Silicone Molds for Stove-Top Metal Casting

Casting metal parts from 3D-printed plastic or Styrofoam models is all the rage these days, and for good reason — casting is a way to turn one-offs into mass-produced parts. Seems like most of the metal casting projects we feature are aluminum in sand molds, though, so it’s refreshing to see a casting project using silicone molds to cast low-melting point metals.

Don’t get us wrong — sand-cast aluminum is a great method that can even be used to build a lathe from scratch. But not everyone wants to build a foundry and learn the sometimes fussy craft of creating sand molds. [Chris Deprisco] wanted to explore low-melting point bismuth alloys and set about making silicone rubber molds of a 3D-printed Maltese falcon. The bismuth-tin alloy, sold as a substitute for casting lead fishing weights, melts on at 281°F (138°C) and is cool enough for the mold to handle. Initial problems with bubbles in the cast led to a pressure vessel fix, and a dull, grainy surface was fixed by warming the mold before the pour. And unlike sand molds, silicone molds are reusable.

Of course if aluminum is still your material of choice, there’s no need for a complicated foundry. A tuna can, a loaf of bread, and a handful of play sand is all you need to make custom parts.

Continue reading “Silicone Molds for Stove-Top Metal Casting”

A Flexible Sensor That Moves With You

If you have a project in mind that requires some sort of gesture input or precise movements, it might become a nettlesome problem to tackle. Fear this obstacle no longer: a team from the Wyss Institute for Biologically Inspired Engineering at Harvard have designed a novel way to make wearable sensors that can stretch and contort with the body’s natural movements.

The way they work is ingenious. Layers of silicone are sandwiched between two lengths of silver-plated conductive fabric forming — by some approximation — a capacitance sensor. While the total surface area doesn’t change when the sensor is stretched — how capacitance sensors normally work — it does bring the two layers of fabric closer together, changing the capacitance of the band in a proportional and measurable way, with the silicone pulling the sensor back into its original shape as tension relaxes. Wires can be attached to each end of the band with adhesive and a square of thermal film, making an ideal sensor to detect the subtlest of muscle movements.

Continue reading “A Flexible Sensor That Moves With You”

Self-assembling Polymers Support Silicone 3D Prints

We all know what the ultimate goal of 3D printing is: to be able to print parts for everything, including our own bodies. To achieve that potential, we need better ways to print soft materials, and that means we need better ways to support prints while they’re in progress.

That’s the focus of an academic paper looking at printing silicone within oil-based microgels. Lead author [Christopher S. O’Bryan] and team from the Soft Matter Research Lab at the University of Florida Gainesville have developed a method using self-assembling polymers soaked in mineral oil as a matrix into which silicone elastomers can be printed. The technique takes advantage of granular microgels that are “jammed” into a solid despite being up to 95% solvent. Under stress, such as that exerted by the nozzle of a 3D printer, the solid unjams into a flowing liquid, allowing the printer to extrude silicone. The microgel instantly jams back into a solid again, supporting the silicone as it cures.

[O’Bryan] et al have used the technique to print a model trachea, a small manifold, and a pump with ball valves. There are Quicktime videos of the finished manifold and pump in action. While we’ve covered flexible printing options before, this technique is a step beyond and something we’re keen to see make it into the hobby printing market.

[LonC], thanks for the tip.

3D Printing With Yarn and Silicone

This one is apparently a few years old, but the idea looks so good that we’re left wondering whatever happened to it.

[Seyi Sosanya] made what amounts to a 3D printer, but one that prints in a unique way: wrapping yarn around pillars and then post-dipping them in a silicone glue. The result is a tough, flexible 3D mesh that’s lightweight and looks fairly resilient. We’re not at all sure what it’s good for, but watching the video about the project (embedded below) makes us want to try our hand at this sort of thing.

So what happened? Where did this project go? Is anyone else working on a glue-plus-fabric style printer? Is anyone doing this with carbon fiber and epoxy? We can also imagine that with the right adhesive this could be used less like a loom and more like a traditional FDM machine, although weaving the layers together may provide additional strength in what would be the Z direction, and for that you’d need the supports.

