The Investigation On The Electrochemical Micromachining (ECMM) With Nanosecond-Pulse Current

With the development of science and technology of 21th century, function integration, ultra-precision and miniaturization have become the direction of high technological produces. Micromachining technology applied in microelectromechanical system (MEMS) has gained the great attention in academe, industrial field and governments. It is considered as one of the important marks of national manufacture level, which determines the machining accuracy and surface quality of mechanical produces. Electrochemical machining (ECM) is a course of the anodic electrochemical dissolution of metallic materials in an electrolytic medium utilizing the electrochemical reaction, so that it can produce nano-precision parts in theory. ECM should be a promising micromachining technique for manufacturing micro parts with dimensions in micrometer order or even in nanometer order. Moreover, it still owns several special advantages, such as non-contact machining without process stress, no tool wear and heat-affected layer, suitable for various kinds of metal material, etc.For applied ECM into micro-machining domain, the stray erosion made by the electric field distributing of electrochemical reaction must be restained availably, and the localization and the stability of ECM process must be notablely improved. Consequently the precision of micro-ECM can well meet the demand of MEMS manufacture. This paper has investigated the micro-ECM using nanosecond pulse, and discussed the mechanism of its. The key technological problems had been researched and solved by considerable experiments.Machining of microstructure with high precision was the goal of this research subject by electrochemical methold. The dissertation consisted of five sections, including:1. According to the non-stationary processes of electrochemical reactions, the mechanism of that nanosecond pulses could improve the localization of ECM was investigated. By analyzing the reaction process on the interface of electrode and liquor, the equivalent electric circuit of electrochemical polarization was carried out. The conclusion was presented that electrochemical process could not achieve the stationary condition owing to the extremely short pulse duration, and electrochemical polarization was the determinant factor of electrochemical reactions. Based on the Butler-Volmer equation and Faraday'laws, theoretical model of micro-ECM was founded.2. The practical electrochemical machining system was developed. The special machining program was designed by LabVIEW software. In this micro-ECM system, microscale feeding could be accurately controlled, and the machining status and result could be detected on real-time. In addition, the appropriate circulation system of electrolyte was employed in order to guaranteer the stability of machining process.3. The essential influence of power supply to the accuracy and stability of ECM process were illustrated firstly. According to the special need of micro-ECM with ultrashort vltage pulses, quartz crystal oscillator, integrated circuit, resistance and capacity were applied to make the nanosecond pulse power supply, which was compose of the frequency generator circuit, counter circuit, squaring circuit and trigger circuit, etc. The developed ultrashort pulse power could export the needed pulse waveform, which provided the necessary device for the research on Micro-ECM with nanosecond pulses.4. The side gap and frontal gap between the cathode and anode were investigated, because they had significant influence upon the machining accuracy and localization of ECM. Using the self-developed experimental system, tool electrode and workpiece were sequentially machined in electrochemical method. Based on the theoretical model, the affections of processing parameters on the experimental result were explored, which demonstrated the preceding analysis of the mechanism of nanosecond pulses micro-ECM. These machining experiments included the machining of micro-hole and micro-groove, the directly etching and the micro-ECM with the forming electrode.5. The experimental research on how machining parameters influence the machining accuracy has been performed. The experiment result with variant parameters showed that electrochemical reaction region should extended as the increased of pulse on-time of power supply and over-potential of electrode. Shorten of pulse on-time could lead the decreased of current density and the descended of stability in the micro-ECM process. With the raised of electrolyte concentration, the machining accuracy and the localization of ECM deteriorated. Because the machining gap reduced as the improved of feeding speed, the width of microgroove would be decreased so that more accurate microstructure could be produced.The investigation on micro-ECM using nanosecond pulse could expand the nontraditional micromachining techniques, and provide a new manufacturing method for machining the high performance material. Applying this technique into the fabrication of micro produces would accelerate potently the development of MEMS.