In this project I will be explaining the procedure in order
to create a lost foam aluminum metal casting. Lost foam is a molding technique where a foam pattern is created using Styrofoam or another foam material and then aluminum is poured in. The Styrofoam will then disappear and the metal will mold to the same geometry of the foam structure. Hence the term lost foam. This method of metal casting works best when a smooth finish is required for the piece. Once cooled, it should require little to no extra machining. Overall, the process from start to finish should only take about 1-2 hours, depending on the complexity of the casting.
- An induction heater or a way to heat the aluminum to a liquid
- A crucible or pouring device
- Gloves, torso cover, goggles, and metal tongs for safety
- A Styrofoam mold with the proper geometry for the component
- Metal ( Aluminum is usually the preferred choice for this mold)
- Sand and a bucket for the entire mold
- Vibration table or means of packing the sand
Very little experience is needed to preform this metal cast.
-The ability to lift the crucible and metal, which may weigh up to 30 pounds
Step 1: Safety
Because you will be
working with aluminum at or above 1200 degrees, safety is a big factor. Heat resistant glove, torso cover, and feet covers should be worn. Goggles should be worn to protect from possible aluminum splatter.
Step 2: Prepare the Metal in the Forge
The first step in
this process is to obtain the desired amount of aluminum and place it into the forge. Depending on the forge and the amount of metal it can vary for how much time it takes for the aluminum to melt. Make sure the aluminum is completely turned to liquid before pouring. While this is melting you are free to move on to the next step.
Step 3: Put Desired Mold Shape Into a Container and Fill With Sand
While waiting for the metal to melt, cut your Styrofoam or
foam substance into a desired shape. Make sure the size of your mold is small enough to fit into the container of sand.This step is very important because the shape of your foam mold will be the same shape of your final part.
Put your desired mold shape into a container and situate it so that the mold is sitting upright. Once this is done, pour your sand around the entire foam shape. A very important point in this process is to make sure that there is a level of your mold sticking out of the sand. This is a very crucial step in the pouring process because the molten metal needs to first make contact with the foam itself.
Possible error: Make sure the foam is perfectly upright. Make sure metal will be able to flow to all parts of the foam. If some parts of the foam are too thin, the metal may solidify and not allow liquid metal to flow to other areas.
Step 4: Place Entire Container on Vibration Table and Pack Sand
Once the container has been filled up to a point where the
foam mold is still visible from the top, place your entire setup onto a vibration table. This step is very important for your final product. By vibrating or packing the sand, this makes the look of your finished product very smooth and free from any cracks.
Possible errors: If there are any pockets of air in the sand, the metal may flow into them causing unwanted bumps in the final product. These would require additional machining.
Step 5: Pour the Liquid Metal Into the Foam Mold
Finally you are ready to pour your molten metal into the
foam mold. Make sure to have on the proper safety equipment such as gloves and no exposed skin. Dip your crucible or pouring mechanism into the liquid metal and bring it up taking care not to spill. Next, pour your molten metal onto the exposed foam mold above the sand. Be aware because when it first hits the foam it will produce a fairly large flame. Take care to avoid the heat and make sure you keep a very steady pour until the mold has been filled.
Possible errors: Make sure the liquid aluminum is not poured too slowly. Once the aluminum hits the much cooler sand and foam, its temperature will drop significantly. If this happens, then sections of the mold may solidify and block the flow of liquid aluminum.
Step 6: Remove Final Product and Let Cool
Allow your molten metal to cool and turn to a solid within
the container. Once you have let sit for 10 to 15 minutes, dump your final product out. Be careful because the product itself will still likely be hot. Put the finished product in water to cool. Once the piece is cool to the touch, it is ready to be dried off. Enjoy your now solid creation.
If the piece seems to be rough on some parts of the surface, this is due to the sand not being packed fully in that area. If a part seems to have fallen off or not fully formed, it is likely the metal solidified before all the metal could fill the void. To fix this, try pouring the metal faster, or making said section thicker to allow better flow.