Soooo... this is not metal. But it is performed in almost exactly the same way as metal.

Last month I visited the virtual foundry, the company that produces these metal filaments. And while I was there, I helped extrude a new kind of filament: Glass filled. 

And it has quickly become one of my favorites. It just has a lot of interesting properties: It’s lighter than PLA, has a high fill but is still flexible and very strong, looks cool, and unlike copper can be sintered overnight in one step (glass is already bound to oxygen, so you don't have to worry about oxygen). 

Here's what comes out of the printer: 

Check out that sparkle. When it prints, it does so super smooth with great detail! Clogs are a frequent issue, though on my creator pro with 0.4 mm steel nozzle. I even upgraded to an all metal hot end to try and fix it, which turned out not to help much. What did help, was lowering the temperature from 220 to 200 or less. I think that the plastic and glass has a tendency to separate when left sitting in the nozzle, and a lower temperature helps somewhat. I have properly taken off my nozzle and removed a solid plug of material at least a dozen times though.

My computer is broke so I can't take a proper scan of it, but I would like to (before and after sintering), because they look really cool.

Debinding and sintering trials: it actually only took two tries to get something to work. Units in Celsius:

Ramp to 0-204 over 30 minutes 

Hold at 204 for 2 hours 

Ramp to 482 over 2.5 hours 

Hold at 482 for 3 hours 

Let cool for 2 hours (possibly unnecessary) 

Ramp to sintering temperature over 4 hours 

Hold at sintering temperature for 2 hours

Sintering temps tried so far (first based on this paper). 700, 800, 900, 1000, 1100 Celsius.

Results:

700 just falls apart when you take it out.

800, 900, and 1000 are white and porous, with decreasing porosity and increasing strength:

You can see that the expansion during debinding is not yet a solved problem: 

But note that there IS isotropic shrink, which was totally unexpected to me — my understanding of sintering involves production of vapor (thanks to a prof who schooled me about it), which I didn’t think glass would do. It also isn’t fair to say that it “melts” at these temperature, but rather just softens. Either way, binder goes bye-bye and glass gets stuck together.

Here is a video (proper hackaday --- hint hint, tip line) where I use the porosity to make coffee:

I tried it so you don't have to! 

One problem is that the aluminum oxide refractory gets fused to the surface of the glass:

This is a problem because uhhh this is a problem. Especially for eventually making transparent pieces. So I’ve been experimenting with using magnesium sulfate as refractory material instead of aluminum oxide, with the idea that, even if it gets stuck, it would dissolve in water afterwards.

This worked but it shrank and became like plaster, being a pain to get out afterwards.

You can see the comparison though, in aluminum oxide on the left and mgso4 on the right. No sticking!

Next I want to take the temperature past 1100, the part where it starts to become solid glass, with the goal of transparency. I think this is possible to some degree --- there's a company that does this using resin, with nanoparticles of glass (the ones in here are a bit bigger, maybe ~50-100 ish microns across). So far it just blobs up. The pieces make that nice glass sound, though.