Research Papers

Modeling of Recast Layer in Micro-Electrical Discharge Machining

[+] Author and Article Information
P. C. Tan

School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798

S. H. Yeo

School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798mshyeo@ntu.edu.sg

J. Manuf. Sci. Eng 132(3), 031001 (Apr 28, 2010) (9 pages) doi:10.1115/1.4001480 History: Received November 09, 2009; Revised March 08, 2010; Online April 28, 2010; Published June 15, 2010

The thickness of recast layers produced during electrical discharge machining (EDM) is an important process performance measure as it may indicate an extent of crack propagation in a machined surface or thickness of a functional layer alloyed onto a machined surface. Thus, the availability of the recast layer thickness prediction models is needed to allow better control of machining outcomes, which becomes more vital for micro-EDM due to the microscale of machined features. The proposed numerical model, based on a multiple discharge approach for recast layer prediction, is developed to fill an existing gap in micro-EDM. The multiple discharge approach accounts for the overlapping nature by which craters are generated on the machined surface and considers the recast layer to be a combination of individual recast regions from individual craters. The numerical analysis, based on finite element methods, is used to determine the melting isotherms due to heat inputs on overlapping crater profiles. Then, a hemispherical-capped crater profile is estimated by applying a recast plasma flushing efficiency to the amount of molten material bounded by the melting isotherm. Finally, the recast region is defined to be bounded by the melting isotherm and crater profile. The model, developed for a peak discharge current of 1.45 A and pulse on time between 166 ns and 606 ns, predicted recast layer thicknesses of between 1.0μm and 1.82μm. It is then validated at pulse on time settings of 244 ns and 458 ns, which generated average recast layer thicknesses of 1.18μm and 1.56μm, respectively. Thus, the numerical model developed using the multiple discharge approach is suitable for estimation of recast layer thicknesses in micro-EDM.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Surface profile and heat flux location for predicting limits of recast layer thickness: (a) heat flux apex of neighboring craters and (b) heat flux at trough of a crater

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Figure 2

Generation of reference machined surface profile: (a, d, i) melting isotherm, (b, e) molten material, (c, f, g) recast regions, and (h) succeeding crater layer

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Figure 3

Flowchart of simulation process

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Figure 4

Typical discharge waveforms

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Figure 5

FEM model and assigned boundary conditions

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Figure 6

FEM models for predicting upper and lower bounds of recast layer thickness: (a) upper bound and (b) lower bound

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Figure 7

Circuit diagram of pulse generator

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Figure 8

Simulated results of fraction of heat flux versus crater radii

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Figure 9

FEM results of simulated recast layers for 166 ns pulse on time: (a) upper bound and (b) lower bound

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Figure 10

Recast layers produced at various pulse on time settings: (a) 166 ns, (b) 362 ns, and (c) 606 ns

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Figure 11

Measured and simulated recast layer thickness values

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Figure 12

Verification of model with additional experimental results




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