A review of the current understanding and technology of powder mixed electrical discharge machining (PMEDM)
This paper reviews the current understanding of powder mixed electrical discharge machining (PMEDM), highlighting particularly the mechanisms proposed for PMEDM under the influence of additive of powders in the dielectric fluids. Generally, the mirror surface phenomenon in PMEDM can be explained by the enlarged gap widths which can expand the discharge channel and thereby reduce the electrical power density since lower power density can yield large and shallow craters that evenly distributed on the machined surface. Moreover, the increment of the inter electrodes distance will limit the capacitive effect and enable a small surface roughness even in a large area. Another possible mechanism, multi-discharge model was also presented in this paper. More investigations on the fundamental mechanism in power mixed EDM are highly desirable since it has not been understood clearly. In this paper, the traditional and some recent development technology for PMEDM is also reviewed. Historically, PMEDM was invented to improve the surface quality of the machined components. Nowadays, some new applications of this technology, such as micro machining, rough machining and surface modification were proposed; some novel variations that based on power mixed EDM, such as PMEDM combined with ultrasonic or abrasive, powder mixed near-dry EDM and powder mixed electrical chemical discharge machining (ECDM) were also developed.
Transient dynamics simulation of the electrical discharge-generated bubble in sinking EDM
The evolution of bubble generated by electrical discharge in sinking electrical discharge machining (EDM) occurs in a very short time period and in a very narrow space, thus making both observation and theoretical analysis extremely difficult. For this reason, the role of the discharge-generated bubble during the material removal process in sinking EDM has not to be understood very clearly. In this paper, the evolution process of the discharge-generated bubble was simulated in three dimensions and the influence of inter-electrode distance was studied. It was found that the evolution of the discharge-generated bubble was significantly affected by the inter-electrode distance. Smaller inter-electrode distances can contribute to a larger pressure and expansion velocity of the bubble as well as a larger force applied on the tool electrode and workpiece. The experimental results showed that the geometry characteristics of the crater were also significantly affected by inter-electrode distance. A smaller inter-electrodes distance can contribute to a larger volume of both melted and removed materials. The simulation results were discussed by relating to the results of single-pulse discharge experiments; some insightful views about the material removal mechanism of EDM were presented in this paper.
Comparison of measured and simulated crater morphology for EDM
Abstract The crater morphology has been investigated in different procedures. An analytical relation between pulse parameters and roughness has been achieved and differences between a single discharge and a sequence of discharges are described. Simulations of thermal-affected zones are identified for a single discharge and a sequence of discharges. The characteristics describing the changed gap conditions of the discharge types in the simulation model are shown. Starting from measured current and voltage curves, the thermal channel base parameters are computed. For single discharges with fixed base localization secure expansion parameters of the discharging channel can be determined if the geometries of measured and simulated thermal-affected regions match. The simulation of moving or jumping bases is considerably more complicated and more time-consuming. The channel movement is determined by more degrees of freedom. These additional degrees of freedom permit multiple solutions and the number of them must be reduced by further limiting conditions.