## 4 The machined Surface Error Distribution Consistency Process Design Model
### Experimental Verification  
To verify the validity of the process design model proposed in this paper for consistency of surface error distribution in milling, milling experiments were conducted. The milling cutter used in the experiment was a five-tooth solid carbide end mill (MC122-20.0A5B-WJ30 TF) made by WALTER (diameter 20 mm, tool length 104 mm, helix angle 50\({}^{\circ}\)); the machine used in the experiment was a three-axis milling processing center (work table 1050 mm, width 560 mm). The milling model was down milling and dry milling, and the workpiece used in the experiment was titanium alloy; the components are shown in Table 6, and the experimental setup is shown in Figure 14.  
The parameters used for the experiments were as follows: the depth of the cut (a\({}_{p}\)) was 10 mm, the width of the cut (ae) was 0.5 mm, and the remaining original process parameters and the new process parameters are shown in Table 7.  
According to the process parameter scheme in Table 7, firstly, we simulated the processing surface morphology of machining, and the simulation results were solved by using the proposed model of selecting the surface feature points of milling machining and the model of characterizing error points of milling machined errors. Meanwhile, an inspection of machined surface errors was obtained experimentally under the conditions of different process parameter schemes using the three-coordinate measuring machine. The results of solving and experimentally testing the machined error distribution under the conditions of the new and old process schemes are shown in Figures 15 and 16. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Element** & **Ti** & **Al** & **V** & **Fe** & **O** & **Si** & **C** & **N** & **H** & **Others** \\ \hline Contents (\%) & Balance & 5.5–6.8 & 3.5–4.5 & 0.3 & 0.2 & 0.15 & 0.1 & 0.05 & 0.01 & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The material composition of the TC4 titanium alloy workpiece. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Serial Number** & \(\begin{array}{c}n\\ \text{(r/min)}\end{array}\) & \(\begin{array}{c}f_{z}\\ \text{(mm/z)}\end{array}\) & \(\begin{array}{c}a_{p}\\ \text{(mm)}\end{array}\) & \(\begin{array}{c}a_{e}\\ \text{(mm)}\end{array}\) & \(\begin{array}{c}\text{\bf Cutter}\\ \text{\bf Tooth Error}\\ \text{\bf(mm)}\end{array}\) & \(\begin{array}{c}i=1\\ \text{\bf(=2)}\end{array}\) & \(\begin{array}{c}i=3\\ \text{\bf(=3)}\end{array}\) & \(\begin{array}{c}i=4\\ \text{\bf(=5)}\end{array}\) \\ \hline \
\begin{tabular}{c} Original process \\ scheme \\ \end{tabular} & 1719 & 0.06 & 10 & 0.5 &
\begin{tabular}{c} \(\Delta z_{i}\) \\ \(\Delta r_{i}\) \\ \end{tabular} & \(\begin{array}{c}-0.004\\ 0.000\\ 0.000\\ 0.001\\ 0.001\end{array}\) & \(\begin{array}{c}-0.001\\ 0.000\\ 0.000\\ 0.001\end{array}\) & \(\begin{array}{c}-0.013\\ 0.000\\ 0.000\\ 0.000\end{array}\) & \(\begin{array}{c}-0.009\\ -0.010\\ 0.000\end{array}\) & \(\begin{array}{c}-0.009\\ -0.006\\ \end{array}\) & \(\begin{array}{c}-0.009\\ -0.004\\ -0.004\end{array}\) & \(\begin{array}{c}-0.009\\ -0.000\end{array}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Validation of process parameters used in the experiment. Figure 14: Milling experimental device: (**a**) Milling experiment site. (**b**) Three-axis milling machining center. Figure 15: Positional reference point error of the old and new process schemes. As shown in Tables 8 and 9, the correlation degree of surface positional error of the new process scheme is above 0.85, showing strong correlation. This proves that the measured results are in good agreement with the calculated results. The correlation degree of angular error of the new process scheme is above 0.8, which is higher than that of the old scheme.