High-area rapid printing, or HARP, system (Northwestern University)
18 Oct. 2019. An engineering team developed a high-speed three-dimensional printing process that can produce large, detailed items of various materials on demand. Researchers from Northwestern University in Evanston, Illinois describe their process in today’s issue of the journal Science.
A team from the engineering and materials science lab led by Chad Mirkin aims to solve a continuing challenge facing additive manufacturing, the industrial application of 3-D printing. A promising technique known as stereolithography uses light-sensitive resins that react to ultraviolet light, and are stacked in layers on a vertically moving plate, resulting in a 3-D object made of stacked 2-D layers. Additive manufacturing today can quickly produce small items with stereolithography on demand, or larger items if given plenty of time. But there’s a trade-off between size and speed.
One reason for the trade-off is items produced with stereolithography use resins that stick to the printing surface and need to be repeatedly separated from the surface. More advanced systems inject a layer of oxygen between the print surface and printed item, called a dead layer, that prevents the item from sticking. Another issue with stereolithography is the high heat produced when ultraviolet light reacts to resins, a hazard to both operators and the printed item, which requires added components to dissipate the built-up heat. While these challenges can be overcome, they add more cost and complexity to printing systems.
To address both of these problems, Mirkin and colleagues devised a process they call high-area rapid printing, or HARP, using fluorinated oil spread on the printing bed where the ultraviolet light activates the resin. The commercially-available fluorinated oil does not mix with the resins, thus separates the printed material from the print bed. As a result, HARP system do not need injections of oxygen to prevent the item from sticking.
The fluorinated oil also serves as a heat exchange medium. In tests of the process, the researchers report using cooled fluorinated oil to absorb the heat and reduce temperatures on the print surface from as high as 180 degrees C to a more manageable 100 to 120 degrees.
Without the limits of oxygen injection and high heat build-up, the team designed a HARP system to 3-D print large items at faster speeds. The lab’s prototype HARP system is 13 feet high, with a 2.5 square foot print bed. Depending on the type of materials used, the HARP system can vertically print items as fast at 430 millimeters or 17 inches per hour. The researchers used HARP to produce items in a hard polyurethane acrylate plastic, a soft and stretchable butadiene rubber, and a silicon carbide ceramic. Because of the rubber’s viscosity and lower reactivity, print speeds with that material were slower.
“If we could print fast without limitations on materials and size,” says Mirkin on a university statement, “we could revolutionize manufacturing. HARP is poised to do that.” He adds that HARP systems can be on the market in the next 18 months. This brief video hosted by EurekAlert shows the HARP system in action.
Mirkin, with co-authors James Hedrick and David Walker, founded the company Azul 3D Inc. in Skokie, Illinois that licenses the technology from Northwestern and is developing HARP systems for the marketplace. Hedrick is the CEO of the three year-old company, with Walker serving as chief technology officer, and Mirkin as board chair.
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