A Computational Response Surface Study of Three-Dimensional Aluminum Hemming Using Solid-to-Shell Mapping

[+] Author and Article Information
Guosong Lin

Department of Mechanical Engineering, The University of Michigan, Ann Arbor, MI 48109guosongl@umich.edu

Jing Li

Department of Industrial and Operations Engineering, The University of Michigan, Ann Arbor, MI 48109

S. Jack Hu

Department of Mechanical Engineering, The University of Michigan, Ann Arbor, MI 48109

Wayne Cai

Manufacturing Systems Research Laboratory, General Motors R&D Center, Warren, MI 48090

J. Manuf. Sci. Eng 129(2), 360-368 (Oct 16, 2006) (9 pages) doi:10.1115/1.2515430 History: Received November 07, 2005; Revised October 16, 2006

Hemming is a manufacturing process of folding a panel onto itself or another sheet. Quality of hemming is characterized by geometry and formability. This paper presents a response surface study of three-dimensional (3D) curved-surface-curved-edge hemming of an aluminum alloy, AA6111-T4, using finite-element (FE) analysis. Solid elements and explicit FE solver are used for simulations of flanging, pre- and final hemming, and shell elements with implicit solver are deployed for springback prediction. A novel procedure called “solid-to-shell mapping” is developed to bridge the solid elements with the shell elements. Verified to be accurate and efficient, the model is utilized in a central composite design to quantitatively explore the relationships between certain key process variables and the hem dimensional quality and formability. The most significant variables are identified as: (i) prehemming angle on roll-in/roll-out; (ii) nominal surface curvature on sheet springback; and (iii) initial sheet strain and flanging die radius on the maximum hemline surface strain of the produced hem. These results provide insights for process parameter selections in designing and optimizing 3D hems under material formability constraints.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Three-step hemming process and associated terminology; (a) flanging, (b) prehemming, (c) final hemming

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Figure 2

Major dimensional hemming imperfections; (a) roll-in/roll-out, (b) radial springback

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Figure 3

Examples of various hemming types according to their surface and edge geometries; (a) flat-surface-straight-edge hem, (b) curved-surface-curved-edge hem

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Figure 4

Simplified FE hemming simulation procedures

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Figure 5

Sheet dimensions and associated coordinate system

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Figure 6

A portion of FE model for flanging, pre- and final hemming simulations

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Figure 7

Stress mapping from solid to shell through embedded membrane elements

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Figure 8

Compensation of shell thickness in ABAQUS/Standard for contact modeling

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Figure 9

Contour plots of effective strain and displacement respectively for forming and springback simulations from solid-to-shell mapping FE model; (a) flanging, (b) prehemming, (c) final hemming, (d) final hemming springback

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Figure 10

Roll-in/roll-out comparisons between FE models and experimental data

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Figure 11

Radial springback comparisons between FE models and experimental data

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Figure 12

Comparisons of maximum hemline surface strain between FE models

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Figure 13

Comparisons of computational efficiency between FE models

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Figure 14

Schematic of CCD structure through two variables

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Figure 15

Definitions of location variables

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Figure 16

Matrix plots of individual variable significances (main effects)

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Figure 17

Layered response surfaces for concerned hemming dimensional quality and formability measures; (a) response surfaces for hemline roll-in/roll-out (mm), (b) response surfaces for radial springback, (c) response surfaces for maximum hemline surface strain



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