Loss PLA Casting




Introduction: Loss PLA Casting

Three-dimensional printing really is amazing isn't it? You can make some incredibly intricate, even decently strong pieces. There's only one problem: minus the industrial, extremely expensive printers, metal 3d printing is out of reach. That's where loss PLA casting comes in. You essentially take a PLA printed part, make a mold out of it and then cast aluminum into said mold. This lesson will be on doing just that.

I am not liable for any injuries incurred while doing this process.

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Step 1: Materials

What you'll need:

1. Foundry: I show you how to make one here:

2. Play sand (left over from foundry build)

3. Plaster of Paris (left over from foundry build)

4. Measuring/pouring cup

5. PLA part (requires a 3d printer) NOTE: I would not suggest hollow parts because without a vacuum chamber, the aluminum has a hard time getting in all the crevices (unless you're able to put enough fill holes)

6. Regular household vacuum

7. Big Ziploc bag

8. Empty Milk Jug

9. Scissors or knife

10. Foam

11. Hot glue gun

12. Steel can

13. SAFETY GEAR - This is not limited to what I say. Please do your own research, as dealing with molten aluminum can be extremely dangerous.

1. Gloves made for foundry work

3. Full face safety shield

4. Body covering made for foundry work

5. Thick, leather boots

6. A utensil to hold the crucible

7. ETC

NOTE: Never allow moisture to get in the crucible

Step 2: Creating Mold

To create the mold, you're going to need your: foam, milk jug, PLA part, hot glue gun, play sand, Plaster of Paris, empty Ziploc bag, cutting tool (scissors/knife etc) and vacuum.

To begin, you want to cut out an almost triangle shaped piece (like in the second photo) from your foam. This will be the pour spout that will allow the molten aluminum to flow into the mold. If your PLA part is wide, cut out a second or third pour spout. Ensure the widest part of the pour spout is quite wide (more-so than mine are in the image above), so your aluminum doesn't harden fast enough.

Next you want to hot glue the pour spout to your part, facing up. Then you cut the empty milk jug according to the volume required to completely cover the part, while allowing some of the pour spout to remain above the mixture.

Now it's time to add your mixture:

1:1 Plaster of Paris and play sand

Add about 70% of the amount of Plaster of Paris you used in water

Ensure you don't over or under fill your jug. If you need more, simply add more mixture (keeping the same amount of each).

Begin stirring with your hand until all the lumps are out of your mixture. This part is extremely important, as any lumps can leave bumps in your final cast.

Now take your bag and put it around the milk jug. Ensure none of the mixture falls out. Now take your vacuum cleaner and put the hose inside the opening of the bag. Make sure the milk jug isn't too full, as the mixture can get sucked in the hose, and you don't want that.

Next, using your hand, wrap the bag around the head of your hose and tighten it so no air can escape the bag. Now turn on your vacuum, and it should begin pulling the air out of the bag. Make sure you lift the vacuum hose above the edge of the milk jug, so it sucks the air out of your mixture. Any bubbles can impede on the final cast.

After you've sucked as much air out of the mixture as you can (maybe a minute or two), remove the hose and take the milk jug out of the bag. Now get your PLA part that's attached to the pour spout(s) and submerge the part in the mixture, making sure the pour spout is not fully submerged. Now either hold it here until the mixture is hard enough to hold it by itself or place something on top to hold it in place.

Step 3: Melting Out the PLA

Once the mold has completely cured (a few hours), it's time to melt out your PLA. Place the mold into your furnace and fire it up (make sure you place the mold in while it's cold so you don't shock the mold with massive temperatures).

Place the top on and wait until the foundry gets up in temperature (15 minutes or so).

Turn the mold on the other side and re-apply the lid. Wait for a good while until you've burned out the PLA.

OPTIONAL: After it's cooled, you may want to use an air compressor to remove any particles that may have gotten in the mold.

Step 4: Pouring the Mold

Now take your mold and, depending on how many pour spouts you have, tape an empty steel can that has both sides cut out (just use a can opener for each side) around each pour spouts. Then place your mold on a brick or some type of surface that can withstand high temperatures.

Heat up your crucible to around melting temperature. Place your aluminum in the crucible and cover with the top. Wait around 15-25 minutes for the aluminum to melt.

Carefully remove the crucible with your tongs and place it on a brick. Then grab it with your pouring tongs and pour the aluminum in each pour spout.

After a couple hours, come back and break open your mold to find an aluminum part where your old PLA piece was. Congratulations!

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    4 Discussions

    DIY Hacks and How Tos

    Nice casting job. This would be perfect for 3D printed models.


    Reply 4 years ago

    Thank you!


    4 years ago

    This is something I've been wanting to try since I got my printer. I have printed parts and casted them in a two part greensand mold. But I haven't tried lost PLA yet. Not many people seem to do it even though the results I've seen are very good. Question. Is the PLA harder to burn out than wax? like if you don't get it extremely hot will some plastic stay inside? Other instructions I've read on lost PLA casting say you need to get the mold red hot to make sure all the PLA is out. Which shouldn't be a problem. I have a diy waste oil burner that reaches 2000°F but was wondering if it's really necessary.


    Reply 4 years ago

    It can be quite hard. You've really got to ensure the inside of the mold can essentially boil it. Aluminum melting temps for a period should work just fine.