Continue reading “3D Printing With Yarn and Silicone”

Flexible, Sensitive Sensors from Silly Putty and Graphene

Everyone’s favorite viscoelastic non-Newtonian fluid has a new use, besides bouncing, stretching, and getting caught in your kid’s hair. Yes, it’s Silly Putty, and when mixed with graphene it turns out to make a dandy force sensor.

To be clear, [Jonathan Coleman] and his colleagues at Trinity College in Dublin aren’t buying the familiar plastic eggs from the local toy store for their experiments. They’re making they’re own silicone polymers, but their methods (listed in this paywalled article from the journal Science) are actually easy to replicate. They just mix silicone oil, or polydimethylsiloxane (PDMS), with boric acid, and apply a little heat. The boron compound cross-links the PDMS and makes a substance very similar to the bouncy putty. The lab also synthesizes its own graphene by sonicating graphite in a solvent and isolating the graphene with centrifugation and filtration; that might be a little hard for the home gamer to accomplish, but we’ve covered a DIY synthesis before, so it should be possible.

With the raw materials in hand, it’s a simple matter of mixing and kneading, and you’ve got a flexible, stretchable sensor. [Coleman] et al report using sensors fashioned from the mixture to detect the pulse in the carotid artery and even watch the footsteps of a spider. It looks like fun stuff to play with, and we can see tons of applications for flexible, inert strain sensors like these.

Continue reading “Flexible, Sensitive Sensors from Silly Putty and Graphene”

A Short Introduction to Staking and Potting

Staking and potting are not often used in the hobby electronics world, not really entering to the common vernacular. However, everyone who’s ever busted out a glue-gun to convince that dang wire that keeps coming loose to stay has done it.

However, as [Sean Thomas] touches on, staking is not necessarily as easy as a dob of hot glue. There is a method to the madness. [Sean] gives some examples in pictures, but also directs people to the excellent NASA standard methods for staking. It’s surprising how many unintuitive caveats there are to the proper technique.

Potting, or covering everything in epoxy forever, is a great way to get a waterproof, unserviceable, and practically mechanically invincible circuit. The big challenge in potting is picking the right material. A soft silicone, for example, might transfer an unexpected force to an unexpected section of the circuit and cause a mechanical failure. A nice hard epoxy may be too insulating and cause a thermal failure. The standard RTV from the big box store has acetic acid that will eat your components.

These two techniques that come in handy when you need them and worth the bit of reading it takes to get familiar. Have you used either in your own workshop? Let us know the application and the material/techniques you have tried in the comments below.

DIY Nozzle Socks For Your 3D Printer

If you have a 3D printer, your nozzle and heater block are invariably covered in a weird goo consisting of decomposed and burnt plastic. There’s only one way around this – a nozzle sock, or a silicone boot that wraps around the heater block and stops all that goo from accumulating.

Right now, E3D sells silicone nozzle socks for their normal-sized heater blocks, with a release for their maxi-sized Volcano blocks coming shortly. [Ubermeisters] couldn’t wait, so he designed a 3D printed mold to cast as many Volcano nozzle socks as he could ever need.

The mold itself is taken from the mechanical drawings of the E3D Volcano hotend, printed in Proto Pasta HTPLA. To create the nozzle sock, this mold is filled with a goo made from GE Silicone I, mineral spirits, plaster of Paris, carbon powder, aluminum powder, titanium microspheres, and bronze powder colorant from Alumalite.

The mold is sprayed with release, filled with silicone goo, and slowly brought together. After a few hours, the silicone has cured, can be removed from the mold, and the flash can be cut away from the finished part. The end result is great — it fits the Volcano hotend well, and shouldn’t be covered in melted, burnt plastic in a week’s time.

All the files for the Volcano nozzle sock mold can be found on YouMagine. Alternatively, you could wait another month or two for E3D to release their ‘official’ Volcano nozzle sock.