Drilling of microholes using electrochemical machining

Few studies have been reported on the drilling of microholes with a diameter of approximately 10 μm or less by electrochemical machining (ECM). The ECM of such holes was therefore attempted using ultrashort voltage pulses. Stainless-steel sheets were drilled using cemented tungsten carbide tool electrodes. As a result, a microhole of 4.5 μm entrance diameter and 4 μm exit diameter was successfully drilled in a 5-μm-thick sheet with a pulse width of 60 ns using a tool electrode 3 μm in diameter. This is the smallest-diameter hole drilled by ECM, to the best of our knowledge. A microhole of 5.5 μm entrance diameter and 4.5 μm exit diameter was also drilled in an 8-μm-thick sheet. Furthermore, the machining properties were investigated. The effect of the tool electrode shape, pulse width, pulse frequency, high-level and low-level voltages, and electrolyte concentration on the drilling speed and hole diameter was examined. The results suggested that a semicylindrical tool electrode, long pulse width, high pulse frequency, high low-level voltage, and high electrolyte concentration were preferable for high-speed drilling without widening the lateral gap between the tool electrode and hole.