# Micromachining in Powder-Mixed Micro Electrical Discharge Machining
## 7 Conclusions  
Micro-EDM is one of manufacturing processes to produce microparts with exceptional accuracy and precision. This article presented an extensive review of power-mixed \(\upmu\)-EDM to the machining efficiency, the application and its accuracy. The following conclusions are drawn based on the presented literature:  
1. There is an optimum powder concentration in power-mixed \(\upmu\)-EDM to achieve the best combination of the material-removal rate, the surface quality, and the tool wear rate. High powder concentration may lead to powder deposition around machining area, whilst low concentration may be insignificant to break single sparks into many small, uniform sparks to achieve a fine surface finish. Powder material with high electrical conductivity will contribute to  
Figure 11: Summary of the machining process variation of powder-mixed \(\upmu\)-EDM. a higher material-removal rate, whilst semi-conductive powder material provides a fine surface finish. The selection of powder material to be used depends highly on the machining stage (roughing, semi-finish or finishing). 2. The machining gap in \(\mu\)-EDM is only in the range of few microns, hence the selection of powder size should be in the range of 1/100-1/150 of the machining gap width to get the optimum machining result. Whilst circular nanopowder is mostly used in power-mixed \(\mu\)-EDM, a cylindrical shape material with an aspect ratio of 40-50 yields will have a higher removal rate and improved surface roughness. Cylindrical shape material surpasses circular shape at the same concentration due to the bridge-forming of micro-length materials; thus, it promotes better bridging networks between the two electrodes. 3. Rough machining requires high energy and often sacrifices the tool to have a high tool wear rate. Semi-conductive materials such as SiC are often used at low concentrations to achieve maximum material removal. Finish machining requires small energy to generate smaller craters, thus yielding a fine surface finish. The presence of nanopowder, either semi-conductive or in combination with other material, is able to break initial discharge into many, small discharges with less energy, hence allowing a fine surface finish by forming tiny craters. 4. Surface modification in microparts can also be done in PM \(\mu\)-EDM by utilizing specific powders for different usage, according to their biomedical, antibacterial, microhardness and wear-resistant properties. Exotic powder materials such as tungsten alloys, molybdenum and titanium alloys are often used for surface modification. The powder melts during spark-time and adheres to the workpiece, creating a thin layer on the top surface with different property than that in parent material. 5. The \(\mu\)-EDM machine detects the first spark as its starting point, which is incorrect since the added powder promotes a spark far above the workpiece surface. To overcome this problem, the depth of machining should not be set as depth but as counted discharge pulse. The combination of these techniques improved both the accuracy and the machining results. 6. Powder sedimentation is another issue in power-mixed \(\mu\)-EDM. Vibrating the dielectric fluid at the ultrasonic level is able to reduce adhesion, prevent powder agglomeration, and leads to improve material-removal rate and surface quality. The presence of powder makes short-circuiting and arcing prone to occur since the powder may connect the two electrodes before the discharge time. The introduction of tool vibration or workpiece vibration helps to better distribute the added powder in the tiny machining gap, and promotes the advanced flushing out of the debris, thus reducing arcing and short-circuiting. Conceptualization, G.S.P. and T.S. ; methodology, G.S.P. and T.S. ; resources, G.S.P., M.M., and T.S. ; writing--original draft preparation, G.S.P; writing--review and editing, G.S.P. and T.S. ; supervision, G.S.P., M.M., and T.S. ; project administration, G.S.P. ; funding acquisition, G.S.P.