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Research Papers

Effect of Material Physical Properties on Residual Stress Measurement by EDM Hole-Drilling Method

[+] Author and Article Information
H. T. Lee1

Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwanhtlee@mail.ncku.edu.tw

T. Y. Tai

Department of Mechanical Engineering, Southern Taiwan University of Technology, Tainan 701, Taiwan

C. Liu, J. M. Hsu

Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan

F. C. Hsu

 Metal Industries Research and Development Centre, 1001 Kaonan Highway, Kaohsiung 811, Taiwan

1

Corresponding author.

J. Eng. Mater. Technol 133(2), 021014 (Mar 21, 2011) (8 pages) doi:10.1115/1.4000219 History: Received November 05, 2008; Revised June 30, 2009; Published March 21, 2011; Online March 21, 2011

When measuring the residual stress within a component using the electrical discharge machining (EDM) strain-gage method, a metallurgical transformation layer is formed on the wall of the measurement hole. This transformation layer induces an additional residual stress and therefore introduces a measurement error. In this study, it is shown that given an appropriate set of machining conditions, this measurement error can be compensated directly using a calibration stress factor σcal computed in accordance with the properties of the workpiece material. It is shown that for EDM machining conditions of 120 V/12 A/6μs/30μs (discharge voltage/pulse current/pulse-on duration/pulse-off duration), the hole-drilling induced stress reduces with an increasing thermal conductivity (k) in accordance with the relation σcal=325.5k0.65MPa and increases linearly with an increasing carbon equivalent (CE) in accordance with σcal=7.6×(CE)+22.4MPa. Therefore, a given knowledge of the thermal conductivity coefficient or carbon equivalent of the workpiece material, an accurate value of the true residual stress within a component can be obtained simply by subtracting the computed value of the calibration stress from the stress value obtained in accordance with the EDM hole-drilling strain-gage method prescribed in ASTM E837.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

The facility of EDM hole-drilling method

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Figure 2

Influence of pulse current and pulse-on duration parameters on hole-drilling induced stress and time required to achieved specified machining depth

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Figure 3

Backscattered electron images showing AISI D2 surface morphology following machining under various EDM conditions (note that the arrows indicate surface cracks)

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Figure 4

Variation in calibration stress with thermal conductivity of workpiece material (note that the EDM conditions are 120 V/12 A/6 μs/30 μs in every case)

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Figure 5

Backscattered electron images showing surface morphologies of current ferrous specimens machined under EDM conditions of 120V/12A/6 μs/30 μs (note that the arrows indicate surface cracks)

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Figure 6

Variation in calibration stress with thermal conductivity (note that the EDM conditions are 120V/12A/6 μs/30 μs in every case; also, the results are presented only for those specimens in which a crack-free recast layer is obtained, i.e., the calibration stress for the AISI D2 specimen is deliberately omitted)

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Figure 7

Variation in calibration stress with carbon equivalent (note that the EDM conditions are 120V/12A/6 μs/30 μs in every case; also the results are presented only for those specimens in which a crack-free recast layer is obtained, i.e., the calibration stress for the AISI D2 specimen is deliberately omitted

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Figure 8

Calibration procedure for ferrous materials in which crack-free recast layer can be obtained

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Figure 9

Calibration procedure for ferrous materials in which crack-free recast layer cannot be obtained

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