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M A Y 2 0 1 4 | 4 5 automate carbon fber composite layup." R&D; was initially based on open-source 3-D printers, which the company refned iteratively to create a more robust and reli- able process. The result is an AM printer that can produce parts made with continu- ous carbon fber in a thermoplastic resin. Because MarkForged is, thus far, unique in its use of continuous reinforcements, Mark says, "we really had to think about control- ling the print process with the machine's software." The Mark One machine was un- veiled at the recent SolidWorks World 2014 conference (see "Learn More"). Unlike typical AM machinery, the Mark One has two print heads, both designed and built by the company. One dispenses polyamide (nylon) or polylactide (PLA) resin, and the second dispenses a con- tinuous towpreg, either carbon or glass (dispensing of aramid fber is in develop- ment). The towpreg is made in a propri- etary process: A single carbon flament is coated with a specially developed ther- moplastic resin, designed specifcally for the printer. The Mark One uses FDM, an extrusion-like process, for placement of resin and towpreg in the fat x/y plane of the part. Mark says that the fber can be oriented, or added selectively only where needed, in the x/y plane, but notes that, at present, vertical, or z-directional, orienta- tions aren't possible. Each build layer is approximately 200 microns in thickness. Says Mark, "The machine's software can choose the optimal fber orientation based on some basic design rules, or in the manual mode, you can specify the ori- entation on a layer-by-layer basis, to al- low for specifc placement, for example, ±45°." MarkForged is currently designing plug-ins to work with the major comput- er-aided design (CAD) programmers, in- cluding Dassault Systèmes' SolidWorks (Waltham, Mass.), so that, eventually, any design software can be used to drive the machine for optimal fber placement. The "stage" on which deposition takes place is a plastic platform, to which the polyamide or PLA resin adheres, similar to other AM machines, explains Mark. "You scrape the fnished part off when fnished," he says. "The platform lasts for roughly 100 prints, then gets replaced." Unique to the Mark One is the use of a high-precision "kinematic coupling" to precisely level and fx the build platform. Used in silicon wafer processing, the cou- pling precisely constrains all six degrees of freedom so that the build stage can simply be "clicked" into place. Set-to- reset leveling is reportedly repeatable to within 10 microns. Strong first steps "For us, using carbon fber and nylon together makes so much sense," asserts Mark. "If you're printing with the com- mon materials such as nylon, being able to incorporate continuous fbers enables an entirely new class of parts." He adds that the Mark One can produce parts that are stronger than 6061 T6 alu- minum, and, based on mechanical test- ing, provide good impact resistance. He cites the part shown at the Solid- Works conference, a baseplate for at- taching a race car wing to a car. Essen- tially a sandwich panel, the part has outer skin layers of neat polyamide for a good wear surface, while inside are three, 200-micron thick layers of carbon fber laid around the outer edge, and a printed nylon honeycomb inside the carbon in the center of the part for in- creased strength to weight properties (see photo, p. 47). After the print is fn- ished, the baseplate is ready to install (the print process creates the mount- ing holes), without the labor of layup or need for cure, and takes 6.5 hours of machine time to print, compared to perhaps a day for conventional infusion processing. "There's no labor, cutting, gluing, trimming, molds or fxtures," Mark points out. "The baseplate sup- ports a wing that is capable of produc- ing 860 lb/391 kg of downforce when the race car is traveling at 200 miles per hour," a sizeable load condition to en- trust to a 3-D printed part. Like any advocate of carbon fber com- posites, Mark faces questions from po- tential customers about cost. "Yes, car- bon fber is an expensive material," Mark admits, but cautions interested parties to put that fact in perspective. "In the end," he points out, "the difference be- tween an all-nylon wing baseplate and a carbon fber/nylon baseplate is $10." And his process is not subject to factors that contribute to part cost in conventional composites processes. "With this tech- nology, there's no waste, no mold cost, no layup labor cost, and when you're fn- ished, you have a net-shape part!" MarkForged isn't just talking, it is producing desktop-sized Mark One ma - chines, beginning at $4,999, for customer shipment in the coming months. "We are actually a '2.5D' system right now," he quips. You're putting down fat layers, and stacking them, but you're not able to follow a trajectory or a con- toured surface." Aerospace companies, for example, will want more dimensions, and larger part sizes. Mark asserts that printing much larger structures is on the company's "road map" and envisions the ability to produce an entire auto chassis or unmanned aerial vehicle (UAV). "We will be able to address those demands, as well as more complex load cases," he predicts. Toward that end, MarkForged will offer more axes, via robotic handling, and larger build boxes, and its proprie- tary build heads will be able to handle the larger parts. Tested material samples top aluminum Continuous carbon/ polyamide parts produced in the Mark One have undergone property testing (shown here), and are used by the company in race car wing applications. Properties are reportedly better than 6061T6 aluminum. Source: MarkForged 0514HPC AdditiveManufacturing-OK.indd 45 4/22/2014 3:14:31 PM