Research On Key Techniques Of Pulses Electrochemical Micromachining

Developed with micro electro mechanical system (MEMS), the micro machining technology was developed. The metal was wiped off or added when the reaction of the oxidation and deoxidization were occurred in electrochemical machining (ECM). Because the minimum unit was ion in the process, ECM plays an important role in micro machining. Developed with the modern electric and electron technology, the direct current power supply was substituted by the pulse power supply aimed to satisfy the requirements of machining precision and surface roughness in ECM, and the frequency of the pulses power supply became higher and higher. The simple electrode could be used to fabricate complex structure due to the development of the computer control technology. Those made ECM widely application.After the electrochemical micromachining (EMM) mechanism was analyzed, the key techniques were discussed, and then the experimental investigations of the EMM were carried out. The processes of anodic dissolution and cathodic deposition were analyzed and researched firstly. In the microcosmic view, whether the single crystal particle could be wiped off from the workpiece lay on the action between escape energy and electric force during the processes of anodic dissolution. The cathodic deposition was carried out where the activation energy was least. After reached the dissolved voltage or deposited voltage, the machining rate lied on the energy during the pulse on time, and it also was influenced by the duty ratio of pulses power supply. The effect of double layer was analyzed in ECM process. Based on the ECM equivalent circuit, the stimulant circuit was put up practically. The validity of the ECM model was detected.Based on the requirement of the micro ECM technology, the nanosecond pulses power supply was developed. It used CPLD and MOSFET mainly, and combined the PFM and PWM, and then the output voltage, current, and the frequency of power supply could be adjusted continuously. Based on the model of electric field in ECM, the producing reason and the influencing factor of the maintaining voltage were analyzed. The maintaining voltage is disrelated with the frequency and duty ratio of the power supply, it relate with the electrolyte character, machining gap, and machining voltage, and it is decided by their collective action. The nonstandard discharging waveforms make the average voltage become big so the surface roughness and machining precision would be influenced. Therefore, the double MOSFET was used to improve the pulses power supply, and then the EMM would be satisfied with the discharging waveforms better.The fabrication of microelectrode was the preparative work for EMM. The microelectrode with several microns in diameter was fabricated by electrical discharge machining (EDM) firstly. The mechanism of fabricating microelectrode was analyzed by the tungsten microelectrode fabricated in the alkaline electrolyte. The factors were studied which influenced the shape and the surface roughness of the microelectrode. The microelectrodes were fabricated successfully in the acidic, alkaline, or saline electrolyte respectively. Some of them were with more 100 in length diameter ratio, and less 0.2 in taper. The microelectrode about 5 microns in diameter was fabricated stably. Otherwise, the scan probe with nanometers in top radius could be fabricated in the alkaline electrolyte based on the speciality of the tungsten, and the least radius was 50nm. At last, the properties of the microelectrodes which were fabricated by EDM or ECM were compared, and the advantages of ECM were shown.The key techniques of pulses EMM were researched systemly. The micro hole was fabricated by ECM drilling firstly, and the experimental investigation was carried out at the same time. The ECM turning technology was raised, and the mechanism and the machining scope were introduced. The technology characteristic and influenced factors were analyzed, and then the workpieces were fabricated by the ECM turning. The technology of ECM milling micro structure was introduced in detail. The ECM milling with cathode side, one layer ECM end milling, and multilayer ECM end milling were studied. The machining thickness, the microelectrode diameter, and the power supply parameter analyzed which influenced the shape precision and the surface roughness in the ECM milling. Several micro 3D structures were fabricated successfully. At last, the electrodeposition was researched.