# Comparison between Laser and Stamping without Die (SWD) for Micro Tapered Hole Forming
## 4 Experimental Results and Discussion
### Microhole Morphology  
#### 4.1.1 Micro Stamping  
Figure 9 shows the schematic diagram of the microhole geometry definition. The OM photos are as shown in Figure 10. The stamping depth is 380 \(\upmu\)m, and there are g  
Figure 8: Laser processing experiment (**a**) laser mechanism (**b**) laser beam in different focusing arrangements.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Condition** \\ \hline Workpieces (Al6061) & 300 \(\upmu\)m \\ Wavelength & 532 nm \\ Frequency & 15 Hz \\ Pumping lamp energy & 16, 17, 18 J \\ Power (Watt) & 20, 30, 40 mW \\ Focal length & 120 mm \\ \hline \hline \end{tabular}
\end{table}
Table 3: Experimental parameters of laser drilling.  
entry due to the stamping process. During the process, the materials around the entry is extruded by the stamping head. The stress along the direction of the level is in tension, while the direction normal to the level is in compression.  
According to the stamping results, it is observed that the inlet hole is enlarged as the stamping depth increases; this phenomenon is the same in both the Al6061 and C2680; however, the plastic deformation around the inlet of Al6061 is smoother than C2680, as the Al6061 has better plastic deformability.  
The inlet diameter and influence area diameter are measured by averaging the measured results in both the \(X\)-, \(Y\)-axial directions. The prominence height is a distance between the workpiece surface and prominence top and measured by averaging the four point measurements at the top of the prominence. Figure 11 shows that the inlet diameter and prominence height increase linearly as the stamping depth  
Figure 10: Optical Microscope (OM) images of micro stamping hole morphology (\(Z=380\)\(\upmu\)m). Scale bars = 50\(\upmu\)m.  
Figure 9: Schematic diagram of hole size measurement.  
increases. Meanwhile, the inlet diameter of Al6061 is larger than C2680, and the diameter difference is about 4 \(\upmu\)m with the same stamping depth. The prominence height has a linear trend with the inlet diameter, as they are related to each other.  
The inlet influence area diameter is as shown in Figure 11. The influence area diameter of Al6061 and C2680 workpieces has a nonlinear trend with stamping depth, and because the influence area diameter is formed from material deformation, in which the lattice extrude each other and the material flows laterally due to the V-shaped structure of the hole wall. The influence area diameter is 238-290 \(\upmu\)m. The influence area diameter increases with the stamping depth.  
The outlet diameter and influence area diameter measurement method is the same as the inlet measurement method. The measurement result is as shown in Figure 12. The stamping results of the two workpieces show that the stamping depth for Al6061 punch forming is 340 \(\upmu\)m, whereas, the C2680 stamping depth is only 320 \(\upmu\)m. This result matches the inlet forming result. As the C2680 material has higher stiffness, the punching result is better.  
The outlet diameter is analyzed in Figure 12. According to the outlet diameters of the two materials, as the punching effect contains rupture and extrusion mechanisms, it is merely ruptured when the perforation begins. The plastic forming stage comes up as the stamping depth increases. Therefore, the larger the outlet size, the better the hole quality. The outlet influence area diameter is approximately the same as the inlet influence area. The influence area diameter increases with stamping depth for both Al6061 and C2680 materials. The prominence height of the outlet increases with the stamping depth; however, the difference is slight, and may because the plastic deformation resulted from punching is low, at about 5-8 \(\upmu\)m.  
Figure 11: Stamping depth/inlet hole geometry analysis.