Study On The Discharge Mechanism And Technology In Powder-mixed EDM

Precision machining has recently become a global trend in electrical discharge machining (EDM), while powder-mixed EDM is an effective method of realizing the precision EDM, in which fine powder, such as silicon, aluminum is put into the dielectric fluid suspended in the inter-electrode gap affects the discharge during machining process. The added powder can effectively improve the surface quality, decrease surface roughness, andrealize the surface finishing of large area. The new technology------powder-mixed EDM thatcan overcome the defaults of conventional EDM has a wide application in die & mould industry. The main difference between powder-mixed EDM and conventional EDM is that the powder added into the working fluid plays an important role in machining results. It is necessary to study the effects of powder on discharge process for improving the machined surface quality and widening the application of powder-mixed EDM. However, since the existence of powder suspended in dielectric fluid causes the discharge process more complex, and makes it difficult to study on discharge mechanism and operational characteristic, powder-mixed EDM hasn't been widely used in die & mold industry till now. In this paper, comparative experiments between powder-mixed EDM and conventional EDM were carried out. Based on a great deal reports, by combining the experimental results and theoretical analysis, the following work has been accomplished in this dissertation.Firstly, the machining mechanism of powder-mixed EDM is studied.By summarizing the theory of free collision, bubble breakdown and impurity breakdown, current carrier is introduced to analyze the discharge process during one pulse duration. Based on it, the physical model of discharge channel for multiple pulse duration is built during one time of cutting UP and DOWN. This model shows that the current carrier and the discharge cavity dimension are different in different pulse duration during one UP and DOWN periodical time. Micrographs of machined surfaces in experiments have validated this physical model. And based on this model, the variations of interelectrode capacitance and discharge gap caused by the powder suspended in dielectric fluid are analyzed from the viewpoint of molecular bond energy. On the other hand, the entropy is introduced to explain the reasons for the variation regularity of the discharge channel shape with the variation of peak current and pulse duration by thermodynamics. The mechanism that surface quality of workpiece improved by powder-mixed EDM is explained from this viewpoint. Then the fact...