## 4 Results and Discussion  
The total material removal volume after the rough and finish machining stages was found to be 4767.27 mm\({}^{3}\), of which the material removal in the rough-machining stage accounted for 92.37%. Figure 9a shows the cross section of the groove obtained by ECMG rough machining. It can be seen from the figure that after rough machining by the spiral slit cathode tool, the flatness of the sidewall was good. The material was removed uniformly, and there was no flow mark on the processed surface. However, the rounded corners and some poorly soluble electrolytic products still existed. Figure 9b shows the cross section of the groove obtained after the finish machining. It can be seen from the figure that after finish machining, the flatness of the side wall and bottom was further improved, and the rounded corners and insoluble electrolytic products were removed. The coordinates of the points on the corresponding profile of the rough and finished grooves were detected by a bridge type three coordinates measuring machine (ZEISS CONTURA, Germany), and the results are shown in Figure 9c. According to the measurement results of the profile, the maximum groove width and depth  
Figure 8: Finishing in the ECMG: (**a**) finishing of groove bottom, (**b**) finishing of groove sidewall. \begin{table}
\begin{tabular}{c c} \hline \hline
**Processing Parameter** & **Value** \\ \hline Processing voltage (V) & 1 \\ Electrolyte temperature (\({}^{\circ}\)C) & 30 \\ Electrolyte pressure (Mpa) & 0.2 \\ Feed rates V\({}_{\text{I}}\)/V\({}_{\text{v}}\)/V\({}_{\text{t}}\) (mm\(\cdot\)min\({}^{-1}\)) & 60/1/1 \\ Cutting depth (mm) & 0.05 \\ Spindle speed (rpm) & 1000 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Process parameters of the finish-machining test. of the roughing were 12.16 mm and 15.67 mm, respectively. The maximum groove width and depth of the finishing were 12.62 mm and 15.93 mm, respectively. After rough machining, the sidewall was relatively flat and there were no pits on the bottom of the workpiece, and the removal margin of finish machining was small. This effectively reduced the finishing removal and tool wear. The surface morphology of the grooves at the rough and finishing stages was detected by a scanning electron microscope (S-3400, Hitachi, Tokyo, Japan). It can be observed from Figure 10a that after rough machining, the surface exhibited severe stray corrosion, which was manifested by uneven selective dissolution, and the microstructure was porous. It can be seen from Figure 10b that the grinding marks on the surface were obvious after finish machining. Ridges were seen on the surface, and the ridge height of the material was different. This was a typical plough and chip formation characteristic in grinding [24]. This shows that during rough machining, the electrochemical dissolution played a leading role. In contrast, the grinding played a leading role in the finish machining. In addition, during the finishing process, the forming of the workpiece surface was no longer affected by stray corrosion. A laser confocal microscope (OLS4100, Olympus, Tokyo, Japan) was used to scan the three-dimensional topography of the processed surface of the grooves after the ECMG rough and finish machining, and to check the surface roughness. The results are shown in Figure 11. It can be seen from Figure 11a that the surface after ECMG rough machining was rough and uneven. It was found that the surface wave peaks and valleys were undulating, and the measured surface roughness Ra was  
Figure 10: Micro-morphology and roughness of surface groove surface after: (**a**) rough machining, (**b**) finish machining. Figure 9: Cross-section profiles and measurement results of the grooves in the rough- and finish- machining processes using the cathode tool with spirally arranged outlet slits: (**a**) cross-section profile after rough machining, (**b**) cross-section profile after finish machining, (**c**) measurement results of the cross-section profiles after rough and finish machining.