Author Options:

Molding Aluminum: With Gravity Die Casting Answered

It's expensive, untested and dangerous.
The idea goes like this. Start with a coffee can foundry, possibly powered with Biodiesel or Propane. Then design a mold for what you want to build using Autocad or some variant thereof. After it's finished, send the design to a machine shop to have it built out of steel. When you receive the permanent mold, melt the aluminum and pour into the mold repeatedly and often.

The idea seems like a good one to me, I'll be testing it soon enough using common screw clamps to keep the mold tightly secure.
Has anyone here done this? The closest I've come to doing it myself is pouring into a muffin tin.
The photo below is a picture of the results which was taken from another board found here, you'll need a login, the photos are located in the forum under Machining and Tooling.

Give me a shout if you dig the idea.

UPDATE 5/24/07

It works! Using my Harbor Freight Mini-Mill I cut out pockets in two pieces of 1018 steel, each about an inch deep, and four inches across. I then cut inlets in both pieces and welded some scrap steel U channel on the tops of both mold sections to form a pool enclosure for the excess aluminum to collect inside of and stay safely contained.
Then I lit the candle on my foundry and melted the aluminum while at the same time pre-heating the molds, (connected using C-clamps) in the oven. When the aluminum melted, I poured it and it instantly solidified. After about 2 minutes of running around in a panic I cracked the mold open. The detail level is incredible. Impressions made in the mold with a fly-cutter can be seen in the casting. The casting is bright, shiny, and seemingly devoid of any burs usually associated with unfinished aluminum castings.
I'll provide photos later of the test mold and casting.


Coming from a bronze foundry background, I would say that it's best to make a rubber mold of the item, and then to cast waxes in that. Once the waxes are chased, they could be sprued on a tree to cast many at once, even if it is in aluminum. Then it's a matter of investing and melting out your waxes. My 2 cents.

what do you need that many parts of?

Whatever, it doesn't matter. If it's made out of aluminum then it's game.

I can't think of a reason why you couldn't do this. There are a couple of constraints that you would want to observe. One is that you'd have to keep the tools very hot, pretty close to the melting point for aluminum. Otherwise they would act as a huge heat sink, and may cause all kinds of unintended problems, such as voids and blockages. That's not a deal breaker. It just means you'll be working in a hot and potentially dangerous environment. I'm pretty sure that steel tools would pay for themselves many times over delicate clay molds, though Another is the aluminum, itself. I believe its molded shape can distort wildly, once it cools. There may be ways to offset that. You might just allow for it. Most casted metal parts are machined in areas where precision is critical. As far as machining the tools, I would love to see someone slice a computer model into sections spaced .125" apart (in this case, mold cavity of the part itself), take those sections over to a laser cutter, cut as many sheets of .125" thick steel, stack them up, grind the cavity smooth, and go to friggin' town. I bet you it would be much less expensive than having a big old chunk of steel machined for the same part. Heck, there are things you could do with that, which relate to casting, that you simply could not do with a CNC mill. Talk to me.

That 1/8" laser cutting is a good idea. It is true that it's best to heat the mold before pouring. Part defects would be kept to a minimum that way. This is a powerful but very dangerous process. It would be a good idea to familiarize yourself with foundry techniques before attempting anything on this order. But if it's done right, large scale production becomes a much simpler prospect. I'll research the laser cutting process and find out how much cheaper it could be.

You can cast aluminum using sand casting techniques. Mix some heavy oil into sand and form it around a wooden, plastic, or whatever mold. I once made a solid aluminum handgun this way. Search for aluminum sand casting and I'm sure you'll find all sorts of information.

Sandcasting is the most common way to mold metals. The permanent mold idea is one for simple mass production. Also, the surface finish is better this way, and you don't have to build a new mold for every piece, just fill, wait, empty and repeat.

Could you go a cheaper route and try and weld/drill/bend yourself a form? That would be pure DIY awesome.

Yes you could bend a couple of forms with wich to mold the aluminum. I hadn't thought of that. Interesting.