Making aeroplane parts without ovens

Materials World magazine
14 Jan 2020
An autoclave used for the production of parts in automotive and aerospace industry.

A technique to eradicate the dependence on huge ovens and pressure vessels has been developed, which can help speed up the manufacturing process of aeroplane parts and high-performance composites structures such as wind turbines. 

According to the engineers from MIT, USA, the new technique will offset the need for building a these large-scale pressure vessels or autoclaves which therefore reduces the time, costs and energy required to pressure the parts like wings or fuselage. The team claimed that producing the composites used only 1% of the energy that would be generated from traditional manufacturing ovens. 

‘Now we can make primary structure materials without autoclave pressure, so we can get rid of all that infrastructure,’ said MIT Aeronautics and Astronautics Professor, Brian Wardle. 

Wardle’s co-authors on the paper are lead author and MIT postdoc Jeonyoo Lee, and Seth Kessler of Metis Design Corporation, an aerospace structural health monitoring company based in Boston. The research was further supported by Airbus, ANSYS, Embraer, Lockheed Martin, Saab AB, Saertex, and Teijin Carbon America through MIT’s Nano-Engineered Composite aerospace Structures (NECST) Consortium.

Conducting heat with electric nano-blanket 

The technique creating a method to make the composites without requiring external heat from an oven to fuse the materials together. This was achieved by wrapping the materials in an ultra-thin film of carbon nanotubes – heat was then generated when an electric current was applied to the film, curing and fusing the materials together from within. 

‘There’s microscopic surface roughness on each ply of a material, and when you put two ply’s together, air gets trapped between the rough areas, which is the primary source of voids and weakness in a composite,’ Wardle said. ’An autoclave can push those voids to the edges and get rid of them.’

Since 2015, the team have made significant progress in exploring out-of-autoclave and out-of-oven techniques to manufacture composites that do not include the use of the huge machines. Most of the techniques the team have explored contain voids in nearly 1% of the material, which can compromise the strength and lifetime of the material, and in turn their overall quality. 

‘The problem with these OoA approaches is also that the materials have been specially formulated, and none are qualified for primary structures such as wings and fuselages,’ Wardle says. ‘They’re making some inroads in secondary structures, such as flaps and doors, but they still get voids.’

The researchers overcame this issue stating the thin film of carbon nanotubes can be sandwiched between two materials, so when the materials are heated and softened, the capillaries between the carbon nanotubes should have a surface energy and geometry which would draw the materials in toward each other, rather than leaving a void between them. The team suggested that the capillary pressure should be larger than the pressure applied by the autoclaves.

By doing so, the researchers found that this resulted in composites that lacked voids, similarly to the aerospace-grade composites that are produced in an oven or autoclave. The researchers then conducted strength tests to see if the layers could be separated, which would occur if voids still remained. 

‘In these tests, we found that our out-of-autoclave composite was just as strong as the gold-standard autoclave process composite used for primary aerospace structures,’ Wardle said.

The team will next look for ways to scale up the pressure-generating CNT film. Part of this will consist of finding ways to manufacture CNT and other nanoporous films at a much larger scale, which would make the process viable for manufacturing entire wings and fuselages. 

‘Now we have this new material solution that can provide on-demand pressure where you need it,’ Wardle said. ‘Beyond airplanes, most of the composite production in the world is composite pipes, for water, gas, oil, all the things that go in and out of our lives. This could make making all those things, without the oven and autoclave infrastructure.