Study On The Mechanism And Application Of Powder-mixed EDM

Electrical discharge machining (EDM) plays an important role in modern manufacturing field, especially in mold & die industry. But there are obvious disadvantages for conventional EDM, such as poor workpiece surface quality, poor finishing machining efficiency, and poor machining stability during large machining area. In order to use the machined surfaces, polishing procedures are usually needed. While using some superfine powder such as silicon or aluminium suspended in the dielectric fluid, the newly developed powder-mixed EDM can overcome the disadvantages of conventional EDM mentioned above, and is promising to be employed as the finishing method of mold & die cavities. However, because of the lack of researching on theories related to it, the new technology hasn't been widely used in mold & die industry till now. For this reason, the mechanism and processing performances of powder-mixed EDM are studied by means of theoretical analysis combined with experimental research in this dissertation to improve the technology.Firstly, the machining mechanism of powder-mixed EDM is deeply studied. Considering the electric field aberration in the interelectrode gap caused by the particles, the influence of the particles on the discharge gap and the dielectric constant of the working fluid is calculated utilizing the "Wagner Model". The calculated results show that the discharge gap and the dielectric constant both increase due to the action of the particles, but the former increases much more than the latter does. So the equivalent capacitance decreases much more in powder-mixed EDM than in conventional EDM, which accounts for the improvement in working stability of powder-mixed EDM.By means of the streamer theory from gas discharging field, the gap breakdown procedure of powder-mixed EDM is discussed, and the shape of the discharge channel is subsequently deduced. It is believed that the discharge channel connects the electrode couple via some certain particle and series-discharging is then conducted. And the single-channel discharge model is accepted rather than the multichannel discharge model according to the analyzed results. The bettering of the machined surface roughness is accounted for the over expansion of the plasma channel radius at the anode which causes a decrease in the local energy density at the anode surface. In addition, because the particles eliminates the dependence of the new discharge position on the last discharge position, the discharge point can be uniformly dispersed all over the machining area, which also accounts for the improvement of the machined surface integrity.Secondly, to study the processing performances of powder-mixed EDM, a series of experiments are conducted in both silicon-powder-mixed dielectric fluid and conventional dielectric fluid. The polarity effect is firstly investigated. Using copper-steel electrode couple...