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Research Papers

Effects of Different Cavity Geometries on Machining Performance in Micro-Electrical Discharge Milling

[+] Author and Article Information
Shrikant Vidya, Alok Kr. Das

Department of Mechanical Engineering,
Indian School of Mines,
Dhanbad 826004, India

Vijay, Aneissha Chebolu, Nagahanumaiah

Micro Systems Technology Laboratory,
CSIR-Central Mechanical Engineering
Research Institute,
Durgapur 713209, India

Swapan Barman

Precision Engineering and Metrology Group,
CSIR-Central Mechanical Engineering
Research Institute,
Durgapur 713209, India

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received July 3, 2014; final manuscript received November 27, 2014; published online January 13, 2015. Assoc. Editor: Stefan Dimov.

J. Micro Nano-Manuf 3(1), 011007 (Mar 01, 2015) (10 pages) Paper No: JMNM-14-1041; doi: 10.1115/1.4029275 History: Received July 03, 2014; Revised November 27, 2014; Online January 13, 2015

Low energy-short pulsed electric discharge coupled with precise movement of circular electrode in micro-electrical discharge-milling (μ-EDM-milling) enables generation of three-dimensional (3D) cavities in the order of few tens of microns. Use of unshaped rotating electrode alters the spark discharge pattern that is primarily driven by the shape and size of the cavities being machined. In this paper, effects of five different cavities: circular, triangular, square, channel, and cross channel (square pillars) on the machining performance have been studied. These cavities having a nominal dimension of 1000 μm were machined on steel sample using 200 μm tungsten carbide electrode. The machining performance has been evaluated by analyzing dimensional accuracy, surface integrity, profile error, and formation of recast layers. The results highlight significant shape effect on machining performance in μ-EDM-milling. Circular holes machined by die sinking (tool advancement in Z-axis) are found to be more accurate, and square shaped pillars machined in two settings by generating cross channels at 90 deg have poor dimensional control. On the other hand, triangular cavities have the highest surface finish and profile uniformity compared to other shapes. The microscopic study in scanning electron microscopy (SEM) reveals significant variations in globule formation, recast layer deposition, flow of eroded molten metal, and final shape of cavities, which are found to be dependent of tool rotation.

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Figures

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Fig. 1

μ-EDM-milling experimental setup (DT-110) with typical discharge image: (a) Machining setup and (b) typical discharge image by high-speed camera

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Fig. 2

Microscale cavities machined on EN-24 sample by μ-EDM-milling

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Fig. 3

Discharge patterns and shape errors in μ-EDM-milling operation

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Fig. 4

Microscopic images (5×) of cavities highlighted with key geometric error: (a) circular (high overcut), (b) triangular (rounding of corner), (c) square (rounding of corner), (d) channel (rough surface), and (e) square pillar (high recast edge)

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Fig. 5

SEM micrographs of cavity showing recast layer with microcracks: (a) circular, (b) triangular, (c) square, (d) channel, and (e) square pillar

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Fig. 6

Effect of tool electrode rotation on melt flow and granules formation: (a) spheroidization effect, (b) circular, (c) triangular, (d) square, (e) channel, and (f) square pillar

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Fig. 7

Surface profilometry of the cavity surface: (a) triangular, (b) square, (c) channel, (d), square pillar (cross channel first), and (e) square pillar (cross channel second)

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