| After 70 years’ development, electrical discharge machining(EDM) has been widely used in machining, such as precision parts or difficult machining materials. But the further expansion of EDM technology has been restricted to a certain degree by insufficient study of the mechanism of machining. In recent years, new observations and simulation technologies, such as high-speed camera technology, digital signal processing and finite element techniques, have been applied to the EDM, which help understand of the mechanism of EDM. In this paper, a finite element model was established using ANSYS to simulate the removal of material, and compared the results with those of single pulse experiments. The current signals of specific stages were measured, a preliminary analysis was conducted by fast Fourier transform.The EDM-ed surface is composed of numerous craters produced by discharge. Therefore, the study of single pulse discharge is the foundation of multi-pulse discharge. In a normal spark discharge, from the formation of discharge channel when the dielectric is breakdown to the end of discharge, the plasma in the channel can been seen as a heat source, so, a detailed analysis of characteristics of the heat source is needed. The heat source can be regarded as a two-dimensional Guassian distribution at a time and the radius of the heat source varies with the machining current and discharge time, moreover, the center position of the heat source is moving during the discharge. Base on mentioned above, a finite model was established. The model also considered the thermal physical properties which change with temperature of materials, and the automatic division of non-uniform grids. Single pulse discharges were conducted by making use of the existing EDM machine tool. The simulated and experiment results of dimensions of craters were compared for different machining current and pulse-on duration. The simulated trends were compliance with the actual machining and the model had a high accuracy.The electrical signals in discharge channel reflect the conditions of actual discharge. A study of current oscillation characteristics has an important theoretical and practical significance. In order to simplify, current signals when the thermal field reach equilibrium are sampled, when the total system can be treated as a linear time-invariant system, the spectrum of which can be obtained by fast Fourier transform. It was found that the machining current, polarity and materials of electrode can both affect the spectrum. The sources may contribute to the oscillation of current were analyzed and classified, including pulse power supply, the automatic adjust feed motion of EDM machine tool, the oscillation of plasma, the movement of high temperature molten metal, and for the first time, a vibration model of a whole grain as a unit. In order to verify the validity of the proposed model, the frequency of a simple second order vibration model for the individual grain with one direction was calculated. The calculated result and the measured results are in line to a certain extent. |
