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Hey, welcome to the shop. In today's video, we're going to be trying to cast this gigantic 3D printed T-Rex skull and turn it into solid aluminum. And this is going to be a challenge because this is by far the biggest thing I've ever tried
Watch the casting of a giant T-Rex skull from 3D printed PLA to solid aluminum using lost PLA ceramic shell casting.
Ask about this video. Answers come from its transcript only — with the timestamp, so you can check them.
Generated from the transcript and can be wrong — check the timestamp.
Key Takeaways
- Lost PLA ceramic shell casting is effective for large, complex aluminum castings.
- Proper preparation of 3D prints and mold reservoirs is critical to manage metal shrinkage.
- Large molds require kiln modifications and careful temperature control to avoid shell cracking.
- Using aluminum from car rims is a practical source for casting metal but requires special cutting tools.
- The casting process is labor-intensive but yields detailed and heavy aluminum sculptures.
What the video covers
- The creator attempts to cast a gigantic 3D printed T-Rex skull into solid aluminum, the largest casting they have attempted.
- The process uses lost PLA casting with ceramic shell molds built by coating 3D prints in liquid ceramic and fused silica sand.
- Special reservoirs are attached to the prints to compensate for metal shrinkage during solidification.
- The 3D printed parts are prepared by gluing, waxing, and adding braces to ensure structural integrity during coating.
- Due to the size, the molds do not fit in a standard kiln, so an extension ring is made from fire bricks.
- Plastic is melted out carefully at 650°F to avoid cracking the ceramic shell, followed by firing the shell at 1500°F.
- Aluminum from car rims is melted in two furnaces simultaneously to pour into the large molds quickly.
- The casting process is challenging due to heat and shrinkage, but results in impressive aluminum skulls weighing over 14 pounds.
- Post-casting involves removing the ceramic shell and cleaning up the castings with sharp blades.
- An experimental technique was also tested but did not succeed, demonstrating the trial-and-error nature of the project.
Chapters
- 00:00Introduction and Project Overview
- 00:46Preparing Reservoirs for Shrinkage Compensation
- 01:41Waxing and Assembling the 3D Printed Parts
- 02:38Applying Ceramic Shell Coatings
- 04:10Preparing Aluminum from Car Rims
- 05:10Kiln Modifications for Large Molds
- 06:08Removing Plastic and Making Relief Cuts
- 07:02Melting Out Plastic and Firing Ceramic Shells
- 08:15Melting Aluminum and Pouring the Castings
- 10:33Casting Results and Post-Processing
Full Transcript — Download SRT & Markdown
Speaker A
to cast. Just look at it compared to this thing, which is my biggest casting so far. Just this piece alone took over 50 hours to print. Now, the way that we're going to cast these things is we're going to use a process called lost
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PLA in ceramic shell. And how that works is we're going to coat these 3D prints in liquid ceramic and build up a thick shell. Once we have a thick shell built up, we can melt out the plastic 3D
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prints and we'll be left with a mold that we can pour molten metal into. But before we start coating these things with ceramic, we need to account for the massive amount of shrinkage that's going to occur as the metal that's poured into
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the molds starts to solidify and shrink, which is why I printed these pieces, which are going to attach to these 3D prints. You can think of these things as reservoirs. They're going to supply the castings with molten metal as they
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solidify and shrink. And they have to be really big like this because they need to be the very last things that solidify. And to attach them to the models, we're just going to use some super glue.
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I'm also adding a brace to the jaw. It'll help keep it from flexing as it's being coated and it'll also give us something to hold on to.
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I'm using a UV light to show you the spots where I added a little bit of wax to smooth out some of the rough areas on the model. These 3D prints don't always come out the cleanest, so just a little
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bit of wax takes care of that. And you can also see where I glued the jaw together. This jaw was too big for the 3D printer that I used, so I had to print it in three pieces and glue it
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together. Here's the ceramic shell we're going to use. This stuff is called suspenda-slurry. I've used it many times before and it works really well. Now, the tricky part about this is getting the stuff onto the 3D models. They're so big that I can't
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stick them in the bucket, so we're going to have to get creative with how we apply this stuff.
