| Powder mixed EDM (PMEDM) can assuage the contradiction between discharge area and surface roughness; effectively improves the discharge state in machining gap and surface properties of workpiece, and has potential ability in die&mould large-area finishing technology. EDM is getting more and more attentions in the fields of the aviation and the aerospace, precision machinery, automobile and electric industry.Discharging process of EDM is more complex, there are many factors to be considered, such as performance properties of fluid, material of workpiece and electrode, character of power supply, process parameters and so on. Suspended powder changes dielectric characteristics of fluid in PMEDM, consequently discharge mechanism is affected. Based on powder characteristic, interaction among powders, powder-liquid two-phase mixture, effects of powders upon tree growth and discharge breakdown mechanism, mechanism and compensation of electrode loss are studied in this dissertation.According to the hot research of PMEDM, the main contents of the dissertation are as following:1. Establishing theoretical system of powder mixed dielectric fluid: Eliminetion methods and mechanism of agglomeration of powders are studied; Considering the electric field aberration in the inter-electrode gap caused by the particles, the polarization of electric field is calculated, concentration, characteristics, size, interaction of powders and their influence on electric field are analyzed, theoretical system of powder mixed dielectric fluid is preliminary established. The results provide theoretical basis for the determination of powder size, concentration, characteristics.2. Theoretical study of discharge in PMEDM: Effects of additive powders on the machining mechanism of PMEDM are discussed based on theory of plasma and dielectric. By analyzing the inception, growth of electrical tree and the ignition of discharges in liquid filled gap, the whole discharging process are proposed. Influence of particles on electrical tree is analyzed. It is explored that the reason of modification of ignition behaves by fine particle powders of metal or semiconductor. Particles attract electrical trees, so the growth of electrical trees is more quick and dispersive. Therefore, the discharge channels is apt to establish and increases much more in PMEDM than in conventional EDM, which accounts for the improvement in working stability of PMEDM. 3. Experimental study: Law of location change of discharging is studied experimentally in PMEDM. Weibull distribution is developed from the basic theoretical model, effects of powder concentration, microcosmic profile of particle on discharge change is researched, and dependency of successive discharging spot is analyzed. Results show law of discharging location is determined by powder concentration, microcosmic profile and tool-lifting frequency; the positions correlate to each other to some extent. Orthogonal experimental method and ANOVA are used to analyze machining parameters on electrode loss and surface roughness; technology specification is summarized in the dissertation.4. Simulation study: Discharging occurs in micro (time and space) scale, microenergy Environment. A 3D electric fields model described by finite element methods of the particles suspended in working fluid in the electric field is built; law of electric field change with electrode loss is simulated. ANNs with back propagation algorithm coupled with an orthogonal design was applied to the modeling of the PMEDM system. The results those methods are helpful to guide application and the work also accelerates research on PMEDM.The research will be beneficial to understanding discharging as well as to providing theoretical basis for mastering breakdown mechanism and processing technology of EDM; meanwhile, it will be offer technical support for the industrial application.
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