After raising $436.8 million in total startup funding, Desktop Metal has already moved onto the introduction of its third 3D printing platform and beyond metal. In addition to its extrusion-based and binder jetting metal 3D printers, the firm has developed a continuous reinforcement fiber 3D printing process dubbed micro automated fiber replacement (μAFP).
The technology features two printheads, one for 3D printing thermoplastic and another for laying down tape made from continuous fiber reinforcement materials, such as carbon fiber. According to the company, this allows it to fabricate parts with twice the strength of steel at one-fifth the weight, making it useful for producing jigs and fixtures, as well as end-use parts.
μAFP is not the first continuous fiber 3D printing technology on the market, and its introduction immediately calls to mind continuous filament fabrication (CFF) from Markforged and composite fiber coextrusion (CFC) from Anisoprint. Both μAFP and CFC differ from Markforged’s CFF in that they feature two inputs, one that feeds continuous fiber material into the machine and one that feeds thermoplastic. However, while CFC uses a single printhead to combine the two in-situ, μAFP uses two separate printheads.
More importantly, though both CFC and CFF extrude a reinforcement fiber-impregnated thermoplastic onto the print bed, similar to any fused filament fabrication (FFF) 3D printer, μAFP actually lays down fiber reinforcement tape in a process that's similar to large-scale industrial automatic fiber placement (AFP) technology. AFP is usually found in massive manufacturing outfits like Boeing or Airbus, where it is used to automatically lay carbon fiber for airplane wings.
Konstantine Fetfatsidis, vice president of Composite Products for Desktop Metal, was able to explain the μAFP process in greater detail in a call with engineering.com. He explained that, unlike other desktop fiber reinforcement 3D printing technologies, μAFP lays out reinforcement material in the form of tape pre-impregnated with a thermoplastic matrix. The tape is heated above the melt temperature of the plastic matrix material before a roller applies impaction pressure to the tape, fusing the tape to the part upon cooling. "You have heat pressure and cooling and that combination consolidates the material together," Fetfatsidis explained.
"We also have a tool changer, so we go from the tape and swap over to the FFF head that extrudes chopped fiber-filled thermoplastics that match the thermoplastic of the prepreg tape," Fetfatsidis said. "Now, we can go in and fill the areas that the tape didn’t cover and create a nice outer shell with a really nice surface finish, so it looks and feels like a chopped fiber-filled thermoplastic part, but inside it is reinforced with this very stiff, much stronger continuous fiber tape."
Fetfatsidis previously led research and development for Aurora Flight Sciences, where he used large-scale industrial AFP technology. Fetfatsidis commented on the benefit of shrinking AFP down to desktop size in the company's recent press release.
“As a long-time user of multi-million-dollar AFP technology for various development-to-production aerostructures programs, I am excited to bring AFP technology to the manufacturing floor for smaller, more complex parts,” Fetfatsidis said. “This new print technology finally brings the material properties of AFP composites to small parts under 20 pounds, which would typically require expensive tooling, extensive manual labor, multiple consumables, and multistep, long process cycles.”
μAFP is expected to ship to customers in spring 2020 via Desktop Metal’s latest 3D printer: Fiber. The system features a build volume of 310 mm x 240 mm x 270 mm. This can be compared to the print envelopes of the Composer A3 from Anisoprint (460 mm х 297 mm х 210 mm) and the X7 from Markforged (330 mm x 270 mm x 200 mm). Fiber units in groups of six or 10 can be networked together for series production.
Upon release, there are two versions of Fiber: Fiber HT and Fiber LT. Fiber HT can print parts with up to 60 percent fiber volume fraction, which is much higher than the typical rate of 30 to 40 percent in carbon fiber 3D printing, and less than 1 percent porosity. The system is able to print using aerospace-grade thermoplastics and can fabricate ESD compliant and flame-retardant parts with temperature resistance over 250°C.
The Fiber LT is less expensive ($3,495 annual subscription) than the Fiber HT ($5,495 per year) and can achieve less than 5 percent porosity. While the LT prints with a prepreg tape made up of PA6 (Nylon) combined with carbon fiber or fiberglass, the HT can print with those tapes, as well as tape made from PEEK or PEKK and carbon fiber or fiberglass. The HT also features two fused filament fabrication printheads, as opposed to the LT’s single extrusion printhead.
Fiber orientation, key to taking advantage of the anisotropic strength of fiber reinforcement materials, is automatically optimized to provide total maximum area coverage. However, with the Fiber HT, custom, targeted reinforcement is also available.
The divergence to fiber reinforcement is an interesting one for a startup with “metal” in its name, particularly given its history with carbon fiber and metal 3D printing competitor Markforged. Before the public launch of Desktop Metal, its founder and CEO, Ric Fulop, was one of three directors of Markforged.
Though Markforged had released its CFF technology to market, it was also privately developing a system, called Metal X, for 3D printing metal parts in an office-friendly environment. Three months after the unveiling of Metal X, Desktop Metal introduced its own metal 3D printer, the DM Studio. Both machines print metal-infused thermoplastic parts that must then be debinded and sintered in a furnace to create a fully dense metal part.
Both companies claim to have invented their technologies, but Desktop Metal was the first to sue Markforged for patent infringement—a case that Markforged won. Markforged then retaliated with a countersuit before the two parties agreed to a settlement in which Desktop Metal agreed to refrain from disparaging its competitors’ technology or face a $100,000 penalty.
Markforged then sued once again when it claimed that Desktop Metal handed out promo materials disparaging its products to over one hundred of its resellers, meaning that each “battle card,” as they’re called, would incur a separate $100,000 fine. This most recent suit was made public in July 2019 and news of its resolution has not yet been released.
Desktop Metal’s μAFP process is quite distinct CFF, but even minor similarities cannot be lost on those familiar with the history of the two companies. Regardless of this fact, there’s no doubt that fiber reinforcement 3D printing could have an important impact on the manufacturing industry.
To learn more about the technology, visit the Desktop Metal website.