Resin transfer injection (RTI) is about to join resin transfer molding and composite layup as a construction technique used for high volume production of aerospace components. Bombardier’s Belfast operations in Northern Ireland (formerly Shorts) have patented this new technique that is being used to build the wings for the Learjet 85 and Bombardier CSeries. AirInsight had an opportunity to tour the facility and learn more about the processes that are changing the way high technology aircraft are built.
What’s different about this technique? In brief, quality, cost, and economic benefits through a more sophisticated and computer precise manufacturing process. Of course, manufacturing wings requires a massive facility – and this facility is state of the art, as illustrated by the massive clean room.
Existing processes such as resin transfer molding, require two halves of a mold to make a composite part, with carbon fiber placed in the mold, the halves closed, and resin injected into it. The problem is that the resulting product reflects the quality of the tool, which eventually wear out and are expensive to produce – not to mention the substantial machining effort required to trim rough edges created by excess material. In addition, a tool to accommodate the size of a CSeries wing would be so massive it would require huge overhead cranes to lift it into place.
Resin transfer injection, by contrast, uses only one side of a mold to provide the outside outline of the part. As with other techniques, carbon fiber is inserted into the mold, but the difference is that the portion inside the mold is formed by vacuum bagging material rather than simply injecting resin into the tool itself. An ultrasonic cutter precisely cuts each carbon fiber ply into the appropriate shape, which is 3-4 times thicker than typical pre-preg composites, and easier to handle.
This lay-up is then placed in production assembly jigs and vacuum bagged, then placed in the autoclave to bake under high temperature and pressure.
Once baked, the part is sent to a five-axis machine tool for precision trimming, with the piece held in place by “pogo sticks” that apply suction to the part in exactly the aerodynamic profile of the wing while the NC machines precisely trim and finish the part.
The parts are then checked using NDT equipment and painted for the aircraft assembly line. This process has several advantages, particularly in finishing the composite parts that are much closer to final form than other methods after emerging from the autoclave.
The process has been fully tested using a shortened wing that doesn’t include that last 12 feet to the wingtip. That test wing has already been mounted to a test wingbox structure and dummy fuselage and tested to 150% of expected loads. Bombardier is confident, based on their testing, that the initial production components expected later this year will easily meet all certification requirements.
The composite wing for the CSeries should provide a strong advantage in fatigue life, and, because it is made from composites, will not corrode. These elements all contribute to the “design for maintenance” concept for the CSeries, which as the first all-new narrow-body aircraft using 21st century technology, promises a full 15% reduction in overall operating costs when compared to existing models. This is a step above the 15% fuel burn reductions of re-engined aircraft that translate to only 7-9% economic improvements over today’s models, leaving a significant competitive economic advantage for the CSeries.
The new 600,000 square foot facility in Belfast was formerly the site of the Harland and Wolff shipyard, from which the most infamous ocean liner of all time, the Titanic, was built. Today, the former metalworking facility would be unrecognizable, modernized and stocked with high tech composite materials, a massive autoclave, precision cutters, and five axis milling machines. The technology revolution in aircraft manufacturing has arrived, and Bombardier is “injecting” new technologies for large scale composite structures into its global supply chain.