# 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
However, in the case of \(2\times 4\) arrays, there is one channel in the horizontal direction, and it is parallel to the direction of the dielectric fluid. The number of channels in the vertical direction is fixed, which is three for all the arrays of electrodes regardless of height. In the horizontal channel, there is a rise in velocity, which improves the flushing conditions as well as the MRR. It can be seen that there is a significant improvement in the MRR, that is, almost 4-fold, due to the improvement in debris removal from the workpiece compared to  
Figure 10: Formation of dielectric fluid flow channels for different arrays of electrode legs. [Solid red arrow indicates dielectric fluid flow direction, Red dotted arrows indicate vertical channels, which are normal to the direction of the dielectric fluid flow. Yellow solid arrows indicate horizontal channels parallel to the direction of the dielectric fluid flow]. Figure 9: (**a**) Entry and (**b**) exit side of silicon workpieces after machining with (6 \(\times\) 4) arrays of electrodes with the electrode leg heights of \(0.2^{\prime\prime}\) and \(0.3^{\prime\prime}\). 1 \(\times\) 4 arrays of electrodes. In the case of 3 \(\times\) 4, 4 \(\times\) 4, 5 \(\times\) 4, and 6 \(\times\) 4 arrays, the increased velocity in two, three, four, and five horizontal channels, respectively, further improved the flushing conditions compared to 1 \(\times\) 4 and 2 \(\times\) 4. The graphite electrodes \"jump\" action toward the silicon workpiece during machining is the principal source of effective flushing during machining. This 'built-in' jumping action of the electrode in the die-sinking EDM machine periodically changes the gap between the electrode and the workpiece due to the up-and-down movement and also introduces turbulence into the gap, which helps in flushing the debris out of the machining zone. This jumping action of the electrode also improves the MRR. As the electrode jumps, the dielectric fluid between the workpiece and the electrode becomes turbulent, cleaning the debris from the spark gap [36]. Figure 11 shows a simple graphical representation of how the jump action works in die-sinking EDM [37]. It can be seen that when the electrode goes upward during the pulse off time (Figure 11a), high-velocity dielectric fluid clears debris from the workpiece, and when the electrode moves down toward the silicon workpiece, it creates turbulence and efficiently sweeps out the remaining debris from the machining zone. With more electrode arrays, turbulence became more intense, due to an increase in the number of electrode legs, which effectively removed debris from the workpiece. As a result, the rate of material removal increased with the number of electrode arrays. Combining these two factors increases the productivity of machining silicon workpieces for increased arrays of electrode legs. Also, it is found that an increase in the number of electrode arrays has an inverse relationship with the buildup of carbon deposition on the graphite electrode. With larger arrays of electrodes, this factor may also hasten improvements in the material removal rate. For the same arrays of electrode legs, electrodes of a 0.2\({}^{\prime\prime}\) height perform better than those of a 0.3\({}^{\prime\prime}\) height in terms of the MRR. The reasoning for this can be referred to as the 1 st cause of improving the MRR, which is the increased velocity in narrow channels of electrodes with higher arrays of electrode legs. Because electrode legs of a 0.2\({}^{\prime\prime}\) height  
Figure 11: Overview of ’jump’ action of EDM electrode during die-sinking EDM of silicon. (**a**) Upward movement (drawing dielectric fluid into the gap). (**b**) Downward movement (pushing dielectric fluid and debris out of the gap) [Redrawn based on the concept from original source in Ref [37]. [The straight white color arrows on the tool indicate direction of tool movement, curved blue color arrows on both sides of the electrode indicate the direction of dielectric flow].