## 3 Experimental Results
### Concurrent Transcription of the Nanotextures onto the Hole Surfaces with Piercing  
The trimmed diamond-coated punch and the core die were fixed into the cassette die for the piercing experiment. In the present experiment, clearance was controlled to be 4%, which is similar to fine blanking process used for automotive parts. Misalignment of the punch to the core die was avoided by the movable x-y stages of the stamper, making the eccentricity negligible. The pierced holes were observed by optical microscopy and SEM under different magnifications. As depicted in Figure 8a, the entire hole surface was metallic and shiny, without any traces of fractured areas. In fact, the burnished surface area ratio was measured to be 100%, as shown in Figure 8b. An SEM analysis with higher magnification revealed that nanotextures were formed on this burnished surface, as depicted in Figure 8c. Nanotextures with a spatial period of 0.3 um were superposed on the fine burnished surface profile. That is, hole surface pierced by the present trimmed punch was characterized by its multi-dimensionally modified profile. It was fully burnished similar to the fine-blanked surfaces under narrowed clearance [19]. In addition, this surface burnished by the trimmed punch features a regular nanotextured microscopic profile dissimilar to the fine-blanked surface profile, with significant roughness in the order of 3 to 5 um at maximum. WLI was also utilized to engage in a nondestructive analysis of the transcribed nanotextures, as shown in Figure 8c. The two-dimensional surface angulation is depicted in Figure 9a. Linear nanotextures were formed along the Y-axis or in the direction of the hole thickness. These textures were periodically formed in the X-axis or in the circumferential direction of the pierced hole. Figure 9b depicts the microscopic profile of nanotextured surface. Although the average height drifted due to the noises in interferometry, the nanotextures were detected to have the same spatial period (\(\Lambda\)) of 900 nm, as seen in Figure 7; i.e., \(\Lambda_{\text{punch}}=\Lambda_{\text{hole}}=900\) nm by WLI. Figures 8c and 9a,b prove that the nanotextures on the punch side surface were transcribed onto the pierced hole surface in a semi-regular nanopattern. In the algorithm of DEAP, the effects of large punch curvatures and pierced hole surfaces on inter  
Figure 7: Measured profile of the trimmed side surface of the CVD-diamond coating using white-light interferometry. (**a**) Two-dimensional surface angulation of the trimmed diamond coating, and (**b**) lateral surface profile of the nano-textured ripples on the trimmed surface. are difficult to avoid when analyzing nanotextured periods. The nanotextures on the punch and hole surfaces with a period of 300 nm were expanded by this curvature effect in the WLI and DEAP analysis to estimate larger periods. We will next describe the differences in hole surface quality for fine piercing under the same clearance when using two different punches; i.e., the bare WC (Co) punch with the normal WC-grain size and the laser-trimmed diamond-coated WC (Co) punch. As depicted in Figure 10a, a normal hole pierced by the bare WC (Co) punch has a dull, fully burnished surface with metallic scratches on the punch side surface from dry shearing without lubrication. The maximum roughness on this burnished surface reaches 3 \(\upmu\)m. In addition, the debris particles and fragments adhered to the bare WC (Co) punch head and side surfaces. This adhesion triggered chipping at the punch edge and shortened the punch life in practice. On the other hand, the hole pierced by the trimmed punch has a metallic, shiny surface without any scratches. In addition, blue-colored luster is also detected by optical microscopy as a surface plasmon in the nanotextures of the hole surface. This reveals that fine burnished and mirror-polished surfaces  
Figure 8: SEM images of the pierced hole surfaces with different magnifications.