Silicon-based tool electrodes for micro electrochemical machining

Stray current always causes undesired material dissolution in micro electrochemical machining (ECM). The preparation of reliable insulating films on micro electrodes is a critical technique to restrict the stray current, and then improves the machining localization. To meet the requirements for insulating films like good insulation property, thin & uniform thickness and good adhesive strength, a novel method of silicon-based tool electrode is proposed. Heavily doped monocrystalline silicon is used as the electrode body. Silicon dioxide and silicon nitride are deposited on electrode sidewall as insulating films. Through simulations of electrode conductivity, the feasibility of the silicon-based tool electrode is preliminarily verified. Then, a fabrication process of the silicon based tool electrode is presented. The electrode body is fabricated by wet etching and insulating films are deposited by low pressure chemical vapour deposition (LPCVD). Consequently, the electrodes with section size of 91 x 52 mu m, 1-2 mm length and 800 nm-thick insulating films are obtained. As the silicon-based electrode is installed on a rotating head in ECM experiments, the electrode with non-circular cross section not only achieves the same effect with a cylindrical electrode, but also is beneficial to removing electrolytic products through the turbulent electrolyte flow. In experimental results, micro grooves with steep sidewall and smooth undersurface (Ra 0.42 mu m) are machined. Micro holes with inlet diameter of 146 mu m and taper angle of 0.58 are obtained. They indicate the feasibility of silicon-based tool electrodes and the effect of insulating films on stray corrosion restriction.