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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.

This project was created on 08/15/2014 and last updated 3 months ago.

Description
Our system uses consumer microwave units to perform burn-out of PLA from molds, and a second microwave to liquify aluminium, to be poured into the mold. 3d printer inspired mechanics will move the aluminium from the microwave, into the target mold under human control across the network, so that there is no risk to the person operating the machine.
Details

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. 

The vision is to automate the process and build machines so that the system can be remotely run by a human being safely from their terminal. 

Automation will be as simple as two to three machines powered by arduino with minimum axes. 

One machine will be a forklift to pickup the item and deposit it safely onto a pair of fire bricks. 

One is a crane to pickup the top from the kiln, and one is a combination of forklift and a x,y table. This will pickup the cup, place over target, and pour through a heated steel funnel into the mold. 

Ideally, we see an operator walking to the machine, starting the microwave on the mold & aluminium. When notified the machine is done, the operator can use gloves to pickup and bury the mold in sand, then walk back to their workstation, and pour the aluminum remotely. This will reduce the risk of injury to an operator to near 0, and not require any dangerous gasses to perform the melt.

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.

Components
  • 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

See all components

Project logs
  • Using the Molds

    3 months ago • 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...

    :o

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

    Voila!

    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

    3 months ago • 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

    3 months ago • 0 comments

    Materials:

    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 :)

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Build instructions
  • 1

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Discussions

william.scott.baker wrote 2 months ago null 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 3 months ago null 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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anon wrote 3 months ago null 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 3 months ago null 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 3 months ago null 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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ganzuul wrote 3 months ago null 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 3 months ago null 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 3 months ago null 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

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Julia Longtin wrote 3 months ago null point

PLA does not burn away when liquid aluminium is applied, and sand is not microwave transparent.

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Damian Paradis wrote 3 months ago null 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 3 months ago null 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.

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Julia Longtin wrote 3 months ago null 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 3 months ago null 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 3 months ago null 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 3 months ago null point

Great!

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Julia Longtin wrote 3 months ago null 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 3 months ago null 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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