Breaking through in aerospace composites manufacturing

Citation

(2007), "Breaking through in aerospace composites manufacturing", Aircraft Engineering and Aerospace Technology, Vol. 79 No. 1. https://doi.org/10.1108/aeat.2007.12779aab.009

Breaking through in aerospace composites manufacturing

Breaking through in aerospace composites manufacturing

New capabilities for manufacturing aerospace composite parts are now available within Canada, due to a recently completed multi-partner project spearheaded by NRC Aerospace that produced an all- composite wingbox structure for a Bell Helicopter Textron Canada Ltd (BHTCL) next-generation tilt rotor aircraft.

In the process, NRC Aerospace developed expertise in manufacturing composite rib chords using resin transfer moulding (RTM), created an adhesive bonding process to join the ribs to BHTLC-manufactured wing skins and carried out non-destructive evaluation (NDE) of these complex composite components. The ribs are the first known primary composite aircraft structures produced in Canada using RTM, and the rib-to-skin bond lines are believed to represent the country's first instance of primary composite aircraft structural bonding.

The project, which started in April 2004, arose out of BHTCL's desire to obtain composite parts for its products from Canadian suppliers. The original plan was to transfer the required technology from their parent company in the US, but from the outset U.S. International Traffic in Arms Regulations made that difficult. NRC Aerospace therefore had to develop many aspects of the technology on its own. Dr Jeremy Laliberte, an NRC Aerospace researcher involved in the project, stated, “We ended up reverse engineering what they were doing to figure it out then realized we could take it farther. In the end, what we produced was a generation ahead of what they had developed.”

NRC Aerospace developed the RTM manufacturing process and fabricated the rib chords at its facility in Montreal. NRC Aerospace composites expert Dr Mehdi Hojjati, said, “We came up with a modular mould concept that allowed us to fabricate two different rib chords using removable inserts within the same pressure cavity. And we didn't need an autoclave; we simply injected the resin then increased the temperature inside the mould.”

While this took place, researchers at the NRC Aerospace facilities in Ottawa constructed a bonding fixture and developed a process to adhesively bond the ribs to the skins using a discrete air-heated oven which could be moved from rib to rib down the wing. Laliberte said, “Our approach was unique in that it included cure monitoring and process control. We added independent heater controls to ensure even heating along the entire rib and monitored the bond line temperature so that if anything went wrong during the critical 20-minute processing window, we could stop it, clean things up, and start again. When you do all these things, you get good quality and repeatability.” Its NDE group performed in-depth inspections of the wing skin components, RTM rib chords and all rib-to-skin bond lines.

Six trial bonds were carried out, followed by eight production bonds. Laliberte said, “Every single one came out as expected. The bond line thicknesses were right in tolerance, and the positions were right where they should be.” The completed wing skins were delivered, on schedule, to BHTCL, which assembled the wing box then shipped it to the States for a critical survivability test.

“We had a pretty tight schedule,” he added, “and the Americans were watching us very closely to see if we could do it. BHTCL couldn't guide us because they had never done this before. We had to juggle a lot of things and developed a really good working relationship with Bell along the way. We came through with flying colours.”

Another outcome of the project was to transfer RTM technology to Delastek Inc., a small, Quebec-based firm, and establish it as a supplier of aerospace- grade RTM parts. Delastek, which initially knew nothing about RTM, did the machining, made the rib mould, and participated in the production process. The effort paid off, as they are now working with BHTLC and NRC Aerospace on another composite technology development project.

The wingbox is currently the most complex aerospace composite component ever built in Canada. Dr Robert Fews, Research director at BHTCL, stated, “This project put Canada on the map by breaking new ground in the demonstration of the RTM manufacturing process and structural bonding technology to primary aircraft structural components. NRC Aerospace completed a quality product in time to meet a tight test window at a U.S. testing facility. This proven technical capability bodes well for future collaborative programs.”