Mar 10, 2016 | By Alec
3D printing has so many advantages, that you might almost completely forget about its biggest disadvantage: speed, or lack thereof. It’s one of the most significant factors holding back adoption of 3D printing as a legitimate manufacturing tool. Fortunately, several ongoing projects are working to optimize that speed, and Autodesk has just shared a handy guide for optimizing their own Ember 3D printer through software and material optimization and exploiting the very nature of resin 3D printer. Through their approach, they managed to reach top speeds of 440 mm per hour, 24 times faster than the original 18 mm per hour.
As they explain in their guide, the lack of speed is a terrible bottleneck. “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,” they say. “If the speed of 3D printing increases, then it can be transformed into a viable manufacturing technique and open up a host of opportunities.”
Though this will require complete hardware and software optimization to realize, they are absolutely right to point out that something as simple as clever design can go a long way. This is illustrated in an insightful tutorial, that every owner of a resin-based 3D printer should check out. “The techniques that we describe here apply to the whole class of DLP SLA printers and can be replicated on many different systems,” they say. “We want to continue advancing the state of additive manufacturing and we expect the best advances in manufacturing processes to come from approaches that combine hardware, materials, and software. […] 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.”
While there are a few steps involved in optimizing your 3D printer, as you can see in the tutorial on Instructables, the core solution can be found in the resin 3D printing process itself. The resin layers produced by the Ember are, of course, lifted out of the bed and are subjected to an enormous suction force from the resin. “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,” they explain.
To minimize those forces, a shear separation mechanism is utilized called Minimal Force Mechanics. In a nutshell, it reduces suction forces by rotating the resin tray. “It allows Ember to reliably, produce parts with incredible detail. 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,” they say. Through this tutorial, that separation step is removed all together, with the optimization of software and materials enabling separation instead.
The first solution essentially consists of using another type of resin, called PR48-High-Speed. It results in thicker layers and cures much faster. You will, however, have to tune the existing PR48 resin yourself – for which you can find help in the tutorial. “The UV blocker concentration in PR48-High-Speed has been reduced by a factor of 4 compared to PR48 to allow it to cure quicker and to a deeper depth,” they say.
Step two consists of configuring the Ember 3D printer, which you can do through emberprinter.com or by SSH into the printer and editing the file /var/smith/config/settings. Simply follow the steps in the tutorial to eliminate the separation step and start printing at 250 micron layers. Then download the supplied example file (featuring a lattice structure that reduces the surface area per layer), and you can actually 3D print at tremendous speeds.
It’s not magic. Key is the lattice structure that reduces the global surface area to less than 15% of a slice. “The global surface area must remain below 15% so that the suction forces, which remember are proportional to surface area, do not become greater than the strength of the cured resin, the tear strength of the PDMS window and the normal force that the linear drive and motor can deliver,” they explain. Any higher, and the model fails. The optimized resin, meanwhile, enables quicker curing and a deeper depth by reducing the photo-inhibitor.
Of course this is not a magical solution for quick 3D printing, as the geometry is several limited to the global surface area percentage, the local surface area, the rate of change of position of local surface area, and the strength of the cured material. This rules out a lot of prints immediately. “For a start, you can't print standard DLP SLA parts like dental restorations, hearing aids or rings. Even thin walled parts like ear shells and dental copings have too much surface area per layer to work (at least on Ember). We have found that all the parts printed using this technique need to be thin strutted lattices,” they say.
But there are some possibilities. The Spark team have developed a CAD tool that transforms your solid files into lattice structures that can be 3D printed using this quick method. “For example, if we take the ubiquitous Stanford Bunny we can create a lattice representation and then use Print Studio to slice it for Ember, but it’s hard to control the end product using this technique. To successfully design for high-speed DLP, you need design software that understands the process, the hardware and materials,” the Autodesk team says.
But instead of seeing this as a simple trick for quick 3D printing, this tutorial can also been seen as a new approach for 3D printing optimization. It’s not just about hardware or materials; there’s still a whole design dimension that can be taken advantage of. “That’s why we're building a connected ecosystem of hardware, software and materials so we can deliver production ready additive manufacturing workflows,” they conclude.
Posted in 3D Printer
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