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Research Papers

# Local Thinning at a Die Entry Radius During Hot Gas-Pressure Forming of an AA5083 Sheet

[+] Author and Article Information
Eric M. Taleff1

The University of Texas at Austin, 1 Univeristy Station C2200, Austin, TX 78712-0292taleff@mail.utexas.edu

Louis G. Hector, John R. Bradley, Ravi Verma, Paul E. Krajewski

Research and Development, General Motors Corp., MC 480-106-212, 30500 Mound Road, Warren, MI 48090-9055

1

Corresponding author.

J. Manuf. Sci. Eng 132(1), 011016 (Feb 02, 2010) (7 pages) doi:10.1115/1.4000884 History: Received January 21, 2009; Revised December 18, 2009; Published February 02, 2010; Online February 02, 2010

## Abstract

Splitting at regions of local thinning below die entry radii is a critically important mechanism of failure in hot gas-pressure forming of sheet materials. Local thinning is controlled by sheet-die friction and die geometry, as well as sheet material properties. In this study, local thinning is investigated at a particularly severe die entry radius during hot forming of a fine-grained AA5083 sheet at $450°C$. Particular emphasis is placed on the relationship between local thinning and sheet-die friction conditions. A simple analysis of the mechanics of this thinning phenomenon is presented. Finite element simulation results are presented for different sheet-die friction conditions. Sheet thickness profiles measured from parts produced in forming experiments using three different lubrication conditions are compared with predictions from simulations. Simulation predictions agree well with experimental data for the occurrence and location of thinning below a die entry radius. Additional insights into sheet-die friction for controlling local thinning and preventing premature necking failure are detailed.

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## Figures

Figure 3

(a) Half of the die geometry is shown with two critical die entry radii locations, A and B. (b) The cross section geometry of the die section used in the FEM simulations and experiments is shown. The numbers that are placed along the surface of the die indicate positions (units of mm) relative to the edge of the left die land region (defined as the origin of measurement, 0). The simulated die width (i.e., in and out of the page) is 20 mm. The total path length of the die surface is 387 mm.

Figure 1

A split below a die entry radius is shown in an AA5083 component formed at 450°C

Figure 2

The effect of friction force, F, on sheet thinning at a die entry radius, curve ABC, is based on a static analysis that assumes symmetry about B. Note that w is the width of the die land, T is the sheet tension that develops due to sheet wrapping about the die entry radius, and θ is related to the contact length along the die entry radius. The sheet is assumed to be rigidly constrained at the left end of the die land region (not shown).

Figure 4

Images are shown from the simulation with μ=0 at times of (a) tf/4, (b) tf/2, and (c) 3tf/4, where tf is the approximate time for complete forming into the lower-left corner from the simulation.

Figure 5

Images are shown from the simulation with μ=0.5 at times of (a) tf/4, (b) tf/2, and (c) 3tf/4, where tf is the approximate time for complete forming into the lower-left corner from the simulation.

Figure 6

The profile of the die section is shown at the top of this graph. The height is vertical distance in the y-direction, see Fig. 3. The path length is the length along the surface of the fully formed part, referenced to the upper left die edge shown in Fig. 3. Shown at the bottom are thickness profiles along the same path length predicted by simulations using the three friction coefficients indicated. The ultimate location of one neck is denoted by the dashed vertical line.

Figure 7

Thickness profiles are shown with path length along the fully formed part for simulations using three friction conditions: (a) μ=0.0, (b) μ=0.1, and (c) μ=0.5. Also plotted with the simulation results are experimental measurements of thickness profiles, produced using graphite lubricant in (b), Mg(OH)2 lubricant, and no lubricant in (c). No experimental data are available for μ=0.0.

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