The consistency in the fabrication of microsurface structures on large workpieces remains a challenge for existing production techniques. Mask electrolyte jet machining (MEJM) is a hybrid mask-based electrochemical machining (ECM) process that combines the flexibility of Jet-ECM to flush the electrochemical by-products and the high throughput processing feature of through-mask electrochemical micromachining (TMEMM). In the present study, a duckbill-shaped nozzle is employed in the MEJM for the batch fabrication of microsurface structures which facilitates more uniform current density distribution over the entire machining area, resulting in better consistency. With a larger slit length, the duckbill nozzle will not only cover more processing area but also facilitates more uniform current density distribution over the entire machining area, resulting in a better consistency for batch fabrication. Thresholds of the ratio of slit length to the machining area were derived from a quantitative analysis, namely the efficient threshold and the performance threshold. The slit length of the duckbill nozzle should be at least twice as large as the machining area to wipe out any observable deviation on current density distribution in the machining area. An efficient and high-performance numerical simulation framework with a virtual gap concept is developed for the mask-based ECM processes to simulate microcavity profiles and associated current density distribution. The concept of a virtual gap is proposed to solve the simulation dilemma of elements being consumed in the mask-based ECM process. Quantitative analyses were carried out to study how the virtual gap influences the electric current density distribution in the interelectrode gap. A virtual gap smaller than 100 nm is recommended. Guidelines on how to ensure a smooth electric field transition across the coarse and fine-meshed zones are presented by conducting a quantitative analysis. As an example, this work has successfully fabricated several cavity arrays with different processing parameters. Both the experimental results and the numerical simulation frameworks are easy-to-implement and easy-to-extend for all the mask-based ECM processes.

The precision in electrochemical machining (ECM) is adversely affected by the generation of gas bubbles due to the inherent electrochemical reactions occurring at the cathode (tool) and anode (workpiece) surface. These gas bubbles are known to cause variations in electrolyte conductivity and lead to uneven dissolution and limit the achievable flatness and surface finish. The demands for precision ECM make it important to investigate the bubble evolution phenomenon. In the prior state of the art, this has been done by means of transparent electrodes and high-speed video observations. The current work involves high-speed video experiments with a specific intention to observe gas bubbles during the early stages of evolution and attempts to address two main research questions: (i) Is it possible to suppress gas bubble evolution in ECM using pulse parameters? (ii) Is it possible to do ECM without gas bubbles? The results reveal that shorter pulse-on times and longer pulse-off times reduce the growth of the concentration boundary layer, thereby suppressing bubble generation. Furthermore, by combining the aforementioned electrical pulse settings with an appropriate flow rate, there is no significant detection of gas bubbles in the experiments conducted here, as can be concluded from the fact that the interelectrode gap (IEG) remains transparent. The industrial applicability-oriented analysis focused on evaluating the final IEG and did not reveal any significant difference due to shorter flow lengths. It is further suggested that by employing high flow rates in combination with shorter pulse-on times, the pulse-off time can be further shortened to raise duty cycles so as to facilitate economic machining without the influence of gas bubbles.