3-D Composites Promise Leap In Efficiency
The aero-acoustic geometry fan blades, fan case and several other parts of CFM International’s Leap engine series will be the first major engine application of a new technology, 3-D woven composites. The process was pioneered by Albany Engineering Composites (AEC), a U.S. company that has teamed with CFM parent company Snecma and has granted the French engine maker exclusivity for its process (for propulsion applications) for the life of the Leap program. With more than 3,600 Leap series engines on the order books, “This is the fastest, steepest ramp-up by far in the history of the aircraft engine industry,” said AEC president and CEO Joseph Morone.
AEC started more than 100 years ago specializing in making industrial papermaking machinery. The belts that carry wet paper slurry through the process required a highly durable yet porous material, and AEC developed looms that wove a strong fabric mesh.
A dozen years ago, Snecma scientists began exploring the idea of adapting the technology to create carbon fiber engine components. Today, the fan blades and fan casing on the Leap engine are woven from carbon fiber using huge industrial looms using a proprietary process similar to that used by AEC for its paper slurry belts.
The continuously spooling process weaves twists of up to 48,000 carbon fibers–each thinner than a human hair–in three dimensions. More than 200 miles of the carbon twists are required for each engine’s 18 fan blades and the fan case, offering the finished blade strength and durability at approximately half the weight of the comparable blade in titanium, and the case one-third the weight of similar aluminum part. That allows the Leap designers to use larger fan blades, which produce a higher by-pass ratio. The jacquard looms can weave in different thicknesses in a single part; in the case of a fan blade thicker at the root, thinner at the tip, making a three dimensional carbon matrix that will not delaminate as blades made from bonded sheets of composite are susceptible to doing.
Each blade takes more than 24 hours to complete, the bulk of time spent waiting for resin to cool and solidify. Upon completion, the composition of the blade is approximately 60 percent carbon fiber and 40 percent resin. According to CFM, the blades are expected to last the life of the engine with little maintenance required due to their extremely high damage resistance. For the fan case, a roll of the specially woven fabric is wound around a form or mandrel and quickly takes shape. It is then enclosed in a mold, treated with resin and baked in the same way as the blades.
Based on the use of the new components, CFM claims a resulting savings of 1,000 pounds per aircraft compared with similar sized engines using metal components. Though composite engine parts are not new, those fabricated with this new process promise to raise the technology to a higher level. “We are nowhere near seeing how much this technology can transform the engine,” said Vincent Garnier, Snecma’s vice president of research and technology.
The process is also currently used to produce some components used on the Boeing 787 Dreamliner’s landing gear and the manufacturers say it could be used to eventually produce larger blades for engines such as the GE90.
While initial production on the blades and fan casings is currently being conducted at AEC’s plant in New Hampshire, last month Safran broke ground on a factory of its own, just down the road. The new 210,000-sq-ft facility will be completed late next year and production is scheduled to begin there in early 2014. A similar plant in France will open a year later. Each plant will employee 400 workers (an even split between Snecma and AEC) and once production ramps up fully by 2019, will combined produce 32,000 fan blades and nearly 1,800 fan casings a year, enough to satisfy the projected annual production rates for the engine.