## 3 Results and Discussions
### Test Results of Laser Surface Finishing of PCD Workpiece  
The results during the previous laser-cutting tests reveal that the final processing path depicted on the right (Figures 3 and 4) yields superior surface quality. Therefore, this path was used for the laser-finishing tests using Methods 1, 2, and 3. To this end, the finishing paths depicted in Figures 3 and 4 were considered. The surface morphologies of the finished surface obtained by these methods were investigated by scanning electron microscope (DSM-6390 LV, JEOL), as shown in Figure 14. The images reveal that the recasts and deposits are removed; moreover, the best surface quality was obtained with Method 3. The inferior surface quality observed with Methods 1 and 2 might be due to the laser beam energy being shielded by the PCD bulk material located above the laser beam focal spot, as shown in Figure 15. The shielding of the laser beam energy increases with processing depth. Thus, the deepest part is subjected to the lowest laser energy, thereby resulting in the incomplete removal of recasts and sidewall deposits as well as inferior surface quality. The finishing Methods 1, 2, and 3 achieved finishing depths of 250 \(\upmu\)m, 231 \(\upmu\)m, and 347 \(\upmu\)m, respectively. However, even though the finishing Method 3 showed the best surface quality, it could not reach the targeted depth of 400 \(\upmu\)m. An unfinished area existed  
Figure 13: Optical microscope images of left and right sides of a laser cut PCD workpiece. (**a**) Left side, where the starting path begins; (**b**) right- side, where the final path ends; (**c**) surface of the cut side, where the starting path begins; (**d**) surface of the cut side, where the final path ends. at the very end of the PCD workpiece. We decided to use higher pulse energy in the finishing process to rectify this issue. To achieve the target finishing depth of the PCD workpiece, pulse width of 200 ns and pulse repetition rate of 30 kHz were used for the laser-finishing test conducted with Method 3. The test results are shown in Figure 16. No significant difference in the surface quality was observed between high pulse width of 200 ns and low pulse width of 50 ns, as shown in Figures 14d and 16b, respectively. The surface roughness of the finished surface of the PCD workpiece was measured by coherence correlation interferometry (CCI; Talysurf CCI-Lite, Taylor Hobson, West Chicago, IL, USA), as shown in Figure 17. The surface roughness before finishing was Ra = 0.378 \(\upmu\)m, and that after finishing was Ra = 0.209 \(\upmu\)m. The laser cut surface showed a flat morphology. The findings of this study reveal the realization of improved surface morphology and roughness after laser finishing of the PCD workpiece. This results in superior surface quality of the cut surface. These results demonstrate good agreement with those reported by [PERSON] et al. (2020). Figure 14: SEM morphologies of the laser finished surface (laser finishing parameters are average power of 30 W, scan rate of 5 mm/s, pulse width of 50 ns, repetition rate of 90 kHz). (**a**) The surface without laser finishing; (**b**) the surface after laser finishing using Method 1; (**c**) the surface after laser finishing using Method 2; (**d**) the surface after laser finishing using Method 3. Figure 15: Schematic diagram of the laser shielding effect. The optical microscope images reveal that the cut edge of the PCD workpiece is titled, as shown in Figure 16a. The titled angle of the laser finishing edge was measured at 5.2\({}^{\circ}\). Although this value was slightly less than that of the laser cut edge, it was not sufficiently low. The titled edge angle was attributed to the layer-by-layer cutting and finishing process from the top of the workpiece to the bottom. The material on the upper layer was subjected to multi-processing, after which more material was removed. This is in agreement with the results of [PERSON] and [PERSON] [PERSON] and [PERSON] (2011) and [PERSON] et al. [PERSON] et al. (2017).