Research On Three-electrode Pulse Power Supply And Fundamental Process Of Micro ECM

There are several disadvantages in micro electrochemical machining(micro ECM) of high-aspect-ratio micro holes and three-dimensional structures, such as the contradiction between machining locality and efficiency, difficulties of electrolyte renewal and products discharg, and of precisely detecting the machining gap. In order to solve above problems, further research on machining mechanism, fundamental process and key techniques of micro ECM is carried out in this dissertation.From the perspective of electrochemical reaction process on the interface of metal and solution, this dissertation deeply studies the rule of influence that selective generation, elimination or reduction of electrolytic products has on micro ECM processing. By analyzing the process of thickening passive film on the machining surface, this dissertation puts forward micro ECM mechanism of gas inhibition and dissolution promotion(GIDP) based on the process of adding acid on interface. In this way machining efficiency and surface quality of workpiece are effectively improved without changing the nonlinearity and eco-friendliness of passive electrolyte.In accordance with characteristics of micro ECM, the changes in relations between the machining gap and the capacitance of electric double layers(EDL) on interface are analyzed. Then the detection method for the machining gap in micro ECM is presented based on the capacitance of EDL. By using the relationship that capacitance value of EDL on tool electrode and solution interface is monotonically increased with the increase of the machining gap, the accurate and rapid online detection on the machining gap can be realized. it provides a new technical approach for precision detecting of micro machining gap.Three-electrode high-frequency pulse power supply(PPS) is developed with inter-pulse outputs(IPO). The process of adding acid on interface and GIDP are realized by utilizing reverse current of auxiliary electrode that is exerted on the interface of workpiece and electrolyte during inter-pulse of machining. The mechanism of GIDP is also extended into ECM using ultrashort pulse and helps to design and implement three-electrode ultrashort PPS. The machining process is completed through compound ultrashort negative pulse voltage which may be synchronized, with equal pulse width, equal cycle or unequal amplitude being exerted on the area among auxiliary electrode, tool and workpiece. The result shows that some gas is released from cathode and the removal volume is increased by 13% simultaneously.Through studying preparation method of electrode used for micro ECM, a welding preparation process of micro nested hollow electrode(MNHE) is presented. The MNHE whose front section is used for machining with the inner diameter of 65μm, the outer diameter of 130μm and the length of about 3.25 mm and the rear section is for clamping and connectivity is obtained. The length of MNHE is optimized by CFD simulation and flow characteristics of electrolyte in the MNHE are analyzed to determine liquid supply pressure. Flow rate for outlet can be up to 10m/s when liquid supply pressure is 1.15 Mpa. This solves the difficulty in electrolyte renewal and products discharge and improves machining efficiency and stability during micro ECM.Fundamental experiments of micro ECM on micro holes and grooves with high aspect ratio are carried out by utilizing three-electrode PPS and MNHE. After the process parameters are optimized, micro array holes are machined with the diameter of about 175μm, to high circular degree and in good form consistency and micro grooves are machined with the width of about 160μm, the depth of about 220μm, at high form accuracy and high surface quality, respectively on 304 stainless steel and 18CrNi8 with the thickness of 0.5mm. Through ECM experiments on micro holes and grooves of high aspect ratio, the result shows that the good machining location, high machining efficiency, machining precision and surface quality can be achieved at the same time by utilizing fundamental process and methods presented in our study. It lays a firm foundation for exploring the machining process of allotype holes with variable section whose diameter is 100~200μm and with higher aspect ratio.