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Thursday, November 30, 2017

Boosting 3D printing by 10x

By Nick Flaherty www.flaherty.co.uk




Engineers at MIT have developed a new desktop 3-D printer that performs up to 10 times faster than existing commercial counterparts. While the most common printers may fabricate a few Lego-sized bricks in one hour, the new design can print similarly sized objects in just a few minutes.

The key is the printer's compact printhead, which incorporates a screw mechanism that feeds polymer material through a nozzle at high force and a laser, built into the printhead, that rapidly heats and melts the material, enabling it to flow faster through the nozzle.

The team demonstrated its new design by printing various detailed, handheld 3-D objects, including small eyeglasses frames, a bevel gear, and a miniature replica of the MIT dome -- each, from start to finish, within several minutes.

"If I can get a prototype part, maybe a bracket or a gear, in five to 10 minutes rather than an hour, or a bigger part over my lunch break rather than the next day, I can engineer, build, and test faster," says Anastasios John Hart, associate professor of mechanical engineering at MIT and director of MIT's Laboratory for Manufacturing and Productivity and the Mechanosynthesis Group. "If I'm a repair technician and I could have a fast 3-D printer in my vehicle, I could 3-D-print a repair part on-demand after I figure out what's broken. I don't have to go to a warehouse and take it out of inventory."

Commercial desktop extrusion 3-D printers, on average, print at a rate of about 20 cubic cm per hour. Now the researchers can print several complex parts, each produced within five to 10 minutes, compared with an hour for conventional printers. 

"Using this screw mechanism, we have a lot more contact area with the threaded texture on the filament," said Hart. "Therefore we can get a much higher driving force, easily 10 times greater force."

The team added a laser downstream of the screw mechanism, which heats and melts the filament before it passes through the nozzle. By adjusting the laser's power and turning it quickly on and off, they could control the amount of heat delivered to the plastic. They integrated both the laser and the screw mechanism into a compact, custom-built printhead about the size of a computer mouse.

Finally, they devised a high-speed gantry mechanism -- an H-shaped frame powered by two motors, connected to a motion stage that holds the printhead. The gantry was designed and programmed to move nimbly between multiple positions and planes. In this way, the entire printhead was able to move fast enough to keep up with the extruding plastic's faster feeds.

"We designed the printhead to have high force, high heating capacity, and the ability to be moved quickly by the printer, faster than existing desktop printers are able to," Hart says. "All three factors enable the printer to be up to 10 times faster than the commercial printers that we benchmarked."

However, they ran up against a small glitch in their speedier design: The extruded plastic is fed through the nozzle at such high forces and temperatures that a printed layer can still be slightly molten by the time the printer is extruding a second layer.

"We found that when you finish one layer and go back to begin the next layer, the previous layer is still a little too hot. So we have to cool the part actively as it prints, to retain the shape of the part so it doesn't get distorted or soften," Hart says.

That's a design challenge that the researchers are currently taking on, in combination with the mathematics by which the path of the printhead can be optimized. They will also explore new materials to feed through the printer.

"We're interested in applying this technique to more advanced materials, like high strength polymers, composite materials. We are also working on larger-scale 3-D printing, not just printing desktop-scale objects but bigger structures for tooling, or even furniture," Hart says. "The capability to print fast opens the door to many exciting opportunities."

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