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Research Papers

Effect of Dielectric Electrical Conductivity on the Characteristics of Micro Electro-Discharge Machining Plasma and Material Removal

[+] 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

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received December 17, 2015; final manuscript received March 24, 2016; published online April 21, 2016. Assoc. Editor: Stefan Dimov.

J. Micro Nano-Manuf 4(2), 021006 (Apr 21, 2016) (9 pages) Paper No: JMNM-15-1085; doi: 10.1115/1.4033344 History: Received December 17, 2015; Revised March 24, 2016

In micro electro-discharge machining (micro-EDM), it is believed that electrical conductivity of the dielectric modified by additives plays an important role in discharge initiation and electrical breakdown, thereby affecting the process characteristics including process accuracy, material removal rate (MRR), and surface finish. However, there has been a lack of systematic efforts to evaluate the effect of dielectric conductivity in micro-EDM. This paper investigates the role of electrical conductivity of the dielectric on the breakdown, plasma characteristics, and material removal in micro-EDM via modeling and experimentation. Experiments have been carried out at four levels of electrical conductivity of saline water, i.e., 4 μS/cm, 362 μS/cm, 1106 μS/cm, and 4116 μS/cm, to study electrical breakdown of the dielectric and resulting craters. A global modeling approach is employed to model the micro-EDM plasma in saline water and predict the effect of dielectric conductivity on electron density, plasma temperature, heat flux to anode, plasma resistance, and discharge energy. It is found from both experiments and model-based simulations that increase in the dielectric conductivity facilitates the electrical breakdown of the dielectric by lowering the minimum breakdown potential at a given interelectrode gap. Experimental results also show increase in the volume of material removed per discharge when dielectric conductivity is increased, which is attributed to the increase in anode heat flux predicted by the micro-EDM plasma model. The model also predicts increase in electron density, decrease in plasma resistance, and decrease in discharge energy as the dielectric conductivity increases.

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References

Figures

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Fig. 1

Typical voltage and current waveforms of a successful micro-EDM discharge and a failed micro-EDM discharge (no discharge): (a) successful discharge and (b) no discharge

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Fig. 2

Three-dimensional image of a typical micro-EDM crater showing positive and negative volumes: (a) 3D view and (b) side view

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Fig. 3

Experimentally obtained voltage-gap domain at different electrical conductivities of water (σ0) showing discharge probability at each voltage-gap combination. White square represents probability ≥0.5, and gray represents probability <0.5: (a) σ0 = 4 μS/cm, (b) σ0 = 362 μS/cm, (c) σ0 = 1106 μS/cm, and (d) σ0 = 4116 μS/cm.

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Fig. 4

Effect of water conductivity (σ0) on crater erosion volume at different gap distances and open gap voltage of 200 V

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Fig. 5

Schematic of the micro-EDM plasma model formulation [22]

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Fig. 6

Plot of wt.% of NaCl versus the electrical conductivity of the solution [24]

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Fig. 7

Model-based prediction of voltage-gap domain at different electrical conductivities of water (σ0) obtained using micro-EDM plasma model. White square represents successful simulation of micro-EDM discharge at the voltage-gap combination, and dark square represents failure of the discharge predicted from the model. (c) σ0 = 1106 μS/cm and (d) σ0 = 4116 μS/cm.

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Fig. 8

Model prediction of minimum breakdown potential versus gap distance for different water conductivities

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Fig. 9

Model-based prediction of the effect of water conductivity (σ0) on the plasma characteristics at V0 = 200 V and L = 1 μm: (a) time-averaged electron density, (b) time-averaged plasma resistance, (c) total discharge energy, (d) time-averaged electron temperature, (e) time-averaged heat flux at anode, and (f) final plasma radius and time-averaged pressure (note suppressed zero)

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