There are two kinds of digital fabrication, additive and subtractive. Composite materials have been closely associated with subtractive methods: CNC routing or milling is used to cut away a block of foam into the desired shape, and the foam is typically used as a mold for glass-fiber or carbon fiber composite lay-up.
Additive methods such as 3-D printing have been limited to homogenous materials, usually thermoplastics, that are deposited drop-by-drop from a computer-controlled gantry, forming a a solid shape. 3-D printing of stronger materials, such as metals, is also possible, but the desktop 3-D printers that spit out plastic are affordable. They have been popular for rapid proto-typing, and form-and-fit testing of mechanical parts. The limitation of these parts has been the low strength of the plastics. You could see if the part fit and could be installed, but it wasn’t always strong enough to test in use.
Now, MarkForged, Inc. is bringing out the Mark One 3-D composite printer. The desktop device can lay down a composite based on a continuous filament of carbon fiber (or Kevlar, or glass fiber) which can be formed into layers. The machine uses a proprietary thermoplastic resin pre-impregnated into the filament. The orientation of the fiber can be controlled and altered as desired for reinforcing purposes.
The device actually has two print heads. One is for Fused Filament Fabrication (FFF), the homogenous plastic process found in the more familiar desktop 3-D printers. The second head performs Composite Filament Fabrication (CFF) as described above.
By using these heads in alternating layers, the machine can make a fully laminated, bonded sandwich panel. In a conventional process of making FRP panels, the layers of reinforced plastic often surround a core of structural foam. The MarkOne can create a honeycomb using FFF to serve the same function as the foam.
“The approach that we’re taking,” explains company Creative Director Jeff Klein, “is that you’re essentially creating sandwich panels. You can determine how much fiber you need for specific product, so it’s a very economical way to print parts. You can define what honeycomb sandwich structure of the nylon is. Because you selectively reinforce, and selectively apply only the fiber you need, you end up saving not only on cost of materials, but overall.”
The MarkOne’s maximum output size – 12” x 5.75” x 6” – is small by choice. “Prior to development,” relates Klein, “we talked with friends and clients. They said the majority of their need wasn’t for anything larger than a shoebox.” Accordingly, the MarkOne is designed to make small but functionally strong parts that are used for testing, or only needed in very small quantities.
However, Klein says that the technology is scalable. That means that it could, theoretically, be applied to making architectural objects. If so, it could offer a mold-less route to fabricating unique elements. It could eliminate a great deal of the manual labor involved in hand lay-up. The major limitation on scaling it up is time. Increasing the size of the object fabricated increases the fabrication-time by the power of three. (i.e. making a part twice as large takes eight times as long.)
A 3-D composite printer costs $5000. The Developer Kit includes a selection of materials as well, and costs $8800. MarkForged is currently taking pre-orders for the MarkOne, and expects to delivers printers by year-end 2014.
Images courtesy of MarkForged, Inc.