A study on the characterization of high nickel alloy micro-holes using micro-EDM and their applications

In this study, the feasibility of fabricating micro-holes in the high nickel alloy using micro-electro-discharge machining (micro-EDM) was investigated. The high nickel alloy is a material with high magnetic permeability. It can be used to shield MEMS prevent interference of the magnetic field. Micro-systems can be assembled and micro-wires can be connected through micro-holes that are drilled in the workpiece. In this way, the internal electronic system can communicate with external system without magnetic wave disturbance. However, since the high nickel alloy is tough and can easily cause cutting tool wear, it is difficult to fabricate micro-holes by the conventional machining methods. In this work, a two-stage cylindrical cutting tool of high hardness was first fashioned. The tool was precisely shaped with a first stage (i.e., tip) having a smaller diameter, and a helically grooved second stage with a larger diameter by the wire electro-discharge grinding (WEDG) process. The first stage of the tool electrode was then used to drill a micro-hole in a plate using micro-EDM process. To improve the roughness of micro-holes, the second stage with helical groove was used for in situ grind machining with SiC particles. Our experimental results show that by optimizing EDM machining parameters, i.e., discharge current of 500 mA, pulse duration of around 4 μs, etc., favorable diameter variation between the entrances and the exits (DVEE), good material removal rate (MRR) and good electrode wear rate (EWR) could be obtained. The addition of the in situ grind machining leads to precise contours, and the surface roughness of micro-holes is reduced to 0.85 μm Rmax, as revealed by SEM photographs.