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Aviation History
1972
1972 - 1970.PDF
FLIGHT International, 3 August 1972 155 ,.:« .-..-J.ijTv *,"'••• : ': Two examples, above and above right, of the use of Prestal for modelling possible structural components in titanium. (I) A proposed floor beam for Concorde; (2) A possible design for a fuselage frame in IMI 318 (6ALJ4V) titanium, with integral flange cheats. Right, diagrams illustrating vacuum forming (top) and blow forming mask, the adjustable punkah louvres and various light switches. The experiment was undertaken of forming an alternative design in Prestal, 0-030in thick. The result was a panel of high definition and entirely adequate stiffness, and it is felt that a superplastically formed part could be produced in Prestal, giving a significant weight saving. Another part, an undercarriage-mechanism cover (also illustrated) in Prestal alloy 0-050in thick, has been con sidered. This part was vacuum-formed on a cast-aluminium die and compared favourably, in terms of weight and stiffness, with cast or polymer alternatives. Originally the cover was produced without the reinforcing ribs in the top surface but, although the cover is normally marked No Step, the ribs were subsequently moulded in to permit it to withstand the weight of a man if it should be in advertently subjected to undue loading. Another example of a possible non-structural applica tion for Concorde is the window shroud and blind box, also illustrated, which is superplastically formed in Prestal alloy, 0-030in thick. The part measures some 15J2in X 9J2in. The metal-fabrication research and development team at Filton is enthusiastic and confident about the future of the superplastic forming technique and its wider applica tion. Blow-forming of superplastic sheet, as practised at Filton, is shown semi-diagrammatically in another illustration. The sheet-metal blank is edge-clamped securely under a cover plate and placed over the female forming die. Blank temperature is indicated by a thermocouple introduced into the cover plate. The entire assembly of blankholder and die is placed between heated platens (or alternatively in an oven), and the forming pressure (air or inert gas) is admitted through the cover plate to the upper side of the sheet-metal blank. As already mentioned, Prestal is worked in the tempera ture range between 240°C and 270°C and IMI 318 between 925°C and 950°C. Forming pressures can be from atmos pheric up to lOOlb/sq in for Prestal and up to 2001b/sq in for IMI 318. As part of an investigation at Filton into the use of titanium in airframes, mouldings in both Prestal and IMI 318 have been made by superplastic forming. Two examples of Prestal mouldings are illustrated, both of them models for proposed titanium parts. Such models are made in order to check part geometry and thickness distribution of the material, in advance of real part manu facture. One model is of a proposed Concorde floor beam, the other is a possible design for a fuselage frame with integral flange cleats for stringer and skin attachment. In both the definition obtained by forming in the superplastic state is evident. Male mould Clamp Heated sheet Vacuum box Sheet Vacuum Contact heating Heating platen Forming Sffli Sheet -Mould .ssssssss.s^a t • METALS THAT EXHIBIT SUPERPLASTIC PROPERTIES Base metal Aluminium Cadmium Cobalt Copper Iron Lead Magnesium Nickel Tin Titanium Zinc Zirconium Alloy addition wt (%) 33 Cu 12Si4Cu 26 Zn 10 Al 10 Mg 10-12 Al 10 Al 4 Fe 38-50 Zn 0-14 C 1-2 Mil 0-1 V 0-34 C 0-47 M 20 Al 0-42C1-9Mn 26Cr6-5 Ni 30Cr60Ni 20 Sn 5Cd 0-5 Zr 6Zn0-6Zr 23 Ni 30 Cu 33 Al nil 0-5P n \ 39 Cr 8 Fe 2 Ti 5 Bl 2-38 Pb 33 Cd 6 AI4V 5 AI2 5Sn nil 0-5 Al 5 Al 22 Al 40 Al "Zircaloy-4" Termpera- ture (°C) 440-530 500 20 1,200 700 500 450-650 900 900 730 870-980 20 0 500 270-310 450 450 400 820 980 20 20 20 900-980 1,000 0-20 20 200-360 200-260 250 900 Grain size (microns) 1-2 — 1-2 0-4 -- -2 2 1-2 2 3 4 20 0-5 -- -8 2 1 1-2 1-2 6 18 1-2 1-2 1-2 1-2 1-10 12 Strain-rate sensitivity (maximum) 0-9 0-4 0-5 0-3 n.d. 0-5 n.d. 0-6 0-5 0-6 0-5 0-5 0-3 0-3 0-5 n.d. n.d. n.d. n.d. 0-5 0-5 0-5 0-5 0-9 0-7 n.d. n.d. 0-7 0-5 0-5 0-5 1 micron = 10'4cm = 00004in. n.d.=not determined.
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