Multi-physical field simulation and experimental research on inner-jet through-mask electrochemical machining of micro-pit arrays

Micro-textures such as micro-pits and micro-grooves play a significant role in regulating the surface properties of metal components. Through-mask electrochemical machining (TMECM) is a non-contact machining method based on the principle of anodic dissolution. It utilizes an insulating mask to generate micro-texture features in batches on the surface of workpieces, playing a significant role in surface micro-structure processing. This work presents an inner-jet TMECM method to address the challenges of limited machining depth and a narrow machining dimension range in a micro-pit array TMECM. A gas-liquid two-phase flow field model and an electric field model were established. Based on the coupled simulation, the influence of different inner-jet cathodes on the changes in physical quantities was investigated. The simulation results showed that due to the small coverage area of the contracted cathode bottom, the flow velocity in the frontal gap was as high as 9.16 m/s. This led to a reduction in the area of bubble aggregation and a decrease in the low-conductivity region. Therefore, employing a contracted cathode was beneficial for obtaining higher precision micro-pit arrays. In contrast, when using right-angled and extended cathodes, the larger coverage area of the cathode bottom reduced the flow velocity in the frontal gap to below 3 m/s. This led to an increase in bubble formation and aggregation area, resulting in greater fluctuations in conductivity. Moreover, the high current density region with a current density higher than 50 A/cm 2 significantly expanded. Therefore, using right-angled and extended cathodes was beneficial for improving the machining efficiency of micro-pit arrays, but the machining accuracy was relatively low. Based on the simulation analysis, comparative experiments were conducted to investigate the coupling effects between inner-jet cathode characteristics and processing parameters on the machining of micro-pit arrays. The resulting variation patterns for micro-pit diameter, depth, and average corrosion coefficient were obtained. Additionally, by utilizing appropriate inner-jet cathodes and machining parameters, the diameter of the micro-pit array can be regulated between 200μm and 470μm, and the depth can be controlled between 0μm and 150μm. This demonstrates that TMECM with an inner-jet cathode can enhance both the dimension range and the depth of micro-pit array machining by regulating the high current density coverage area and electrolyte fluid kinetic energy. • A simulation model containing a gas-liquid two-phase flow field and an electric field was developed. • The coupled effects of cathode characteristics and processing parameters on the micro-pit profile variations were obtained. • By adjusting the cathode characteristics and processing parameters, the fabrication of diverse micro-pit arrays was achieved.