By Jan H. Schut
There’s a new kind of “micro extruder” out there these days. Micro extruders used to mean the smallest size of conventional extruders with screw diameters from 5⁄8 to ½ inch for pellet-fed lab models down to ¼ inch for a powder-fed lab model from Randcastle Extrusion Systems Inc., Cedar Grove, NJ (www.randcastle.com), which is probably the smallest.
The new so called micro extruders are an unusual geek product – inexpensive desk top 3D printers, fed by plastic filament from a spool and designed for the broadest possible use. Full sized 3D printers have been around for over 25 years, but they’re large expensive machines bought or leased by mold makers, prototyping service bureaus, and large companies that produce durable products to make prototypes, quick molds, jigs and fixtures for product development and some end use parts for aerospace.
Small desk top 3D printers, also known as micro extruders, are an emerging development since 2009 when an early patent from Stratasys Ltd., Eden Prairie, MN (www.stratasys.com), expired (U.S. Pat. # 5121329). Stratasys developed large industrial “fused deposition” modeling machines using filament, but never built the desktop model. Most new desktop 3D printers, however, are based on Stratasys’ concept for a small programmable filament laying machine. The new machines developed rapidly, many funded over the web by small investors and have become so inexpensive that any business, architect, or designer could afford one. There are supposedly even some home users.
In January 2012, Makerbot Industries LLC, Brooklyn, NY (www.makerbot.com), launched one of the first inexpensive commercial micro extruders, the second generation Replicator for $1,999 with 11.2 x 6.1 x 6 in. build space and 100-micron layer resolution. Stratasys bought Makerbot in 2013. Replicator is now on its fifth generation, and there’s a Replicator Mini for only $1,375 with 5.9 x 5.9 x 5.9 in. build space and 80-micron resolution.
In 2009 3D Systems Inc., Rock Hill, SC (www.3dsystems.com), which builds large 3D printers using laser sintering, acquired assets of Desktop Factory Inc. from Idealab, Pasadena, CA (www.idealab.com). Desktop Factory developed technology to build parts by sintering powdered nylon using a halogen lamp, not laser, but never commercialized the machine. In 2010, 3D Systems also bought Bits from Bytes Ltd., which grew out of the University of Bath in the U.K. (www.bath.ac.uk), and built filament-type desktop 3D printers. Then in January 2012, 3D Systems launched its Cube 3D printer for $1,299, based on filament, not sintering, and in June this year launched Cube3 with 6 x 6 x 6 in. build space for $999.
In October 2013, Zeepro Inc., Stamford, CT (www.zeepro.com), introduced the Zim micro extruder for only $599 with 5.9 x 5.9 x 5.9 in. build space, 80-micron layer resolution, and two print heads. C Enterprise (UK) Ltd., Portishead, Bristol, U.K. (www.cel-robox.com), is developing the CEL-Robox, priced at UK 700 pounds ($910) with 8.3 x 5.9 x 3.9 in. build space, 20-micron layer resolution, and two print heads. Robox and Zim intend their dual print heads potentially to make complex shapes with overhangs using a structural polymer and a sacrificial polymer, which can be washed away later like HIPS, which dissolves in limonene, or PVA, which dissolves in water. 3D Systems’ latest CubePro, introduced in June, has three print heads. Over 100 more desktop 3D printers are available or under development, mostly in China.
BUT ARE THEY EXTRUDERS?
These micro extruders don’t have much in common with conventional extruders. Instead of requiring operators with years of plastics experience, these micro extruders require no plastics experience at all. C Enterprise boasts in its literature that a 5-year-old will be able to operate its Robox. Nor do makers of desktop micro extruders describe how they melt plastic. Stratasys’ patent describes “ratchet teeth” that pull plastic filament into a supply chamber in the print head, where the filament is melted at controlled temperature by an electric cartridge heater. The patent compares the process to a hot glue gun. Colors are changed by changing the print head.
Only one micro extruder, called David (as in Goliath), under development by Sculptify LLC, Columbus, OH (www.sculptify.com), will use lower cost pellets, not filaments. There are only two other full sized 3D printers that use pellets, so David will be unusual among 3D printers of any size. David presumably melts pellets with some kind of screw, though the literature doesn’t say. The hopper holds 1 ¼ lb. of pellets and the “extruder” goes up to 626 °F, an astonishing temperature for a desktop model. Build space is 7.8 x 8.6 x 7.3 in. with 100-micron layer resolution. Head positioning accuracy is described as 8 microns on the x- and y- axes and 3 microns on the z-axis.
Typically micro extruder print heads are moved in x, y, z directions by two or three stepper motors, programmed to follow a CAD design and deposit a thin layer of plastic to form a simple part. Their biggest limitation is accuracy, which doesn’t mean accurate layer thickness, but accurate positioning of the print head. Polar 3D LLC, Cincinnati, OH (www.polar3d.com), is developing a micro extruder model with a stationary print head and moving base on a turn table, hoping to improve accuracy. Polar 3D’s printer, which is being beta tested now, will cost $799 with 12.8 x 8 x 14.8 in. build area.
PLA is the preferred material for desktop 3D printing because of its low processing and printing temperature, typically between 390 °F and 450 °F, whereas ABS is printed at 450 F and higher. PLA printing has low odor (a slight sweet smell), where ABS gives off a stronger styrenic smell. Some desktop micro extruders also process ABS, but they require a heated base or build chamber to avoid warping as a part builds and cools, which adds cost. Pirate3D Inc., Palo Alto, CA (www.pirate3d.com), introduced the Buccaneer micro extruder in April this year for only $347 with 5.7 x 5 x 5.9 in. build space and 50-mm resolution, which sounds great except that Pirate3D told investors Buccaneer would use PLA and ABS, but it doesn’t.
New durable filament materials are being introduced all the time. In the New Technology Forum on 3D printing at the Society of Plastics Engineers ANTEC 2014 conference last April, PolyOne Corp, Avon Lake, OH (www.polyone.com), reported on advanced materials for additive manufacturing including glass and carbon fiber composites in engineering polymers. These materials target large 3D printers, which can process ABS, PA 12, PC/ABS, PC, PEI, and PPSU filaments in addition to PLA. Desk top models don’t typically have high heat capabilities, but some new models will. Robox’s components are designed to use nylon and PC as well as PLA. 3D Systems also recently added nylon filament for the Cube and CubePro and says it sees a surge of interest in consumer and commercial use.
NatureWorks LLC, Minnetonka, MN (www.natureworksllc.com), is now developing durable PLA grades for 3D printing, based on existing crystalline formulations for injection molding. “Preliminary results show that these new grades match or exceed the toughness and heat resistance of ABS along with PLA’s traditional printing performance,” says Daniel Sawyer, global leader of new business at NatureWorks, who will present “Innovating with Ingeo Biopolymer for 3D Printing” for the first time at an Upper Midwest SPE Minitech at Century College, White Bear Lake, MN, Nov. 11 (www.uppermidwestspe.org/events.htm).
Micro extruders are so new that even their most optimistic creators haven’t a clue what they’ll end up being used for. Most are pictured making things like simple trinkets and chess pieces. But it would be a mistake to dismiss them as toys. Sales of 3D micro extruders are growing rapidly, and they’re processing real plastic. In August United Nude shoe stores in New York (www.unitednude.com) launched a line of custom high-fashion shoes made of ABS, called “Float.” Customers build their shoes in the store or at home on Cube or CubePro printers, choosing their own size and color combination.