Microwave Aluminium Printing

Metal parts for people other than blacksmiths. A system to perform aluminium "lost PLA" casting with no propane, and no danger to humans.

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Our process uses consumer microwave units to perform burn-out of PLA from molds, and a different microwave to liquefy aluminium, to be poured into the mold.

What is working and what we're working towards:

What works now is that we are able to successfully melt aluminum inside a microwave and supply our molds to get fine quality crafted aluminium parts.

All of the software will be released under the GNU GPL V3 as the project advances, with the hardware designs released under the TAPR OHL.

  • 1 × 1200W consumer microwave with an emitter mounted in the top of the unit. this is for melting the aluminium. the rotating mechanisms must be removed.
  • 1 × consumer microwave this is for microwaving out the plastic from the molds. the rotating mechanisms should be preserved.
  • 1 × bag of plaster of paris Used for the mold mixture.
  • 1 × 1 pound container of 1200 grit silicon carbide powder Used in molds to burn PLA
  • 1 × bag of perlite Used in mold mixture.
  • 1 × water used in mold mixture
  • 1 × Alcohol used in mold for burning away PLA. We used 140 proof isopropyl alcohol.
  • 1 × powdered sugar used in mold for burning away PLA.
  • 1 × bunch of styrofoam Used as channels in the mold.
  • 1 × High Heat Furnace Cement used for the kiln

View all 11 components

  • Facing a new year...

    Julia Longtin04/03/2016 at 15:04 0 comments

    Tightening up the scope of the project to just the aluminium casting techniques.

  • Using the Molds

    pizza cat08/21/2014 at 05:54 1 comment

    Fresh baked molds. The one on the right used a more refined recipe and came out great.

    We used a hairdryer to blow out the ash from the inside. You can use any form of compressed air.

    Creating sprue extenders, used so that liquid aluminum causes pressure inside of the chamber. They need to be skinny & tall!

    Attaching the sprue extenders atop of the mold. Good ol' duck tape can be used for this to keep out the sand.

    Our sandbox with a small layer of sand on the bottom. Place the molds in the sandbox and then cover with sand until it reaches near the top of the sprue extenders.

    Carefully pouring the aluminum.

    Oops. Aluminum will burn through the sprue extenders. It is important to fill the box until the sand reaches near the top of the sprue extenders. Our box nearly caught on fire..

    Taking our mold out of the sand. This is the most fun part of the process, seeing what is inside...


    Chisling the plaster away with a screwdriver or whatever you got.


    Now you have a part to remove from its mountings! This part came out great! However, we learned a lot about the mounting of the part when attempting to remove it. That will be covered in the next project log. :)

  • Microwave Casting Pt. 1

    Julia Longtin08/20/2014 at 21:31 0 comments

    We're going to microwave out our molds. Here's some science about whats happening. 

    Two important stages:

    Stage 1: Remove all water - will sweat profusely the water content in the form of vapor - may need towel to keep microwave from flooding.

    [] Warning []  Use safety precautions! We did this outside and stood atleast 30 feet away from the microwave.

    During this stage, we have seen conditions where the mold could split and explode. This was mostly in part due to heating the water in the mold too rapidly in one spot. The microwave that caused this problem had no spinning plate. This is bad because then the microwaves will target one particular point and will begin to overheat the mold. We observed a chain reaction when this happened. Once a section of the mold began to overheat, a hot-spot forms and it grows as it absorbs microwaves at a higher rate [becoming a susceptor!]. This is what caused Porygon's brains to blow out of the mold and become captured in aluminium.

    Stage 2:

     It was hard to capture the smoke escape the mold. Microwave in short bursts starting at a lower temperature.

    We set our microwave at 50% [1100 watts] and zapped it in short bursts of around 5 to 15 minutes on average.

    The investment will of evaporated and start smoking (non-profusely). The susceptor absorbs the microwaves at a higher rate at which the contents from the mold incinerate and create the cavity inside. Make sure that no plastic is visible in the bottom of the sprues and wells and use a form of compressed air [we had a hairdryer) to blow out the ash and residue from the inside. 

