Researches On Electrochemical Micromachining

Electrochemical machining (ECM) is a non-traditional machining technology based on electrochemical anodic dissolution of metal in electrolyte. ECM becomes an important technology in manufacturing of aviation and weapons because of hard material could be machined regardless of its property and there is no stress and recast on the machined workpiece. Furthermore, ECM could machine the material ion by ion and shows its potential in micro-machining system. In this dissertation the microstructures with size from a few microns to a few hundred microns in industry are researched. Some key technologies in electrochemical micromachining (EMM) are studied, including preparation of the micro-electrodes, gap control and detection between cathode and anode, increasing the efficiency for EMM, wipping off the sludge in the interelectrode gap and machining of complicated shape, etc.The four-feed CNC micro-ECM machine tool is used in the research. The numerical control system is developed on the basis of the characteristics of micro-ECM. It consists of motion control, detection and analysis of experimental date, electrolyte and power supply. Detection of the intereletrode gap and protection of the short circuit are also studied in this research. Low voltage is used to detect the tool contaction exactly. The machining gap could be measured and kept exactly as smaller as 20 micrometers by periodic tool positioning. The localization and the accuracy are improved. The electric signal in the experiment is detected in real time. The control system responds quickly to the signal gathered. Short-circuit and sparks could be avoided during the machining, the stability of the machining process is improved.The preparation of the micro-electrode in EMM is very important. The author studies the fabrication of the micro-pin on the basis of electrochemical principles. Tungsten is selected as the electrode material because of its good heat and electricity exchanger ability and rigidity. By controlling the applied voltage, the different shaped micro-pins could be obtained, including the STM tip and cylindrical micro-pin. Furthermore, the relationship between diameter of the micro-electrode and machine time is proposed. Various parameters affecting the formation of the micro-pin, such as electrolyte concentration, immerging depth, electrifying mode are discussed in detail. STM tips with size less than micrometers and the micro-pin electrode with size from 3 micrometers to several tens of micrometers are produced. The author also presents a method to process the multiple microelectrodes in order to improve the machining accuracy of EMM. Current density distribution on the anode becomes uniform by optimizing the shape of cathode in ECM. Finally, a row of multiple electrodes with cylindrical shape is machined.The author studies the performances of micro-ECM by processing the micro-hole and micro-holes array. The effects of various parameters on the machining accuracy and stability are investigated, including electrode feeding mode, electrolyte, electrical parameters and shape of electrode, etc. Results indicate that pulse current, low concentration electrolyte, low voltage and spiral microelectrode could attribute good performance of EMM. Machining accuracy, stability and machining velocity could be improved. By using the optimized parameters micro-holes array are produced by using the row of multiple micro-electrodes fabricated in advance.In this dissertation, the author also presents the machining method of a kind of cooling hole with ring ribs on the hole wall. These ribs are called turbulators. A shaped electrode is selected as cathode to machine the turbulators using ECM. The shaped cathode is a metal hollow tube with groove on the surface. These grooves are machined by electrochemical machining. After the insulated treatment, the shaped electrode could be used in preparation of the turbulated cooling duct. In order to obtain the good processing parameters and dimension accuracy, numerical simulation is applied. Different processing parameters are used to perform the simulation of the ECM process. Parameters with good accuracy and high efficiency are selected to machine the ribs in the experimentation. Finally, Computational Fluid Dynamics (CFD) model is used to analyse the heat transfer of this kind of cooling hole. Results indicate that the cooling duct with turbulators has a considerablely higher cooling efficiency than smooth cooling hole.