Hybrid steady-flow electroforming process for high-aspect-ratio tapered microhole arrays

This study proposes a hybrid steady-flow electroforming process integrating steady-flow immersion and gradual rising for fabricating high-aspect-ratio tapered microhole array microstructures. A high-precision tapered micropillar master mold was fabricated by planetary electrical discharge machining (p-EDM), and a steady-flow electroforming system with automatic makeup water control, temperature regulation, and a tubular auxiliary anode was developed to stabilize electrolyte conditions and improve ion transport. The gradual-rising mode suppressed current crowding and promoted layer-by-layer nickel deposition within deep microstructures. Under the optimal conditions of a rising velocity of 0.3 μm/min, current density of 0.7 ASD, and auxiliary anode slot width of 0.5 mm, a 5 × 5 tapered microhole array with an aspect ratio of 13:1 and a taper ratio of 1:15 was successfully fabricated. The proposed process achieved high dimensional uniformity, dense deposition, and precise replication, demonstrating strong potential for precision flow-control and high-pressure jetting applications.