Electrochemical milling of narrow grooves with high aspect ratio using a tube electrode

Metallic narrow grooves with high aspect ratio, referred to here as deep narrow grooves (DNGs), are used widely in precision instruments, medical devices and other industries. However, because DNGs are usually less than 4 mm in width with depth-width ratio (aspect ratio) more than 2, it remains extremely challenging to machine them with high precision and efficiency, especially for blind (i.e., closed-end) cases. Therefore, this paper proposes a novel method of electrochemical milling using a tube electrode to fabricate a DNG by single-pass milling. A multi-physics coupling model, including a gas-liquid two-phase flow field and an electric field, was built to investigate the flow field distribution in the inter-electrode gap as well as the current density distribution at the DNG edge with different electrolyte pressures. Related experiments were also conducted. The simulation and experimental results indicated that a higher pressure was associated with a high electrolyte velocity, and had a significant influence on the machining process. First, the high electrolyte velocity in the inter-electrode gap could enhance the mass transfer and improve the sectional profile of the DNG. Second, when the electrolyte flowed out, the high electrolyte velocity could overcome self-gravity and reduce the accumulation at the edge of the DNG, which decreased the electrolyte volume fraction in the two-phase flow field at the DNG edge. Thus, the current density distribution at the outlet edge was decreased, and the corner radius at the edges of the DNGs was reduced. Then, systematic experiments were performed with different machining parameters (including electrolyte pressure, pulse parameters and feeding speed) to investigate their influence on the DNG dimensions; with the optimized parameters of an electrolyte pressure of 0.9 MPa, applied voltage of 12 V, pulse frequency of 9 kHz, pulse duty cycle of 40 % and feeding speed of 0.36 mm/min, a complex narrow groove of width 1.32 ± 0.02 mm (mean ± standard deviation) and depth 8.05 ± 0.01 mm was well fabricated with single-pass milling, and the aspect ratio reached 6.1, showing a high precision and efficiency machining method.