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Research Papers

Deformation Behaviors and Critical Parameters in Microscale Laser Dynamic Forming

[+] Author and Article Information
Huang Gao, Chang Ye

School of Industrial Engineering, Purdue University, West Lafayette, IN 47907

Gary J. Cheng1

School of Industrial Engineering, Purdue University, West Lafayette, IN 47907gjcheng@purdue.edu

1

Corresponding author.

J. Manuf. Sci. Eng 131(5), 051011 (Sep 23, 2009) (11 pages) doi:10.1115/1.4000100 History: Received July 27, 2008; Revised August 13, 2009; Published September 23, 2009

Microscale laser dynamic forming (μLDF) is a novel microfabrication technique to introduce complex 3D profiles in thin films. This process utilizes pulse laser to generate plasma to induce shockwave pressure into the thin film, which is placed above a microsized mold. The strain rate in μLDF reaches 106107S1. Under these ultrahigh strain rates in microscale, deformation behaviors of materials are very complicated and almost impossible to be measured in situ experimentally. In this paper, a finite element method model is built to simulate the μLDF process. An improved Johnson–Cook model was used to calculate the flow stress, and the Johnson–Cook failure criterion was employed to simulate failure during μLDF. The simulation results are validated by experiments, in which the deformation of Cu thin foils after μLDF experiments are characterized by scanning electron microscopy and compared with simulation results. With the verified model, the ultrafast μLDF process is generally discussed first. A series of numerical simulations are conducted to investigate the effects of critical parameters on deformation behaviors. These critical parameters include the ratio of the fillet radius to film thickness, the aspect ratio of mold, as well as laser intensities. The relationship of laser pulse energy and the deformation depth is also verified by a series of μLDF experiments.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) The schematic setup of a laser dynamic forming process (3), (b) the SEM micrograph of a Cu foil after laser dynamic forming using a microgrid as a mold, and (c) the shockwave pressure generated by glass confinement and graphite ablation, with a laser pulse width of 5 ns

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Figure 2

The SEM image and the dimensions of mold cavity fabricated by a FIB

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Figure 3

(a) The cross section and deformation depth characterized in high resolution SEM and (b) the necking and deformation depth predicted by the FEM model; the time history of Y displacement at the center of the cavity

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Figure 4

(a) The prediction of the FEM model in ABAQUS , fracture occurs at the fillet with the FEM mesh highly deteriorated, (b) the SEM image of deformation with fracture, and (c) the cross section at the fracture characterized by an ion beam, presenting the highly elongated grains by channeling the effects of the ion beam

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Figure 5

Four critical stages of deformation after the shockwave propagation through the thickness of the thin film (highlighted are the values and locations of the max Von Mises stress in each stage)

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Figure 6

(a) Six sampling points at the bottom surface, middle thickness, and top surface of the material at the fillet and center, (b) time history of total plastic strain at the fillets, and (c and d) time history of plastic strains in the transverse direction and film thickness at the center

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Figure 7

Comparison of vertical displacement, max Von Mises stress, total plastic strain, and necking ratio for three molds with different dimensions and aspect ratios

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Figure 8

Simulation results on effects of the aspect ratio of mold: at fillet, the time history of (a) Von Mises stress, (b) equivalent plastic strain (PEEQ), and (c) maximum principal strain rate

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Figure 9

The time history of (a) Von Mises and (b) PEEQ at fillet for various laser intensities, at the fillet

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Figure 10

The time history of equivalent plastic strain (PEEQ) at three points near the necking area (laser intensity=0.9 GW/cm2 and pulse width=5 ns)

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Figure 11

The relationship between the laser pulse energy and the vertical displacement in the center

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Figure 12

(a) The relationship between the deformation depth and laser intensities for various thin film thicknesses and (b) the surface profile of a 2.5 μm Al thin film after fully formed into a microgrid mold (W:54 μm  and  D:6.7 μm)

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