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Research Papers

A Discharge Separation Model for Powder Mixed Electrical Discharge Machining

[+] Author and Article Information
Bülent Ekmekci

Mechanical Engineering Department,
Bülent Ecevit University,
Incivez 67100, Zonguldak, Turkey
e-mail: bekmekci@hotmail.com

Hamidullah Yaşar, Nihal Ekmekci

Mechanical Engineering Department,
Bülent Ecevit University,
Incivez 67100, Zonguldak, Turkey

1Corresponding author.

Manuscript received October 15, 2015; final manuscript received March 2, 2016; published online March 29, 2016. Assoc. Editor: Y. B. Guo.

J. Manuf. Sci. Eng 138(8), 081006 (Mar 29, 2016) (9 pages) Paper No: MANU-15-1516; doi: 10.1115/1.4033042 History: Received October 15, 2015; Revised March 02, 2016

Added powders in a dielectric medium substantially influence the features of electrical discharges due to altered interelectrode conditions during the electrical discharge machining (EDM) process. The main discharge channel is disturbed due to the added powders in dielectric liquid and leads formations of secondary discharges. Such altered discharge conditions generate a unique topography on the machined surface and consequent subsurface microstructure beneath it. Ti6Al4V work material machined using SiC powder mixing in de-ionized water for an extensive set of pulse-on duration and pulse currents. Then, different forms of secondary discharges were identified from the resultant surface features and corresponding subsurface microstructures. The results pointed out that generation of unevenly separated secondary discharges increased the material transfer rate from the powder mixed dielectric liquid to the machined surface by means of the decomposed ions in the plasma channel. Complete separation of the main discharge channel into evenly distributed secondary discharges is possible under specific machining conditions that suggested minimal deformation of the machined surface regarding microcracks, roughness, and heat affected layer thickness. Under such machining conditions, another means of material transfer mechanism is activated that lead a powder particle build-up process on the machined surface. Consequently, five different discharge forms were proposed to describe the resultant surface topographies and subsurface microstructures. The material migration phenomena and the mechanisms are discussed in relation to the pulse-on time and pulse current.

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Figures

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Fig. 1

Experimental setup: (a) A general view of the experimental setup and (b) prepared sample for machining in aluminum reservoir

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Fig. 2

SEM and magnified back scattered images of surfaces PMEDM using 2 A pulse current and (a) 400 μs, (b) 100 μs, (c) 25 μs, and (d) 6 μs pulses on time

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Fig. 3

Cross-sectional examination of samples PMEDM using 2 A pulse current and (a) 400 μs, (b) 100 μs, (c) 25 μs, and (d) 6 μs pulses on time

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Fig. 4

PMEDM using 100 μs pulse on time and 2 A pulse current. Upper: A section view; Below: Vickers microhardness distribution on different layers.

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Fig. 5

SEM images and corresponding EDS analysis of PMEDM surfaces using 100 μs pulse on time: (a) Pulse current is 2 A and (b) Pulse current is 22 A

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Fig. 6

SEM images of surfaces PMEDM using 12 A pulse current and (a) 400 μs, (b) 100 μs, (c) 25 μs, and (d) 6 μs pulses on time

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Fig. 7

Cross-sectional examination of samples PMEDM using 12 A pulse current and (a) 400 μs, (b) 100 μs, (c) 25 μs, and (d) 6 μs pulses on time

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Fig. 8

Suggested forms of discharges (a) single column, (b) uneven branching, (c) central separation in the primary discharge, (d) complete separation, and (e) further uneven separation

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Fig. 9

Thicknesses of heat affected layers, proposed discharge forms and SEM view examples

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Fig. 10

Cross-sectional examination of samples PMEDM using 72 A pulse current and (a) 1600 μs, (b) 400 μs, and (c) 100 μs pulses on time

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Fig. 11

SEM and corresponding back scattered image of surface PMEDM using 7 A pulse current and 50 μs pulse on time

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