    You're ready to move onto the next step when the mold has been cleared of ash and residue, making aluminium!!

    ** Don't reuse the microwave for food again **

  • Molding Process pt. 2

    Julia Longtin08/20/2014 at 18:54 0 comments


    Investment [mold]: Equal parts of Perlite / Plaster of Paris / Water

    Something to stir with and a bowl to stir in

    Old plastic Tupperware

    Vibration table of sorts [to remove the air bubbles from the container] 

    It took about 3.5 cups of each ingredient equally in order to fill our mold. 

    Mix "investment": equal parts perlite + plaster of paris + water. Mix dry ingredients before adding one part water (equal to the perlite or the plaster). Investment should have the consistency of thick soup (think: pancake batter). Do not stop stirring for more than 15 seconds after you add water or the investment will harden. Stir until ready to pour, then pour quickly! You're looking for a thick soupy consistency like pancake batter.

    Pour a little investment into the container to server as a 'floor' for the object to rest on.

    Place the object on top of the investment. 

    Cover the object with the remainder of your investment, until the object is no longer visible. 

    You will want to vibrate the mold with the container so that the air bubbles inside can escape. We might try to use a laundry machine next time and see how that goes. 

     We added a little weight atop of our mold while the investment hardened. Set for ~ 1 hour. 

    We had accidentally got Tupperware that was too firm it caused a problem to remove the settled mold.

    Use older / plastic Tupperware that has flex and wiggle in it so that after the 'investment' has settled you can remove it easier :)

  • Molding Process

    Julia Longtin08/19/2014 at 07:09 0 comments

    Before showing the molding process, it'd be helpful to be familiar with the terminology associated with the gating system for metal casting. 

    Elements Of A Gating System:

    Pouring Basin [cup]: 

    This is where the molten metal employed to manufacture the part enters the mold. we use red bull cans to extend the sprue into a basin, as pictured.

    Down Sprue:

    From the pouring basin, the molten metal for the casting travels through the down sprue. This should be tapered so its cross-section is reduced as it goes downward.

    Ingate/Choke Area [Sprue Well]:

    Once at the sprue base, the molten material must pass through the ingate in order to enter the inner area of the mold. we make these areas as small as "reasonable" since we later have to dremmel this part off.


    Runners are passages that distribute the liquid metal to the different areas inside the mold. We use at least one runner, to access the gate on the bottom of the object.

    Main Cavity [Actual casting]: 

    The impression of the actual part to be cast is often referred to as the main cavity. this is the space left over after the PLA part has burned away.


    Vents help to assist in the escape of gasses that are expelled from the molten metal during the solidification phase of the metal casting process. Typically just a thin shaft from the top of the mold is made to the main cavity.


    Risers are reservoirs of molten material. They feed this material to sections of the mold to compensate for shrinkage as the casting solidifies. We are not yet using risers in any of our castings.

    Plan the placing of gates and runners. Materials used include a cutting board / hot glue / xacto knife / styrofoam.

     The 3D printed part will serve as the main cavity. This bottom gate is for draining out any ash from the cavity. we run a runner to this gate from the downsprue used to pour aluminium into.

    Sideshot of the downsprue, runner, and gates.

    One downsprue for entry, and one for exit from the mold

    The large inlets serve as the pouring basin for the material to run through. 

    This is what will be going into the mold as documented in the next steps. 

  • Homemade Susceptor for Induction Based Heating

    Julia Longtin08/18/2014 at 08:51 0 comments

    A suceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat (which is sometimes designed to be re-emitted as infrared thermal radiation). The susceptor takes the microwaves and converts it into heat at a very high efficiency. A common example of susceptors everyone is familiar with may be the 'crisping sleeves' found in Hot Pockets and the like. This is used to burn away the object from within the mold. We need a tacky susceptor and used a combination of the following: 

    Sugar - to ensure the while the object is burning away, the susceptor does not run down the object and pool at the bottom. Sugar will carbonize the susceptor and leave it on the wall. 

