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Research Papers

An Efficient and General Finite Element Model for Double-Sided Incremental Forming

[+] Author and Article Information
Newell Moser

Department of Mechanical Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208
e-mail: newellmoser2018@u.northwestern.edu

David Pritchet

Department of Mechanical Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208
e-mail: davidpritchet2013@u.northwestern.edu

Huaqing Ren

Department of Mechanical Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208
e-mail: huaqingren2013@u.northwestern.edu

Kornel F. Ehmann

Department of Mechanical Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208
e-mail: k-ehmann@northwestern.edu

Jian Cao

Department of Mechanical Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208
e-mail: jcao@northwestern.edu

1Corresponding author.

Manuscript received November 15, 2015; final manuscript received April 18, 2016; published online June 20, 2016. Assoc. Editor: Rajiv Malhotra.

J. Manuf. Sci. Eng 138(9), 091007 (Jun 20, 2016) (10 pages) Paper No: MANU-15-1593; doi: 10.1115/1.4033483 History: Received November 15, 2015; Revised April 18, 2016

Double-sided incremental forming (DSIF) is a subcategory of general incremental sheet forming (ISF), and uses tools above and below a sheet of metal to squeeze and bend the material into freeform geometries. Due to the relatively slow nature of the DSIF process and the necessity to capture through-thickness mechanics, typical finite element simulations require weeks or even months to finish. In this study, an explicit finite element simulation framework was developed in LS-DYNA using fully integrated shell elements in an effort to lower the typical simulation time while still capturing the mechanics of DSIF. The tool speed, mesh size, element type, and amount of mass scaling were each varied in order to achieve a fast simulation with minimal sacrifice regarding accuracy. Using 8 CPUs, the finalized DSIF model simulated a funnel toolpath in just one day. Experimental strains, forces, and overall geometry were used to verify the simulation. While the simulation forces tended to be high, the trends were still well captured by the simulation model. The thickness and in-plane strains were found to be in good agreement with the experiments.

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References

Figures

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Fig. 1

Common machine setups in ISF: (a) SPIF utilizes one tool and can optionally involve a backplate, (b) TPIF uses a partial die or similar support structure, and (c) DSIF uses two independent forming tools

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Fig. 2

Nd:YVO4 (532 nm wavelength) laser marking setup

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Fig. 3

Desired cross section of axisymmetric funnel geometry

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Fig. 4

The Voce hardening law was fitted to the rolling direction of the AA5754-O material

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Fig. 5

DSIF machine with a forming area of 200 × 200 mm

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Fig. 6

Shown are multiple views of the formed funnel part with the laser-marked circle grid

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Fig. 7

The distribution of sheet thickness plotted onto the measured funnel surface

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Fig. 8

Full-scale (200 × 200 mm) simulation comparison between reduced integration shell and reduced integration solid elements. Both models contained elements with an in-plane size initially chosen to be 1 × 1 mm.

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Fig. 9

The forming forces of the full-scale simulation using reduced-integration elements. Negative force values correspond to the bottom tool. The shell element model experienced unstable oscillations toward the end of the simulation due to sheet thinning.

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Fig. 10

Reduced simulation domain (150 × 150 mm) is compared to the full-scale model. All simulations were completed to the final time, but are only plotted up until unstable oscillations were observed.

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Fig. 11

Finalized model with a reduced domain (150 × 150 mm) utilizing full-integration shell elements

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Fig. 12

Forming forces for the full-integration model with different element sizes

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Fig. 13

Cross section profiles from the simulation and experiment, post-springback. Red and blue arrows denote the location of where the bottom tool first lost contact.

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Fig. 14

Comparison of thickness distribution, major strains, and minor strains

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