# Study on the Machinability of Ni-Based Superalloy by
## 3 Result and Discussion  
### Effects of Milling Parameters  
In Figure 3, the surface roughness gradually decreases with the increasing cutting speed. When the cutting speed ranged from 64.06 m/min to 75.36 m/min, the surface roughness decreased slowly. When the cutting speed increased from 47.10 m/min to 75.36 m/min, the surface roughness decreased from 2.17 m to 1.46 m, improving by 48.6%. The surface roughness increased gradually when the feed per tooth was from 4 m to 9 m, as shown in Figure 4. When the feed per tooth was greater than 9 m, the slope increased obviously, which is due to the increase in the spacing between the adjacent milling blades. Therefore, on the premise of meeting the surface roughness of the workpiece, the feed per tooth can be appropriately increased to improve the processing efficiency. As can be seen from Figure 5, with the increase in the radial cutting depth, the surface roughness of the workpiece increased significantly. When the radial cutting depth was higher than 0.05 mm, the increase rate of the surface roughness accelerated. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number**} & **Cutting Speed \(v\)** & **Air Pressure** & **Lubricating Flow** & \multirow{2}{*}{**Cooling Mode**} \\  & **(m/min)** & **(Bar)** & **(L/h)** & \\ \hline
1 & 37.68 & & & Dry milling \\
2 & 56.52 & & & Dry milling \\
3 & 75.36 & & & Dry milling \\
4 & 37.68 & 4 & & Air cooling \\
5 & 56.52 & 4 & & Air cooling \\
6 & 75.36 & 4 & & Air cooling \\
7 & 37.68 & 4 & 0.0279 & MQL \\
8 & 56.52 & 4 & 0.0279 & MQL \\
9 & 75.36 & 4 & 0.0279 & MQL \\
10 & 37.68 & 4 & 0.0279 & Nanofluid MQL \\
11 & 56.52 & 4 & 0.0279 & Nanofluid MQL \\
12 & 75.36 & 4 & 0.0279 & Nanofluid MQL \\ \hline \hline \end{tabular}
\end{table} 
Table 4: GH4169 milling experiment scheme with different parameters. Figure 3: Variations in GH4169 surface roughness with cutting speed: (**a**) \(v\) = 47.10 m/min; (**b**) \(v\) = 75.36 m/min; (**c**) changing law. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Number**} & **Cutting Speed \(v\)** & **Feed Per Tooth \(f_{z}\)** & **Radial Cutting Depth \(a_{p}\)** \\  & **(m/min)** & **(\(\mu\)m)** & **(mm)** \\ \hline
1 & 47.10 & 7 & 0.05 \\
2 & 56.52 & 7 & 0.05 \\
3 & 65.94 & 7 & 0.05 \\
4 & 75.36 & 7 & 0.05 \\
5 & 65.94 & 4 & 0.05 \\
6 & 65.94 & 10 & 0  
According to the influence law of the milling parameters on the milling force shown in Figure 6, the milling force \(F_{y}\) is the largest, followed by the milling force \(F_{x}\), and the milling force \(F_{z}\) is the smallest. With the increase in the cutting speed, the milling force began to decrease. When the cutting speed exceeded 69.54 m/min, the milling force showed an increasing trend. The milling force \(F_{x}\), \(F_{y}\), and \(F_{z}\) showed a positive correlation trend with the feed per tooth. The radial cutting depth has a significant influence on the milling force, mainly because the increase in the radial cutting depth leads to the increase in the material removal volume per unit time, so the milling force increases with the increase in the radial cutting depth. The radial cutting depth of cut has a significant effect on the milling force, which is mainly because the material removal volume increases in unit time, so the milling force increases with the increase in the radial cutting depth. During the milling process, the microstructure of the processed material changes under the combined action of thermal softening and strain hardening. The characteristics of milling-induced microstructural changes in GH4169 near the machined surface are highlighted, as shown in Figure 7. The relative slip between the tool tip and the workpiece surface caused some grains near the milling surface to deform and twist along grain boundaries. On the other hand, improper milling parameters can result in uneven milling surfaces and broken grains. A high cutting speed and low feed per tooth and radial cutting depth are beneficial to maintain the flatness of the machined surface.