Lockheed Martin is drawing upon its experience in the practical use of advanced metals to make a number of significant improvements to the manufacturability and supportability of its three most important aircraft: the C-130J, F-22, and F-35.
On the Super Hercules, Lockheed Martin is now qualified to use friction stir welding in the manufacture of the transport’s aluminum structures, particularly its cargo ramp.
“This saves hundreds of fasteners and dozens of parts,” said Andy Poole, Research Manager in the technology development and integration organization within Lockheed Martin’s Advanced Development Programs (ADP) office. “While there is some weight reduction associated with part-count reduction, the significant cost savings is in maintainability, not necessarily in weight reduction.”
The terminology of friction stir welding is interesting given that “weld” has always been a four-letter word in aircraft manufacturing because it is considered a process that is not well in control and also one that generates defects due to porosity and cracking.
“A technical challenge is tuning the friction stir joining process to the material and application,” said David Chellman, Corporate Senior Fellow in structures and materials within the ADP office. “Fusion welding is more an art, not a science. Friction stir welding enabled us to weld things we couldn’t weld before, like 7000 series aluminum.”
On the Raptor, Lockheed Martin has reverted to using metallic nose-gear doors made of 7050 aluminum. It was difficult to control the processes used to manufacture the previous composite doors. The new doors provided a 30% cost savings.
“The original graphite-epoxy door had producibility issues,” said Poole. The aluminum door is basically weight-neutral in that it does not save weight, but it does save money.
More than 100 Raptors have been delivered to date, and a total of 183 are on order to the U.S. Air Force. All F-22s are getting the aluminum nose-gear doors, including spares.
Those are two instances in which Lockheed Martin is using metals to make incremental improvements. There is nothing slight, however, about the use of large-scale aluminum-alloy die forgings on the Joint Strike Fighter (JSF).
Alcoa is under contract to design and manufacture all the large aluminum structural die forgings for the program. Forgings with Alcoa’s 7085 aluminum alloy include: 15 large bulkheads (the primary structural supports for the wing and engine that can have a mass of 1800 to 6000 lb each and range from 10 to 23 ft in length), and six wing-box parts that serve as important components of the skeletal structure to the wing.
Alcoa Forged and Cast Products’ Cleveland operations is supplying the 7085 alloy to the F-35 program under a 10-year, $360 million contract signed last October. The first application of 7085 was for large die forgings on the Airbus A380 wing spars.
“JSF has the integrated capability of a forging design, and you can turn the design very quickly,” said Poole. “Where you would have had to wait outside the forge shop for a year to a year and a half, the die forging can be done in half or one-third of that time. That helps meet performance and weight targets, helps with scheduling issues, and eventually it will show up in the cost, as well.”