    Water - The universal solvent, used to dissolve the sugar and silicon carbide. 

    Alcohol - We suspect that the alcohol will prevent the water from beading up too much.

    The spray is used as a medium to apply the mixture thinly and evenly across the surface area. We used some printed out PLA test strips for our experiment to design an ideal recipe. 

    Results: Test 2 has been the most successful. Notice the clean, thin light grey layer that is produced :) 

    50 mL water

    10 mL alcohol [70% I  - AL

    1 tbs powdered sugar  - PS 

    1 tbs susceptor [silicon carbide] - SC

    Use the widest available setting available for the nozzle [mist]. Hold about 6" away from the surface to avoid beading and apply a few even broad coats to the surface of the 3D printed part. We found that 2 layers with about 3-4 coatings each did the trick. Wait 15 minutes between each coat and careful not to spray too close or you will have undesirable dripping. 

    You will want to spray this mixture on the object, sprue, runners, and gates. Allow to dry and you'll be ready to move onto the next step, creating the mold!

  • Motion Control

    Julia Longtin08/18/2014 at 05:30 0 comments

    The hard work is done - we have successfully got the Aluminum to melt in our microwave kiln, and we have been able to cast objects from the molds that we designed. The system works - huzzah! 

    Now, we must build a simple remote-controlled automation system to remove the kiln from the microwave and pour the material into our mold. Design for this system is complete and the construction is underway.

    The three main stages of design are:
    I. Remove the kiln from the microwave.
    II. Remove the top of the kiln.
    III. Remove the crucible holding the aluminum, pour it into a heated steel funnel.

    And then replace everything exactly as it was.

    The proposition (Part I):

    The base of the assembly consists of a plate mounted atop two long threaded rods. On the end of each rod is a 5/8" nut that is connected to a motor. The motor turns the stationary nut, and thus the rods move forwards and backwards. Both motors will be controlled by the same Pololu motor controller. On this plate will be 2" of firebrick to place the kiln on.

    Two more long threaded rods are mounted perpendicular to the base, about 6" apart. The microwave will be resting roughly 18" from the ground - attached perpendicularly to these rods (oriented towards the front of the assembly), roughly 20" && 28" from the ground, will be two sets of 5/8" x 15" steel rebars. The bottom set will be equipped to move vertically through the same nut-motor system as the base.

    How it works:

    The threaded rods that the base of the assembly rests on will extend under an open table on which the microwave is seated. The kiln will have two sets of holes drilled through it - one set on the base, and one set on the top. The whole assembly will slide forward towards the microwave, in such a way that the steel rebars slide into the aforementioned holes. The bottom set of rebar will move upwards slightly (to obtain some traction), and the assembly will slide backwards, removing the kiln from the microwave. The bottom set of rebar will move the kiln down and set it on the firebrick atop the base; the top set will remain stationary and suspend the top of the kiln.

    The first two stages are thus complete. Next time: Stage III! 

  • Design Process Thinking

    Julia Longtin08/16/2014 at 22:13 0 comments

    Design Process thinking: One of our early prototypes included an extruder for 3D printers.

    After 3D printing the part, we can now begin the mold. The process of creating the mold requires planning and some new vocabulary. Gates allow the material to enter the cavity. Runners are passages that distribute the liquid metal to the different areas inside the mold. Risers are reservoirs of molten material. They feed the material to sections of the mold to compensate for the shrinkage as the casting solidifies. 

    Molding process: Plan the gates / runners. Attach runners to gates then the gates to object. Above is a completed mold, there will be another picture showing a cross section and making of the mold. Right now the 3D printed parts are coming out a bit off so the printer needs to be recalibrated for newer test pieces.

  • Status

    Julia Longtin08/15/2014 at 07:47 0 comments

    microwaving aluminium until it melts was a success, and our molds are producing objects when we fill them with aluminium. now its 'just' the motion systems left!

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Enjoy this project?



Keith Olson wrote 12/28/2015 at 16:22 point

This is pretty unbelievable!  As an alternative to plaster of paris, here is something to consider:

  Are you sure? yes | no

Julia Longtin wrote 03/14/2016 at 23:52 point

in our testing (science!), we found that sand is not microwave transparent.

