Novel structure of a sidewall-insulated hollow electrode for micro electrochemical machining

Abstract

Adopting the sidewall-insulated hollow electrode (SIHE) is an ideal approach to achieve electrolyte-refresh and stray corrosion inhibition functions in micro electrochemical machining (ECM) processes. Most of the traditional SIHEs are made of metal substrate and non-metal thin films. The insulating film has poor durability, and the preparation approach of the traditional SIHE is complex and has limited repeatability. This research presents a novel structure of a SIHE with an insulated substrate and an internal conductive film. The machining performance of the novel SIHE is primarily verified by a potential distribution analysis in the numerical simulation. According to the concept of the novel SIHE, a silver-plated glass tube electrode (SPGTE) is presented: the glass tube acts as the insulated substrate, and the plated silver layer acts as the working cathode. Then, a fabrication process for the SPGTE is proposed. Silver layers are tightly bonded on the glass tube surface by electroless plating. The thickness of the silver layer is approximately 3.5 μm, and its electrical resistivity is approximately 5 × 10−5 Ω cm. In micro ECM experiments, microstructures with steep sidewalls with taper angles of <5° are machined, which is attributed to the stray corrosion inhibition of the insulated substrate. Micro holes with an aspect ratio of approximately 3 are machined. There is no accumulation of electrolytic products and short circuits, which verifies the excellent electrolyte-fresh performance. Compared with the traditional SIHEs, the novel SIHE could provide a simpler and more reliable way of fabricating sidewall-insulated electrodes. The proposed electrode structure can further inspire new electrode preparation schemes based on new substrate materials and film preparation approaches.