3D Printers

Northwestern researchers develop large scale SLA HARP 3D printer with record throughput

Researchers at Northwestern University in Evanston, Illinois, have developed a new 3D printer that they claim can print half a yard (457.2 mm) in an hour, a reportedly record-breaking throughput in 3D printing. 

Called HARP (high-area rapid printing), the speed and size of the system, standing at 13-feet (3962 mm) tall, can allow users to 3D print objects “the size of an adult human” on demand, according to the research team. Utilizing stereolithography technology, HARP can be used to produce parts for medical devices, cars, airplanes, construction and more. 

Chad A. Mirkin, a professor at Northwestern and leader of HARP’s product development, predicts that the novel 3D printer will be commercially available in the next 18 months. It will be provided through 3D printing outfit Azul 3D, a spin-off of Northwestern University launched by Mirkin and his colleagues. He also claims that HARP can potentially have a large impact on the manufacturing industry overall: “3D printing is conceptually powerful but has been limited practically.”

“If we could print fast without limitations on materials and size, we could revolutionize manufacturing. HARP is poised to do that.”

The HARP 3D printing process. Photo via Northwestern University.
The HARP 3D printing process. Photo via Northwestern University.

Patented SLA utilizing ‘Liquid Teflon’, volumetric throughput of 100 liters per hour

HARP is based on a patent-pending version of SLA technology that aims to overcome the limits of 3D printing. The researchers claim to have developed a solution for resin-based 3D printers that are either limited in size in order to increase printing speed, or conversely hampered by low throughput for a larger build volume. 

Explaining the limitations, the Northwestern research team pinpoint the issue in the heat generated by SLA 3D printers when running at fast speeds, which causes printed parts to crack and deform. The heat becomes more intense as the 3D printer size gets bigger.

Northwestern’s solution to the problem lies in a nonstick liquid that behaves like liquid Teflon, known as a fluorinated oil. HARP’s 3D printing process uses a projected light through a window that solidifies the resin on top of a vertically moving plate. The nonstick liquid then flows over the window in order to remove the heat, and then circulates it through a cooling unit, therefore maintaining temperatures at high print speeds. As it is nonstick, the resin resists adhesion to the print bed, which increases print speed as parts do not have to be cleaved from the bottom of the print-vat. 

Close-up of 3D printed object emerging from the vat. Photo via Northwestern University.
Close-up of 3D printed object emerging from the vat. Photo via Northwestern University.

Carbon’s Continuous Liquid Interface Printing (CLIP) technology also prevents adhesion between part and the bottom of the print vat. The process uses oxygen to create a “dead layer”, which in turn enables continuous 3D printing with increased print speed. However, the researchers explain that CLIP technology is still subjected to the limitations caused by heat in the 3D printing process. “Our technology generates heat just like the others,” Mirkin explains. “But we have an interface that removes the heat.”

Thanks to its liquid Teflon solution, the HARP 3D printer has been able to achieve continuous vertical print rates exceeding 430 millimeters per hour, with a volumetric throughput of 100 liters per hour. 

No more warehouses

Currently, a prototype, the HARP 3D printer is 13-feet tall with a 609.6 mm by 381 mm print bed, capable of printing both large parts, and many small objects at once. Mirkin posits the system’s capabilities as a solution to the space taken up by warehouses in common manufacturing processes today. “When you can print fast and large, it can really change the way we think about manufacturing,” Mirkin adds. “With HARP, you can build anything you want without molds and without a warehouse full of parts. You can print anything you can imagine on-demand.”

HARP can print soft, flexible parts, in addition to hard, durable objects. Photo via Northwerstern University.
HARP can print soft, flexible parts, in addition to hard, durable objects. Photo via Northwestern University.

The HARP 3D printer will be commercialized by Azul 3D, a startup company that has been operating in stealth mode over the last few years. It was founded by Mirkin alongside David Walker and James Hedrick, both researchers in Mirkin’s Northwestern laboratory. Hedrick is the CEO of Azul 3D, while Walker acts as CTO and Mirkin Chairman of the Board. 

“Obviously there are many types of 3D printers out there — you see printers making buildings, bridges and car bodies, and conversely you see printers that can make small parts at very high resolutions,” explains Walker. “We’re excited because this is the largest and highest throughput printer in its class.”

Large scale SLA 3D printing

HARP is not the first 3D printer promising larger-scale solutions for stereolithography technology. 

RPS, an industrial 3D printing specialist based in the UK, develops the NEO800 3D printer, a stereolithography system that maintains a maximum vat fill capacity of 555 liters (630kg) of material. The print area of the NEO800 is 800 x 800 x 600mm, with the machine itself measuring 1350 W x 1630 D x 2300 H mm.

In April 2019, Massachusetts based 3D printer OEM Formlabs announced the availability of its Form 3L 3D printer, which represents the company’s entry into large-scale SLA. The Form 3L’s build volume measures at 335 W x 200 D x 300 H mm. 

The Northwestern team’s study, “Rapid, large-volume, thermally-controlled 3D printing using a mobile liquid interface,” is published in the journal Science. Mirkin is the George B. Rathmann Professor of Chemistry in Northwestern’s Weinberg College of Arts and Sciences and director of the International Institute of Nanotechnology. David Walker and James Hedrick co-authored the paper. 

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Featured image shows timelapse of HARP 3D printing process, sped up x100. Video via Northwestern University.

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