Additive manufacturing (AM) today is viewed by the composites industry primarily as a faster and less-costly method of producing prototype and low-volume composite parts. That perception is changing, however, as companies explore new techniques that will enable competitively priced 3D parts production on a much larger scale.

The industry’s growing interest in AM stems in part from the increased availability of desktop and medium-sized industrial 3D printers, according to Rick Neff, an AM technical and marketing consultant. Companies are experimenting with these printers, which typically combine carbon, glass or even aramid fibers (and sometimes tapes) with thermoplastic or photo-cured polymers.

At the same time, the technology for large-scale additive manufacturing (LSAM) has advanced. Thermwood Corporation, for example, has built upon the basic concepts of the Big Area Additive Manufacturing (BAAM) machine developed by Oak Ridge National Laboratory (ORNL) and private industry partners. Thermwood’s LSAM machines use a continuous cooling process to ensure each printed layer is at the optimal temperature to accept the next layer. This produces composite tools with vacuum integrity. “Other processes haven’t been good enough to create a tool without some sort of additional step to try to seal the tool or put a different surface on it that can hold a vacuum,” Neff explains.

In 2014, BAAM’s largest printed part was six feet long, 20 feet wide and eight feet high; Thermwood’s 1540 LSAM machine can produce parts 40 feet long, 15 feet wide and five feet tall and at a much faster speed. That’s led to new opportunities in the fast production of larger tools for aerospace and marine manufacturers.

“When we look at the cost of developing a prototype airplane, a large part of both the cost and the lead time can be attributed to tooling,” says Neff. “If it takes you months to get tools, it takes you months to build a plane. But if you can get tools in a week or two that revolutionizes the whole process of prototyping an airplane.”

Neff also notes that materials suppliers have developed a wider range of products specifically designed for AM. A manufacturer using an injection molding process can tolerate material shrinkage, which makes it easier to remove a part from a mold. But manufacturers don’t want a printed part to shrink, so they add carbon fiber or glass fiber to lower the coefficient of thermal expansion by a factor of 10, or an order of magnitude. “When you print parts, the hot layer on top doesn’t shrink a lot and cause the part to warp and change its shape,” he says.

Construction Applications

Neff believes that advances in additive manufacturing, especially LSAM, will provide new opportunities in construction markets. While there’s a lot of hype around 3D printing concrete for buildings, he believes the real innovations – and the better economic proposition – is in printing composite forms for casting concrete.

Architects have discovered the potential of employing 3D-printed composites to create unique shapes for artwork or for retail store displays and museum exhibits. One example is the Al Davis Memorial Torch at the Las Vegas Raiders’ stadium, created from 225 composite material blocks that were 3D-printed with carbon fiber.

Architect Platt Boyd founded Branch Technology because he was frustrated with the constraints of traditional construction methods and materials. Inspired by natural forms and structures, Boyd found a way to incorporate those elements into buildings using the design freedom made possible by robotic, free-form 3D printing.

“We have a proprietary extrusion mechanism and proprietary algorithms that guide the robot through the path,” says David Goodloe, Branch Technology’s program development manager. “The material actually solidifies in free space as extruded, allowing us to print as if the robot was a giant pen tracing a three-dimensional path through the air and leaving behind a reinforced polymer in its wake.”

The result is volumetric lattice structures that have strength similar to comparable solid forms but use 20 times less material to build. If additional strength is needed in one area of the structure, the size of the honeycomb cells can be varied to increase the structure density in that location. Branch Technology works with a palette of materials that includes pelletized thermoplastic polymer resins with chopped carbon fiber and various additives.

The company currently has 14 robots, 12 for printing and two for milling. “Each one has its own build envelope, so we upload a specific part to a specific robot, and it prints that part within its own designated work cell,” explains Goodloe. Although the robot can print parts 30 feet long, 10 feet wide and 12 feet high, most parts range around 15 x 8 x 8 feet. Goodloe notes the size of the composite parts is usually constrained by logistical choke points such as a doorway or a truck, not by the printing technology.

Branch has three products. Branch Matrix™ is the exposed lattice structure of polymer resin and fiber additives. “It’s for architectural and sculptural applications – big, sweeping geometries,” says Goodloe. Nature Clouds, four giant hanging gardens in the center hall of Chicago’s Field Museum of Natural History, were printed by the company.

BranchClad™ is a mass-customized, ventilated rainscreen system and building skin that attaches to the structure of a building. Made with a lattice structure and a fire-rated, energy-efficient infilling foam, it enables the construction of unique exteriors. For a bank in Chattanooga, Tenn., Branch manufactured BranchClad panels with a wave pattern reminiscent of the waves on the bank’s logo. The company is currently working on cladding for the U.S. Space and Rocket Center in Huntsville, Ala., which will replicate the topology of the moon.

In partnership with Sto Corp., a prefabricator of construction components, Branch recently introduced StoPanel® 3DP, which provides builders with a wall assembly fully finished on both the exterior and interior sides.

Branch’s technology may be headed for space. The company is working with NASA to develop automated construction technologies for the moon and Mars. “The challenge is to print with in-situ materials to create habitats on these new worlds,” says Goodloe.

A Lego® Model for AM

The explosion of 3D-printed motor mounts for a drone launched Cole Nielsen, founder and CTO of Orbital Composites, on a quest to rethink additive manufacturing. To start, he spent 18 months studying every manufacturing method used today, with a special emphasis on advanced composites and sequential process compatibilities. Fundamentally, he found that carbon fiber, copper wires and electrically insulating polymers could monolithically create most of a vehicle system for any environment, but only if fibers were placed independently and arbitrarily. The matrix-to-reinforcement ratio would also need to be non-constant.

Nielsen developed a new type of printer head, the coaxial extruder. A nozzle within a nozzle, it encases a filament, such as continuous carbon or glass fiber or copper wire, inside a tube of thermoplastic or thermoset resin. This technology permits the inclusion of a variety of materials in the printing process. For example, a fiber optic cable introduced in the inner nozzle can be placed in the desired location on the part while simultaneously being encased with glue to hold it in place.
Nielsen also invented a high-force, high-pressure filament driver that enables faster printing and reduces filament failures. He notes that most failures in polymer extrusion printers are due to “snakebites” or filament drive failures.

Orbital Composites doesn’t use a conventional 3D printer with a gantry. Instead, the system employs single and multi-robot setups, with smaller robots stacked on top of larger robots. Their different end effectors perform specific tasks, such as printing and pre- or post-processing. The robots can work together in overlapping motion spheres, speeding production. They can easily print onto curved shapes and, unlike 3D printing systems that use gantries, the robots can manufacture products nine times their size. If a robot breaks down during the manufacturing process, another can take its place. “The robots can fail, or they come and go, but the object remains in the manufacturing process,” Nielsen says.

The company designs each printer setup around the product it’s producing. Nielsen likens it to putting together different Lego blocks to achieve a desired shape.

While this hardware is important, it’s only part of the story. “Fifty percent and maybe even more of our engineering effort is software. One of the ways that we use brute-force machine learning is to try to figure out how the robot needs to move to finish the print – literally how many different ways you can try to get through the maze,” Nielsen explains.

Affordable, High-Volume Production