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After every coat, except for the first two, we're going to sprinkle these things with fused silica sand. This adds strength, but it also helps bulk up the shells a little bit. Each coat added a little over a pound to these pieces, so
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10 coats later, this thing was almost 12 lb, which makes it really awkward. All right. While we're working on the shells, let's get some aluminum ready.
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For these castings, we're going to be using aluminum from car rims because they're made of really good aluminum for casting.
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The only downside of using car rims is that they're really hard to cut up. So, we're going to have to break out the fourth state of matter cutter and that should make really quick work of these things.
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There, now we have a big pile of aluminum to use and hopefully that's enough for these castings.
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Another challenge with these big molds is that they just don't fit inside my relatively small kiln. So, I had to make an extension ring out of some fire bricks and hopefully that'll solve the problem.
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It's been about 2 weeks since we started dipping these shells and now they have 10 layers on them. So, we can start moving on to something a little bit more fun. The next step is to get rid of
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these handles and start melting away as much plastic as we possibly can before we put these things in the kiln. And the reason we want to do that is because as this plastic starts to melt, it's going to expand and crack the shells almost
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certainly. So, we can mitigate that a little bit by cutting some relief cuts along the inside of these larger sections here. That way it'll give the plastic somewhere to expand into and hopefully prevent it from cracking the shells too badly. And I think I have the
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perfect tool here. I got this recently at a garage sale. It's a really big soldering iron. This thing should work really well.
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And we're going to do this in the grinding room because this room has an exhaust fan.
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Here's what they look like after removing some of the plastic. You can see those relief cuts I was talking about.
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Both of these shells actually cracked during this process, but it really shouldn't be a problem as long as they don't get any worse.
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All right, it's finally time to melt out the plastic. We're going to heat up the kiln until the 3D prints start to melt out of the shells. I find that 650° F is a good temperature.
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It's hot enough that the plastic becomes very liquid and flows out of the molds easily, but it's not so hot that the smoke ignites as soon as we open up the kiln. And I've had that happen before and that's no fun.
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And I didn't mention it earlier, but the plastic we're using here is called PLA.
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And the reason we use this stuff is because it burns away almost without leaving a trace. There will be a very tiny bit of ash left behind, but we can just blow that out with an air compressor.
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All right, we got most of the plastic out of there. Now we can crank up the temperature to completely burn away any remaining plastic and turn the shells into ceramic.
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We'll leave it in there and let it heat up to about 1500° F. Basically, we're going to fire the shell and turn it into a piece of pottery.
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Well, it's been a few hours since we put this in here, so we can open it up and see what it looks like.
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That nice ring that we can hear means that the shell actually did not crack.
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It's in one piece, which is really amazing. So now we're going to do the same thing with the jaw and hope for the same result.
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Well, I'm absolutely shocked, but neither one of these pieces cracked. I would have bet money that they would crack, but I'm happy to be wrong.
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Now we can use some compressed air to remove any ash that's left behind, and then get ready to start casting these things.
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Now that they're nice and clean, we can place them back into the kiln and warm them up a little bit. That way they're not super cold when we pour in the liquid metal. I'm not sure if this is
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absolutely necessary when casting with aluminum, but it really can't hurt. These castings are so big that we're going to have to use both furnaces, melt two crucibles of aluminum at the same time, and then pour in those crucibles
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back-to-back as quickly as possible. And hopefully that's enough to fill the molds. I know it'll be enough to fill the jaw mold, but I'm not exactly sure about the larger one.
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Sometimes when I add metal to a crucible, I'll just turn off the gas and that makes it a little bit easier. It's not quite as hot as I'm feeding metal into the crucible. And then when I put the lid back on, I just turn on the gas
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flow again and it's so hot in the furnace that the gas immediately ignites. Well, this one was just a little bit too cold, so it allowed the gas to build up a little bit more than I would have
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liked, and then this happened. I decided to cast these things at night inside the shop because I thought it would be a little bit cooler in here. It was 115 today. It turned out that actually having both of these furnaces
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going inside the shop made it pretty miserable. Even with the large shop door open, these things put out so much heat that my cameras were overheating. It was really horrible inside the shop.
