# Effectiveness of Electrode Design Methodologies for Fast EDM Slotting of Thick Silicon Wafers
## 3 Results and Discussion
### Effect of Electrode Arrays on Machining Speed with Varied Electrode Leg Heights
#### 3.1.3 Analysis of Quality of the Machined Features on Silicon  
This section presents the quality of the machined features on silicon workpieces for mirror images of graphite electrodes. Firstly, visual analysis of the entry and exit side of the workpieces for 1 \(\times\) 4, 2 \(\times\) 4, 3 \(\times\) 4, and 6 \(\times\) 4 arrays of electrodes for the two heights will be shown in Figures 8 and 9, and for 4 \(\times\) 4 and 5 \(\times\) 4 arrays, can be seen in Appendix B as Figures 12 and 13. It can be observed that the quality of the machined features improved with increased arrays of electrodes, especially at the exit side. For higher arrays of electrodes, there is less chipping observed at the exit side of machined features on the silicon surface compared to lower arrays of electrodes. Overall, it is found that the quality of the machined slots suffers lesser defects at the entrance compared to the exit side, although the dimensions of the slots were found to be slightly higher at the entrance. The defects at the exit holes come mostly in the form of chipping at the edges or more specifically at the corners. This is due to the accumulation of carbon at the side and bottom surfaces of the electrode legs, which causes secondary sparking at the side wall and exit corners of the electrode legs. The most interesting finding is that the amounts of defects found were reduced with the increase in arrays of electrodes. It is hypothesized that the 'jump' action of the electrode holder results in increased dielectric fluid flow at the narrow channels of electrode arrays, and that as the number of channels increases with the number of arrays, the flushing becomes more effective. The spaces between the electrode legs in different rows (horizontal) and columns (vertical) work as narrow channels for dielectric fluid flow during die-sinking EDM, which is a probable explanation for why the material removal rate improves and the number of defects reduces on the machined slots, with larger electrode arrays, regardless of the electrode leg height. As we know from the equation of continuity of the fluid flow, the flow velocity of non-compressive fluid is inversely proportional to the cross-sectional area of the pipe at any given flow rate, meaning that the fluid flow inside a smaller diameter pipe has a higher velocity than that of a larger diameter. In a die-sinking EDM dielectric tank, the flow rate and direction of the dielectric fluid are fixed. Therefore, the channels created between rows in the electrode, that are parallel to the direction of the flow, effectively control the dielectric fluid flow during machining. When the fluid goes through these narrow channels, the velocity increases significantly compared to the fluid velocity at other areas of the machining zone, which improves the flushing condition, and thus results in an increment in the MRR. This hypothesis is explained in Figure 10.  
Figure 7: Variation in material removal rate for different arrays of electrodes with electrode leg heights of 0.2′′ and 0.3′′. Figure 8: (**a**) Entry and (**b**) exit side of silicon workpieces after machining with \(1\times 4\), \(2\times 4\), and \(3\times 4\) arrays of electrodes for electrode leg height of \(0.2^{\prime\prime}\). Figure 9: _Cont._  
Figure 10 demonstrates the channel formation with increased arrays of electrodes and the direction of the dielectric fluid flow. In Figure 10, a solid red arrow indicates the direction of the dielectric fluid flow, dotted red arrows represent the vertical channel, which is normal to the direction of the dielectric fluid flow, and solid yellow arrows indicate the horizontal channel, which is parallel to the direction of the dielectric fluid flow. In the case of \(1\times 4\) arrays of electrode legs, there is a single row, and no channels exist in the horizontal direction. Three channels can be seen in the vertical direction, but those are normal to the direction of the flow of dielectric fluid. As a result, these channels do not have any effect on improving the flushing conditions.