Fabbing and sintering objects from different materials

... here: [fabathome.mae.cornell.edu] is an interesting paper about fabbing (with a f@h-printer) and sintering objects fromm steel-powder-slurry.

It's very short, but touches some points we had discussions about - warping, shrinking, heated syringes, paste-extruding and such ...

Viktor

Well it is interesting, as long as you have a sintering furnace that can maintain an argon/hydrogen atmosphere that can operate at ~1,400C and the money to run it for 8 hours.

Mind, the idea is sound. It's just that Hod Lipson doesn't see to be acquainted with the concept of cost control.

You might want to look at this...

[home.c2i.net]

...and this...

[www.microwavekiln.com]

This one will hit 900C which will do aluminum, bronze and cast iron in small quantities.

Hi Forrest,

... replace the steel with other low-melting materials and you'll be on the way

I'm on a similar route with my 'room-temp-paste-fabbing' and have some possibilities around for heating samples until 600

Polysaccharide binder is most definitely sugar. Perhaps a similar mixture could be used a reusable support material.

BTW is there anyway to adjust the temperature of a microwave kiln?

Gene Hacker Wrote:
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>
> BTW is there anyway to adjust the temperature of a
> microwave kiln?
>

Yup. Adjust the amount of heat absorbing material in the melt enclosure.

I mean is it possible to practically adjust the temperature and the rate it changes so you can go through various sinter cycles?

Gene Hacker Wrote:
-------------------------------------------------------
> I mean is it possible to practically adjust the
> temperature and the rate it changes so you can go
> through various sinter cycles?


Many microwaves have variable wattage settings (often just high/low), and I imagine you could hack one to have a continuous range. It would take some calibration to translate energy in to heat production, but I think that is a practical approach.

Gene Hacker Wrote:
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> I mean is it possible to practically adjust the
> temperature and the rate it changes so you can go
> through various sinter cycles?
>
Sure. It's "possible". There is a company that makes high temperature (~1500C) microwave kilns out of kitchen microwaves. My suspicion is that the temperature sensor of one of those is the most expensive part of the whole thing. Consider what kinds of metals that you're going to have to use for such a thermometer for it to be able to handle those kinds of temperatures. Some of the stuff I've seen uses a synthetic ruby optical fibre and a Fabry-Perot sensor. Imagine!

Mind, microwave is the way to go. Conventional electric ovens use magnitudes more electricity to do the same job. Keep in mind that sintering is not a really fast process for the higher temperature metals and ceramics.

I'm the student responsible for this project. I've been browsing the RepRap forums periodically to look for good ideas we can be sharing especially that we are engaged in a major redesign.

Just to clarify a bit, though this project used the Fab@Home, it is not necessarily directed towards home use. We are well aware that high-temperature, controlled-atmosphere furnaces cost several times what a Fab@Home costs. But, this project is demonstrating an alternative to the existing methods for metal or ceramic fabrication which are at least as expensive (and incompatible with home use).

On the other hand, as some of you already pointed out, there are some possibilities for home use. It is possible to convert a home microwave into a high-temperature oven. There is even a paper which I can dig up if anyone is interested describing doing just this for sintering ceramics. You can get temperature control just the same way that many industrial temperature controllers do it, by pulsing the heat input. This kind of furnace still would not be capable of doing steels, but there are other metals or ceramics that could be done that are interesting.

As for the question of the speed of the sintering process, it is not necessarily as slow as described in the paper. The majority of that time is heating and cooling the furnace. The time required at temperature is only around 1 hour so in a rapid heating and cooling microwave furnace, total times can be much less than 8 hours.

I'm also glad to see that someone pointed out that the polysaccharide binder could be useful as a support material as we are also investigating this.

Also, the document referenced is just a conference poster. If any of you are interested, there will be a somewhat more detailed paper available soon.

Thanks,
Max

Edited 2 time(s). Last edit at 09/16/2008 11:38AM by maxlobovsky.

maxlobovsky Wrote:
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>
>There is even a paper which I can dig up if anyone
>is interested describing doing just this for sintering ceramics.
>
I'd be really interested in seeing that. Building a rig like that is something I've been itching to do for a couple of years now. The biggest mystery for me so far, though, is figuring out where you can buy powdered silicon nitride. I've had no luck whatsoever finding a source.

Hi Max,

i'm interested too!

I have two main areas for sintering ceramics or metallic compunds:
- first room-temp-fabbing and/or IR-presintering 'green' parts and finish in the kiln
- second combining paste-extruding and laser-sintering for fabbing ceramics with embedded conducting 3D-segments 'on the fly' ...

Viktor

> It is possible to convert a home microwave into a high-temperature
> oven... You can get temperature control ... by pulsing the heat
> input. This kind of furnace still would not be capable of doing
> steels, but there are other metals or ceramics that could be done
> that are interesting.

There's an interesting discussion elsewhere in these forums
(http://forums.reprap.org/read.php?70,14695 toward the bottom)
about the sintering of metal powder made of grains of 0.2 mm diameter. I think this could be done with a microwave oven, and if you choose the right metal (probably a question of oxidation) you might not need a controlled atmosphere around it. Sounds like a good idea to me.

I have a little trouble envisioning a switching circuit hefty enough to pulse-width modulate a microwave oven. But they must exist, since many microwaves use open-loop PWM to get different power levels. If you can find the internal switcher and use it yourself, that would be good. As used now, they aren't very quick, typically having an on-off period of ten or fifteen seconds, but they could perhaps be run quicker.

Hi ..

I've been reading the comments above and am also very interested and curious about all these possibilities.
I lay in Chemistry, but I've been thinking and I think the Sugar, water (distilled, burricada) more any type
of alkaline liquid (alcohol, methanol or other) may be useful for the production of 3D parts
the method Ultra_Violeta. Perhaps even more with the addition of a thin resin plus a catalyst
high speed. Methanol is highly reactive (Indy) and flammable and can accelerate catalysis or
crystallization of the mixture (Water more sugar and the thin resin). Think about it.

Thank you ..

Saulo Q.

InovaStar