# Micro-Slit Cutting in an Aluminum Foil Using an Un-Traveling Tungsten Wire
## 4 Result and Discussion  
### Width Consistency of Slits  
During the experiment, the slit length was 5 mm. At first, the aluminum foil was machined under the initial velocity for 1 mm as the tungsten wire needs to generate tension and produce a breach. At this position, the stress generally exceeds the tensile strength of aluminum according to Figure 2, preparing for the second stage. After finishing the first stage, the cutting process is paused for several seconds. Afterward, the aluminum foil was machined under secondary velocity till the preset length.  
Considering the slit machined is rather long compared with its width, the width consistency should be a central index to assess machining quality. Figure 5 shows the SEM micrographs of slits using different initial and secondary velocities. It is observed that plastic flow exists at both sides of each slit. In the cutting process, material near the slit is extruded and plastic bulge deformation appears. As a result, these regions will be a little bit thicker than other regions for about 2 to 5 um, as shown in Figure 6.  
In this study, eight measure points were sequentially selected on each slit to obtain average width and standard deviation. The first measure point was 0.5 mm away from the kerf and the interval was 0.5 mm between the two measure points. Figure 7 shows the width data of each slit and the average width of each slit as well as standard deviation. It can be observed that the average width of each slit is between 44.82-48.75 um, which is a little smaller than the diameter of the tungsten wire. It is probably caused by minor elastic deformation between tungsten wire and aluminum foil. After cutting, the slit will spring back slightly. Besides, the machined slits are rather straight and have great width consistency.  
For a single slit, the width machined under initial velocity shows no difference from the width machined under secondary velocity. The maximum width standard deviation is 2.95 um with an average width of 47.94 um, which proves this method has great stability. In addition, it is worth mentioning that slits machined with an initial velocity of 25 um-s\({}^{-1}\) show the best consistency compared with others as shown in Figure 8.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Composition** & **Content** \\ \hline Al & 99\% \\ Fe & \textless{}0.7\% \\ Si & \textless{}0.5\% \\ Rest & \textless{}0.2\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Chemical composition of aluminum foil.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Tungsten wire diameter & 50 μm \\ Aluminum foil thickness & 100 μm \\ Initial velocity & 10, 25, 50 μm-s\({}^{-1}\) \\ Secondary velocity & 50, 100, 250, 500 μm-s\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Machining conditions.  
Figure 8: Summary of measurement result: (**a**) average slit width; (**b**) standard deviation.  
Figure 6: The tiny bulge near the machined region.  
Figure 7: Width data of slits with different initial velocities: (**a**) 10 \(\upmu\)m-s\({}^{-1}\); (**b**) 25 \(\upmu\)m-s\({}^{-1}\); (**c**) 50 \(\upmu\)m-s\({}^{-1}\).