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The forming and straightening of complex aircraft parts usually requires development to overcome springback, and often requires elevated temperature to minimize scrappage and reduce detrimental stresses. Also, it is more of an art than a controlled process. A new forming concept has been developed which employs shot peening of the part while it is restrained to a predetermined, elastic tensile stress. The process, called stress-peen forming, demonstrates excellent predictability by balancing the stress profile across the cross section, applying standard, strength-of-materials equations. The process provides ideal compressive stresses on all surfaces.
This paper presents the development of the process from its initial theory to preliminary straightening tests. The work includes the development of a mathematical model which (a) determines the initial stress in a complex forged part when it has been restored to its straightened position, and (b) predicts the amount of elastic prestress and permits the determination of the selected peening process parameters to produce the required balance stress equilibrium across the section. Limited compressive stress profiles due to shot peening and preliminary straightening test data are also presented.
metal forming, metal straightening, warpage, aluminum alloys, shot peening, aircraft equipment, prestressing, mathematical models, stress analysis, bending stress, residual stress
Producibility methods engineer, Materials and Processes, Lockheed-California Company, Burbank, Calif