Paradigm-changing composite technology comes to aerospace engineering

A new piece of equipment was recently installed at the University of Illinois Urbana-Champaign bringing the latest technology in additive manufacturing to campus. Unlike the better-known plastic or metal additive manufacturing, this machine can print large and lightweight structural composites like those used in aerospace structures. It is the first continuous fiber 3D printer by Continuous Composites to be installed outside the company and in academia.

According to Founder Professor of Engineering Jeff Baur, “This is a paradigm-changing composite technology because it allows you to create structures with complex shapes that have mechanical properties approaching those of traditional aerospace composites. Currently, high-performance composites are made by laying resin-filled fabric or fibers by hand and cooking them for a long time in a pressure cooker called an autoclave. Now, we lay the fibers by robot, snap-cure them into shape and then cure them in an oven in a fraction of the time. Due to the strength of the continuous fibers, we believe we currently have the world’s strongest additively printed composite, but there is still a lot of technical work that needs to be done.”

The CF3D printer comes with a unique industry/academic partnership between UIUC and Continuous Composites, Inc. Baur said the agreement with Continuous Composites will provide some supplies, tech support, and hardware updates to his lab. In return, he said, “We’ll provide the company with free and open feedback about our experiences with the equipment so they can make improvements for their future customers."

After over 25 years in the Air Force, Baur joined the faculty last year to head the composite processing and additive manufacturing lab in the Department of Aerospace Engineering. He is also a part of the Autonomous Materials Systems Group at the Beckman Institute.

“I saw this technology coming four or five years ago. I knew where we were in terms of additive for polymers and it was clear to me that we would never get the mechanical properties we needed to be successful unless we went to very long or continuous fiber,” he said.

Both Baur and Composite World magazine surveyed additive manufacturing companies using continuous carbon fiber and came to the same conclusion. “For thermosetting composites like those used in the majority of aerospace applications, Continuous Composites was ahead of everyone else.” Unlike thermoplastics composites which require high temperatures and pressures to consolidate, thermosetting composites are bonded together using chemical reactions. This not only provides a rich palette of chemical options and properties, but also uses less energy and enables more sustainable manufacturing at the “cradle” or start of the aerospace structure’s service life. Of course, the biggest impact for composites in sustainment is making vehicles lighter weight which results in using less energy and lower emissions over the life of the vehicle.”

Baur described one example of how this new technology can also address sustainability at the “grave” or at the end of a part’s service life. Due to the durability of most thermosetting composites, it is difficult to recover the expensive fiber from the resin matrix and then recycle or reuse either. Large composite structures like wind turbine blades, for example, have a 30-year lifespan and then are buried in landfills. “Through a recently awarded Department of Energy funded center, called RE-MAT and headed by UIUC through the Beckman Institute, researchers are designing resin molecules that, under the right conditions, can unzip to make the fibers recoverable, the resin recyclable, and both reusable.  Additive printed composite can accelerate the evaluation and development of these new materials and enable a circular economy for thermoset composites.

In addition to a ceremonial ribbon-cutting, Baur coordinated a symposium to bring together technical leaders from UIUC, Continuous Composites, the Air Force Research Lab, Arkema, Hexcel, Siemens, and Comeau.

Hosting the event was key. “This isn’t the kind of thing that academia typically gets invited to,” Baur said. “But at the symposium, we had participation from government, industry, and academia. It was a way to bring all the players together to have a conversation around a shared vision. Everybody wanted to see it. It was a big moment for the technology.”

According to Baur, the CF3D printer will be used in research on multiple levels.

“Imagine you have a new fiber, a new reinforcement, maybe a bio-derived fiber and you want to use it to make a structural composite. This machine should be able to handle that. At a completely different level, we can use this machine to make big structures like wind tunnel prototypes or structures that can be deployed in space. When you print with structural composites, your prototype can be at the performance level you need for the final structure.”

Baur already has a team of aerospace students working on a variety of projects.

“We can do work at the University of Illinois that is both fundamental and impactful to industry,” he said. “One of my students is developing new methods for topology optimization of these printed structures. One is working on shape-changing composites using novel composite designs. Another is working on characterizing the additive resin that will enable recyclable thermoset composites. And most will be using this machine in some capacity.

“In the future, we’ll be looking at new materials, new formulations of composites, new designs of those composites, and new applications for those composites, including adaptive structures, and even multifunctionality with embedded devices.”