## 3 Results and Discussions
### Laser Cutting of PCD Workpiece  
#### 3.2.1 Influence of Various Processing Parameters on Kerf Depth of PCD Materials  
To obtain better cutting efficiency, this study compared the effects of various scan rates, number of processing passes, and various processing parameters on the kerf depth of the PCD workpiece. The parameter settings that yielded the best cutting efficiency were used in the subsequent tests. Figures 6 and 7 reveal that the kerf depth decreases with an increase in scan rate. When the scan rate was less than 5 mm/s, there was very little increase in the kerf depth. This was because the laser energy accumulation had reached its limit and the cutting efficiency could not be improved further, even when higher laser energy was input. The local accumulation of a large amount of heat will enlarge the heat-affected zone. Therefore, in this study, a 5-mm/s scan rate was considered as the operating parameter for subsequent testing. This was followed by changing the number of cutting passes per path. Figures 8 and 9 illustrate an increase in the kerf depth corresponding to an increase in the number of cutting passes. However, the observed increase in the kerf depth becomes less pronounced as the number of cutting passes per path exceeds five. This is because the initial increase in the kerf depth with the cutting-pass count causes the material in the bottom layers subjected to laser beam irradiation to be over-focused. Because the laser energy in this over-focused region is lower compared to the material-ablation threshold, no further material removal can be realized. Therefore, five cutting passes per path were considered in this study for subsequent testing. Moreover, the test results revealed that changing the number of cutting passes was better than changing the scan rate to increase the kerf depth. The effects of variation in pulse width and pulse energy of laser cutting on the PCD workpiece was studied at the fixed average power of 30 W. The lowest pulse repetition rate for a specific pulse width at which the maximum peak pulse power was obtained was selected, and the kerf depth and surface quality of the cut surface were discussed. In the laser cutting studies, the processing scan rate was set at 5 mm/s, and the number of cutting passes was set at one pass per path. The lowest pulse repetition rate corresponding to the specific pulse width, maximum pulse energy, and maximum peak power is listed in Table 5. The information in the table reveals that the lowest pulse repetition rate decreases corresponding to an increase in the pulse width under the constant average-power setting. Correspondingly, the pulse energy and peak power increase and decrease, respectively. Figure 8: _Cont._  
Figure 6: Optical microscope observation of the effect of variation in the scan rate on the kerf depth in laser cutting of PCD workpiece (laser processing parameters were set at average power of 25.5 W, pulse width of 200 ns, and repetition rate of 170 kHz): (**a**) scan rate of 1 mm/s; (**b**) scan rate of 3 mm/s; (**c**) scan rate of 5 mm/s; (**d**) scan rate of 7 mm/s; (**e**) scan rate of 9 mm/s. Figure 7: Relationship between scan rate and kerf depth (laser processing parameters are average power of 25.5 W, pulse width of 200 ns, and repetition rate of 170 kHz). Moreover, a large pulse width corresponded to an increased kerr depth, as depicted in Figure 10. Therefore, the maximum kerr depth corresponded to the pulse-width and pulse-repetition-rate values of 200 ns and 30 kHz, respectively. Furthermore, Figure 11 reveals that the kerr depth increased with an increase in pulse energy. Therefore, it can be inferred that conditions involving the maximum pulse width (200 ns) (at lowest pulse repetition rate) and highest pulse energy (1 mJ) would yield the maximum kerr depth. In addition, the maximum pulse width of 200 ns corresponded to the lowest peak power, as illustrated in Figure 12. Therefore, despite the peak power corresponding to its lowest value, it was sufficient to exceed the material ablation threshold.