In this project, I'll be showing a simple way to cast a raw model, of your desire, called "lost foam casting".
Lost foam casting is based on styrofoam, as the material for your model.
As an example, i'm going to make a small copy, of the instructables robot logo.
- A heat source (I used a small forge that i made a year ago, but you can also use a blowtorch or a campfire*)
- A crucible (I used an empty tuna can, but you can also use something more advanced, like a cheramic crucible)
- Tongs (an oldschool pair of steel tongs, without any plastic parts, should do)
- A hobbyknife (for cutting out the styrofoam, if you have a special tool for that, I recommend you use it)
*If you use a campfire, it's important to have an air source, which supplies the fire with oxygen.
- Styrofoam (the styrofoam is representing your final product)
- Metal (I'm using aluminium, but you can use any metal for the casting)
- Sand (you're going to cast the metal in sand)
Step 1: Preparing
Preparing the forge:
Before doing anything else, it's important to light the fire, and make sure you have an air source. The air source is going to supply the fire with oxygen, which causes the temperature to go up. For my forge, i build an oldschool-looking bellows, but you could also use a hairdryer or compressor. If you choose to use a blowtorch, you don't need an air source, but a blowtorch can't deliver as much heat.
After you started the fire, you can go on to the next step, while the fire builds up.
Step 2: Making the Styrofoam Model
Cutting the model:
In lost foam casting, the metal is replacing a styrofoam model, by evaporating the styrofoam and taking its place. Therefore, you will have to make a model, of your desired product. In this project, I'll be making a copy of the Instructables robot logo.
I started off, by drawing a silhouette of the robot. Then I grabbed a hobbyknife, and started to cut the robot out of the styrofoam, making shure not to rip it apart.
Step 3: Preparing the Casting
Melting the metal:
The first thing you have to do, is melting the metal. All you have to do, is to place your crucible in the fire, which causes it to heat up. After placing the crucible at the hottest point, you need to fill it with enough metal, to cast your product. When doing this, it is better to use too much metal, than too little.
If you use a campfire or forge, it might be a good idea to make a lid for your crucible, to prevent ash and coal from polluting the metal. I made a simple lid, just by bending a small steel plate.
Making the mold:
While the metal is heating up, you'll have to make the mold. My mold was made of a mixture, consisting of sand, water and clay. By mixing clay into a small amount of water, you'll get a runny sort of mud, which will help the sand stick together.
When making the mold, you'll have to bury the styrofoam model in the sand/water/clay mix.
I started off, by covering the bottom of the pot*, that held my mold, with the mix, then placing the styrofoam model in the mold mix. While the mold mix held the model, I could start pouring the mix into the pot, until the styrofoam model was almost covered in the mold mix. At this point, it's a good idea to press down the mold mix, causing any holes in the mold to collapse. After doing this, you can proceed by placing a leftover piece of styrofoam, on top of the model, making it possible to pour in the molten metal. When the leftover piece is secured in the mold mix, it's time to fill up the pot*, in which the mold is placed. When the mold is ready, you'll need to compress the mold mix again, and then place a piece of a steel tube** or similar to prevent the metal from flowing down the side, instead of into your mold.
*I used a pot, to contain my mold, but you can use a metalbucket instead, as long as it can withstand high temperatures.
**I just used a piece of a propane can, that i cut off.
Step 4: Casting
The casting itself:
When the metal is molten, all you have to do, is to pick it up with a pair of tongs, and then pour the molten metal into your mold. When pouring in the metal, the styrofoam will evaporate, and make a small firepuff, when getting out of the mold.
After the casting:
While the molten metal is cooling down inside of the mold, it's recommended that you place down the crucible, to cool as well.
In my case, it took about 8-10 minutes, before I pulled up the newly casted robot logo. When pulling up the product, it's important not to touch it! It may still be very hot!
Step 5: The Result
The robot logo
After pulling up my instructables robot replica, I left it to cool off, for 10 minutes. When I was able to touch it, I used a file, to make the most of the surface shine, but still leave some of the raw look.
When using styrofoam casting, the product surface can vary, according to the sand used in the mold.
Styrofoam casting is used for casting rough mechanical parts, or replicas. I do not recommend styrofoam casting for casting rings, or other sorts of jewelry.