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TECHNICAL PAPERS

Laser Forming of Varying Thickness Plate—Part II: Process Synthesis

[+] Author and Article Information
Peng Cheng

Department of Mechanical Engineering, Columbia University, New York, NY 10027pc2052@columbia.edu

Yajun Fan, Jie Zhang, Y. Lawrence Yao

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

David P. Mika, Wenwu Zhang, Michael Graham, Jud Marte, Marshall Jones

Global Research Center, General Electric Company, Niskayuna, NY

J. Manuf. Sci. Eng 128(3), 642-650 (Nov 12, 2005) (9 pages) doi:10.1115/1.2162912 History: Received November 07, 2005; Revised November 12, 2005

Laser forming (LF) is a non-traditional forming process that does not require hard tooling or external forces and, hence, may dramatically increase process flexibility and reduce the cost of forming. While extensive progress has been made in analyzing and predicting the deformation given a set of process parameters, few attempts have been made to determine the laser scanning paths and laser heat conditions given a desired shape. This paper presents a strain-based strategy for laser forming process design for thin plates with varying thickness, which is utilized in determining the scanning paths and the proper heating conditions. For varying thickness plates, both the in-plane membrane strain and the bending strain need to be accounted for in process design. Compared with uniform thickness plate, the required bending strain varies with not only the shape curvature but also with the plate thickness. The scanning paths are determined by considering the different weight of bending strain and in-plane strain. A thickness-dependent database is established by LF finite element analysis simulation, and the heating conditions are determined by matching the ratio of bending strain to in-plane strain between the required values and the laser forming values found in the database. The approach is validated by numerical simulation and experiments using several typical shapes.

FIGURES IN THIS ARTICLE
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Copyright © 2006 by American Society of Mechanical Engineers
Topics: Lasers , Shapes , Thickness , Heating
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Figures

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Figure 1

Flow chart of laser forming process design for varying thickness shapes

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Figure 2

Desired shapes (a) case 1: Gaussian curvature=0; (b) case 2 (pillow): Gaussian curvature>0; (c) case 3 (saddle): Gaussian curvature<0. All the shapes are amplified in Z direction (x2) for viewing clarity.

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Figure 3

Principal minimum in-plane strain for the case1 shape (a) with uniform thickness (b) with varying thickness; and principal minimum bending strain for the case 1 shape (c) with uniform thickness (d) with varying thickness plate

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Figure 4

Vector plot of in-plane strain of the (a) pillow shape with varying thickness, (b) saddle shape with varying thickness; and vector plot of bending strain of the (c) pillow shape with varying thickness, (d) saddle shape with varying thickness

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Figure 5

Vector plot of the averaged in-plane strain and bending strain of the (a) pillow shape, and (b) saddle shape, both of which have varying thickness along the Y direction

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Figure 6

Determined heating paths of (a) pillow shape, and (b) saddle shape, both of which have varying thickness along the Y direction

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Figure 7

Averaged plastic strain obtained from laser forming simulation through the thickness direction at a typical location (thickness=2mm, beam size=8mm) (the color contour shows the distribution of plastic strain in the cross section)

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Figure 8

Plastic strain distribution of laser forming on varying thickness plate along the scanning path (under condition of power=1000W, scanning speed=20mm∕s, and spot size=8mm)

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Figure 9

Variations of the ratio of bending strain to in-plane strain with varying thicknesses (a) under the condition of constant power and various scanning speed; and (b) under the condition of constant scanning speed and various powers

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Figure 10

Database for the determination of heating conditions (a) the ratio of bending strain to in-plane strain as the function of line energy (P∕V) and thickness, and (b) the in-plane strain for a typical thickness (h=2mm) as the function of power and scanning speed

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Figure 11

Laser formed pillow and saddle shapes with varying thickness

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Figure 12

Deviations of top-surface geometry between the formed shape and the desired shape for (a) pillow shape, and (b) saddle shape. The formed plates were measured by CMM and the error unit is mm.

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