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Applications: Cold-Compressed Aluminum Forgings

 
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   - make cut
   - measure surface
   - calculate stress
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download paper paper on these measurements and FEM model

Results:
Stress maps measured on 7050-T7452 forging
  • Shows stress maps on two cross sections of same forging, shown in blue and red in sketch
  • Periodic stress variations from cold compression process described below
  • Because of large size of part and intricate spatial variations of stress, probably no other technique could have measured this
  • These forgings are critical aerospace components, and residual stresses cause distortion problems in manufacture
  • Dashed lines are zero stress contours
Highlights of this measurement and specimen:
Specimen and EDM cutting:
  • 7050 Aluminum alloy hand forging
  • Original dimensions: 107 mm X 155 mm X 710 mm (4.2" X 6.1" X 28")
  • Solution heat treated and quenched into Alcoa Proprietary Quench
  • Picture shows one piece of forging being cut by wire EDM. This cut is the one shaded in blue in the graphic at the top of the page. The forging had already been cut in half lengthwise.
  • Cuts were made using 150 µm brass wire and "skim cut" settings
Piece of aluminum forging during EDM cut

Quenching Stresses :
  • 7050-T74 Aluminum forging
  • This is BEFORE cold compression stress relief
  • Dimensions: 107 mm X 155 mm X 710 mm (4.2" X 6.1" X 28")
  • Solution heat treated and quenched into Alcoa Proprietary Quench
  • This is from cutting forging in half lengthwise before red and blue cuts in graphic at the top of the page.
MEasured quenching stresses

Stress Relief :
  • A second forging was stress relieved by overlapping cold compression
  • Now the material is 7050-T7452 Aluminum
  • This is attempt at relieving stress by uniform plastic deformation. For plate this is done by stretching and is very effective, see measurements of stress relief in plate.
sketch of cold compressions

Measure contour :
  • After EDM cut shown in picture farther up on page, measure surface contour
  • Measured using CMM, 1 mm diameter ruby tip
  • Measured on 2 mm grid, giving about 14,000 points
  • Peak-to-valley is about 60 µm, easy to measure
  • This is for cut shaded in blue in the graphic at the top of this page
Measured surface contour

FEM stress calculation:
  • To calculate stress, elastically forced FEM model into opposite of measured contour (shown just above this)
  • Displacements exaggerated to show shape
  • This shows calculation for cut shaded in blue in the graphic at the top of this page
  • The background image on the home page is the FEM model for the other cut, the red one in the graphic at the top of this page
Deformed 3D FEM model

 

 

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Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
contact: Mike Prime at prime@lanl.gov | Copyright & Disclaimer
U.S. patent 6,470,756 | Last Modified: December 21, 2007

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