Multiphysics research on electrochemical machining of micro holes with internal features

Micro electrochemical machining (ECM) is practicable for machining micro holes with internal features by adjusting machining parameters along with machining depths. However, it is difficult to maintain the shape accuracy due to dramatically varied electrolyte temperature (T) and gas void fraction (vol) caused by the parameter variations. Taking the reverse tapered hole as an example, this research presents a multiphysics model to investigate the effects of machining parameters on T and vol and further optimize parameters for shape accuracy improvement. Firstly, the rules of current efficiency with various pulse-on times are measured from dissolution experiments. The gas fluxes are calculated from the Faraday current, and then multiphysics models coupling electric field, electrolyte flow, gas transport, and heat transfer are established by COMSOL software. The effects of the machining voltage, pulse-on time, duty ratio, and inlet pressure are investigated. Simulation results indicate that T and vol increase with the machining voltage or duty ratio and decrease with the inlet pressure. By using a smaller duty ratio or a higher inlet pressure, the sidewall dissolution region expands in a larger range. Increasing the inlet pressure is beneficial for reducing the negative influence of rising T and vol. However, excessive inlet pressure causes undesired material dissolution. The optimal inlet pressures are obtained from simulation results of the electrolyte vortex area. Micro ECM experiments are carried out to verify the simulation results and optimize the parameters. Micro reverse tapered holes with sidewall straightness of 8.6 μm are machined, and the shape accuracy is significantly improved.