Inducing electrochemical discharges on insulating surfaces for damage-free electrochemical jet machining of glass

Abstract

A key limitation of electrochemical jet machining (EJM) is its inability to process insulating materials. While electrochemical discharge machining (ECDM) can handle such materials, its contact-based nature often causes thermal damage. Additionally, the challenge of initiating electrochemical discharges on the insulating workpiece, rather than on the tool electrode, remains unresolved. This study presents a new mechanism for directly inducing electrochemical discharges on insulating surfaces through the controlled interplay of electro- and hydrodynamic fields. For the first time, we demonstrate damage-free machining of insulating materials using an electrolyte jet, in a new process termed jet-electrochemical discharge machining (Jet-ECDM). This is achieved by generating electrochemical discharges at the jet-impingement zone on the insulating workpiece surface, with the gas evolved at the nozzle electrode acting as a dielectric. The spatiotemporal dynamics of discharges, including location, frequency, and intensity, are analyzed and shown to critically influence machining results. High-speed imaging visualizes the gas bubble behaviors, while simulation reveals how discharges are focused onto a localized machining area through concentrated electric fields and gas distribution. Key process parameters, including voltage, working gap, and electrolyte flow rate, are identified for effective process control. Thermocouple measurements show a discharge-induced average temperature rise of ∼160 °C at the machining site. Unlike conventional ECDM, Jet-ECDM's non-contact approach avoids thermal damage, enabling stress-free, purely chemical material removal. This is validated by machining microfeatures in quartz glass, achieving superior surface finishes (∼Ra 50 nm) and a damage-free subsurface. This research extends the material applicability of EJM to insulating materials and introduces a novel method for stress-free machining of glass and ceramics using electrochemical discharges.