Unsurprisingly, some of the most innovative 3D printing research has come from the Massachusetts Institute of Technology (MIT), whether the university is working on faster 3D design, developing improved protective gear, making childhood trips to the doctor less painful by combining multiple vaccines into one shot, or even improving 3D printing itself. One name we hear often when talking about the 3D printing work coming out of MIT is Anastasios John Hart, an associate professor of mechanical engineering whose lab is often at the center of the university’s latest AM innovations.

Hart has taught multiple courses on the technology, and is also the director of MIT’s Laboratory for Manufacturing and Productivity and the Mechanosynthesis Group. He has been working recently with MIT engineers to develop a desktop 3D printer that can perform up to ten times faster than commercial 3D printers currently on the market, which could obviously open up a lot of new production opportunities.

A. John Hart

“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. 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,” Hart said. “I don’t have to go to a warehouse and take it out of inventory.”

Hart and 2015 MIT graduate Jamison Go, a former researcher in Hart’s lab, published the results of their work on developing their FastFFF 3D printing system in a paper, “Fast Desktop-Scale Extrusion Additive Manufacturing,” in the journal Additive Manufacturing.

The two worked together previously to determine what causes the limited speed of most common desktop FFF 3D printers, and discovered that commercial desktop extrusion 3D printers can only print at an average rate of 20 cubic centimers an hour, which Hart notes is “really slow.”

This original research team found three main factors  – how fast a 3D printer moves its printhead, how much force the printhead applies to materials to get it through the nozzle, and how fast it transfers heat to melt a material and make it flow – that limited how fast a 3D printer could 3D print (how much wood could a woodchuck chuck?).

Hart said, “Then, given our understanding of what limits those three variables, we asked how do we design a new printer ourselves that can improve all three in one system. And now we’ve built it, and it works quite well.”

While most desktop 3D printers can make a few LEGO-sized bricks in an hour, the MIT FastFFF system is able to produce the same amount in just minutes, thanks to its newly designed, compact printhead. Typically, a pinch-wheel mechanism feeds plastic through a 3D printer’s nozzle – two small wheels inside the printhead rotate to push the filament through, which works fine at slower speeds. However, the wheels will lose their grip if more force is applied to speed the process up, and Hart says that this ‘mechanical disadvantage’ is responsible for limiting the speed of most desktop 3D printers.

Hart and Go got rid of the pinch-wheel, and added two new components to its printhead that will enhance the 3D printer’s speed, the first of which is a screw mechanism that turns inside the printhead. It grips the textured surface of filament while it turns, feeding it through the nozzle at a high force and speed.

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

The second component is a laser that’s built into the printhead downstream of the screw mechanism, which rapidly heats and melts the material before it’s fed through the nozzle so it can flow faster. While most commercial 3D printers heat the nozzle walls with conduction to melt the plastic, the researchers’ method allows the material to melt more quickly. Additionally, by turning the laser quickly on and off, and adjusting its power, Hart and Go were able to control how much heat was applied to the plastic.

Both the screw mechanism and the laser were integrated into the team’s small, custom printhead. Then, they designed a high-speed, H-shaped gantry mechanism, powered by two motors connected to the motion stage holding the printhead, and programmed it so it was able to move rapidly between different planes and positions and keep up with the fast feed of the extruding plastic.

Hart explained, “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. All three factors enable the printer to be up to 10 times faster than the commercial printers that we benchmarked.”

To demonstrate the abilities of its fast 3D printer, the researchers fabricated various complex, handheld objects, like a miniature replica of the MIT dome and tiny eyeglass frames. Each one was 3D printed within five to ten minutes, versus the hour it would have taken on a conventional 3D printer.

Collection of objects and test samples printed on the new 3D printer. [Image: Chelsea Turner, using images provided by the researchers]

The speed of the 3D printer did cause an unexpected issue – because the extruded plastic is fed through the nozzle at such elevated temperatures and forces, by the time the second layer is being extruded, the first layer may still be a little molten.

“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,” Hart explained. “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.”

The team is working to fix this design challenge, along with finding new materials to send through their new 3D printer.

Hart said, “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. The capability to print fast opens the door to many exciting opportunities.”

Let us know your thoughts on this and other 3D printing topics at 3DPrintBoard.com, or leave a comment below.

[Source: MIT News]

 

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