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Research Papers

Forming Limit and Fracture Mode of Microscale Laser Dynamic Forming

[+] Author and Article Information
Ji Li, Huang Gao

School of Industrial Engineering, Purdue University, West Lafayette, IN 47906

Gary J. Cheng

School of Industrial Engineering, Purdue University, West Lafayette, IN 47906gjcheng@purdue.edu

J. Manuf. Sci. Eng 132(6), 061005 (Oct 19, 2010) (10 pages) doi:10.1115/1.4002546 History: Received November 05, 2009; Revised June 10, 2010; Published October 19, 2010; Online October 19, 2010

The microscale laser dynamic forming (LDF) process is a high strain rate microfabrication technique, which uses a pulse laser to generate high pressure by vaporizing and ionizing an ablative coating, and thus produces complex 3D microstructures in thin foils. One of the most important features of this technique is ultrahigh strain rate (typically 1067s1), which is theoretically favorable for increasing formability. However, due to the lack of measurement techniques in microscale and submicroscale, the formability of workpieces in LDF is hardly studied. In this article, experiments were carried out on aluminum foils to study the forming limits and fracture of thin films in LDF. The deformation depth was measured by an optical profilometer and the formed feature was observed using a focused ion beam and a scanning electron microscope. Meanwhile, a finite element model based on a modified Johnson–Cook constitutive model and a Johnson–Cook failure model was developed to simulate the mechanical and fracture behaviors of materials in LDF. Experimental results were used to verify the model. The verified model was used to predict the forming limit diagram of aluminum foil in LDF. The forming limit diagrams show a significant increase in formability compared with other metal forming processes.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Features formed by micro laser dynamic forming: (a) arrays of micro squares; (b) repeated hexagonal shapes

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Figure 2

Schematic setup of laser dynamic forming process

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Figure 3

A mold (mold 1) cut by FIB

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Figure 4

Calculated temporal distribution of laser shock pressure according to different laser intensity

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Figure 9

The cross section of deformed feature cut by FIB (4 μm foil, mold 2, laser intensity is 0.48 GW/cm2): (a) a SEM picture of the feature, (b) a focused view of the cross section, and (c) a simulated result of the cross section

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Figure 10

Comparison of measured and calculated cross section thickness variation at positions 1, 2, and 3 shown in Fig. 9 for 4 μm foil deformed in mold 2 by 0.48 GW/cm2 laser intensity

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Figure 11

Comparison of measured and calculated cross section thickness variation at positions 1, 2, and 3 shown in Fig. 9 for (a) 4 μm foil deformed in mold 1 by 0.34 GW/cm2 laser intensity, (b) 2.5 μm foil deformed in mold 1 by 0.16 GW/cm2 laser intensity, and (c) 2.5 μm foil deformed in mold 2 by 0.16 GW/cm2 laser intensity

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Figure 12

The cross section of fractured sample cut by FIB (2.5 μm foil, mold 1, laser intensity is 0.31 GW/cm2): (a) a SEM picture of the sample, (b) a focused view of the cross section, and (c) a simulated result of the cross section corresponding to (b)

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Figure 13

Comparison of measured and calculated cross section thickness variation at positions 1, 2, and 3 shown in Fig. 1

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Figure 14

Predicted FLD of a 4 μm aluminum foil in LDF

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Figure 15

Predicted FLD of a 2.5 μm aluminum foil in LDF

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Figure 8

Fractured sample (2.5 μm foil, mold 2, laser intensity is 0.31 GW/cm2): (a) simulated result and (b) SEM picture of the sample

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Figure 7

Comparison of measured and simulated relationships of laser intensity and deformation depth: (a) 4 μm thick foil deformed in mold 1, (b) 2.5 μm thick foil deformed in mold 1, (c) 4 μm thick foil deformed in mold 2, and (d) 2.5 μm thick foil deformed in mold 2

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Figure 6

Experimental data of laser intensity versus deformation depth of samples in LDF

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Figure 5

Typical deformed samples of aluminum foils. (a) A feature fabricated by LDF (foil thickness is 2.5 μm, laser intensity is 0.13 GW/cm2, and mold 1 is used). (b) A fractured feature (foil thickness is 2.5 μm, laser intensity is 0.27 GW/cm2, and mold 1 is used).

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