials, the additive and subtractive processing alternate with each other; this results in the subtractive processing being performed in a high-temperature environment. Therefore, laser melting is studied. Wire additive manufacturing Ti6 Al4V titanium alloy deposits have important guiding significance for the milling performance under hot, dry milling conditions. Figure 7 shows the residual stress under different initial temperatures and milling speeds. Figure 7a shows the equivalent Mises stress comparison of the milling surface. It can be found that when the initial temperature increases, the milling surface residual stress decreases gradually. As the initial temperature increases from room temperature to 400 \({}^{\circ}\)C, the maximum value of the milling surface average equivalent Mises stress drops from 122 MPa to 90 MPa, an average drop of about 26%. In Figure 7b, the residual stress in the \(X\) direction of the milling surface gradually decreases with an increase in the initial temperature. When the initial temperature increases from room temperature to 400 \({}^{\circ}\)C, the stress in the \(X\) direction of the milling surface decreases by 136.5% on average and the \(X\) direction residual tensile stress is greatly reduced, which can effectively reduce the risk of cracks and other defects in the additive part perpendicular to the \(X\) direction. Figure 5: Cutting temperature of forged and additive Ti6 Al4V at different milling speeds. Figure 6: Residual stress of milling surface and original forming surface under different milling depths: (**a**) von Mises stress; (**b**) \(X\) direction stress; (**c**) \(Y\) direction stress; (**d**) \(Z\) direction stress. Figure 7: Residual stress of milling surface under different initial temperatures and milling speeds: (**a**) von Mises stress; (**b**) \(X\) direction stress; (**c**) \(Y\) direction stress; (**d**) \(Z\) direction stress. At the same time, as seen in Figure 7b, the milling speed has a significant influence on the directional stress. As the milling speed increases, the \(X\) direction stress gradually decreases or even becomes a compressive stress.