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Research Papers

Model-Based Prediction of Plasma Resistance, and Discharge Voltage and Current Waveforms in Micro-Electrodischarge Machining

[+] Author and Article Information
Soham S. Mujumdar

Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Champaign, IL 61801
e-mail: mujumda2@illinois.edu

Davide Curreli

Assistant Professor
Department of Nuclear, Plasma
and Radiological Engineering,
University of Illinois at Urbana-Champaign,
Champaign, IL 61801
e-mail: dcurreli@illinois.edu

Shiv G. Kapoor

Professor
Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Champaign, IL 61801
e-mail: sgkapoor@illinois.edu

David Ruzic

Professor
Center for Plasma-Material Interactions,
Department of Nuclear, Plasma
and Radiological Engineering,
University of Illinois at Urbana-Champaign,
Champaign, IL 61801
e-mail: druzic@illinois.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received July 2, 2015; final manuscript received October 7, 2015; published online October 29, 2015. Assoc. Editor: Bin Wei.

J. Micro Nano-Manuf 4(1), 011003 (Oct 29, 2015) (8 pages) Paper No: JMNM-15-1041; doi: 10.1115/1.4031773 History: Received July 02, 2015; Revised October 07, 2015

In electrodischarge machining (EDM), the thermal energy causing material removal at the electrodes is given by the electrical energy supplied to the discharge. This electrical energy, also known as the discharge energy, can be obtained from time-transient voltage and current waveforms across the electrodes during a discharge. However, in micro-EDM, the interelectrode gaps are shorter causing the plasma resistance to be significantly smaller than other impedances in the circuit. As a result, the voltage and current waveforms obtained by a direct measurement may include voltage drop across the stray impedances in the circuit and may not accurately represent the exact voltage drop across micro-EDM plasma alone. Therefore, a model-based approach is presented in this paper to predict time-transient electrical characteristics of a micro-EDM discharge, such as plasma resistance, voltage, current, and discharge energy. A global modeling approach is employed to solve equations of mass and energy conservations, dynamics of the plasma growth, and the plasma current equation for obtaining a complete temporal description of the plasma during the discharge duration. The model is validated against single-discharge micro-EDM experiments and then used to study the effect of applied open gap voltage and interelectrode gap distance on the plasma resistance, voltage, current, and discharge energy. For open gap voltage in the range of 100–300 V and gap distance in the range of 0.5–6 μm, the model predicts the use of a higher open gap voltage and a higher gap distance to achieve a higher discharge energy.

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Figures

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Fig. 1

Schematic of the enhanced micro-EDM plasma model formulation

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Fig. 3

Comparison of model prediction of voltage, current, and plasma resistance waveforms with the experimental measurements: (a) voltage across P3 and P4, (b) plasma current, (c) plasma voltage, and (d) plasma resistance

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Fig. 4

Model-predicted evolution of electrical characteristics of a typical micro-EDM plasma (V0 = 100 V and L = 1 μm): (a) plasma resistance, (b) voltage, (c) plasma current, and (d) power

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Fig. 5

Effect of open gap voltage and interelectrode gap distance on the electrical characteristics of micro-EDM plasma: (a) final plasma resistance (i.e., at t = 5 μs), (b) time-averaged plasma current from t = 0 to t = 5 μs, (c) final plasma voltage (i.e., at t = 5 μs), and (d) discharge energy

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Fig. 2

Schematic of the electrical circuit used for micro-EDM: (a) hybrid RC-transistor circuit for micro-EDM and (b) equivalent discharge circuit showing all the circuit components

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