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All right, here's the moment of truth. Hopefully, we have enough metal to fill this mold.
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Well, that ended up being just about perfect. I had just a little bit of metal left in one crucible.
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And check this out. You can see just how much that aluminum shrinks as it solidifies. And it doesn't seem like it's that big of a deal, but if we didn't have this big feeder here, all of that shrinkage would be taking place in
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the casting. Check out how much these shells crack as they cool. I'm not really sure why this happens. Maybe it's because as the castings cool down, they contract and just break the shell apart as that's happening, but I'm not re
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All right, let's break these things open and see how well we did. One really nice thing about casting aluminum in this ceramic shell is that the shell doesn't really stick to the aluminum. So, it breaks away very easily
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unlike with copper or bronze. So, I'm hoping because of that we won't really have to use a sandblaster.
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These things look absolutely incredible. They actually look way better than I had hoped, but it's really difficult to get rid of the shell that's on the inside.
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So, let's get rid of it the easy way and break out the pressure washer.
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I haven't used this thing in a long time for this and the last time I did it was about 40° outside. So, it's a lot nicer to use it today when it's 110° out.
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All right, let's cut these things off. In this workshop, I have a whole bunch of fancy ways of cutting metal, but I think for this I'm just going to use a hacksaw.
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This is definitely going to take a while, but with a few sharp blades, it shouldn't be that bad.
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All right, so we removed the sprues, and now we need to figure out how we're going to attach the jaw. So, you'll notice that there are these pieces here, and this is from the original 3D print.
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The reason these are here is because obviously this is supposed to be plastic, so you can just bend the plastic model, and it'll spring into these holes here, and that holds the jaw just fine. But, I chose to leave these
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on here cuz I figured we could just start grinding away material until we can flex this enough for them to pop in.
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At least that's my plan. We'll see what happens. Well, that was way easier than I thought it was going to be. Now, all we have to do is clean it up a little bit, and it's done. And I really do mean a little bit.
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Straight out of the mold, this casting already looks amazing, so it really doesn't need much.
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All right, here it is. This project went way easier than I thought it would.
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Every once in a while a project actually works out that way. Usually it's the other way around.
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The final weight of the casting is 14 lb 2 oz, or 6.4 kg. And the overall weight with all the sprues, so everything that we poured into the molds, weighs 25 lb 13 oz or 11.7 kg. That is quite a lot.
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You might be wondering why I chose this particular model and not one that's more anatomically correct. Well, the simple answer is that this model is just available at the time of printing this and it was actually 4 years ago that I
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printed this thing. And it's also optimized for 3D printing, which makes printing something large like this piece here, which I told you took 50 hours to print, it just makes it a lot more reliable to print something that's
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optimized for it, rather than having to deal with potential failures 40 hours into a 50-hour print. However, I did alter the original model to optimize it for casting. This skull here is actually one of my very first metal castings and
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I cast it using an experimental technique that really didn't work out. It's not a bad result, but it it pretty much failed. But the reason I'm showing you this is because I wanted to show you how I altered the original 3D model and
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made it a lot better for metal casting. Really what I did is I just removed as much mass in the model as I possibly could because when it comes to metal casting, you really want your part to be
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as thin as possible. So, if you decide to cast one of these things, and there's a bunch of different ways that you can do it, you don't have to do it the way we did it here today, uh I highly
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recommend using the model that I'll make available for you. It's just a much better model for metal casting.
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All right, well, that's going to do it for this video. Thanks for watching and if you liked it, please don't forget to give it a thumbs up. It really does help it out. Also, I want to thank all of my
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Patreon supporters for their continued support. You guys are awesome and really do help keep this channel alive. So, thank you. And if you want to become a Patreon member, then you'll gain access to some of the behind the scenes things
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that I do in the shop, as well as all of my 3D printing files. Well, thanks for watching and I'll see you guys in the next one.
Topics:lost PLA castingceramic shell mold3D printed castingaluminum castingT-Rex skullmetal casting processcar rim aluminumlarge scale castingmetal shrinkageWheelium