  Are you sure? yes | no

Peter Walsh wrote 08/07/2015 at 19:40 point

Quick tip: To make a proper riser, use a "tin" can instead of an aluminum can (the kind of can food comes in, such as a soup can).

Normally one would have a pipe sticking up through the top of the sand, place the can over the pipe, pack sand between the pipe and can, then remove the pipe (to create the riser). You'll probably need a different method for plaster molds, but a food can works pretty well for a riser.

Sand mixed with a little sodium silicate ("water glass", used in canning and available at some supermarkets) will solidify the sand a little, like a baked cookie. You can use this method to pre-make risers as fat rings to place over your sprue holes.

And to remove embedded gas from the aluminum, wrap a teaspoon of calcium carbonate (ground up chalk from the dollar store, or just buy the powder for pennies on eBay) in aluminum foil and push it to the bottom of the melt with a rod. This will generate CO2 gas which bubbles up through the melt and removes other dissolved gases. Do this two or three times to get bubble-free cast aluminum.

Make sure your riser extends from the topmost section of your part, else the trapped air will prevent aluminum from filling and you'll get a void. If your part has several sections that stick up, attach small wires at each section (before casting the mold) to create channels that allow air to escape when the aluminum is poured.

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baltsar wrote 04/26/2015 at 12:57 point

I will help you. Maybe you should take a break. My mistake. Sorry.

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clothier.bruce wrote 04/17/2015 at 09:02 point


This has all the hallmarks of a scam. AFAIK you cant melt metal inside a domestic microwave, so the authors have to come lean and explain.

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Jerry Biehler wrote 04/27/2015 at 18:24 point

You can, there have been a few people working on it in the past few years. They use various materials that absorb the microwaves and heat up. That is what melts the aluminum. It's kind of silly, just use a small kiln.

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Dylan Bleier wrote 04/27/2015 at 19:36 point

materials such as?

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Jerry Biehler wrote 04/27/2015 at 19:43 point

Carbon, often in graphite form.

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Peter Walsh wrote 08/07/2015 at 19:18 point

I do hobbyist casting at home, and have looked into this.

You make a ceramic crucible with impurities that absorb microwaves, such as graphite. The crucible absorbs the heat and transfers to the aluminum, melting it.

There's lots of articles and YouTube videos on the net explaining this.

  Are you sure? yes | no

Julia Longtin wrote 03/14/2016 at 23:51 point

I'm right here, now. I think the results speak for themselves. :)

  Are you sure? yes | no

Dylan Bleier wrote 04/16/2015 at 20:03 point

How is this printing and not casting??

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Vitran Accad wrote 01/03/2015 at 00:20 point

I am curious about *how* you melted the aluminum. I do not understand how the aluminum is melting in the microwave. Can you show some pictures and instructions of how you melted the aluminum? From my understanding, the microwave should not heat aluminum unless one was at much higher frequencies.

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dudesom wrote 12/18/2014 at 11:11 point
Awesome project!
Would a microwave with a side emitter work? Why must the emitter be on top to melt aluminum?

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william.scott.baker wrote 09/24/2014 at 16:56 point
One method I've seen used to remove air bubbles is to simply place a random orbital sander on the table next to the item & turn it on. The sander vibrates the table, which in turn vibrates the container.

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Spud wrote 09/08/2014 at 20:41 point
Could silica cartbide be added to PLA pellets and extruded into your own filament? Making your own microwaveable filament might be another great way to create an alternative over PVA or Hips+Limonene.

SiC embedded filament. Oh yea...might need to buy a filament making machine.

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MTO wrote 04/11/2016 at 18:38 point

Silicon carbide is really hard, and used to make tools that will cut tool-steels, IIRC. I would think that a plastic+SC filament would double as a sort of hacksaw and erode your extrusion nozzle.

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anon wrote 08/25/2014 at 10:15 point
Ok, first I wanna say that this is an awesome project that i'll definitely have to try when I finally build a 3d printer.

