Composite material suppliers and processors face a continuing challenge in bringing down their costs to compete effectively. Today's key word in the industry is affordability. A decade ago, the dynamics in the military community were geared primarily toward material performance. Now, procurers want performance at affordable prices and, to hold down costs, may add weight that would degrade performance.
Recently, improvements in high-performance composites drove up costs at a time when businesses and government were pushing to lower costs, perhaps by using commodity materials that cure at lower temperatures.
Customers want a composite product that costs less than the alternative, and often they like to tackle the difficult proposition of comparing life-cycle costs. Different base-line materials and varying business-government approaches complicate the matter.
The base line in commercial transport, for instance, is aluminum, and generally the operators buy or lease the aircraft so they have strong input into the materials and costs.
The base line in military aircraft is titanium. Polyimide, a costly thermoplastic, can take higher temperatures than titanium, but users want to replace titanium at the same or lower cost. Procurement and operation commands in the military tend to be more independent of each other's functions than their commercial counterparts.
Design becomes a key in bringing down costs. Eventually, better computerized databases will improve design properties and extend the combination of digital and composite technologies that was used for the Boeing 777 twin-jet now in production. Advanced composites comprise 9 percent of the aircraft's structural weight, most prominently in the horizontal stabilizer, vertical fin and passenger cabin floor beams.
Polymer composites make up about 18 percent of the airframe structure of the Navy F/A-18 upgrade, scheduled for its first flight in December in St. Louis. Composites may approach 30 percent of the structure of the Air Force's next-generation F-22 advanced tactical fighter, now in development.
Issues of affordability permeate the Pentagon's joint advanced-strike technology program. The 2-year-old JAST effort seeks commonality among Air Force, Navy and Marine Corps versions of an unnamed next-generation attack aircraft.
Efforts to create a set of industry standards for composite materials move slowly but are important in facing the affordability issue. The Pentagon's shrinking defense budget cannot fund a program at this time, and, while interested in paying their shares, the aerospace principals and their suppliers have fiscal limitations.
Meanwhile, the firms continue to work through the industry's Standardization Task Force to seek ways to achieve material standardization and cut costs to the end user.
Ultimately, affordability becomes a question for the customer, according to John Fish, research and development engineer with Lockheed Martin Corp.'s Skunk Works subsidiary in Palmdale, Calif.
``If you want a lower-cost product, you have to give up something,'' he said.
The subsidiary formerly was known as Lockheed Advanced Development Co.
``Cost begins with the requirements, and there is always a trade between cost and performance,'' Fish said. ``The requirements, as they relate to cost, need to be challenged up front to effectively address affordability.''
Fish organized a Sept. 19 technical session on ``Affordable Fabrication Processes for Com-posite Aircraft Structures'' as part of a three-day conference in Los Angeles. The American Institute of Aeronautics and Astronautics and the Society of Automotive Engineers were the conference organizers.
Fish sees affordability as a process that evaluates cost/producibility tradeoffs early in the design stages.
``The challenge is to meet the requirements at minimum cost'' across a range of competencies including ``materials and process selection, structural design, tool design and producibility,'' he said.
``Part of the problem is defining affordable,'' Keith Burgess, chief engineer of Techniweave Inc., said in an interview. ``Affordable relative to what? Usually, material selection is based on cost-effectiveness, and even exotic metals are better than composites in situations such as high out-of-plane loads.''
Techniweave of Rochester, N.H., incorporates three-dimensional woven preforms as inserts in laminated composites. The technique allows the use of all-composite materials and the elimination of metal fittings.
The Pentagon began a five-year, $370 million program for affordable composites for propulsion in May 1994. United Technologies Corp.'s Pratt & Whitney unit heads the vertically integrated program.
``We've come a long way, particularly on engine-frame activity,'' said Larry Gintert, engineering manager at Dow-UT Composite Products Inc., a joint venture in Wallingford, Conn.
He aims to demonstrate certifiable processes to make a composite 10-foot-diameter engine case that could replace the conventional steel-welded structure.
``It's partially verified in the shop, and we will test a full case at the Pratt & Whitney facility'' in East Hartford, Conn., he said.
Gintert said the technology is being applied to make wing spars and internal fuselage frames for the F-22.
Dow Chemical Co. and UTC formed the venture in 1989 to manufacture composite parts for aerospace, defense, commercial and industrial applications.
Garrett Sharpless, president of Fiber Innovations Inc. in Norwood, Mass., said braided and stitched composite preforms that are consolidated through resin transfer molding can challenge aluminum for certain parts such as J-frames.
Sharpless cited an analysis in which Lockheed Martin's NASA programs manager concluded that fuselage frames of braided preforms and RTM would be 26 percent cheaper than aluminum parts in production.
Fiber Innovations employs 17 and works with aerospace principals on RTM components for aircraft parts.
Automated fiber placement is another composite process moving into production, said Jon Poesch, engineering manager for the specialty structures group of Alliant Techsystems Inc. inMagna, Utah.
``Numerically controlled machines automatically lay down prepreg bands formed from up to 32 tons [of carbon] at speeds up to 100 feet per minute,'' he said.
The affordable composites for propulsion program uses fiber placement to build fan cowl doors and containment and exit case components.
``Recent trials of this process on engine cowl structures have decreased hand labor by more than 75 percent and decreased scrap to less than 5 percent,'' Poesch said.
He noted that fiber placement is used on inlet ducts, fuselage skins and horizontal stabilator skins for the F/A-18 upgrade; aft-and side-fuselage skins for the Marine Corps' V-22 vertical take-off-and-landing aircraft; and the horizontal stabilator attachment shaft and spar for the F-22.
Getting control of the process for aerospace products can transfer techniques into construction and infrastructure applications where materials and applications may be different but the manufacturing techniques are the same. But the same question will apply: Can a user afford to use composites instead of alternate materials?