The key to the team’s design lies in the printer’s compact printhead, which incorporates two speed-enhancing components: 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.
Anastasios John Hart, associate professor of mechanical engineering at MIT, said the printer demonstrates the potential for 3D printing to become a more viable production technique. “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,” he explained.
His team identified three factors limiting a printer’s speed: how fast a printer can move its printhead, how much force a printhead can apply to a material to push it through the nozzle, and how quickly the printhead can transfer heat to melt a material and make it flow.
In most desktop 3D printers, plastic is fed through a nozzle via a ‘pinch-wheel’ mechanism, in which two small wheels within the printhead rotate and push the filament, forward. This works well at relatively slow speeds, but if more force were applied to speed up the process, at a certain point the wheels would lose their grip on the material, limiting how fast the printhead can push material through.
The MIT team replaced the pinch-wheel design with a screw mechanism that turns within the printhead. They fed a textured plastic filament onto the screw and, as it turned, it gripped onto the filament’s textured surface and could feed the filament through the nozzle at higher forces and speeds.
“Using this screw mechanism, we have a lot more contact area with the threaded texture on the filament,” Prof Hart said. “Therefore, we can get a much higher driving force, easily 10 times greater force.”
The team added a laser downstream from the screw mechanism, which heats and melts the filament before it passes through the nozzle. In this way, the plastic is more quickly and thoroughly melted, compared with conventional 3D printers, which use conduction to heat the walls of the nozzle to melt the extruding plastic.
Prof Hart found that, by adjusting the laser’s power and turning it quickly on and off, they could control the amount of heat delivered to the plastic. The team 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 between multiple positions and planes. In this way, the entire printhead could move fast enough to keep up with the extruding plastic’s faster feeds.
However, there was a glitch in the 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,” Prof Hart said.
That’s a design challenge that the researchers are currently addressing, as well as exploring 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 3D printing, not just printing desktop-scale objects but bigger structures for tooling, or even furniture,” Hart added. “The capability to print fast opens the door to many exciting opportunities.”
