Polyurethane, Meet 3D Printing

September 3, 2017 by Elliot Williams 9 Comments

3D printing makes prototyping wonderful. But what do you do when your plastics of choice just aren’t strong enough? For [Michael Memeteau], the answer was to combine the strength of a vacuum-poured polyurethane part with the ease of 3D-printed molds. The write-up is a fantastic walk through of a particular problem and all of the false steps along the way to a solution.

The prototype is a connected scale for LPG canisters, so the frame would have to support 80 kg and survive an outdoor environment. Lego or MDF lattice were considered and abandoned as options early on. 3D printing at 100% infill might have worked, but because of the frame’s size, it would have to be assembled in pieces and took far too long anyway.

The next approach was to make a mold with the 3D printer and pour the chosen polyurethane resin in, but a simple hollow mold didn’t work because the polyurethane heats as it cures. The combined weight and heat deformed the PLA mold. Worse, their polyurethane of choice was viscous and cured too quickly.

The solution, in the end, was a PET filament that deforms less with heat, clever choice of internal support structures to hold the stress in while being permeable, and finally pouring the polyurethane in a vacuum bag to help it fill and degas. The 3D-printed hull is part of the final product, but the strength comes from the polyurethane.

Mold-making is one of the killer apps of 3D printing. We’ve seen 3D prints used as molds for spin-casting hollow parts, and used as a sacrificial shell for otherwise epoxy parts. But for really complex shapes, strength, and ease of fabrication, we have to say that [Michael]’s approach looks promising.

Collider Prints Hollow Shells, Fills Them

December 21, 2016 by Elliot Williams 20 Comments

3D printing is full of innovations made by small firms who’ve tweaked the same basic ideas just a little bit, but come up with radically different outcomes. Collider, a small startup based in Chattanooga TN, is producing a DLP resin printer that prints hollow molds and then fills them.

That’s really all there is to it. The Orchid machine prints a thin shell using a photocuring resin, and uses this shell as the mold for various two-part thermoset materials: think epoxies, urethanes, and silicones. The part cures and the shell is dissolved away, leaving a solid molded part with the material properties that you chose.

This is a great idea for a couple of reasons. DLP-based resin printers can have very fine features, but they’re slow as dirt when a lot of surface area needs to be cured. By making thin-walled molds, this stage can go faster. The types of UV-curing resins out there for use in resin printers is limited by the need to photo-cure, while the spectrum of two-part plastic materials is much broader. Finally, resin printers are great for printing single topologically-simple objects, and molds are essentially just vases.

Continue reading “Collider Prints Hollow Shells, Fills Them” →

3D Printed Molds And Silicone Caulking

March 13, 2015 by James Hobson 36 Comments

Have you ever had a pair of ear buds fit perfectly out of the package? Probably not. Well, [Joe] decided to take matters into his own hands and cast his own silicone ear bud covers custom made for him.

The traditional route would have been to make an ear bud model, make a mold from it, cast a copy from it… etc, etc. But [Joe] wanted to try something else — he designed and 3D printed the two-part mold, and used plain old silicone caulking to fill it.

First he 3D modeled the ear bud covers in SolidWorks, then he had to learn how to design the mold for it, but luckily, there’s a handy tutorial. After printing the mold he opted to use 100% silicone caulking in order to make the part since he had some lying around the house. The problem is, this stuff can take days to cure — unless you mix in some cornstarch.

The golden ratio [Joe] found was about 5:1 silicone to cornstarch, which resulted in a cure time of about 20 minutes.

After curing you just need to trim off the excess silicone. In the molding process this is known as “flash”.

Since this is caulking he’s using, you’re going to want to wash off the part a few times because this type of silicone produces acetic acid as it cures.

The ear buds fit great and inspired [Joe] to try molding even more things, like a custom sleeping mask using the 3D scan of your own face!