One alternative for large-scale parts is vacuum-only processing. “AFP processes are getting to a pretty high level of consolidation, where you may just need a final, vacuum-only process to fully consolidate the part,” says Leach. “You may not even need that; you may be able to fully in-situ consolidate the part.”
To achieve the necessary cost reductions and speed for production of larger parts and variable thickness parts, manufacturers will need to move to automated layup; it’s just not practical to lay up and pack the plies by hand, says Leach. Some companies are using pick-and-place robotic systems, which can lay the fabric forms (dry or prepreg) and increase or decrease the number of plies in certain areas. This enables manufacturers to more easily tailor parts for weight, stiffness and strength.
Injection overmolding is being used to consolidate aircraft components, adding stiffener or attachments to a part. “If you’re going to use continuous fibers, you’re limited in geometry, whereas injection molding can give you much more complex geometry,” says Leach. At high volumes, this can be a very cost-effective way of creating complex shapes.
Although thermoplastics manufacturing is moving toward more automated production, there’s still a need for humans in the production process, Leach says. He expects to see an increase in cobots (collaborative robots) that are small enough and safe enough to work alongside people on the manufacturing floor. The cobots can handle the dangerous, repetitive parts of the job, such as transferring a hot blank to a stamp forming machine. That frees up people to take on jobs that require judgment, like parts inspection.
Thermoplastic materials can be melted and reformed, which allows for parts to be welded together to create larger, more complex components. Welding reduces the need for fasteners, which saves production time, reduces the weight of parts and eliminates the need to put holes in laminates.
“Any composites designer or stress engineer out there will tell you that a primary limiting factor of composites is the fastener,” says Young.
Induction welding of CFRTP is attracting a lot of attention in the industry. The process uses a robot equipped with an induction coil, which creates a magnetic field that interacts with the electrical and magnetic properties of carbon fiber to induce heating. The weld is formed when two carbon fiber laminates are brought into contact and a robot moves the induction coil just above the areas where the heat is needed.
Over the last three years, a project team at Qarbon (formerly Triumph Aerospace Structures) has been working to refine this process. Since the electrical properties of various carbon fiber materials vary, they react differently to the induction welding process. So, the Qarbon team has patented a way to focus weld energy without a susceptor and developed sophisticated methods to design the induction coil for specific materials and processes. (Susceptor material, usually metallic, is sometimes included at the joint of the composite part to induce heating, but potentially lowers joint strength.) Qarbon’s technology will enable OEMs to create a part using the material that best suits their needs; the manufacturer can then create the induction welding coil optimized for that material and that part, according to Young.
There’s no diminution in the composite part strength with welding. During a test program with an aircraft OEM, the Qarbon team demonstrated that the joint strength of an induction weld exceeds that of an equivalent fastener and other joining technologies.
In developing the induction welding technology, the project team has produced both a flat demo box, which resembles a horizontal aircraft tail, and a curved box, which is the shape of many aerospace structures.
“We are ready to take this technology to an OEM’s production program, whether it be urban air mobility, commercial aviation or military customers,” says Young. “We want to take their specific designs and start implementing our intellectual property [i.e., software] so that we can understand how to best manufacture for their optimized airframe design.”
Young says that several OEMS have expressed interest in induction-welded parts, and he expects that they will be flying on demonstrator planes within the next two to three years.
Urban Air Mobility
It’s not only traditional aircraft manufacturers who are interested in thermoplastic composite parts. Companies that are producing Electric Vertical Takeoff and Landing vehicles (eVTOLs) also understand their benefits. These urban air mobility vehicles, which will be used to transport people and packages within a range of about 60 miles, need the advantages that thermoplastic parts provide.
“Urban air mobility is going to have even more critical weight requirements than standard aircraft or even rotorcraft. They’re trying to be a repeat use air vehicle, and their operational tempo is fairly high,” says Young. eVTOLs will be powered by batteries, so weight reduction is critical if the aircraft are going to achieve the desired range.
eVTOL producers need production speed as well. “Some of these eVTOL companies are saying that they want to build 4,000 units a year later this decade. You could never get a thermoset autoclave process to hit 4,000 units a year; the required infrastructure would make the economics of an air taxi unpalatable compared to thermoplastic material systems,” says Young.
Thermoplastic composites can solve both problems. “The manufacturing gets faster because we’re doing it with a robotic dynamic assembly versus drill-and-fill operations with fasteners,” he says. Manufacturers will enjoy the double value of both weight and cost savings.
Young notes that acceptance by the eVTOL sector could speed the traditional aerospace industry’s adoption of thermoplastic parts as well. Most OEMs tend to be risk adverse and will be more accepting of thermoplastic technology once it has been proven. Conversely, Young asserts that eVTOL OEMs seem to be focused on speed to market and willing to incorporate a certain level of risk.
“I think the broader industry is going to start accepting that structural thermoplastics is something for the future and not just far-off science,” says Young. “We are really able to marry the design and the manufacturing processes to leverage the benefits and get to where we need to be for cost and weight opportunities in the aerospace industry.”
Mary Lou Jay is a freelance writer based in Timonium, Md. Email comments to firstname.lastname@example.org.