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Research Papers

Edge Fracture Prediction of Traditional and Advanced Trimming Processes for AA6111-T4 Sheets

[+] Author and Article Information
X. H. Hu

Computational Science
and Mathematics Division,
Pacific Northwest National Laboratory,
Richland, WA 99354
e-mail: Xiaohua.hu@pnnl.gov

K. S. Choi, X. Sun

Computational Science
and Mathematics Division,
Pacific Northwest National Laboratory,
Richland, WA 99354

S. F. Golovashchenko

Manulfacturing and Processes Department,
Ford Research and Advanced Engineering,
Scientific Research Laboratory,
Dearborn, MI 48124

1Corresponding author.

Manuscript received March 25, 2013; final manuscript received November 15, 2013; published online February 12, 2014. Assoc. Editor: Brad L. Kinsey.

J. Manuf. Sci. Eng 136(2), 021016 (Feb 12, 2014) (11 pages) Paper No: MANU-13-1104; doi: 10.1115/1.4026273 History: Received March 25, 2013; Revised November 15, 2013

This work examines the traditional and advanced trimming of AA6111-T4 aluminum sheets with finite element simulations. The Rice-Tracy damage model is used for the simulation with damage parameters estimated from experimental observation of grain aspect ratio near the fracture surface of trimmed parts. Fine meshes at the shearing zone, adaptive meshing, and adaptive contact techniques are used to accurately capture the contact interactions between the sharp corner of the trimming tools and the blank to be trimmed. To the knowledge of the authors, these are the first trimming simulations that can predict the effects of shearing clearance on burr heights with quantitative accuracy for AA6111-T4 aluminum sheets. In addition, the models have also accurately reproduced the crack initiation site as well as burr and sliver formation mechanisms observed experimentally.

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Figures

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Fig. 1

Finite element models for the traditional (a) and advanced (b) trimming processes where the middle section of the blank has much finer meshes (c)

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Fig. 2

Examples of a trimmed blank (21% clearance) by the traditional trimming (a)–(c) and the advanced trimming processes (d)–(e)

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Fig. 3

Ludwik fitting of the uniaxial tensile flow curve of AA6111–T4 sheet alloys

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Fig. 4

The micrograph near the fracture surface (a) and the estimated rice-tracey fracture locus (b)

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Fig. 5

Tool-mesh penetration is observed if contacts are inadequately defined between the internal nodes and the tools (a). The penetration is prevented if sufficient contacts are defined (b).

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Fig. 6

The blanked part sides and scrap sides predicted by finite element simulations and the corresponding experimental observations for various clearances

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Fig. 7

The blanked part sides and scrap sides predicted by FE simulations and the corresponding experimental observations for various clearances

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Fig. 8

(a) the normal and tangential (frictional) reaction forces exerted from the deforming sheet on the tools during trimming operations for clearance of 43% (b) the sketch of actual total horizontal and vertical reaction forces on the punch tool for cutting clearances of 10% and 43%, respectively

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Fig. 9

The burr height (b), blank thickness (t), and final cutting clearance (g′), measurements for cutting with 21% clearance.

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Fig. 10

The variation of finite element and experimental relative burr heights (b) for different clearances

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Fig. 11

Stress triaxiality before crack initiation for the simulation with 43% blanking clearance

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Fig. 12

The deformed mesh after crack initiation for the simulation with 43% blanking clearance

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Fig. 13

The deformed mesh after the formation of sliver by the punch roll-over over the tool fillet indent feature for the simulations of the blanking process with 43% clearance

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Fig. 14

The variation of normalized burr height and friction coefficients with friction coefficient for clearance of 43%

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Fig. 15

The variation of equivalent plastis strain with friction coefficient for clearance of 43%

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Fig. 16

The variation of normalized burr with clearances for different friction coefficients

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