## 3 Results and Discussions
### Laser Cutting of PCD Workpiece
#### 3.2.2 Test Results of Laser Cutting of PCD Workpiece  
To achieve the best cutting efficiency, the laser cutting parameters were selected based on the results obtained in Section 3.2.1. The selected cutting parameters were scan rate of 5 mm/s, pulse width of 200 ns, pulse repetition rate of 30 kHz, and maximum average power of 30 W. During the cutting process, the PCD workpiece was fixed with an overhang and clean dry air was supplied at pressure of six bar. The cutting process was plotted as in Figure 2, with 5 cutting passes per path; the cutting path was arranged from left to right (shifting by 10 \(\upmu\)m per path, with seven shifts in total). The workpiece stage was lifted along the vertical Z-axis to cut the next layer (for example, the Z-axis lift can be set to 50 \(\upmu\)m per layer). This test showed that the PCD workpiece could be cut through when the stage  
Figure 11: Correlation between variation in pulse width, pulse energy, and kerf depth. Both pulse energy and kerf depth increase with an increase in pulse width. Figure 10: Effect of variation in pulse width on kerf depth in laser cutting of PCD workpiece. The fixed average power was 30 W, and the lowest pulse repetition rate for a specific kerf width was selected, as shown in Table 5. (**a**) Pulse width of 4 ns; (**b**) pulse width of 8 ns; (**c**) pulse width of 14 ns; (**d**) pulse width of 20 ns; (**e**) pulse width of 30 ns; (**f**) pulse width of 50 ns; (**g**) pulse width of 100 ns; (**h**) pulse width of 200 ns. was lifted along the Z-axis 24 times by 50 \(\upmu\)m per layer to achieve a total processing depth of 1200 \(\upmu\)m.  
Subsequent cutting tests were conducted with different lifting heights along the Z-axis to determine whether the cutting efficiency can be improved (i.e., the shortest cutting time can be attained) by increasing the lifting distance. The optimal value will be used as the final operating parameter for the laser cutting process of the PCD workpiece. In these tests, the total stage lift along the Z-axis was set at 1200 \(\upmu\)m. We compared the test results for different stage lift settings: 50 \(\upmu\)m, 80 \(\upmu\)m, and 100 \(\upmu\)m per layer. The test results are shown in Table 6. The results reveal that the PCD workpiece can be cut through with stage lifts of 50 \(\upmu\)m and 80 \(\upmu\)m, whereas it cannot be cut through with the stage lift of 100 \(\upmu\)m. This result may be related to the horizontal shifting distance of 10 \(\upmu\)m; although the data from the cutting tests showed that the kerf depth would reach 155 \(\upmu\)m with 5 passes of cutting per path, the space measured between the two paths was less than 7 \(\upmu\)m at the lifting height of 100 \(\upmu\)m (indicating that less amount of material was removed from the bottom surface of the workpiece). Thus, in the case of a 100-\(\upmu\)m stage lift per layer, the bottom material cannot be removed entirely by laser power alone. Under this situation, the accumulated depth becomes insufficient, thereby resulting in an incompletely cut PCD workpiece. Based on these tests, we selected the stage lift along the Z-axis of 80 \(\upmu\)m per layer for subsequent testing. After the PCD workpiece was cut into two parts, the starting path side (left side, Figure 13a) and final path side (right side, Figure 13b) of the cut surface were observed by an optical microscope, as shown in Figure 13. A tilt of approximately 5.4\({}^{\circ}\) was observed on the final path, which appears smoother than the starting path, as shown in Figure 13b,d. On the contrary, the starting path appears very rough with numerous recasts; \begin{table}
\begin{tabular}{c c c c} \hline Stage lifting distance (\(\upmu\)m) (a) & 50 & 80 & 100 \\ Number of lifts (b) & 24 & 15 & 12 \\ Total lifting distance (\(\upmu\)m) (=a \(\times\) b) & 1200 & 1200 & 1200 \\ Number of paths per lifting & 8 & 8 & 8 \\ Number of passes per path & 5 & 5 & 5 \\ Cutting through & yes & yes & no \\ \hline \end{tabular} Note: distance between paths = 10 \(\upmu\)m.  
\end{table}