“If you look at the current conventional 3D printing technologies, first you’ll notice that most of them are 20 to 30 years old,” said Robert Swartz, founder of Impossible Objects. “One of the things you might like to improve upon would be the ability to make things faster, to have better mechanical properties so that you can make functional parts, and the ability to use a wider range of materials. If you think about 3D printing for very long, you quickly realize that these issues are largely a materials science problem.”
Swartz’s company, based in Northbrook, Ill., has been developing a new 3D printing technology that is almost ready for beta purchase. The process, dubbed the composite-based additive manufacturing method (CBAM), is meant to address all of the issues and problems that Swartz mentioned in his interview with ENGINEERING.com. Not quite like any other 3D printing technology on the market, CBAM is able to produce multimaterial, carbon fiber–reinforced parts at potentially unprecedented rates.
How It Works
Like every other 3D printing technology, CBAM begins with a CAD file that is sliced into individual layers. In CBAM, those layers are then converted into bitmaps. Inkjet heads containing an aqueous-based printing solution then deposit the bitmap layer shapes onto a substrate sheet made from the reinforcement material of choice, which will often be carbon fiber for its high strength-to-weight ratio, but may be a number of different fiber materials.
The substrate sheet is then flooded with a thermoplastic powder, which adheres only to the areas where the inkjet solution has been deposited. The excess powder is subsequently blown or vacuumed off, leaving only the plastic sticking to the bitmap layer shape. This process is repeated with each layer until the complete object is transformed into a stack of these sheets.
The sheets are compressed, placed into an oven and heated until the plastic powder fuses together, at which point, the object is removed and the excess reinforcement material is removed either by sand blasting or a chemical bath. The end result is a geometrically complex object made up of thermoplastic and reinforcement fibers that may be up to ten times stronger than parts made with plastic extrusion or other 3D printing technologies.
If this almost sounds like an assembly line process, that’s because it is, with sheets printed and moved onto a conveyor belt that removes excess powder. While it may seem as though it requires a number of individual steps, the process is automated and CBAM has a number of advantages over other 3D printing and manufacturing technologies, including speed.
Unlike a 3D printing system that deposits viscous inks, such as HP’s Multi Jet Fusion (MJF), PolyJet or the new technology from Rize, Impossible Objects jets a water-based solution. This enables the liquid to be deposited onto the substrate quickly.
The CBAM inkjet head depositing the liquid solution. (Image courtesy of Impossible Objects.)
CBAM also has advantages over fused deposition modeling (FDM), which sees thermoplastic extruded through a print head. As CBAM does not rely on melting and forcing plastic through a print head, CBAM has a much wider selection of materials to choose from and an operate much more quickly. Similar material flexibility can be seen in relation to the fiber composite substrate chosen for the CBAM process, as well.
“The advantage of this approach is significant,” Swartz said. “One, our CBAM technology can scale to use inkjet heads that run 100 meters per minute so you can get very high speeds. Two, you can use pretty much any thermoplastic that you want. We’ve done polyethylene, nylon and high-performance materials like [polyether ether ketone], and it’s going to give you a much wider variety of polymers that you can use. Three, you can use high-performance materials like carbon fiber and get much greater strength— up to ten times stronger—than you would get from the conventional processes like [selective laser sintering] or FDM.
He added, “In addition, because it’s a fiber-based process, we can not only get better material properties but we can also use a wide variety of substrates—carbon fiber, fiberglass, polyester, PLA, polyvinyl alcohol, cotton and silk.”
While the technology as a whole promises unlimited geometric complexity, every 3D printing process has its limitations when it comes to the exact shapes a system can produce. For instance, FDM may not be able to create certain moving parts and is dependent on the ability to produce support structures for overhanging parts of a design. As selective laser sintering (SLS) is a powder bed process, printed parts require the creation of an exit cavity from which the excess powder within a print can be removed.
When it comes to CBAM, the geometry is partially determined by the chosen substrate material. Removing carbon fiber requires sand blasting, creating similar limitations faced by SLS due to the fact that the sand must be able to access the interior of the part to remove excess carbon fiber.
However, a chemical process is used to remove other reinforcement materials, such as Kevlar and polyester. In those cases, the geometric complexity is more similar to that possible with FDM, when using soluble supports.
