Abstract
A 2D axisymmetric plasma model for micro-electrical discharge machining (μEDM) is developed, and the discharge phenomenon is discussed in this paper. Variations in different plasma properties, such as density, temperature, and collisions of the electrons bombarding the anode and cathode electrodes, were simulated to comprehensively explain the discharge process. The said properties of the plasma channel will be extremely helpful in determining the heat flux available at the tool and workpiece of μEDM. The governing equations of electrostatics, drift-diffusion, and heavy species transport were coupled together and solved simultaneously for computing the properties of the plasma channel in water vapor. The simulation describes the movement of electrons and ions in the inter-electrode gap during the discharge initiation under the applied electric field. The anode spot responsible for the material removal was formed much earlier compared to the cathode spot formed at the tool. Both the temperature and the density of the electrons were observed to be higher near the workpiece, compared to the tool electrode. The temperature of the electrons and the current density of the plasma obtained during the simulation will be useful to determine the heat flux responsible for the material removal. The non-equilibrium nature of the plasma sheath is responsible for the steep changes in the collisional power loss and higher capacitive power deposition near the workpiece electrode.
Highlights
Owing to the advantages of better accuracy, ability to machine hard-to-cut conductive materials, and producing arbitrarily curved surfaces, micro-electrical discharge machining has a wide range of applications in the field of precision machining.1,2 EDM is known as the spark erosion process as the immediate source of energy that is responsible for the material removal comes from the discharge of a spark in the inter-electrode gap with a dielectric fluid as the conducting medium
The finite element method was used by the Comsol Multiphysics to solve the 2D axisymmetric model for the plasma for computing the properties of the plasma channel formed during the μEDM process
The plasma channel formed during the μEDM process was simulated and the properties of the plasma were calculated by using the Multiphysics finite element based software
Summary
Owing to the advantages of better accuracy, ability to machine hard-to-cut conductive materials, and producing arbitrarily curved surfaces, micro-electrical discharge machining (μEDM) has a wide range of applications in the field of precision machining. EDM is known as the spark erosion process as the immediate source of energy that is responsible for the material removal comes from the discharge of a spark in the inter-electrode gap with a dielectric fluid as the conducting medium. The most popular and widely adopted modeling strategy for the EDM process is electro-thermal modeling, in which the plasma channel formed in the inter-electrode gap was assumed as a heat source. There exists a clear disagreement on the fraction of the plasma channel energy distribution among the μEDM models proposed by different authors Another reason for the nonapplicability of the heat source models for μEDM is the assumption of constant voltage and current during the discharge, which is not the case during the μEDM discharge process.. It is of prime importance to study the plasma channel as it is without assuming it as a heat source and considering the different losses of the energy of the plasma channel to model the μEDM process and improve its performance. The medium of the computational domain is taken as water vapor because the plasma channel during μEDM forms inside a vapor bubble. The present study is intended to simulate the formation of only the plasma channel in μEDM, which may be followed by a coupled finite element analysis of the present plasma model with the heat transfer to the anode surface and the molten metal pool formation as discussed previously by Mujumdar et al.
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