Study On The Powder's Effect In Powder-mixed EDM

Powder-mixed electrical discharge machining (EDM) is a new technology that can overcome the defaults of conventional EDM. The remarkable difference between powder-mixed EDM and conventional EDM is that electric powder suspended in working fluid plays an important role in machining process. Researching the powder's effect on the machining process is helpful to improve the machined surface quality and widen the application area of powder-mixed EDM.In this paper, the effect of powder characteristics and powder materials on technics rules of the surface performance, etc. is analyzed. Comparative experiments between powder-mixed EDM and conventional EDM were carried out. Combining the experimental results and theoretical analysis, the following work has been accomplished. (1) Reasons of the decrease of interelectrode capacitance and the increase of discharge gap caused by the powder suspended in dielectric fluid are explained. And the mechanism that surface quality of workpiece improved by powder-mixed EDM is analyzed from this viewpoint. (2) The variation regularity of the percentage of silicon on the machined surface of workpiece has been summarized according to the experiment results when silicon powder was added into the working fluid. The entropy is introduced to explain the reasons for this variation regularity by thermodynamics. (3) The dimensional accuracy is greatly influenced by the overcut resulting from discharge gap and electrode wear in practice application. Empirical formulas for the overcut in EDM and powder-mixed EDM are established based on the experimental results using the ternary linear regressive method in this paper. (4) The influence of main factors on the machined surface characteristics has been evaluated based on the orthogonal experimental design method (Taguchi method). (5) In order to study the mechanism of powder-mixed EDM process, molecular dynamics method has been used to simulate the activities of particles in working conditions. Dynamic model of the particles suspended in working fluid in the electric field has been built to predict transient positions and velocities of the particles in discharge process. The results show that this method would serve as a good way to learn the performance of particles in the process of discharge.The conclusions from the above work are helpful to make up the research work of mechanism model in EDM, and would be useful for attempting to simulate the discharge process.