Out-of-autoclave (OOA) manufacturing expands composite opportunities by offering cheaper processes with more size options.
Out-of-autoclave (OOA) manufacturing has grown as a way to process next-generation structures, particularly in the aerospace industry. But what is leading manufacturers to adopt OOA, especially considering they’ve already invested so much capital in autoclave systems? It boils down to two main factors – money and part size. Traditional autoclave curing systems are expensive to buy and operate and are available in limited sizes.
Manufacturers in aerospace and other industries are increasingly turning to OOA to cure parts only in an oven. Out-of-autoclave is less capital-intensive and less costly, especially as parts increase in size and number. Several of the latest advancements push the technology even further, offering curing solutions that are out-of-autoclave and out-of-the-oven. Among the solutions under development are integral liquid heating/cooling and induction heating. These technologies offer the same benefits of OOA and then some – fewer steps, less material and shorter cycle times.
The Argument for Out-of-Autoclave
OOA is most heavily utilized by aerospace industry manufacturers. However, seen as a solution to the drawbacks of autoclave processing, a variety of sectors are adopting OOA methods, from renewable energy to automotive and consumer electronics. They hope to improve their products, increase throughput, cut down on production time, and decrease capital, operating and labor costs.
Autoclaves are capital intensive: The price of a single autoclave often runs six figures. Those costs can skyrocket even higher, particularly in aerospace where bigger parts lead to larger autoclaves and larger price tags. “In 2007, NASA looked into what it would cost to acquire a 40-foot diameter autoclave, and the cost came out to $100 million, including installation,” says John Russell, technical director of the Manufacturing and Industrial Technologies Division at the Air Force Research Laboratory. “For parts that aren’t frequently replicated, that is a cost we can’t justify.”
Dale Brosius, president of Quickstep Composites in Dayton, Ohio, says autoclave also has long turn around and cycle times, which takes expensive equipment out of the equation for too long, further increasing costs for manufacturers. This applies to new parts as well as part repairs. “Bonder/heater configurations are more economical through focused and localized heating of a repaired part,” says Eric Casterline, president of HEATCON Composites Systems in Seattle. “OOA avoids heating the whole part (automobile, aircraft etc.) during a repair operation.”
OOA also allows for faster production of parts.“Long-term success of carbon fiber [reinforced polymer] will require higher rate production methods not possible with autoclave,” says Brosius. “For example, the build rate for next-generation fighter aircraft will increase to one per day, which is well above historical production rates.” He adds that the next iteration of the Boeing 737 will need to be produced at rates of 45 per month, much higher than the Boeing 787’s required production of 15 per month. “To create lighter, more fuel-efficient aircraft, the next generation will also have a very high composite part count,” says Brosius. “And that puts pressure on every level of the composite manufacturing supply chain.”
Curing times are the industry’s biggest bottleneck, says Michael Rauscher, chief technical officer of NONA Composites in Dayton, Ohio. The company’s name is an abbreviation for the solutions it offers – no oven, no autoclave. “To hit higher production rates and drive down cost, we must address curing times,” he says. It is such an important issue to manufacturers that companies are sending employees to trade shows in search of new OOA processes, says Benjamin Luedtke, technical manager for Quickstep Composites.
This doesn’t mean that OOA is the silver bullet for further composite adoption. Each market segment requires qualifications for new products and materials, and these qualifications mean an investment in both capital and time. On the scale of testing stringency, aerospace ranks highest, taking years to approve a new material and/or process, then automotive, renewable energy and other growing markets, such as consumer electronics and medical equipment. “If the volumes are low, qualifying a new process may not be worth it,” explains Brosius.
OOA Advancements and Applications
French company RocTool, with U.S. headquarters in Charlotte, N.C., has been at the forefront of innovative OOA systems. The company uses induction heating to create aerospace parts and internal car parts, such as textured trim pieces for the new Mini Cooper. A growing part of its business is in consumer electronics, where RocTool won an industry award as part of the Motorola Mobility team for the composite rear housing of the new Motorola Moto X smartphone.
In 2000, the company began changing OOA methods with a resistive heating process where electricity would go through the fiber and heat the resin as well. Then RocTool evolved to its Cage System® with inductors around the mold to heat the entire surface. “It was an interesting process, but we were limited in the materials we could use,” says Mathieu Boulanger, business development director for RocTool.
Four years ago the company released 3iTech® with induction coils integrated in channels that can heat the tool very quickly. In June, RocTool introduced a light induction tooling (LIT) molding system. It features a metallic female mold and a male silicone mold. Unidirectional or woven fiber reinforcements are placed in the female mold, the male mold is closed, and then pressurized air is injected into the mold up to 420 psi. The LIT system heats up to 280 C in 45 to 90 seconds depending on the material and part. Water then cools the mold and part in one to two minutes. “The LIT system requires no preheating, provides a resin-rich surface, requires no resin injection, allows for thin walls and offers good temperature control,” says Boulanger.
