MIT opening AM center, designs faster 3D-printer

This cutaway rendering of the MIT printhead shows how the threaded filament enters from the top and is pulled along by a rotating nut that has matching internal threads for maximum contact. It passes into a quartz chamber covered by gold foil. There, a laser beam enters from the side and is reflected through the core of the filament to preheat it. The filament then passes into a hot metal block, where it melts before being extruded from the nozzle.

MIT recently announced two developments related to additive manufacturing: The opening of the MIT Center for Additive and Digital Advanced Production Technologies (ADAPT), and a printer head capable of extrusion rates 14 times higher than existing heads.

ADAPT’s aim is to “accelerate the implementation of AM and to invent its future,” according to a press release published by the university. “As such, ADAPT convenes its members and MIT experts with a mission to perform visionary research, continually and critically assess the status of AM technology, develop model-based decision tools and open strategic frameworks, build a vibrant academic-industry network comprised of MIT students, and accelerate critical AM education initiatives for professional audiences.”

The roster of industry members includes GM, Bosch, Volkswagen, Autodesk, Formlabs, EOS, and Protolabs. The center’s director is John Hart, associate professor of mechanical engineering and director of the MIT Laboratory for Manufacturing and Productivity.

“ADAPT’s membership fees support research projects on visionary new AM technologies, breakthrough materials, computational methods, and more,” the release says. “Our research leverages the multidisciplinary strengths of ADAPT’s faculty and students--spanning mechanical engineering, materials science, computer science, and business--and enables members to reach beyond the constraints of today’s AM technologies and work hand-in-hand with MIT.”

To complement its technical research, ADAPT performs strategic analyses of the present and future capabilities of AM and of digitally driven manufacturing systems. “Broadly, we seek to identify the ‘scaling laws’ of AM technologies and create insights that enable members to act decisively in this rapidly changing arena. These analyses include accurate, up-to-date cost models of AM, tools for value analysis, and a library of case studies derived from member interests. Key insights and detailed reports are shared with members far in advance of academic publication.”

Click here to read the full report on the MIT website. To learn how to join ADAPT, email John Hart (ajhart@mit.edu).

Hart also figures into the news about research into a faster 3D-printing head. Extrusion, a common method of 3D printing, starts with a polymer rod, or filament, explains an article written by Nancy W. Stauffer that MIT published about the development. The filament is heated, melted, and forced through a nozzle in a printhead. The printhead moves across a horizontal surface (the print bed) in a prescribed pattern, depositing one layer of polymer at a time. On each pass over the print bed, instructions tell the printhead exactly where material should and shouldn’t be extruded so that, in the end, the layers stack up to form the desired, freestanding 3D object.

To find out what slows down current 3D printers, Hart teamed up with Jamison Go, a mechanical engineer at Desktop Metal, and Adam Stevens, a doctoral student in Hart’s lab, to examine several commercial, extrusion-based desktop models. They concluded that these units’ so-called volumetric build rates were limited by three factors: how much force the printhead could apply as it pushed the material through the nozzle; how quickly it could transfer heat to the material to get it to melt and flow; and how fast the printer could move the printhead.

Based on those findings, the trio designed a machine with special features that address all three limitations. In their design, a filament with a threaded surface enters the top of the printhead between two rollers that keep it from twisting. It then enters the center of a rotating nut, which is turned by a motor-run belt and has internal threads that mesh with the external threads on the filament.

As the nut turns, it pushes the filament down into a quartz chamber surrounded by gold foil. There, a laser enters from the side and is reflected by the gold foil several times, each time passing through the center of the filament to preheat it. The softened filament then enters a hot metal block, which heats it further (by conduction) to a temperature above its melting point. As it descends, the molten material is further heated and narrowed and finally extruded through a nozzle onto the print bed.

MIT Associate Professor John Hart (right), doctoral student Adam Stevens, and Jamison Go (not shown) developed a printer that reportedly extrudes material 14 times faster than currently available units.

The design overcomes the limits on force and heating that slow current 3D printers. In a standard printer, the filament is pushed by two small, rotating wheels. Add more force to speed things up, and the wheels lose traction and the filament stops moving. That’s reportedly not a problem with the new design. Matching the threads on the filament and the nut ensures maximum contact between the two. As a result, the system can transfer a high force to the filament without losing its grip.

The standard printer also relies on thermal conduction between the moving filament and a heated block, and that process takes time. At a higher feed rate, the core may not completely melt, with two impacts: Pushing the material through the nozzle will be harder, and the extruded material may not adhere well to the previously deposited layer. Preheating the filament with a laser ensures that the filament is thoroughly melted by the time it reaches the nozzle.

Tests showed that the researchers’ printhead can deliver at least two and a half times more force to the filament than standard desktop models can, and it can achieve an extrusion rate that’s 14 times greater.

The researchers aren’t ready to estimate the potential cost of their printer, the article reports. “Their prototype system costs about $15,000, two-thirds of which comes from the laser and motors. Thus, it’s unlikely to replace today’s personal desktop systems. But it should be cost-competitive with state-of-the-art professional systems while offering decreased operating costs from faster output.”

Click here to read the entire article.