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.