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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.
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