The ability to blend materials and incorporate fiber reinforcement opens CBAM up to a number of uses. These include the 3D printing of electronics enclosures reinforced with carbon fiber because, due to the material’s conductivity, the enclosure can create a Faraday shield for the electronics inside.
A 3D-printed drone propeller made by Impossible Objects. (Image courtesy of Impossible Objects.)
Other applications include 3D printing drone, satellite and Formula One parts as well as producing tooling for injection molding. In addition to working with a major manufacturer to 3D print custom molds for producing components for consumer goods, Impossible Objects has signed a collaborative research agreement with Oak Ridge National Laboratory (ORNL) to 3D print tooling for making carbon fiber composites. The research involves improving the thermal coefficient of expansion of an injection mold.
ORNL is also currently working with Cincinnati Inc. on the Big Area Additive Manufacturing (BAAM) system, which has been used to 3D print large-scale structures like entire auto chasses, and Cosine Additive to create a Medium Area Additive Manufacturing machine. In turn, the agreement with Impossible Objects is at least ORNL’s third carbon fiber 3D printing project. Whereas the BAAM machine 3D prints with about 5 percent carbon fiber and 95 percent ABS, Impossible Objects will bring much higher reinforcement to the U.S. Department of Energy lab.
A 3D-printed femoral stem implant made with carbon fiber and PEEK. (Image courtesy of Impossible Objects.)
Swartz sees his system as positioned between conventional 3D printing and high-end custom carbon fiber layup. The technology may not be able to achieve the same strength as carbon fiber layup, but it produces parts stronger than other 3D printing technologies, making it ideal for fabricating geometrically complex and durable parts much more affordably than—and oftentimes not even possible—with traditional carbon fiber manufacturing methods.
Simultaneously, CBAM is much quicker and more automated than the labor-intensive and costly carbon fiber layup process. “When it comes to manufacturing, you’ve got a choice of metal, conventional polymers or carbon fiber. There’s really nothing in between, whereas our process gives you something in between but also gives you the advantage of the complex geometries,” Swartz said. “If you need the absolute highest possible strength, then hand-laid carbon fiber composites are wonderful. But if you don’t need that absolute best strength, we represent a much faster, inexpensive alternative.”
Currently, there are very few methods for 3D printing plastic parts with fiber reinforcement. Aside from comparatively weak chopped carbon fiber filaments, the only carbon fiber 3D printers on the market are the Mark One and Mark Two from Markforged, which fill FDM parts with strands of continuous carbon fiber.
Due to the lack of soluble support material, this process cannot produce parts that are as geometrically complex as other 3D printing technologies, and because it relies on FDM methodology it would be difficult to scale for significantly greater size or speed.
On the horizon, however, is the selective lamination composite object manufacturing machine from EnvisionTEC. Unveiled at RAPID 2016, this process stacks massive sheets of woven fiber composites and fuses them with thermoplastic before a massive blade cuts the parts out. The use of woven fiber composites will likely enable the production of parts that are stronger than those made by CBAM, but it will probably be slower than CBAM and limited to simpler geometries. Additionally, removing the support material may be quite labor intensive. More than that, the system is priced at roughly $1 million. With that price tag in mind, Swartz sees EnvisionTEC as targeting a much different market than his own technology.
In the immediate future, Impossible Objects plans to ship beta pre-production machines at the beginning of next year. The aim is to sell the system at prices that are less than high-end Stratasys and EOS machines and even HP’s MJF printers. The package will likely include a heating machine that is more efficient than a conventional oven and may come with specialized equipment for automated post-processing.
With its current prototype machine, Impossible Objects has scaled its technology to print sheets with a robust size of 12 in x 16 in (304mm x 406mm); however, Swartz explained that the company envisions scaling up even further to print objects the size of a car hood.
“We’re also working on high-speed production rates,” Swartz added. “We think in the long term we could see printing at 100 meters per minute to produce parts faster than injection molding from a production rate perspective. If you look at printing these things on sheets that are 30 in x 40 in, which is not unreasonable, there are people who can run those at 18,000 sheets an hour. There are certainly lots of inkjet printers that will run at 3,000 to 5,000 sheets per hour. So, theoretically, you can have speeds that really are unprecedented as compared to conventional methods.”
Before we can see geometrically complex carbon fiber–reinforced parts flying off of the CBAM assembly line at 100 meters per minute, we’ll have to wait for the beta pre-production machines to ship next year.