A Low-Cost Retrofitted CNC Platform with Mobile-Terminal Control for Micro Electrical Discharge Deposition: System Design and Process Characterization

Micro electrical discharge deposition (micro-EDD) enables maskless direct-write metallic tracks on conductive substrates, but reported implementations rely on purpose-built machines with programmable pulse generators and gap servos. This paper reports a low-cost micro-EDD platform retrofitted from a desktop CNC router driven by GRBL firmware, extended with an Android control application for path definition and process supervision. Discharge is produced by an RC relaxation circuit with no pulse generator and no gap feedback. Copper, aluminium, nickel, and titanium electrodes were deposited onto silicon substrates in an argon atmosphere, maintaining a 10 μm separation. The working point, pd ≈ 0.76 Torr·cm, lies within 20% of the argon Paschen minimum. Track width rises linearly with supply voltage over 330–400 V (w = 0.570 V − 99.2 μm, R2 = 0.994), extrapolating to a deposition threshold of 174 V, 37 V above the argon breakdown minimum—indicating an energy threshold distinct from breakdown. Across electrode materials, width shows a trend consistent with thermal diffusivity as w∝α0.46 (R2 = 0.69, N = 4), resolving the inconsistency that copper, the best conductor, gives the widest track. Polarity reversal changes width by factors of 4.6 (Cu) and 7.5 (Al), consistent with anode-dominated energy partition. Péclet numbers remain below 3 × 10−4 and overlap ratios above 103, excluding thermal advection and insufficient overlap as causes of the feed-rate collapse. A five-axis kinematic extension is derived, with Z travel identified as the bounding constraint.