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Microwave sintering

Posted by dudesom 
Microwave sintering
March 14, 2013 09:10PM
This has probably been gone over before but I couldn't find it after searching so I thought I'd ask:
Has anyone tried sintering powdered aluminum/steel/copper with a microwave oven's magnetron?

[www.accessscience.com]

I just happened to bump into this page today and I read the bit at the end about powders being microwave absorbent when fine enough. Would a vacuum chamber still be necessary?
VDX
Re: Microwave sintering
March 15, 2013 12:01AM
... there were some test for sintering complete 'green' parts made of metal powder and an organic binder ... but magnetrons can't be focussed enough to be usefull for 3D-printing.

Read for MASER instead - this is a sort of laser, amplifying/resonating microwaves ... but not really in our actual DIY-scope ...


Viktor
Re: Microwave sintering
March 15, 2013 10:27AM
Ah sorry then. For some reason I was thinking magnetrons functioned like MASERs. Thanks for setting me strait.
Re: Microwave sintering
September 01, 2014 02:15AM
This seems to me not quite the dead end VDX implies. With reported 1000 C generated in conventional microwave ovens from some of the foundry experiments I have read about it seems entirely possible to sinter useful metal parts in bronze for example.
You would still probably need a reducing atmosphere to prevent oxidation at the particle surface, but this seems worth investigation.
Re: Microwave sintering
December 18, 2014 02:53PM
It just occurred to me, while Microwaves might be bad for sintering metal, would it be feasable to print water on layers of well-dried nylon powder and then put the whole block in a microwave, melting and fusing the selectively moistened plastic and leaving the dry powder undisturbed? If it works it might be a best-of-both-worlds compromise between SLS and powder-and-binder printers?

If dry nylon powder is still heated by (or opaque to) microwaves, is there a hydrophilic thermoplastic that might work with this kind of method?

Edited 1 time(s). Last edit at 12/18/2014 02:53PM by Feign.
VDX
Re: Microwave sintering
December 18, 2014 03:26PM
... this sort of 'complete layer sintering' is better done with SIS (Selective Inhibition Sintering) or layer sintering with an IR-heater.

With SIS you'll print only a separation contour line with a salt solution, then heat the complete surface with a moving IR-heater, so all dry particles melts and fuses together, while the 'salted' particles stays separated through the microscopic salt crystals on the surface preventing fusion.

In the layer sintering you'll print all parts, that should melt, with black paint - then move an IR-heater over the surface, that only melts the black, good heat-absorbing areas, but let the white areas untouched ...


Viktor
Re: Microwave sintering
December 18, 2014 08:28PM
The behaviour of powdered metal in microwave sintering is not really a problem. Indeed some improved properties are possible using microwaves. See Microwave Sintering of Metallic Materials.
The other thing to be aware of is that materials my be transparent to the microwave at x temp but are not at an elevated temp. Therefore intelligent use of a suseptor (think crisper) can raise the temperature of the target to the point where it takes over.
I like the idea of microwaves because of the efficiency, the availability, and the hackablity.

I also like the Idea of separating the build and sinter phases. First it allows for independent optimization. If I don't need atmosphere and temperature control in my build area I can optimize my build platform for speed and precision. I can then optimize the sintering environment to handle those tasks. Now I can work with a variety of materials both binders and base to optimize between the two. This allows for an iterative process that can be distributed to the community. This would also allow for the development of a filaments that could produce acceptable parts.
Re: Microwave sintering
December 24, 2014 09:15PM
SIS - that's the same as the announced HP powder bed printer that uses the ink bar and thermal fuser, right?

I'm working in a similar vein, but on a sugar powder bed that uses sugar and binder, and will use a halogen lamp to fuse/dry each layer after printing. I'm working on a design where the part z layer has multiple powder passes, since the binder shrinks the powder thickness when applied and baked.

No parts printed yet (z piston woes) but it's the direction I am investigating.
Re: Microwave sintering
May 01, 2017 04:21PM
See this filament:
[shop.thevirtualfoundry.com]
They say it is possible to sinter to solid metal using a klin.
Why not using a microwave klin? There are on the market mani available for glass. And they are pretty cheap. Anybody tried?
Re: Microwave sintering
May 01, 2017 04:33PM
Interesting [techcrunch.com]
VDX
Re: Microwave sintering
May 01, 2017 11:58PM
... it's not so easy to get dimensinal accurate parts with this type of metal powder filled filaments or powders.

Read this part:

Quote

The plastic is loaded with 60% metal powder and a two-part plastic system.
The primary plastic binder is then dissolved out of the part.
This creates a 20% reduction in material, and turns the part into a sponge.
Next you put it into a sintering oven.
The oven burns off the remaining 20% plastic through the sponge structure (in an environment tuned for the metal) and then brings the part very close to the melting temp.
There are four methods of mass transports, but the net effect is that the atoms diffuse together (sinter), the part shrinks by 20%, and you get a fully dense part (in casting terms, this is 98% or more).

You'll get around 20% percents shrinkage of the parts ... and even this percentage is not accurate, but can vary some percents up or down.

For design parts this won't be problematic - simply design the object bigger ... but what, if you need construction- or dimensional accurate replacement parts confused smiley

Comercial manufacturers solve this by CNC-milling the solidified parts to the accurate end dimensions ...

Edited 1 time(s). Last edit at 05/02/2017 12:01AM by VDX.

Viktor
Re: Microwave sintering
May 02, 2017 08:10PM
yeah kinda useless, the 20% reduction in material might be able to be used in a good way, but size changing not so good, still saving for the CNC, opportunity getting closer but still just out of reach, Not done any printing for about a month, one part yesterday, hoping a CNC would get much more use as it's a little too expensive to have sitting idle.
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