May 10, 2016 | By Alec

While 3D printers do definitely provide users with unprecedented prototyping power, they do have one huge drawback: Speed, or a total lack of speed. There's no such thing as quickly seeing how a 3D printable design looks like in real life; even at the lowest settings, prototyping can take hours. Cornell University's Huaishu Peng and Rundong Wu were all too aware of this problem, and have developed a revolutionary prototyping solution. Called On-The-Fly Print, it's an incremental 3D printing setup that builds mesh prototypes in a manner of minutes. What's more, it does all that while you are still working on your CAD design and uses a rotational platform and a cutting tool to incorporate any alteration you can think of. A 3D printing system that truly deserves to be called a high-speed prototyping tool.

Designing an aircraft model with On-the-Fly Print in 10 minutes.

Huaishu Peng himself is no stranger to 3D printing, and has previously worked on numerous remarkable 3D printing solutions as a PhD student at Cornell. Among others, he realized a groundbreaking fabric 3D printer with Disney Research and even the D-coil wax extruder. But his latest project with fellow PhD student Rundong Wu is perhaps the most revolutionary of all, and will be unveiled at the CHI 2016 convention in San Jose, CA, today. It has also been detailed in a paper entitled 'On-The-Fly Print: Incremental Printing While Modeling'. Cornell professors Steve Marschner and Francois Guimbretière acted as supervisors and this work is supported by NSF.

As the PhD student explains to, he and Rundong Wu have sought to break through the barriers that are limiting 3D digital modeling. As they rightly say, design is almost completely a digital activity. You spend hours on a detailed design, and then wait hours to 3D print it. "Because the user cannot check the design early on, in many cases, this output is not ideal so it usually takes several iterations to complete the design process," he argues. A frustrating and familiar process. "So is it possible to create a 3D printing system that can print fast enough to keep up with the CAD design speed, so that CAD users can have a timely, low-fidelity physical preview while they design?" he wonders.

Fortunately, there is a precedent. Way back in 2014, professor Guimbretière worked on the WirePrint with Stephanie Müller from Hasso Plattner Institute, Berlin. This software solution generates low fidelity wireframe previews of designs that can be 3D printed on just about any 3D printer. Because of the open structures it generated, the WirePrint realizes prototyping speeds that are up to ten times faster than a regular print. For On-the-Fly Print, the PhD students have essentially optimized that wireframe concept and have packed it in a powerful platform that automatically starts 3D printing while you are modeling.

Print head design with extended extruder tip and mist cooling sprays.

5DOF add-on design to an off-the-shelf Delta 3D printer.

It almost sounds too good to be true, but On-the-Fly Print really enables 3D printing parallel to the use of CAD software. "As primitives are added to the digital model, our 3D printer instantiates them using a low-fidelity wireframe representation. During the creation of the digital model, the designer can remove the building platform [attached with magnets] from the printer and observe the model in the context of its future use. She can then return the model to the printer and further modify the digital model as needed while the printer synchronizes modifications to the physical model," the developers explain.

All of this is realized on a customized Mini Kossel delta 3D printer, driven by a Beagle Bone Black connected to a CRAMPS 2.0 module. Through numerous modifications and optimized build queues, it puts the completed prototype in your hand just minutes after you finish modeling. Part of that speed is realized by 3D printing thicker and fewer strands (1 mm thick) through an extended print head that reaches deeper into models. "Because our goal is to quickly offer low-fidelity tangible feedback, speed is more important than resolution," they explain. These thicker layers of ABS are solidified in seconds thanks to the addition of two water mist sprays. The result is a 3D printing setup that can realize 28 x 28 x 28 mm wireframe structures in as little as 32 seconds – two minutes faster than the WirePrint.

Speed comparison between the original WirePrint (a) and On-the-Fly Print (b).

But the machine's success obviously relies on the ability to add design modifications to any segment of the model – not just on the top. To add more degrees of freedom, the delta 3D printer is fitted on a circular acrylic rail with a 260mm radius that provides six degrees-of-freedom (DOF): five in motion and one for the extrusion system. This gives the print head access to almost any part of the model, something which is perfectly illustrated by the production of an airplane prototype in the clip below. By simply altering the angle of the prototype, additions can be made almost anywhere. Thanks to a retractable cutting blade, the system even allows for error corrections and subtractive operations to make new room for further additions.

Such a complicated setup obviously requires quite a bit of software backing. As the designers explain, the software needs to take care of all computation steps to allow for a complete focus on digital modeling. This is all provided by a custom Rhino plugin that immediately converts all geometric forms into 3D printable G-code. "For additive operations, this includes creating a mesh for the shape to be added as well as any connecting structure necessary; for subtractive operations and corrections, this includes converting the input into a cut operation and then creating any repairs necessary," they say.

What's more, their custom plugin even optimizes print queues to maximize printability without distracting you from design. Whenever a new geometric shape is placed on the print bed or attached to the first design and left unchanged for 5 seconds, the plugin decides it is ready for 3D printing. The plugin calculates its printability in regards to the existing model and determines if any cuts or angle changes need to be made. "As a default, our system will orient the model so that printing proceeds upward," they add. If a cut is necessary with the blade, supporting patches of filament are added where necessary, while a new contour is added to the opened region to 'heal' the completed cut. And all that is going on while you're working on some other part of the CAD file. Only additions that cause a collision between the model and the print head will not be completely printed, but you still get a fantastic idea of the state of your prototype.

Reordering. The user designs the bottom branch first (b) and the top branch later (c). Noticing that the print of the bottom branch will block the way for printing the top branch, the system reorders the print sequence (g, h).

Dinosaur legs are printed at an angle to avoid collision.

Example of omitted details. Printing the teapot handle would collide with body, so the system omits the part that would cause collisions and prints the rest.

All in all, On-The-Fly Print seems like a complete prototyping tool. While we were previously convinced that real-time 3D printing during design was nothing more than a utopian dream, Huaishu Peng and Rundong Wu have broken through barriers with their clever rotation setup and cutting tool. To be sure, some improvements still need to be made. No options for using the cutting tool to improve print head access, for instance, exist yet. But aside from a few little things, the On-The-Fly Print platform deals with each and every obstacle that impedes parallel production. It gives us a glimpse of the future of prototyping.



Posted in 3D Printing Application



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shin wrote at 5/10/2016 9:29:31 PM:

At this point someone should mention if you have a low poly mesh and haven't confirmed the subdivision modifier, you can do this to any mesh in seconds with the skin tool in blender, and then it will print a "wire frame" when you export the STL. Probably not the most refined way to do what's being discussed, but it gets the job done.

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