One of the principal advantages of 3D printing is that it can be used to manufacture parts that cannot be made using any other technique giving the designer great freedom and permitting them to produce highly optimized parts. A typical example would be a strut optimized for minimum weight while maintaining adequate strength for the application.
Despite this advantage, one of the factors holding back the adoption of 3D printing in manufacturing, is speed. The output of today's 3D printers (across all technologies) is much slower than that of other manufacturing processes such as CNC milling, injection molding or forging. As a result, the cost to manufacture 3D printed parts is prohibitive and often outweighs any benefit from the optimized part (there are some exceptions, such as dental and hearing aid industries, where 3D printers have replaced manual labor and thus led to significant cost savings). If the speed of 3D printing increases, then it can be transformed into a viable manufacturing technique and open up a host of opportunities.
In this Instructable, we're going to look at how to increase the speed of a Digital Light Processing Stereolithography (DLP SLA) 3D printer, specifically the Autodesk Ember 3D Printer. The techniques that we describe here apply to the whole class of DLP SLA printers and can be replicated on many different systems.
The Ember printer is open which means it can be easily used to explore the limits of DLP SLA 3D printing. Through optimization of the printer settings, software, and material (without hardware modifications) it is possible to increase the standard print speed of Ember from 18mm/hour to 440mm/hour an increase by a factor of 24 for a particular class of geometries.
So why is this important and why as a software company is Autodesk conducting this research?
This research is the first step towards realising high speed 3D printing in a production environment.There are unique design rules that apply for high-speed DLP SLA that are beyond the capabilities of the current generation of design software. By researching in this field, our goal is to drive the additive manufacturing industry forward by developing a connected ecosystem that can provide designers and manufacturers the software they need unlock this class of technology.
We also want to demonstrate the power of an open approach to technology. If Ember were a closed system, then researchers would be unable to explore the limits of additive manufacturing. With Ember, we have created a powerful research platform that gives scientists, engineers and designers the opportunity to explore the future of additive manufacturing.
If this sounds interesting, read step 1 to learn about the science behind Ember. If you're already familiar with how DLP SLA works skip ahead to step 2 to learn how to configure Ember for high speed.
This is how the process works:
You may have noticed in the GIF above, that after each exposure the resin tray rotates back and forth 60 degrees, lets look at this in more detail.
As you expose and create each layer the hardened resin acts as glue, binding the build head to the optical window in the resin tray. The resins that are used in Ember are acrylates and methacrylates photopolymers that cure through a free radical photopolymerization process. To prevent the printed layer binding to the optical window we coat the window with a thin layer of Polydimethylsiloxane (PDMS), which is an oxygen rich silicon rubber. Free radical polymerization is inhibited by the presence of oxygen thus the oxygen in the PDMS prevents a very thin layer of resin, around 5 microns thick, from curing at the surface of the PDMS. This means that the printed layer is not adhered to optical window.
With thin, uncured layers of resin, there would be enormous suction forces exerted on the printed layer if you were to lift up the build head directly. These suction forces are inversely proportional to the thickness of uncured resin, in other words, the thicker the uncured layer of resin the lower the separation force. The suction forces are also proportional to the surface area of the part, the larger the part, the greater the forces.
To take advantage of this in Ember we use a shear separation mechanism. The resin tray rotates 60 degrees until the build head is no longer above the optical window with the uncured resin layer acting as lubrication and minimizing the shear force. After the rotation, the build head is directly above a channel that is deeper than the optical window. At this point, there are over 1000 microns of resin between the printed layer and the bottom of the resin tray, this means the suction force is reduced by a factor of 200 and thus becomes negligible, and you can lift up the build head with a minimal suction force exerted on the printed part. The tray rotates back 60 degrees and then next layer is printed.
We call this process Minimal Force Mechanics, and it allows Ember to reliably, produce parts with incredible detail, like the peacock feather above. BUT it takes around 2-3s per layer and thus represents about 50% of the print time and limits the print speed at 25-micron layers to 18 mm/hour.
If you're interested in learning more about the Ember mechanics, you can download the mechanical CAD and it explore it, the Ember CAD is shared under a Creative Commons Attribution-ShareAlike license.
I'm now going to show you that by optimizing the software and materials you can eliminate this separation step and print at 440mm/hour.