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TECHNICAL PAPERS

Microstructure Integrated Modeling of Multiscan Laser Forming

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

Department of Mechanical Engineering, Columbia University, New York, NY 10027

J. Manuf. Sci. Eng 124(2), 379-388 (Apr 29, 2002) (10 pages) doi:10.1115/1.1459088 History: Received March 01, 2001; Revised September 01, 2001; Online April 29, 2002
Copyright © 2002 by ASME
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References

Figures

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Algorithm for (a) recovery/recrystallization, and (b) phase transformation constitutive modeling (index j denotes the jth phase)
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Geometry of workpiece and coordinate system
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Typical temperature history of points on the scanning path along the thickness direction from FEM results (AISI 1012 steel)
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Typical heating and cooling rate on the top surface along the scanning path (X=40 mm, and Y=0 mm, and Z=0.89 mm) from FEM results. Note: positive value as cooling rate, and negative values as heating rate
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SEM micrographs of the cross section perpendicular to the scanning path, showing the hardened (dark-colored, no melting involved) zone below the laser scanned top surface of AISI 1012 steel under the conditions of (a)P=400 W,V=25 mm/s and (b)P=800 W,V=50 mm/s (grain refinement is seen in the region surrounded by dashed lines)
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Isothermal temperature contours from FEM results on the cross section normal to the scanning direction when laser is scanning under the conditions of (a)P=400 W,V=25 mm/s, and (b)P=800 W,V=50 mm/s (half of the cross section is simulated due to symmetry). The dotted lines the extent of the darkened areas in Fig. 5 and are used as the non-equilibrium lower transformation temperature A1ne. No melting is involved.
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Superposition of cooling time history of laser forming from FEM results on CCT curve of AISI 1012 steel 28
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Detailed SEM micrographs of AISI 1012 steel after laser forming under the condition of P=800 W, and V=50 mm/s (a) primarily martensite structure within the hardened zone (x2500) and (b) microstructure around the boundary between the hardened (dark colored) and untransformed (light colored) zone (x700) (also see Fig. 5)
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Y-axis plastic strain and peak temperature (both on the laser scanned top surface) with the Y-axis extent of the grain refined zone (Fig. 5(b)) of 1.26 mm to estimate the critical plastic strain
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Comparison of numerical bending angle history w/ and w/o microstructure consideration (MS) with experimental measurements in 10-scan laser forming. Note: FEM computes 1000s for each scan including cooling.
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Comparison of experimental multiscan bending angle with numerical results w/ and w/o microstructure consideration (MS)
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Detailed view of the first two scans from Fig. 10 (MS-microstructure consideration)
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Parametric studies of single scan bending angle (experimental and numerical results w/ and w/o microstructure consideration (MS)) (a) vs. scanning velocity, and (b) vs. laser power
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Comparison of numerical results of Y-axis stress history w/ and w/o microstructure consideration (MS)
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Comparison of yield stress from numerical modeling w/ and w/o microstructure consideration (MS) with experimental yield stress measurements (samples are scanned for 2, 4,[[ellipsis]], 10 times, respectively)

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