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Research Papers

Experimental Study of the Dry and Near-Dry Electrical Discharge Milling Processes

[+] Author and Article Information
Jia Tao, Jun Ni

Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125

Albert J. Shih1

Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125shiha@umich.edu

1

Corresponding author.

J. Manuf. Sci. Eng 130(1), 011002 (Jan 16, 2008) (9 pages) doi:10.1115/1.2784276 History: Received June 07, 2007; Revised August 10, 2007; Published January 16, 2008

This study investigates the dry and near-dry electrical discharge machining (EDM) milling to achieve a high material removal rate (MRR) and fine surface finish for roughing and finishing operations, respectively. Dry EDM uses gas and near-dry EDM applies a liquid-gas mixture as the dielectric medium. Experimental studies leading to the selection of oxygen gas and copper electrode for high MRR dry EDM and the nitrogen-water mixture and graphite electrode for fine surface finish near-dry EDM are presented. Near-dry EDM exhibits the advantage of good machining stability and surface finish under low discharge energy input. A 251 fractional factorial design is applied to investigate the effect of discharge current, pulse duration, and pulse interval on the MRR and surface finish in dry and near-dry EDMs. Lower pulse duration and lower discharge current are identified as key factors for improving the surface finish in near-dry EDM.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 8

Effect of the discharge current on the finishing EDM (ti=4μs, t0=8μs, ue=60V, and ui=200V, copper electrode)

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Figure 9

Effect of the input pressure of the spray delivery device to the finishing process (ie=1A, ti=2μs, t0=16μs, ue=20V, and ui=200V, graphite electrode with kerosene-air mixture)

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Figure 12

Optical micrographs of the quasiexplosion mode EDM surface with deep craters (a) top view and (b) cross section view (ie=30A, ti=12μs, t0=8μs, ue=60V, and ui=260V)

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Figure 13

Projected surfaces of (a) MRR and (b) Ra versus ti and t0, ie and t0, and ie and ti for finishing EDM

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Figure 1

Dry and near-dry EDM experimental setup: (a) rotary spindle and electrode, (b) spray delivery device, and (c) nozzle to deliver cold air

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Figure 2

Configuration of EDM milling: (a) Overview and (b) close-up view of the electrode and cutting region

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Figure 3

MRR and Ra results of different dielectric fluids for copper and graphite electrode materials: (a) at high discharge energy input (ie=20A, ti=4μs, t0=8μs, ue=60V, and ui=200V) and (b) at low discharge energy input (ie=1A, ti=4μs, t0=8μs, ue=60V, and ui=200V)

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Figure 4

Graphite electrode in near-dry EDM at high discharge current: (a) Damaged workpiece surface due to arcing and (b) damage tool (ie=20A, ti=4μs, t0=8μs, ue=60V, and ui=200V)

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Figure 5

Worn electrode and grooves milled using oxygen as a dielectric fluid (ie=20A, ti=4μs, t0=8μs, ue=60V, and ui=200V): (a) Without using cold gun (Ra=14.2μm; MRR=20mm3∕min) and (b) using cold gun (Ra=13.2μm; MRR=22mm3∕min)

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Figure 6

Effect of the depth of cut on dry EDM rough cutting with oxygen (ie=30A, ti=4μs, t0=8μs, ue=60V, and ui=200V)

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Figure 7

Effect of the discharge current on high energy input dry EDM with oxygen (ti=4μs, t0=8μs, ue=60V, and ui=200V)

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Figure 11

Optimal micrographs of EDM surfaces at normal discharge mode: (a) Without milling mark, Ra=4.32μm (ie=20A, ti=12μs, t0=8μs, ue=40V, and ui=160V) and (b) with milling mark, Ra=6.13μm (ie=20A, ti=4μs, t0=20μs, ue=80V, and ui=260V)

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Figure 10

Projected surfaces of (a) MRR and (b) Ra versus ie and t0, ie and ti, and ti and t0 for roughing EDM

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