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TECHNICAL PAPERS

Finite Element Modeling and Analysis of Warm Forming of Aluminum Alloys—Validation Through Comparisons With Experiments and Determination of a Failure Criterion

[+] Author and Article Information
Hong Seok Kim, Jun Ni

S. M. Wu Manufacturing Research Center, College of Engineering, University of Michigan, Ann Arbor, MI 48109

Muammer Koç1

S. M. Wu Manufacturing Research Center, College of Engineering, University of Michigan, Ann Arbor, MI 48109mkoc@umich.edu

Amit Ghosh

Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109

1

To whom correspondence should be addressed.

J. Manuf. Sci. Eng 128(3), 613-621 (Sep 19, 2005) (9 pages) doi:10.1115/1.2194065 History: Received December 21, 2004; Revised September 19, 2005

In this study, thermomechanically coupled finite element analysis (FEA) was performed for forming aluminum rectangular cups at elevated temperatures. In order to identify the onset of a failure during FEA, applicability, accuracy, and repeatability of three different failure criteria (maximum load, minimum thickness, and thickness ratio) were investigated. The thickness ratio criterion was selected since it resulted in accurate prediction of necking-type failure when compared with experimental measurements obtained under a variety of warm forming conditions. Predicted part depth values from FEA at various die-punch temperature combinations and blank holder pressures conditions were also compared with experiments, and showed good agreement. Forming limit diagrams were established at three different warm forming temperature levels (250°C, 300°C, and 350°C). An increasing limiting strain was observed with increasing forming temperature both in FEA and experiments. In addition, strain distributions on the formed part obtained under different die-punch temperature combinations were also compared to further validate the accuracy of FEA. A high temperature gradient between die and punch (Tdie>Tpunch) was found to result in increased formability; i.e., high part depths.

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Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Comparison of 2D FEA predictions with experimental results in deep drawing of a circular cup. (a) FEA modeling and (b) limiting drawing ratios (LDR) at various temperatures and punch speeds (8,17).

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Figure 2

Experimental and simulation models. (a) Schematic diagram for the experimental set up (11) and (b) quarter of the FE model. Dimensions are listed in Table 1.

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Figure 3

Stress-strain relationship of Al5182+Mn at three different temperatures and strain rates (6). (a) T=25°C, (b) T=200°C, and (c) T=350°C.

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Figure 4

The variation of thickness and thickness ratio around the neck in various tooling temperature conditions. (a) Variation of thickness distribution and (b) variation of thickness ratio.

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Figure 5

Comparison of part depth values predicted from three different failure criteria with experimental measurements (11)

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Figure 6

Comparison of FEA predictions with experimental findings (11). Effect of die and punch temperature on part depth (BHP=1.1MPa). A higher temperature gradient (i.e., differences) between die and punch suggests higher part depths.

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Figure 7

Comparison of FEA predictions with experimental findings (11). Effect of blank holding pressure on part depth at different die-punch temperatures.

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Figure 8

Comparison of FEA prediction with experimental findings (11). Effect of forming temperature on forming limit diagrams.

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Figure 9

Strain distribution along the major axis at Tdie=350°C, Tpunch=200°C(BHP=1.1MPa). (a) Longitudinal strain distribution el and (b) transverse strain distribution et.

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Figure 10

Strain distribution along the minor axis at Tdie=350°C, Tpunch=200°C(BHP=1.1MPa). (a) Longitudinal strain distribution el and (b) transverse strain distribution et.

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Figure 11

The characteristic of strain distribution at two different die-punch temperature combinations: Tdie>Tpunch, and Tdie<Tpunch(BHP=1.1MPa)

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Figure 12

Equivalent plastic strain distribution during forming when Tdie=200°C, Tpunch=350°C(BHP=1.1MPa). (a) Contour plot at the failure and (b) strain values along diagonal contour.

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Figure 13

Equivalent plastic strain distribution during forming when Tdie=350°C, Tpunch=200°C(BHP=1.1MPa). (a) Contour plot at the failure and (b) strain values along diagonal contour.

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