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Applying 2.5-axis milling constraints with generative design

3D printing shop uses generative design to improve its own additive capabilities

Image courtesy of PrintCity, MMU

Streamlining additive manufacturing

Situated on the campus of Manchester Metropolitan University in the northwest of England, Print City is a unique additive manufacturing facility that serves as a student workshop and lab, in-house service bureau, and contract manufacturer for a wide range of local and national customers.

“All kinds of people depend on us for 3D printing,” says Mark Chester, the innovation development manager for Print City. “We help engineering and product design students as well as those in fashion, textiles, chemistry, and many other fields. And we work with businesses who need help with 3D printing, scanning, and prototyping.”

Over time, Print City has acquired an extensive lineup of additive manufacturing capabilities, including fused deposition modeling (FDM), binder jetting, material jetting, metal printing, and stereolithography, among others. One of the most popular printers in the shop is a large-format FDM machine that feeds filament through an overhead tube.

“We had pretty good results, but we realized the machine wasn’t set up for our specific needs,” Chester says. “There was too much friction in the tubes feeding the head of the printer, because some of our filament reels weigh 5 kg or more. We wanted to mount the reels on top of the print head for a more direct approach. That meant we needed a much lighter, more versatile reel that was still quite strong. And then we realized we could use generative design to solve it.”

Finding the sweet spot

Generative design has a reputation for producing extremely organic designs. But it can also be constrained to create design ideas that align with a specific manufacturing technique. In this case, Chester was looking for a little bit of both.

“I went into Fusion 360 and started with unrestricted outcomes, just to see how light we could make the reel,” he says. “I wanted it to look very generative, so to speak, to show off those structures, and then iterate from there.”

The first round of ideas looked “amazing,” according to Chester, and were very lightweight. But they proved to be very difficult to manufacture, even when split into two more manageable halves.

“The support materials weighed more than the part itself, which didn’t make sense,” he says. “But knowing what sort of look we wanted, we were able to go back into Fusion 360 to reduce the support material as well as the printing time.”

Generative design capabilities within Autodesk Fusion 360 helped Print City optimize the design of a bracket holding the filament spool for one of its large-format 3D printers, which in turn improved final print quality.

Chester ended up splitting the reel into three parts: a base plate that attached to the printer and two sides that would hold the reel. By applying 2-axis and 2.5-axis constraints to the design, he was able to optimize for strength, weight, and manufacturability much more easily.

“It’s a little ironic because generative design is very popular for part consolidation,” Chester says. “But in this case it made more sense to split it up. We ended up choosing a 2-axis design for the base plate and a 2.5-axis design for the sides.”

The freedom of design constraints

The design Chester landed on weighs slightly more than the first iteration but is much easier to manufacture, requiring much less material overall — 407.91 cm3 compared to 1295.68 cm3 — and could be printed in less than half the time. Most important, the total cost was cut in half.

“With Fusion 360, you can easily create geometry that is simple enough for 3D printing, even though you’re working with generative design,” Chester says. “The big takeaway for us is that you can utilize different constraints to produce better results, regardless of your intentions. In other words, you can use CNC constraints for an additive part.”

Using 2-axis and 2.5-axis constraints, PrintCity was able to optimize the filament spool bracket for strength, weight, and manufacturability.

The software also streamlined the workflow, allowing Chester to make relatively minimal modifications to the generative simulation in order to produce ready-to-print CAD files. All he had to do was mirror one side of the base plate to the other to make it more structurally sound, then go into the splines of the holders and increase the thickness slightly for optimal strength.

“It was good to go, pretty much straight from Fusion 360,” he says. “We put the finished reel on our big printer and it worked very well — much better than the original manufacturer’s components. We’re getting a better feed into the extruder and our final print quality is noticeably better.”

Gaining a competitive edge

Chester has found that moderation is an important consideration when working in generative design. If the initial resolution is set too high in the study settings, he notes, the results can take too long to return. But by using a setting slightly over the default, the parts come back more quickly.

Constraining the filament spool bracket to the 2.5-axis design significantly reduced the manufacturing time.

“I’ve played around with different settings to make the results come back quicker,” he says. “It’s most convenient for us to let the simulation do its work overnight. Of course, it’s nice that it happens in the cloud, so it doesn’t tie up resources on our machine. That’s a big plus for me.”

Of course, Fusion 360 is also an important part of Print City’s educational capabilities, giving students with very little CAD experience a way to interact with enterprise-grade tools after only a few hours of instruction. At the same time, it is robust enough to help Print City save time and money while strengthening its competitive position.

“Large-format additive manufacturing really makes Print City stand out in our market,” Chester says. “We can do bigger and better projects with it. Improving print quality is extremely important for us, and this project shows how small changes can make a big difference.”

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