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Research Papers

Modeling of the Anode Crater Formation in Electrical Discharge Machining

[+] Author and Article Information
Jia Tao, Jun Ni, Albert J. Shih

Department of Mechanical Engineering,  University of Michigan, Ann Arbor, MI 48109

J. Manuf. Sci. Eng 134(1), 011002 (Jan 11, 2012) (11 pages) doi:10.1115/1.4005303 History: Received October 28, 2009; Revised September 17, 2011; Published January 11, 2012; Online January 11, 2012

This research presents a numerical model and the experimental validation of the anode crater formation in electrical discharge machining (EDM) process. The modeling is based on the theory that the material removal process in EDM is composed of two consecutive phases: the plasma heating phase in which intensive thermal energy density is applied locally to melt the work-material and the bubble collapsing phase in which the fluidic impact expels the molten material. A mathematical heat source model with Gaussian distributed heat flux and time variant heating area is applied in the plasma heating phase. Standard modules of a commercial computational fluid dynamics software, fluent , are adapted to model the crater formation in EDM. The material melting is simulated using transient heat transfer analysis and an enthalpy balance method. The volume of fraction (VOF) method is used to tackle the multiphase interactions in the processes of bubble compression and collapsing and molten material splashing and resolidification. Crater and debris geometries are attained from the model simulation and validation experiments are conducted to compare the crater morphology. The simulation and experiment results at different discharge conditions show good agreement on crater diameter suggest that the model is able to describe the mechanism of EDM crater formation.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

EDM surfaces of H13 tool steel with (a) negative polarity showing surface with clear feature of individual discharge craters (discharge current, ie  = 1 A, discharge duration ti  = 0.5 μs, open circuit voltage and ui  = 210 V) (b) positive polarity showing rough surface with rugged features (ie  = 2 A, ti  = 4 μs and ui  = 210 V) (electrode: copper)

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Figure 2

Discharge waveforms of three experimentally measured discharge conditions

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Figure 3

Profile of Gaussian distributed heat flux

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Figure 4

Schematics of the bubble collapsing model

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Figure 5

Simulation of the plasma heating phase

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Figure 6

Simulated bubble collapsing phase in wet EDM under discharge Condition III

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Figure 7

Simulated work-material fraction for near-dry and wet EDM craters under discharge conditions I, II, and III

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Figure 8

Discharge craters generated by continual discharge process (near-dry EDM with discharge condition II)

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Figure 9

Experimental craters under six EDM conditions

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Figure 10

Dimensional comparison of experimental and simulated craters

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Figure 11

Effect of initial bubble pressure in near-dry EDM on crater geometry in three discharge conditions

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