Lost Foam Casting





Introduction: Lost Foam Casting

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.

Tools needed:
- 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.

Materials needed:
- 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.



    • Creative Misuse Contest

      Creative Misuse Contest
    • Oil Contest

      Oil Contest
    • Water Contest

      Water Contest

    49 Discussions

    I enjoyed this instructable. I have tried aluminum casting a couple of times. My attempt with sand was a major fail. I believe it was because I had problems getting my metal hot enough to pour. Melting the metal in the sand mould didn't work out but I was able (after trial by error) to use plaster of paris reinforced by iron wire to make my mould. I successfully cast three pieces of jewelry sized pieces. I had carved the designs in styrofoam. After burning out the styrofoam I used the mould to melt my metal. Heating it to a state where one could pour it was a problem but it became malleable enough to persuade it to fill the mould.

    Now that our temperatures are becoming more moderate I am looking forward to trying charcoal casting. Using a charcoal soldering block (available and jeweler's supply stores) the design is carved into the soldering block then the metal is melted directly in the block. Once the metal is molten enough another piece of charcoal soldering block is placed on top and pressed into the mould. When I worked at a jewelery store I did a charcoal block casting in 14k gold. I carved a nugget shaped disk in the charcoal and it cast beautifully. I am also looking forward to seeing if charcoal briquettes could be used. Charcoal soldering blocks run around $14.00 (last ones I bought) and that is a bit more expensive than I like.

    Lost wax and lost styrofoam each have their own advantages and disadvantages.

    One can generally get much better detail from a lost wax casting. There are two main reasons for this, first, the wax is hard enough to take great detail itself. Second, the investment one normally uses with lost wax is also capable of capturing greater detail with less need of extensive finishing. Another advantage is that in many cases it is easier to reproduce the wax models so if one wishes to produce more than one of an item it is much easier and quicker than carving as many masters as one needs. I have looked for a way to cast or mold styrofoam to make masters but have had little success in finding a way. I am also looking for a way to make my own charcoal blocks. I haven't had great luck with that either.

    Disadvantages of using lost wax is first ,that carving a master from wax is more difficult as the wax has to be hard enough to hold detail and this makes it more difficult to carve. Secondly, burning out the wax pretty much requires a kiln of some sort. I have heard of people using an electric hotplate and a foil lined clay flowerpot as kind of an improvised burnout kiln. I have not tried this but with no way to determine temperatures I think it would become very much a trial and error proposition. I think too that the burnout process is not a quick one. As I recall (its been many, many years since I helped do lost wax castings at the jewelry store) the burnout took hours.

    Advantages of styrofoam include low expense. Your model making supplies (styrofoam) can be free. I suspect that sand would also be cheaper than investment powder. Another advantage is that styrofoam is much easier to carve than the wax used in metal casting. Ease of carving and no separate burnout process make for a much quicker process. Unfortunately some of the time you save in the casting process may be lost in the extended clean up of your casting. Styrofoam is not capable of holding the same fine detail as wax which is ok because sand isn't able to reproduce the same fine detail as investment.

    Sorry to be so long winded. Hope this helps. :)

    5 replies

    Hey Paqrat :D

    First of all, thanks for the feedback, I really appreciate when you guys comment constructive feedback and usefull experiences! Secondly, I wonder how to work with wax? I've tried it before, but couldn't get the right finish... I just used a knife, so it might be a tool-problem. Please enlighten me on how to carve the wax :D

    Assuming that you are using high density carving wax from supplied by jeweller's stores, there are both wax carving tools and bits and wheels for a flexible shaft pendant motor (cost app. $50-60)

    have you ever attempted to make reusabe two piece plaster of paris molds?....i have cast lead in these....they deteriorate quickly but you get about 3 reasonable casting of diminishing quality before they become throw away......pieces break out of the molds as you remove the castings......i wish to attempt casting in aluminium now....anybody got any ideas on prolonging the life of the mold?....

    i did try coating the faces of the moulds with polyester resin....the plaster absorbes the resin and it sets hard....it helps to keep the mold together a little longer but eventually burns and the mold breaks...

    I have not attempted to make two piece molds. The ones I have made and from which I have only cast two castings, one from each mold were openface molds. I used metal wire wrapped inside the plaster mold that seemed to help the mold hold up but I don't know if it would be enough to do a second casting from the one mold. I purchased some cement designed to be used in furnaces. I thought this might hold up the the heat better but I have not yet tried it.

    I also used the lost foam casting method and already made a miniature Yoda (from Starwars) a octopus and the international mark of scouting (the french lily).

    The techinque of lost wax casting is my next project
    But I liked the instructable very much.


    3 years ago

    Styrofoam burnt gives off dead fumes which are highly toxic (read, can kill in under a minute). If you must do this (wax is a lot better and safer) use good ventilation and fume rated respirator.

    4 replies

    Wax is perhaps safer but also requires you to remove the wax model in some way( it will not burn out the same way the styrofoam will without the use of a kiln). I think there might be a real problem in transporting the sand mould from the burnout oven you have used to burn out the wax model in that during transport the mould could be compromised unless you have mixed something in your sand to make it hold its form. If I were going to use wax to be burned off I'd also go with using investment instead of sand. This does require a kiln of some sort which entails a greater expense both in time and money.

    So far, i haven't been able to try cire perdue casting yet, but I would love to try it!
    When it comes to the ventilation, i hope that being outside counts :D

    The toxic fumes created by lost foam casting are only deadly if they are released in a confined and unventilated area. Performing this method of casting outside is as safe as a campfire: don't breathe the smoke or get too close, and you're fine. If this is performed inside however, yeah, fume hood and carbon-filter respirator (HEPA filters are for fine particle dusts).

    Perhaps I missed it but I did not see anything about waiting for the water to dry out of the sand. I have read that if the sand is wet you run a danger of the molten metal turning the water into steam and blowing your mould up. If it was very wet I think it could possibly harm someone by the steam causing the molten metal to be blown out of the mould

    1 reply

    If you scroll down, you'll see that wet sand is a very debated subject. I suggest you seek for answers in the comments, cause honestly, i'm confused about whether or not the sand has to be dry...

    Hey pretty nice instructable! :D

    I've seen comments about better results with wax or plaster, but this is the best it's gonna get. Casting is just the first step in most parts manufacturing, the part then needs to be machined to it's final form. This is exactly what you should expect from a casted part.

    (if someone else wants to compare, this is a professionally - almost only - casted part https://sidewalkcity.files.wordpress.com/2010/08/brasilia-img_1653.jpg - even though even this one needs a little finishing)

    We did aluminum casting in school "way back when", and my fatherand I both worked in steel mills....this said, another important safety point is that on small items such as this minimal gas is released from the cooling mold, however larger projects require an escape for those gasses as well as slow cooling to prevent gas pockets within the mold or simple pressure exploding the piece. I am not sure at what volume this would be an issue, however it appears to me that it would be safer to place larger pieces so that they had a large area exposed to the surface as oposed to in the casting substrate.

    Great use of the clay pot as a casting pit!!!

    2 replies

    I don't quite understand this part:

    "it would be safer to place larger pieces"

    Larger pieces of what? It might just be me... (I'm from Denmark, and therefore might misunderstand some of the terms/expressions you use)

    But I'd like you to explain it to me. BTW thanks for the compliment on the pot as casting pit :D

    "Pieces" refers to the objects being cast. Like a piece of art, I guess. The word can refer to the object itself rather than a part of something.