Micro-EDM

Electrical Discharge Machining

Electrical discharge machining (EDM) is non-contact process capable of removing material at very small lengthscales without creating mechanical stresses. The material is removed through highly localized melting and evaporation as a result of electrical discharges from an electrode to the material. The discharges, which form tiny plasma channels with temperatures up to 10,000 °C, locally melt very small amounts of material. As the plasma collapses when the current flow is shut off, the resulting vacuum pulls out the molten material into the surrounding dielectric medium. For discharges to occur, the material needs to have sufficient electrical conductivity whereas material hardness is of no consequence. As such, any metal as well as many semiconductors are candidates for this process.
Micro-EDM is a specialized form of EDM whereby the workpieces have features as little as 10 microns (0.0004 inches). These small features are achieved with electrodes that are also very small in size. For EDM sinker and EDM milling, the typical features are internal geometries such as holes, slots, etc. Therefore, the electrodes are typically a tiny bit smaller than the features to be machined. For wire-EDM (micro-WEDM), where most features are external, this restriction is not necessarily the case.

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EDM machinability of various materials (Source: Lee et. a., Effect of metal coating on machinability of high purity germanium with wire electrical discharge machining, J Mat Proc 213, 2013)

Micro-EDM Examples - 0.1 mm (0.004 in) brass wire

0.4 mm (0.016 in) pitch microelectrode array, 5x5mm (0.2 x 0.2 in) with 144 electrodes of 5 mm height (0.2 in). Material: doped silicon	0.4 mm (0.016 in) pitch microelectrode array, 5x5mm (0.2 x 0.2 in) with 144 electrodes of 5 mm height (0.2 in). Cross section of electrodes is varied along length to increase flexibility. Material: doped silicon.
0.4 mm (0.016 in) pitch microelectrode array, 5x5mm (0.2 x 0.2 in) with 144 electrodes of 5 mm height (0.2 in). Cross section of electrodes is wavy to increase flexibility. Material: doped silicon	0.4 mm (0.016 in) pitch microelectrode array, 5x5mm (0.2 x 0.2 in) with 144 electrodes of 5-9 mm height (0.2 -0.35 in). Cross section of electrodes is tapered towards tip to increase flexibility. Material: doped silicon

Micro-EDM Examples - 0.05 mm (0.002 in) steel wire

0.15 mm (0.006 in) pitch microelectrode array, 3x3mm (0.12 x 0.12 in) with 1156 electrodes of 1.0 mm height (0.04 in). Cross section of electrode is curved to increase flexibility. Material: brass	Turbine vane test windows with very small corner radius of 0.03 mm (0.0011 in) and matched curvature as well as very tight tolerance relative to a non-conductive out layer. Material: nickel-superalloy. Courtesy of Prof. Kevin Hemker and Binwei Zhang, Johns Hopkins University.

Micro-EDM Examples - 0.05 mm (0.002 in) steel wire

0.05 mm pitch (0.002) microelectrode array, 1.5x3mm (0.06 x 0.12 in) with 3000 electrodes of 0.2 mm height (0.008 in). Material: brass	0.05 mm pitch (0.002) microelectrode array, 1.5x3mm (0.06 x 0.12 in) with 3000 electrodes of 0.2 mm height (0.008 in). Electrodes are slanted to increase electrode flexibility. Material: brass

Micro-EDM Examples - 0.012 mm (0.00047 in) tungsten wire

0.04 mm pitch (0.0016) microelectrode array, 0.3x0.3mm (0.012 x 0.012 in) with 9 electrodes of 0.4 mm height (0.016 in) - before cleaning. Electrodes have a revere bendslanted to increase electrode flexibility. Material: copper berylium

Micro-EDM Examples - rotational features

1.0 mm pitch (0.04 in) helical microswimmer machined with rotary axis. Material: 1mm diameter nitinol tubing. Courtesy of Prof Jake Abbott, University of Utah	0.3 mm pitch (0.012 in) helix support for artificial muscles. Material: 1mm diameter nitinol tubing. Courtesy of Prof Stephen Mascaro, University of Utah

Further reading

• Experimental investigation of wire electrical discharge machining of NdFeB permanent magnets with an RC-type machine, Greer J, Petruska AJ, Mahoney AW, Nambi M, Bamberg E, and Abbott JJ, Journal of Materials Engineering and Performance 23(4), pp. 1392-1401 (2014). Download document here
• Effect of metal coating on machinability of high purity germanium using wire electrical discharge machining, Lee S, Scarpulla MA, Bamberg E, Journal of Materials Processing Technology 213, pp 811- 817 (2013). Download document here
• Application- specific customizable architectures of Utah neural interfaces, Sharma R, Tathireddy P, Lee S, Rieth L, Bamberg E, Dorval A, Normann R, and Solzbacher F, Procedia Engineering 25, pp 1016-1019 (2011)
• Velocity control with gravity compensation for magnetic helical swimmers, Mahoney AW, Sarrazin JC, Bamberg E, and Abbott JJ, Advanced Robotics 25(8), pp 1007-1028 (2011). Download document here
• Material removal rate, kerf, and surface roughness of tungsten carbide machined with wire electrical discharge machining, Shah A, Mufti NA, Rakwal D, Bamberg E, Journal of Materials Engineering and Performance 20(1), pp 71-76 (2011). Download document here
• Fabrication of high aspect ratio silicon micro-electrode arrays using micro-wire electrical discharge machining (micro-WEDM), Rakwal D, Heamawatanachai S, Tathireddy P, Solzbacher F, and Bamberg E, Microsystem Technologies 15(5), pp 789-797 (2009). Download document here
•  Slicing, cleaning and kerf analysis of germanium wafers machined by wire electrical discharge machining, Rakwal D, and Bamberg E, Journal of Materials Processing Technology 209(8), pp 3740-3751 (2009). Download document here
• Electrical discharge machining promises high-quality, lower-cost substrates, Rakwal D, and Bamberg E, Compound Semiconductor, March 2009, pp 17-18 (2009)
• Orbital electrode actuation to improve efficiency of drilling micro holes by micro-EDM, Bamberg E, and Heamawatanachai S, Journal of Materials Processing Technology 209(4), pp 1826-1834 (2009).. Download document here
• Experimental investigation of wire electrical discharge machining of gallium doped germanium, Bamberg E, and Rakwal D, Journal of Materials Processing Technology 197(1-3), pp 419-427 (2008). Download document here