With each of these developments, Boulanger points out that RocTool never considered autoclave or oven systems. “We are focused on reducing steps, and OOA is the best option,” Boulanger says. RocTool continues to improve its processes and demonstrate a variety of temperatures (useful to produce various parts) and an increase in manufacturing speed. “If a cycle time is more than 30 minutes, we wouldn’t look at it,” says Boulanger. “Most of our cycle times are between two and eight minutes. And one of the best things is that whereas in past years we were considered exotic, today people are comfortable working with us.”
Meanwhile, Quickstep Composites utilizes integral heating/cooling for curing composite materials, primarily used in aerospace. With the company’s heat transfer fluid (HTF) process, the laminate is placed between a rigid or semi-rigid mold that floats in an HTF. A flexible membrane separates the mold and laminate from the circulating fluid, which can be quickly heated and then cooled to cure the laminate.
While conventional autoclave processing cures at 100 psi and requires long cycle times, Quickstep’s heat transfer fluid (HTF) process enables precise control of process temperature throughout the curing process, says Luedtke. The process utilizes existing autoclave-qualified prepregs so as to limit recertification costs. On one prepreg system, the process has demonstrated the ability to cut cycle times from 20 hours to four hours. “Because it can accurately control the mold temperature and its increased ramp rates, it saves on process time, energy costs, investment and overall component manufacturing costs,” says Luedtke.
In 2010 Quickstep teamed with Vector Composites on a research project to demonstrate the ability to cure CYCOM 977-3 unidirectional epoxy prepregs to aerospace standards. These processes were accepted, and now the project has moved to the next phase – preparing laminate parts for testing. Test results are expected by summer 2015.
Quickstep also is making inroads in the automotive sector with its resin spray transmission process (RST) process, an automated, fast-cure system for composites requiring a Class A surface. “There are companies in Europe that we’re working with to create OOA parts,” says Luedtke. “This process hasn’t taken off in the U.S. yet because it isn’t under the same pressure as Europe, but it’s the goal.”
A Look Ahead
OOA is evolving to address application problems ranging from part size, manufacturing costs, part quality and curing time. It also is adapting across sectors, including aerospace, automotive, renewable energy, consumer electronics and even farm equipment. However, in order to keep up with the growing demand for composites across industry sectors, manufacturers need access to more CFRP. “CFRP is being sucked up by the aerospace industry and not a lot is left for everyone else,” says Luedtke. “Because they can’t access high-quality carbon fiber, companies are turning to natural fibers such as jute and hemp, and natural resins such as corn, soy and even cashew shells.”
Casterline adds that training also is important to the growth of OOA applications. “There needs to be overview education for middle and senior management, technical skills training and possibly an industry standard certification for technicians,” he says.
Perhaps the most successful demonstration of large out-of-autoclave manufacturing is the Air Force Research Laboratory-Lockheed Martin X-55A Advanced Composite Cargo Aircraft. Using a Dornier 328 cut off behind the cockpit to bypass new flight control expenses, Lockheed Martin added a 60-foot composite fuselage comprising eight pieces. This allowed the company to manufacture a military transport representative airplane in only 18 months while adhering to a $50 million budget.
Since its successful completion, others have followed in its steps. “Boeing built the Phantom Eye that uses a significant amount of OOA,” says John Russell, technical director of the Manufacturing and Industrial Technologies Division at the Air Force Research Laboratory. “Commercial aircraft are also looking into OOA, because they realize you can make bigger parts that cannot be made in the current largest autoclave.”
The Defense Advanced Research Project Agency (DARPA) is conducting testing that will eventually reduce the number of specimens needed to qualify a part for aerospace applications. Its results will be considered the “holy grail” for manufacturers in the defense industry. “If we can cut down the number of tests without increasing risk, it would lower the hurdle for companies to look at new materials,” says Russell.
Despite all of the research and development efforts conducted by the military and defense sector, most organizations are in a holding pattern. “A lot of decisions are determined by the federal budget,” says Russell. “There are studies being done on the next-generation mobility airplane, bomber and fighter. The Department of Defense will determine if it will build new aircraft or repair to existing ones.” Russell adds if the military requires new aircraft to replace C-5s and C-17s or a replacement for the B-52 or B-1, then OOA is a great solution because of the large size those aircraft are projected to be. “However, if it’s a fighter plane, I don’t see the need for OOA,” he says. “The parts are small enough to use the existing autoclaves in the industrial base.”