Ember Optimized for (More) Rapid Prototypes
Roopinder Tara posted on March 24, 2016 | 7317 views

At the Autodesk 3D printing press event that recently took place at the company’s Pier 9 office in San Francisco, Pierre Lin, a principal engineer at Autodesk, hit the start button on two Ember 3D printers. A live demo is not something most 3D printer vendors would perform, given a startlingly high failure rate for most 3D printers. But one of these Embers had been tweaked to perform for optimized speed. Whereas the one on the left was making a part at the usual (grass growth) speed, the one on the right was growing an object right before our eyes. Printing in full view of the assembled media, a lattice structure was lifted out after a little more than an hour.

The optimized ember printed at a speed of 440mm/hr. versus the 18mm/hr. of its slower counterpart. (Image courtesy of Roopinder Tara.)
The optimized ember printed at a speed of 440 mm/hr. versus the 18 mm/hr. of its slower counterpart.

True to the open-source nature of their 3D printer, Autodesk reveals exactly how that 24x speed improvement has been achieved in a highly detailed guide published on their Instructables DIY platform. That way, other Ember users or even owners of other 3D printers that rely on similar technology can push the speeds of their own machines. Interestingly enough, not one of the changes made to Ember was hardware related—no upgrades in motors or electronics—just a unique solution to the problem of suction.

Autodesk’s Ember 3D printer printing at 24 times its normal speed.

To understand how they made it faster, it’s essential to know how the Autodesk 3D printer works. The Ember is a digital light processing (DLP) stereolithography printer, meaning that it shines a digital projector onto a vat of UV-curable resin in order to fabricate objects. In the case of Ember, the projector shines light below the vat through an optical window, hardening the resin into the shape of a given layer, and the print bed is lifted upwards out of the resin. To prevent the print from adhering to the optical window, a 5-µm-thick layer of polydimethylsiloxane (PDMS) silicon rubber coats the bottom of the vat. However, if the print bed were to simply lift upwards, the suction forces between the uncured resin and the hardened print would cause the object to snap off the bed—that, or the silicon would tear or the z-axis on the printer would jam.

The resin tray of the Ember 3D printer rotates by 60 degrees with every layer to decrease suction forces. (Image courtesy of Autodesk/Instructables.)
The resin tray of the Ember 3D printer rotates by 60 degrees with every layer to decrease suction forces. (Image courtesy of Autodesk/Instructables.)

Tackling this issue meant increasing the ratio of uncured resin to cured resin, as doing so also decreases the suction forces. For that reason, the vat is rotated by 60 degrees with every layer, moving the print away from the optical window to an area where there is a bit more uncured resin (more than 1,000 µm worth). In turn, the suction forced is cut by 200 times, but rotating the vat takes about two to three seconds with each layer, representing nearly 50 percent of the total print time and limiting the print speed to 18 mm/s when printing 25-µm layers. Get rid of the suction andthis vat rotation, and Ember can print 24 times faster at an astounding 440 mm/s.

The formula for success involves, in addition to eliminating the vat maneuver described above, changing the recipe of the resin used and the geometry of the part printed. Everything about Ember is open source, including the material. If you’ve got a background in chemistry and your own lab, you can whip up a batch of Ember’s photopolymers at home, including their newest PR48-high-speed formulation for ultra-rapid 3D printing. This material has been engineered to harden more quickly and at thicker layers through a drop in the concentration of UV blocker present in the resin.

This lattice structure is necessary for high-speed 3D printing, as the reduced surface area limits the amount of suction force applied as the print is lifted from the resin vat. (Image courtesy of Autodesk/Instructables.)
This lattice structure is necessary for high-speed 3D printing, as the reduced surface area limits the amount of suction force applied as the print is lifted from the resin vat. (Image courtesy of Autodesk/Instructables.)

As it turns out, the lattice structure the Ember had printed at the press event was not chosen randomly but was picked for its decreased surface area. The less surface area a printed object possesses, the greater the forces of suction are mitigated. Printing such an object prevents the need for rotating the vat, as the suction forces are not strong enough to break the print, jam the z-axis or tear the silicon rubber. With this geometry, Ember can lift the print directly from the vat, saving two to three seconds per layer.

The final component to making Ember faster does involve a tiny bit of cheating. Instead of printing with 25-µm layers and very fine detail, the Autodesk team bumps the resolution up to 250-µm layers. This causes Ember to 3D print 10 times faster, but at much rougher output quality.

Autodesk’s Lattice Infill tool can convert any CAD file into a lattice-filled object for potential use with high-speed DLP 3D printing. (Image courtesy of Autodesk/Instructables.)
Autodesk’s Lattice Infill tool can convert any CAD file into a lattice-filled object for potential use with high-speed DLP 3D printing. (Image courtesy of Autodesk/Instructables.)

All of this adds up to a remarkably fast printing experience, but it does have some limitations. For instance, the geometry is constrained to similar lattice-type structures that reduce both the overall surface area of an object, as well as the surface area of individual parts of the object. With software such as Autodesk Dreamcatcher or even this simple Lattice Infill tool, it’s possible to generate such geometries into existing CAD models. DLP 3D printing, however, is often used in the jewelry and dental industries to 3D print objects with much finer details than 250 µm as well as solid structures. These are often 3D printed and cast in metal, and this high-speed printing technique likely wouldn’t be able to produce such output.

That doesn’t mean that all is lost for Autodesk’s high-speed 3D printing technique. Everything about the printer could be made stiffer so that Ember can resist the suction forces as it more quickly lifts the print bed out of the resin. Increasing the thickness of the initial inhibition layer could also reduce the suction forces. And lowering the viscosity of the resin and making it even more UV curable would further allow for increased speed.

In the meantime, Ember users have a complete guide for 3D printing a very specific type of object at very fast rates. Interestingly, this process may not be as quick or versatile as the continuous liquid interface production (CLIP)technology implemented by Silicon Valley startup Carbon, in whom Autodesk invested $10 million last year. This technology uses an oxygen-permeable window for frictionless DLP 3D printing. Still, the experiment in high-speed printing can provide useful information for other DLP 3D printer manufacturers to make their own processes more rapid as well. Autodesk sees this open-source approach as driving innovation in the 3D printing industry overall. And what’s good for 3D printing is good for all of us, isn’t it?

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