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TECHNICAL PAPERS

The Influence of Sheet Metal Anisotropy on Laser Forming Process

[+] Author and Article Information
Peng Cheng, Y. Lawrence Yao

Department of Mechanical Engineering,  Columbia University, 220 Mudd Building, MC 4703, New York, NY 10027

J. Manuf. Sci. Eng 127(3), 572-582 (Jul 28, 2004) (11 pages) doi:10.1115/1.1949620 History: Received September 10, 2003; Revised July 28, 2004

Cold-rolled sheet metal that is often used in laser forming exhibits anisotropic properties, which are mostly caused by preferred orientations of grains developed during the severe plastic deformation such as cold rolling. In the present study, the textures of cold-rolled mild steel sheets are characterized and the influence of the plastic anisotropy on laser forming process is investigated. Deformation textures are measured in terms of pole figures and orientation distribution function (ODF) plots obtained through electron backscatter diffraction (EBSD). The anisotropy index (R-value) of the material with different rolling reductions is obtained by uniaxial tensile tests. Both are compared and agree with the texture development theory. Effects of the plastic anisotropy on bending deformation during the laser forming process are investigated experimentally and numerically. Various conditions including different laser power, scanning speed, and number of scans for sheets of different rolling reductions are considered and results are discussed. The simulation results are consistent with the experimental observations.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Rolled-sheet coordinate system and terminology: RD, rolling direction; TD, transverse direction; and ND, normal direction; and (b) schematic laser forming system scanning path along the RD or TD

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Figure 2

(a) {001}, {110}, {111}, and {112} pole figures of AISI 1010 cold-rolled steel sheet of 1.4mm thick; and (b) orientation distribution functions (ODFs) of the same sample

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Figure 3

Euler space (0deg⩽φ1,Φ,φ2⩽90deg) for a cubic crystal system and orthorhombic sample system. Two relevant textures fibers are depicted schematically

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Figure 4

{001}, {110}, {111}, and {112} pole figures of AISI 1010 cold-rolled steel sheet of 0.89mm thick

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Figure 5

SEM micrographs of grain structures of cold-rolled AISI 1010 steel 1.4mm thick (×1000) (a) cross section perpendicular to the transverse direction (TD); and (b) cross section perpendicular to the rolling direction (RD)

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Figure 6

(a) Comparison of R-values between theoretical values and measured values; (b) comparison of yield stress ratio between theoretical values and calculated values by R-values and Hill’s criterion

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Figure 7

(a) Numerical and experimental bending angles of 1.4mm thick steel sheet with scanning along the RD and TD, respectively; and (b) simulated time history of plastic strain in the y direction, which is perpendicular to the scanning path (results on isotropic sheets also included)

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Figure 8

(a) Numerical and experimental bending angles of 0.89mm thick steel sheet with scanning along the RD and TD, respectively; and (b) simulated time history of the temperature on top and bottom surface, and the plastic strain in the y direction, which is perpendicular to the scanning path (results on isotropic sheets also included)

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Figure 9

Numerical and experimental bending angle difference between scanning along the RD and TD (for 80×80×1.4mm, P=1200W, V=50mm∕s, spot size=6mm; and for 80×80×0.89mm, P=800W, V=50mm∕s, spot size=4mm)

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Figure 10

(a) Bending angle and (b) differences of bending angle between scans along the RD and TD (constant laser power and varying speed)

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Figure 11

Simulated peak temperature strain rate, and yield stress when scanning along the rolling direction and transverse direction

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Figure 12

SEM micrographs of the cross section perpendicular to the scanning path, showing the heat affect zone (HAZ) (dark colored, no melting involved) and the grain refinement in the HAZ under the conditions of (a) P=800W, V=50mm∕s, and (b) P=800W, V=90mm∕s

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Figure 13

(a) Bending angle and (b) differences of bending angle between scans along the RD and TD (constant speed and varying power)

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Figure 14

(a) Bending angle and (b) differences and increment of difference of bending angle between scans along the RD and TD in multiscan laser forming

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