Northwestern Spin-Out Launches Massive, Fast DLP 3D Printer
Michael Molitch-Hou posted on December 03, 2019 |

We’ve long known that 3D printing technology was going to continue improving, even after the bubble of 2014, but it continues to be exciting to watch these developments unfold. Seeing the technology get faster and bigger is particularly fun for the inner Tim “The Toolman” Taylor in all of us.

The enormous HARP 3D printer from Azul. (Image courtesy of Azul.)
The enormous HARP 3D printer from Azul. (Image courtesy of Azul.)

High Area Rapid Printing (HARP) 3D printing from a startup called Azul achieves both of these capabilities, producing objects 20 times the size and at 100 times the speed of some 3D printers. This results in 2,000 times the throughput of the most common industrial 3D printing technology.

To understand how this is possible, we reached out to Azul CEO and cofounder James Hedrick.

The Birth of HARP

HARP is a patent-pending form of digital light processing (DLP) that projects ultraviolet (UV) light to cure photopolymer resin. Azul’s first 3D printer featuring HARP technology stands at a massive 13 feet tall and can print up to half a yard per hour. Surprisingly, however, the process wasn’t developed with such a large scale in mind.


At the lab of Northwestern Chemistry professor Chad Mirkin, the team that would go on to establish Azul was actually aiming to 3D print tiny objects, according to Hedrick. “This project started with the intention to develop the world’s smallest 3D printer with nanometer resolution,” Hedrick said. “When we learned the obstacles facing 3D printers today, we applied our technology to a completely different scale to solve the problem. The biggest obstacle was the learning curve when going from studying printed parts that are too small to see, to fabricating a printer that is twice as tall as you are.”

What may be more impressive than the sheer size of the HARP 3D printer is its speed. Though the HARP system is 20 times larger than a standard DLP printer, it prints at 100 times the speed of a standard stereolithography (SLA) printer. This combines to give HARP a throughput that is 2,000 times greater than industrial fused deposition modeling, the most common 3D printing technology found in industrial settings today.

How Does HARP Work?

Of course, the technologies chosen by Azul for comparison help beef up HARP’s numbers, as SLA is much slower than DLP and FDM is slower still. Nevertheless, those numbers are impressive. So, how does Azul pull off such neck-breaking speed at such a jaw-dropping size?

Traditional forms of SLA and DLP cure resin onto a print bed before a mechanism is used to detach the print with each layer printed. To improve speed, newer forms of continuous DLP rely on specialty techniques to render this mechanical cleaving process obsolete. Carbon, for instance, uses an oxygen permeable membrane (which the firm refers to as a “dead zone”) to ensure that its continuous DLP technology can continuously UV-cure resin without the need to repeatedly detach the print from the bed.

Both traditional SLA/DLP and newer continuous DLP technologies are limited in part by the amount of heat generated during the printing process, with excessive speeds creating even greater heat. If a DLP or an SLA printer gets too hot, parts can deform or crack.

HARP overcomes both the mechanical cleaving and excess heat issues so that it can print even more quickly across a wider build area and with a broader array of materials. Instead of an oxygen-based dead zone, HARP uses a layer of constantly moving fluorinated oil (think Teflon) to minimize adhesion to the build plate.

A schematic of how the HARP process works. (Image courtesy of Science.)
A schematic of how the HARP process works. (Image courtesy of Science.)

Not only does the oil prevent sticking, but it is also used to regulate the temperature of the material. It can even be regularly filtered to remove any microparticles that may cause cloudiness in the final part.

Hedrick put it this way, “HARP utilizes a mobile interface that simultaneously performs two actions. First, the shear force from the motion of the interface enables the z arm to continuously pull vertically without adhesion to the bottom of the vat, while also dragging in fresh resin to replenish the vat. Second, this mobile interface regulates the temperature of the part by absorbing the heat generated from the chemical reaction that transforms the liquid resin into a solid part.”

Thermal regulation with mobile interface and active cooling. (Image courtesy of Science.)
Thermal regulation with mobile interface and active cooling. (Image courtesy of Science.)

The Advantages of HARP

Without worrying about excess heat, Azul was able to scale the 3D printing process. With surface adhesion taken care of, speed could be ramped up as well. The icing on the cake is the fact that HARP can also print with a wider variety of materials than some other continuous DLP processes.


“Continuous DLP printers rely on an oxygen-based ‘dead layer,’ which requires oxygen-sensitive resins in order to be used on their printer,” Hedrick said. “The HARP printer does not rely on a ‘dead layer,’ which means both oxygen-sensitive and -insensitive chemistries are possible on our system.”


Some materials the team was able to print, as described in a journal article for Science, were a hard polyurethane acrylate, an elastomeric butadiene rubber, and a silicon carbide ceramic, which would not have been possible using oxygen-dependent DLP technologies.


The Science article also mentions that surface ridging poses an issue when printing parts with thicker walls; however, Hedrick said that the team had resolved this issue. “When running at a fixed vertical speed and fixed interface flow rate, this does indeed become a limiting factor. Going beyond the paper, we are now implementing dynamic speed and flow rate that solves this limitation,” Hedrick said.

Azul is currently working with beta customers and plans to deploy full commercial release within 18 months, at which point the company believes it may be able to truly impact the larger world of industrial manufacturing.

“The specific application that we envision for this technology is the direct manufacturing of industrial-grade parts. Throughput has been the missing puzzle piece to bridge the gap between prototyping and manufacturing,” Hedrick said. “3D printing brings truly remarkable benefits to manufacturing such as customization and localized production. The problem has been that throughput and cost have been obstacles from a manufacturing perspective. We see this technology as a viable route to solving these problems. In doing so, it will enable manufacturers to deploy all the amazing benefits already seen in the prototyping industry.”

From the outset, it does look like Azul can deliver all that is necessary to turn polymer 3D printing into a truly manufacturing-grade technology: high throughput with industrial quality materials. Whether it can deliver on its promises is another matter.

To learn more, visit the Azul website.

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