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TECHNICAL PAPERS

Control of Transient Thermal Response During Sequential Open-Die Forging: A Trajectory Optimization Approach

[+] Author and Article Information
W. G. Frazier

Miltec Inc., NCPA Coliseum Drive, University, MS 38677

T. Seshacharyulu, S. C. Medeiros

AFRL/MLMR Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433-7746

Y. V. R. K. Prasad

Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India

J. Manuf. Sci. Eng 124(3), 502-508 (Jul 11, 2002) (7 pages) doi:10.1115/1.1467076 History: Received October 01, 2000; Revised October 01, 2001; Online July 11, 2002
Copyright © 2002 by ASME
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References

Seagle,  S. R., Yu,  K. O., and Giangiordano,  S., 1999, “Considerations in Processing Titanium,” Mater. Sci. Eng., A, 263, pp. 237–242.
Seshacharyulu,  T., Medeiros,  S. C., Morgan,  J. T., Malas,  J. C., Frazier,  W. G., and Prasad,  Y. V. R. K., 2000, “Hot Deformation and Microstructural Damage Mechanisms in Extra-Low Interstitial (ELI) Grade Ti-6Al-4V,” Mater. Sci. Eng., A, 279, pp. 289–299.
Stengel, R. F., 1994, Optimal Control and Estimation, Dover, New York.
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Seshacharyulu,  T., Medeiros,  S. C., Frazier,  W. G., and Prasad,  Y. V. R. K., 2001, “Strain-Induced Porosity During Cogging of Extra-Low Interstitial Grade Ti-6Al-4V,” J. Mater. Eng. Perform., 10(2), pp. 125–130.
Frazier,  W. G., Malas,  J. C., Medina,  E. A., Medeiros,  S., Venugopal,  S., Mullins,  W. M., Chaudhary,  A., and Irwin,  R. D., 1998, “Application of Control Theory Principles to Optimization of Grain Size During Hot Extrusion,” Mater. Sci. Technol., 14, pp. 25–31.
Berg,  J. M., Frazier,  W. G., Chaudhary,  A., and Banda,  S. S., 1998, “Optimal Open-Loop Ram Velocity Profiles for Isothermal Forging: A Variational Approach,” ASME J. Manuf. Sci. Eng., 120(4), pp. 774–780.
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Figures

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Microstructures of defects occurring during hot working of ELI Ti-6Al-4V: (a) cracking at the prior β grain boundaries at temperatures below 1103 K, and (b) void formation within the prior β grains at temperatures above 1235 K
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Schematic illustrating the cogging process
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Illustration of multi-step cogging used to convert initial lamellar microstructure (bottom left) to the desired equiaxed microstructure (bottom right). The shaded region represents the temperature range for avoiding microstructural defects.
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Block diagram illustrating simulation/optimization-based design structure
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Illustration of finite-difference grid structure and boundary conditions
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Plot of objective function (furnace time) as a function of iteration number
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Temperature profiles during first cogging cycle: (a) after 5.9 hours of soaking in the furnace, (b) at the beginning of cogging #1, and (c) at the end of cogging #1
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Transient thermal response of the surface and center of the billet during the entire sequence (initial heat up not shown for better resolution). The vertical bands represent the out of furnace time intervals.
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Transient thermal response of the maximum and minimum values of the billet’s temperature distribution (initial heat up not shown for better resolution). The vertical bands represent the cogging time intervals.
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Evolution of differential thermal profile with reduction in thickness: (a) before cogging #2, (b) before cogging #4, and (c) before cogging #6

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