Dec 7, 2018 | By Cameron
Professors Jamison Go and John Hart of the Massachusetts Institute of Technology (MIT) Mechanosynthesis Group have developed new hardware that enables what they call FastFFF (fast fused filament fabrication). And it’s fast, see for yourself.
Desktop 3D printers are fantastic at creating high-quality and complex parts on demand, but their greatest weakness has always been speed. They can only print one object at a time, one thin layer at a time. And there are several speed-limiting factors to FDM/FFF 3D printers, with the main four being: the amount of force that can be applied to the filament as it’s pushed through the nozzle, how quickly heat can be transferred to the filament to melt it, how fast the printhead can move around the build area, and the rate that the material solidifies after it’s extruded because it needs to support the next layer.
The solidifying problem they solved like most other developers, by blasting air at it. The remaining hurdles required more creativity. When filament is pushed, it’s typically done by running it between a drive gear and an idler; tension is put on the drive gear, which has little teeth that bite into the filament and push it down as the drive gear turns. If there’s too much tension on the filament, the drive gear eats into the filament and builds up with plastic before eventually losing grip. Too little tension results in slippage and gaps in extrusion.
Go and Hart decided to thread the filament and run it through a threaded nut; when the nut is turned by a motor (via belt), the filament goes down. Anti-twist rollers prevent the filament from twisting as the nut turns. This method of extrusion is not only faster but also much more precise than the typical drive gear setup.
The next holdup of heating the filament fast enough to melt it completely was addressed with lasers. A quartz chamber is lined with gold reflectors, and as the filament goes through the chamber a laser is bounced around inside and pre-heats the filament before it goes through a traditional heating block. All technologies are improved with lasers.
Finally, Go and Hart designed a servo-driven parallel gantry system that rapidly and accurately moves the printhead around with little backlash, the shake or ripple movement that most desktop 3D printers exhibit when printing too fast. Here, the speed is mostly enabled by using a heavy-duty frame and powerful motors rather than a novel solution.
The new printer smoked the competition in speed tests, including a $100,000 commercial 3D printer. The 3D printer built by the research team cost $15,000 so this isn't likely to hit the market any time soon. This extrusion method is seven to 10 times faster, producing up to 127 cubic centimeters per hour. The quality of the prints could be better, likely improved by tuning the retraction and pathing settings, but the quality is still very good considering the speed at which they were 3D printed.
Hart also worked with Sebastian Pattinson, a lecturer at the University of Cambridge, to demonstrate a technique of 3D printing with cellulose. Cellulose is cheap, renewable, and has desirable mechanical properties, but 3D printing with cellulose has proven difficult due to its tendency to decompose when heated. By treating cellulose with acetate, they could dissolve it in acetone and successfully extrude it with a 3D printer. The acetone evaporates (and is captured), leaving just the cellulose acetate. A final bath in sodium hydroxide removes the acetate and a cellulose part is the result. The duo 3D printed a set of medical tweezers and even infused 3D prints with an antimicrobial dye that proved to be 95% more resistant to bacteria.
Posted in 3D Printer
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