Getting Super Jumbos off the Ground
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When it goes into service in 2006, the Airbus A380 will be the largest passenger aircraft in the world. |
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All of the fibre-and-resin composite components of the aircraft will be made in molds made of the iron-nickel alloy Invar. Here, an Invar support structure for the A380 wing box is being assembled at UCAR in Irvine, California. |
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Composites will be essential in reducing the weight of the new Airbus A380.
All composite components will be made in Invar molds. By Carroll McCormick
Nickel magazine, February 2003 -- Since the mid-1980s, the aerospace
industry, especially defense, has made increasing use of fibre-and-resin composite parts in aircraft
construction. In a high-profile passenger aircraft application, Europe's aircraft manufacturer Airbus will
use some 40 tonnes of composite parts to reduce the weight and operating costs of its new 150-tonne,
twin-deck, 555-passenger A380 super jumbo, due to enter service in 2006.
Since the resins are cured by heating to about 177ยบ C, the composite parts are typically made on, or in, molds constructed of an alloy that matches the coefficient of thermal expansion of the cured composite material. Otherwise, the heated mold would warp and ruin the part, or, in the case of an injection-mold, expand and then crush the part as it cools.
The material that best fits the bill is K93600, an iron alloy with 36 per cent nickel. Charles-Edouard Guillaume invented Invar (R), as it is best known, in 1896, and an alloy with more suitable properties has yet to be developed.
"Invar 36 is used in aerospace because there is no other material as durable and that has the [right] coefficient of thermal expansion," says Jerry Anthony, president of mold and tooling manufacturer UCAR, in Irvine, California, U.S.A. "It has nothing to do with price. Invar stands alone."
Airbus contracted UCAR to design and build seven lay-up molds for the outer skin of the A380 wingboxes, situated where the main wings attach to the fuselage. In addition, UCAR has built two resin transfer molds,which will be used to make I-beam stiffeners inside the wingboxes. And the company is in the process of building a third.
The average size of the seven molds is 3.2 by 7.4 by 0.8 metres. They weigh an average of 12.2 tonnes apiece and add up to nearly 86.5 tonnes of K93600. UCAR utilized K93600 and weld wire manufactured by Special Metals of Huntington, West Virginia, U.S.A.
In 1993, K93600 tool making represented five per cent of UCAR's business; today it represents 60 per cent. As manufacturers design larger aircraft and struggle to wring more fuel efficiency out of their creations, they will use even more composite parts. "Weight for weight, composites are much stronger than aluminum," says Anthony. "The composite parts can be made thinner and more complex than aluminum pieces." Single-piece composite parts can also replace assemblies traditionally made of many pieces of aluminum that are bolted and riveted together, thus achieving important cost savings.
To build a lay-up mold, UCAR begins by constructing a support structure for the mold surface on which the composite part will be laid up. Called an egg crate base, the support structure is made from pieces of 6.35-millimeter-thick plate oriented vertically and welded to each other to form the mold structure (see acompanying photo). The upper edges of the egg crate base are cut to a 25.4-millimetre offset of the finished surface of the mold. Then 25.4-millimetre-thick face sheet is bump formed on a break press to form the rough shape of the finished surface and then GMAW (MIG) welded to the upper edges of the egg crate base. The face sheet surface is then finished machined with a 5- or 6-axis milling machine to a contour tolerance of plus or minus 0.19 millimetres, the thickness of five human hairs. It is then polished to form the mold surface.
The A380 will use composite parts in the nose and main landing gear doors, engine nacelles, spoilers,
flaps, the central torsion box and much of the tail, including the vertical and horizontal stabilizers. If
ongoing research in Europe is successful, the use of composites in the aircraft of the future will
increase.
Carroll McCormick is a Montreal-based freelance writer.
Photos: AIRBUS Diagram: NiDI
 Jerry Anthony President UCAR Composites Inc. 5 Burroughs Irvine, California U.S.A. 92618 Tel: 1 949 455 0665 ext. 107 Fax: 1 949 455 0061 E-mail: Janthony@ucarcomposites.com Website: www.ucarcomposites.com |
