Powder bed with Microwave post-process

Here my an idea:
A typical powder bed machine using powdered PLA, but instead of spraying epoxy, the print head sprays some type of dopant that absorbs microwaves. once the print is finished, the bed is exposed to microwaves, which heats the doped areas until the plastic fuses.

I'm pretty sure PLA is transparent to microwaves at the wavelengths in a home microwave, since food containers made of it can be microwaved. Water would be an easy choice for a dopant, except it will evaporate and cause bubbles. i think finding a liquid carrier for a colloid or suspension of dopant might be tricky. something that evaporates very quickly and doesn't dissolve the plastic.

dopant would probably be ceramic or metal powders

problems that come to mind:
-the liquid will bleed into the surrounding plastic, decreasing accuracy.
-the plastic, if molten, will fuse with surrounding plastic, creating a rough exterior surface.
-precise heating might be difficult.

does anyone have experience with microwaves? is this pratical?

... google for SIS (Selective Inhibition Sintering) - here the topmost powder surface is painted with an ink containing salt, then an aerial IR-heater heats the surface and all areals not painted with the salt will melt and fuse to the underlying already sintered volumes.

With painting the surface black you can melt/sinter only the black areas in a similar but 'inverse' way.

Fusing a volume embeded in some centimetres of powder won't work stable as you will have reflections, absorptions and 'shadowing' for hollow or interlayed structures ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

ok i think i understand: your saying that, for example, if the MW emitter is at the top of the printer, higher (z-axis) doped layers will shadow lower doped layers. Also, reflections off of complex model shapes like we print will lead to unpredictable heating.

Both are good points i hadn't considered. Perhaps, microwave after each layer? it's probably possible to spray a MW reflective material/pattern on the non-doped areas as well, to prevent heating below the powder surface, though would likely make the powder unusable a second time.

I've also got a thread going for the EM properties fo PLA
RF & MW properties of PLA/ABS

... why not simply heat the surface with a halogen heater?

Much safer handling than with MW and no housing needed ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

i can't think of a good reason yet, other than curiosity :-)

... it's for selective surface fusing or selective inhibition sintering (see above and here), where you fuse selected areas of the topmost powder surface to the underlying object ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

actually i was saying i can't think of a good reason to use microwaves, other than curiosity. i should have been clearer.

... before lasers ruled the market, there were some development in MASER's - could be interesting to get hands on a small device emitting a focussed MW-beam ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

sounds like a goal: print some meta-materiel microwave super lenses. that's the kinda stuff that gets funding grants.

... exactly

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]