Original Date: 11/03/1996
Revision Date: 01/18/2007
Information : Multiple Thin Sheet Production
NASA Marshall Space Flight Center needed thin (0.05 to 0.08-inch) sheets for destructive testing to determine the dynamic fracture performance of space station wall panels. Requirements included manufacturing the sheets from aluminum 2219; withstanding hypervelocity impact of small space debris at speeds up to 11 kilometers per second (24,000 mph); and possessing a fracture toughness which could withstand crack propagation.
Typically, the material for a test sheet was taken from the center inch of a three-inch aluminum slab. To produce a 0.08-inch test sheet, the manufacturer started with a 3 x 48 x 72-inch slab and then removed 1.46 inches from the top and bottom by milling. This technique avoided the long grain structure found near the surface of the slab. However, the cost of material and labor made this method unacceptable. After unsuccessful attempts to locate a better method in industry, NASA approached Y-12.
Starting with a 3 x 48 x 72-inch aluminum slab, Y-12 used a horizontal bandsaw (modified to cut metal) to slice six 0.2-inch thick sheets from the center, 1.5-inch section of the slab. Next, a rolling belt sander ground the sheets to the desired thickness. By using a grid technique with a custom-built, hand-held dial indicator, Y-12 verified the final thickness of the sheets against customer requirements.
The new procedure realized a significant savings in material and labor costs. Material costs decreased by six fold while labor costs were reduced by at least five fold. As an added benefit, sheets produced by sawing and belt sanding had lower residual stress in the material than those made by machining. Data achieved through strain gauge hole drilling methods (Figures 2-6 and 2-7) confirmed this attribute.
Figure 2-6. Residual Stress after Machining
Figure 2-7. Residual Stress after Sawing and Milling
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