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TECHNICAL PAPERS

In Process Control of Strain in a Stretch Forming Process

[+] Author and Article Information
D. E. Hardt, W. A. Norfleet, V. M. Valentin, A. Parris

Lab for Manufacturing and Productivity, Massachusetts Institute of Technology, Cambridge, MA 02139

J. Eng. Mater. Technol 123(4), 496-503 (Aug 10, 2000) (8 pages) doi:10.1115/1.1397780 History: Received August 10, 2000
Copyright © 2001 by ASME
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References

Valjavec, M. 1999, “Closed-Loop Shape Control in Aerospace Panel Forming Systems,” Ph.D. thesis, MIT Department of Mechanical Engineering, Jan.
Valjavec, M., and Hardt, D. E., 1999, “Closed-loop Shape Control of the Stretch Forming Process over a Reconfigurable Tool: Precision Airframe Skin Fabrication,” Proc. ASME Symposium on Advances in Metal Forming, Nashville, Nov.
Swift,  H. W., 1948, “Plastic Bending Under Tension,” Engineering, 166, pp. 333–335 and 357–359.
Baba,  Akijiro, and Tozawa,  Yasuhisa, 1964, “Effect of Tensile Force in Stretch-Forming Process on the Springback,” Bull. JSME, 7, No. 28, pp. 835–843.
Parris, Andrew, 1996, “Precision Stretch forming for Precision Assembly,” Ph.D. thesis, Department of Mechanical Engineering, Massachusetts Institute of Technology.
El-Domiaty,  Aly, and Shabaik,  A. H., 1984, “Bending of Work-Hardening Metals Under the Influence of Axial Load,” J. Mech. Work. Technol., 10, pp. 57–66.
El-Domiaty,  Aly, 1990, “Stretch Forming of Beams of Non-Uniform Section,” J. Mater. Process. Technol., 22, pp. 21–28.
Ewert, Lee R., Sargent, Sumner, B., and Leodolter, Walter, 1991, US Patent Number 4,989,439, February 5.
Hessami, M. A., and Yuen, W. Y. D., 1988, “Residual Stresses Induced by Stretch-Bending,” Proceedings of the Fourth International Conference on Manufacturing Engineering, Brisbane, pp. 78–83.
Tozawa,  Y., 1977, “Dynamics of Springback,” Journal of Japan Society of Plasticity 18, No. 202, pp. 953–963 (in Japanese).
Tozawa,  Y., 1990, “Forming Technology for Raising the Accuracy of Sheet Formed Products,” J. Mater. Process. Technol., 22, pp. 343–351.
Ueda,  Masanobu, Ueno,  Keii, and Kobayashi,  Masaro, 1981, “A Study of Springback in the Stretch Bending of Channels,” J. Mech. Work. Technol., 5, pp. 163–179.
Valentin, V., 1999, Implementing Strain Control in Stretch Forming,” SM thesis, MIT Department of Mechanical Engineering, Jan.

Figures

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Steps of drape forming operation
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Schematic and key variables for a stretch forming process
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Strain distribution for constant die radius in drape forming
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Isotropic work hardening model
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Stress distribution for a forming sequence with some compressive plastic deformation and subsequent work hardening
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Force-strain sensitivity to yield stress changes
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Springback ratio sensitivity to material thickness
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Springback sensitivity to yield stress
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Springback sensitivity to strain hardening coefficient
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Springback sensitivity to material thickness
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Springback sensitivity to yield stress
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Springback sensitivity to strain hardening coefficient
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Placement of the strain gage to measure average strain. The gage is located at the midpoint of the free section between last die contact with the stretch jaws.
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Springback ratios for variations of yield strength (test set 1)
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Springback ratios for variations in thickness (test set 2)
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Leading edge part on die
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Separation of part from die
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Run chart for lot “A”
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Run chart for lot “B”
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Locations of strain measurements
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Run chart for strain-controlled lot “C”
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Reduction of contour variation for all 3 modes of optimized settings

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