However, in Radius-Pultrusion, the gripping mechanism is held stationary while the tooling elements (die, mandrels, fabric guides) move in an arc concentric to the radius of the part being pultruded.
According to Ken Workinger, a process engineer at Shape, the process can handle unidirectional, biaxial, triaxial and even quadaxial reinforcements. To date, Shape has tested fiberglass, carbon fiber, aramid, basalt and other natural fibers combined with either polyurethane or epoxy resins. Manufacturing trials have been conducted on both E-glass and carbon fiber.
While Shape says the process is highly flexible, not every reinforcement type is ideal for Radius-Pultrusion. Workinger explains that the most important criteria for selecting a material is its “drape-ability” – the ability to conform to a complex surface. Continuous filament mats, he says, are a good example of reinforcements with good drape-ability, while woven rovings are not.
“You wouldn’t use a 54-ounce woven roving through this kind of process. It just doesn’t have the conformability,” says Workinger. “The bundles need to be able to slide over each other to be able to behave nicely as you try to get them to conform to the shape you want as well – to conform to a curve. It’s not a developable surface. You’ve got to be bending in two directions at once and that puts a premium on the architecture of the fabrics you choose to use.”
Due to the inherent complexity of the process, one of the most notable benefits of Radius-Pultrusion is design flexibility. It also can help OEMs save money by eliminating the need to do extra manufacturing on a straight composite part that doesn’t naturally fit a vehicle’s package space.
“Package space is a strong driver of part design, and we don’t see a lot of straight lines on cars. While there are some straight parts, there are mostly curved parts,” reemphasizes Jacobson. “To try to fit a part that already has the limitation of a constant cross section, and then also have the limitation of being straight only, it narrows the possibilities immensely.” Radius-Pultrusion, he says, helps eliminates some of those constraints.
The company’s next step is to continue improving the process to maximize throughput. Jacobson says Shape may venture into a “variable radius” – essentially being able to go from pultruding straight to curved and back again in a continuous process. In fact, in the past decade, Shape has developed a similar variable radius process for its advanced high-strength steel roll forming mills.