# Micromachining in Powder-Mixed Micro Electrical Discharge Machining
## 4 Application of Power-mixed \(\upmu\)-EDM (PM \(\upmu\)-EDM)
### Application of PM\(\mu\)-EDM in Geometrical Accuracy  
Another objective of powder-mixed dielectric fluid in \(\mu\)-EDM is to acquire a higher dimensional accuracy of the produced microparts, which plays an important role in microfabrication. [PERSON] et al. [73] performed microhole machining on a Ti-6 Al-4V plate by utilizing different types of dielectric fluids, i.e., hydrocarbon oil, kerosene and non-hydrocarbon oil, de-ionized water mixed with B\({}_{4}\)C powder. The cylindrical tungsten of 300 \(\upmu\)m in diameter was used as the tool electrode. Peak current and pulse-on-time, which are the most significant process parameters in micro-EDM processes, were varied from 0.5 A to 2.0 A and from 1 to 20 \(\upmu\)s, respectively. This study concentrated on the accuracy of the microholes taper and circularity produced under different types of dielectric fluid. The result revealed that at low-discharge energies, it was found that the taper of microholes was lower under pure kerosene compared to the result under B\({}_{4}\)C powder-mixed kerosene. This is due to the stronger adhesion of carbon on the workpiece created by the presence of B\({}_{4}\)C in dielectric fluid, resulting in lower material removed from the exit of microholes. Thus, there is a significant difference of diameter at the entry and exit holes. In terms of circularity, machining under B\({}_{4}\)C powder-mixed dielectric fluid provided non-uniform microholes compared to pure dielectric fluid. This was due to the presence of debris from the workpiece and B\({}_{4}\)C powders. The debris created secondary discharges to produce a non-uniformly circular microholes. [PERSON] et al. [74] investigated \(\mu\)-EDM machining of Ti-6 Al-4V for microhole fabrication by using three different types of dielectric fluids, such as DEF-92 (EDM oil), deionized water and Cu powder-mixed deionized water at a concentration of 2 g/L. A cylindrical brass of diameter 300 \(\upmu\)mwas used as the tool electrode. The machining parameters considered in this EDM process were peak current at the range of 0.5-2 A and a pulse time of 8 \(\upmu\)s. The works focused on the influence of Cu powder-mixed dielectric fluid to the circularity, over cut and taper, on microholes produced during the machining process of Ti6 Al-4V. It was found that at the peak current range from 0.5 to 1.5 A, the taper under deionized water was less than the taper produced with Cu powder-mixed deionized water. However, when the peak current increased from 1.5 to 2 A, the machining in the Cu powder-mixed deionized water showed an improvement in the microholes taper. In the case of circularity, in the range of the peak current from 1.5-2 A, pure deionized water gave a better circularity than the Cu powder-mixed deionized water. At this peak current range, the pure deionized water dissipates heat better from the melted workpiece surface, which further reduces the adhesion of debris onto the machined surface. [PERSON] et al. [75] investigated the effect of suspended powder on the inaccuracy of the depth of microholes produced. In a \(\upmu\)-EDM process, the occurrence of first discharge, which becomes the starting point for the machining processes, is considered as the surface of the workpiece. Due to the presence of powder in the machining gap, the first discharge commences far above the surface of the workpiece. Therefore, the depth of the microholes produced was not accurate. In order to improve the accuracy of the microhole depth, the powder-mixed dielectric in the \(\upmu\)-EDM process was assisted by the discharge pulse-counting method. Instead of setting the hole's depth in the numerical control (NC) code display, micromachining was performed by entering the number of discharges required in fabricating the blind microholes. The result showed that the combination of these two techniques significantly improved the accuracy of the microholes produced regardless of the concentration of the suspended powder.