# Intelligent Air Cutting Monitoring System for Milling Process
## 5 Results and Discussion
### Verification
#### 5.3.4 Experiment Verification 4  
A tungsten carbide end mill cutting tool, with a diameter of 10 mm and four flutes, is used in this experiment. The workpiece experiment is square medium carbon steel, with a length of 100 mm, and the cutting parameters are shown in Table 7. In this experiment, the cutting vibration signal judgment is used. The experiment method is divided into two:  
Figure 10: Results of verification experiment 2. \begin{table}
\begin{tabular}{c c} \hline \hline  & **Value** \\ \hline Spindle speed (rpm) & 4000 \\ Feedrate (mm/min) & 600 \\ Width of Cut (mm) & 0.3 \\ Depth of Cut (mm) & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Cutting parameters for experiment 3. The experiment results for the two kinds of methods are shown in Tables 8 and 9. The workpiece with grooves has a groove length of 22 mm, 32 mm, and 52 mm on side 2, 3, and 4, respectively, as shown in Figure 12. This means that the theoretical air cutting on these three sides should be 2.2 s, 3.2 s, and 5.2 s longer, respectively. From the comparison of the experimental results, it can be seen that the cutting time result is close due to there being no empty groove on the first side in both experiments. The second side has two empty grooves of 9 mm and 13 mm, and a total 22 mm groove length, so the air cutting time is 2.57 s (8.65-6.08 s). Compared to the theoretical air cutting time (should be 2.2 s), the deviation is 0.37 s. This may be because there are two empty grooves on the side, so the system needs to spend more calculation time on judgment and calculation. On the third side, there is a 32 mm empty groove, and the air cutting time is 3.35 s (9.55-6.2 s). Compared to the theoretical air cutting time of 3.2 s, the deviation is 0.15 s, for which the deviation value is smaller than that of the second side. On the fourth side, there is an empty groove length of 52 mm, and the air cutting time is 5 s (11.44-6.44 s). The air cutting deviation is 0.2 s, when compared to the theoretical air cutting time of 5.2 s. The uncertainty of the measurement without empty groove (Table 8) for cutting time, air cutting time, and machining time were 0.48%, 3.21%, and 1%, respectively. Meanwhile, the uncertainty of the measurement with empty groove (Table 9) for cutting time, air cutting time, and machining time were 0.46%, 3.21%, and 1.01%, respectively. According to the air cutting monitoring result, with/without empty groove on three sides, the proposed air cutting monitoring system is adequate, accurate and stable. From the four experiment verifications, the judgment using spindle load current can judge the machining state faster than that using vibration signal. This is because the spindle load current can directly be used, without any conversion or further signal processing, while the vibration signal from the accelerometer needs further signal processing, such as RMS calculation. However, when the cutting load was very small, the spindle load current from the CNC controller was always displayed between \"L0\" and \"L1\" during the cutting process, and did not stably maintain \"L1\", which would indicate cutting. When the spindle load current displayed \"L0\", the system judged that there was no cutting, so it could not correctly judge the machining state. The reason for this problem is the resolution of the spindle load current of the CNC controller is not enough, so it displays no change for small cutting loads. On the other hand, with the use of a proper vibration accelerometer (high sensitivity), it can provide more clear cutting vibration signal for small cutting loads (micro-cutting), so the cutting or non-cutting state can be better indicated. This developed intelligent air cutting monitoring system can be implemented in engineering practice because the process information and spindle load current can be