As for the microwave radiation issue, it can most likely be solved with a large home built faraday cage similar to the one that comes as part of the microwave, you might also want to invest in a microwave oven leakage meter, it might give you a little insight into how much microwave radiation you're exposing yourself to during the whole process

if you don't mind me asking, what is the part in the pictures for? some kind of bracket or mount?

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prof_braino wrote 08/25/2014 at 18:41 point
The part in the picture look like a version of the triangle frame corner of a RepRap Prusa 3D printer. I have a similar plan to print out a set of printer parts in PLA and cast them in aluminum. The idea to avoid the PLA parts warping when we print ABS etc that has a higher melting point than the PLA and needs a heated chamber.

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PointyOintment wrote 08/26/2014 at 17:44 point
> how much microwave radiation you're exposing yourself to during the whole process

That is not really a cause for concern. It is simply radio waves—quite powerful compared to Wi-Fi, etc., but not ionizing, so cannot cause cancer. It only heats up your body slightly (just like cell phone signals).

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Dylan Bleier wrote 04/26/2015 at 15:11 point

not necessarily true.... sub-millimeter radio waves have been shown to cause cancer through a resonant mechanism that unravels DNA 

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ganzuul wrote 08/26/2014 at 21:04 point
There does exist a risk in that microwave radiation may penetrate into the inner organs where no nerves to detect temperature exist. This way one can expose oneself to dangerous durations of localized heating without ever noticing the problem.

There is no need for the microwave oven to have a window which you can see through, so by replacing the screen with a solid shield you can make it safer. You should totally have a device to measure microwave radiation if you're going to do that though, and a solid grasp of what each component does.

BTW, always use a grounded outlet with a MWO. They conduct 2000V pulsed DC through the chassis.

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Julia Longtin wrote 08/26/2014 at 21:56 point
we do no modification to the microwave other than removing the glass plate. this should be as safe as running a microwave to cook a turkey, which many of these machines were designed to do.

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razorfish_sl wrote 08/21/2014 at 01:53 point
to remove air, you can try a metal box with a vacuum cleaner, it's what I use to remove air from resin casts.

Or you can use foundry sand to completely remove the need for the plaster in the first place, then hot pour into the polystyrene and it will vaporize and burn off rather than the extra step in the microwave

  Are you sure? yes | no

Julia Longtin wrote 08/21/2014 at 02:41 point
PLA does not burn away when liquid aluminium is applied, and sand is not microwave transparent.

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Damian Paradis wrote 08/20/2014 at 16:16 point
OK this is awesome. I just got my Rigidbot 3D printer, and I've been playing around for a little over a year with the Gingery charcoal foundry for green sand aluminum casting. If you guys need any help let me know.

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Tinydot wrote 08/20/2014 at 13:11 point
So how long do you actually have to microwave the aluminium before it can be cast?
For instance for your red-bull canned extruder part.
I've molten aluminium on a charcoal/coal forge before, and it takes quite a while to set up, which is especially annoying if you only want to cast 1 part. I wonder if this would be a decent alternative for small parts.

  Are you sure? yes | no

Julia Longtin wrote 08/21/2014 at 02:43 point
our current kiln melts a cup of aluminium in about two hours, but it has several defects. when we have the procedures down, we predict three hours of work from PLA part to aluminium poured.

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Darius wrote 08/18/2014 at 00:34 point
I really can't wait for the automation to begin from first stage to final stages. I'm going to follow up on this.

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Julia Longtin wrote 08/19/2014 at 03:52 point
Thanks! we fought with the chemical/thermal problems first, since mechanics is the easier part. we're all 3d printer tinkerers to begin with. :)

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Hemingway wrote 08/16/2014 at 23:09 point

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Julia Longtin wrote 08/15/2014 at 17:26 point
1200 watts, and we ventilated the microwave outside, so that no noxious fumes ended up in our house. ;)

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NigelSamhain wrote 08/15/2014 at 08:47 point
How many watts was the microwave you used to melt the aluminum and what modifications to the cabinet did you require if any?

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