New Film Bakes Plane Parts at 1,000 Degrees, No Oven Needed

The photo above depicts one of the giant ovens the Air Force uses to bake composite layers onto its C-5 Galaxy transport aircraft body panels. That’s Lucion Foreman, the panel shop supervisor at Robins Air Force Base in Georgia, standing in front to offer scale.

Composite fuselage and wing parts made of sandwiched materials like carbon fiber, honeycomb metal and polymer layers are rolled into ovens like this in commercial and military facilities around the world. Inside, the parts are heated to temperatures that can exceed 750 degrees Fahrenheit to bake the separate layers into a single strong, stiff one. This process is crucial to make lighter airplane bodies that can stand up to the demands of flight.

But it’s also highly inefficient, with huge amounts of energy wasted to power the heating elements, warm the air inside the oven and, finally, to heat the part to the necessary temperature.

Now MIT engineers say they have a solution that can do away with the big ovens altogether. They’ve developed a film that can be directly applied to an uncured multilayer composite surface. When electric current is applied to the film, it heats the composite to the point that it solidifies into a single layer. The film is baked into the topmost surface, adding a tiny amount of weight to the finished product. Testing has shown that their method creates a material that is just as hard as those baked in big ovens while using just one percent of the energy.

“Typically, if you’re going to cook a fuselage for an Airbus A350 or Boeing 787, you’ve got about a four-story oven that’s tens of millions of dollars in infrastructure that you don’t need,” said aerospace engineer Brian Wardle, who lead the team that is developing the new process. “Our technique puts the heat where it is needed, in direct contact with the part being assembled. Think of it as a self-heating pizza. … Instead of an oven, you just plug the pizza into the wall and it cooks itself.”



The heating film is built out of aligned carbon nanotubes, hollow cylinders of bound carbon atoms that are strong and stiff while also being thermally and electrically conductive. Tests showed that the film could generate heat up to about 1,000 degrees F before burning out, a significant amount over what high-end composite layers require to fuse together. This capability, Wardle says, opens up their process to use in any industrial application in which composite parts are built.

(A new film of carbon nanotubes cures composites for airplane wings and fuselages, using only 1 percent of the energy required by traditional, oven-based manufacturing processes. Photo courtesy of Jose-Luis Olivares/MIT.)

“The energy losses and geometric constraints associated with conventional curing techniques of polymeric systems motivate the study of a highly scalable out-of-oven curing method using a nanostructured resistive heater comprised of aligned carbon nanotubes (A-CNT),” the team writes in a paper on their work published last week in the journal ACS Applied Materials & Interfaces. “The experimental results indicate that, when compared to conventional oven based techniques, the use of an ‘out-of-oven’ A-CNT integrated heater leads to orders of magnitude reductions in the energy required to process polymeric layered structures such as composites.”



(When connected to a voltage source, the film generates heat, directly curing composites without the need for large, commercial ovens. Photo courtesy of Jose-Luis Olivares/MIT.)

Top Image: Robins Air Force Base panel shop supervisor Lucion Foreman walks in front of one of the autoclaves used to bake the C-5 Galaxy panels. Photo courtesy of Sue Sapp/U. S. Air Force.