Introduction: Lost Foam Casting

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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.


paqrat (author)2015-03-24

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. :)

Dr_ain (author)paqrat2015-08-26

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

AbubakrS3 (author)Dr_ain2017-07-26

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)

afridave (author)paqrat2015-08-21

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?....

afridave (author)afridave2015-08-23

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

paqrat (author)afridave2015-08-22

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.

ROFLalways (author)2015-08-28

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.

baysel (author)2015-02-27

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.

paqrat (author)baysel2015-03-24

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.

phil2544 (author)baysel2015-03-03

Burning a small amount of styrofoam (like in the instructable) won't harm you or the environment significantly. It would take a lot, before it could hurt anybody, and haven't seen Dr_ain inhale large amounts of styrofoam.

Read more :

Dr_ain (author)baysel2015-02-27

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

Clever_Alchemist (author)Dr_ain2015-02-28

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).

paqrat (author)2015-03-21

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

Dr_ain (author)paqrat2015-03-22

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...

Fikjast Scott (author)2015-03-14

Lots of great things in your instructables, the pots etc.. I like the use of the can ring. great job

Dr_ain (author)Fikjast Scott2015-03-14

Thank you, nice of you to give examples :D

vfernandes4 (author)2015-03-05

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 - even though even this one needs a little finishing)

ajs1313 (author)2015-03-03

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!!!

Dr_ain (author)ajs13132015-03-05

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

WurdBendur (author)Dr_ain2015-03-05

"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.

Creak (author)Dr_ain2015-03-05

I think they mean, if you were casting something as large as a brick vs a keychain. In that case you may need an escape for the expanding air heated be the molten metal to prevent an explosion. So, vent holes along the piece?

PopsicleGhoul (author)2015-03-01

Nice casting! I like your robot.

You may want to try using plain sifted play sand. I found that it creates a smoother surface. The sand doesn't need to be wet (moisture can create steam imperfections) because the aluminum will fill the cavity left by the vaporizing foam before the sand can collapse. I've also heard that coating the foam mold in drywall plaster can make a smoother finish. Great job on the forge, by the way!

Dr_ain (author)PopsicleGhoul2015-03-02

I actually tried using dry sand, but the mold collapsed, and ruined the casting.
But great tip about the plaster! It sounds like it will work :D

Bosun Rick (author)Dr_ain2015-03-02

The use of "dry sand" was the cause of your collapse. The sand needs a certain amount of moisture to hold it's shape (if it packs lie a snowball, that's close). I learned sand casting with aluminum in high school, but the patterns we used were wood or aluminum, not Styrofoam. we had to make 2 sided pouring flasks, (one patterned, the other just flat for wall hanging). the sand was sifted into the forms, then packed with wooden 'mallets' IE: baseball bat sized round stock but without a handle, you just held them in your hand and GENTLY firmed up the sand around the pattern. A wooden dowel was used to make the pour spout, and welding rod was used to form vent sprouls (the porcupines mentioned elsewhere) for air escape. Were I to make a casting in the manner of this I'ble, I would apply a light coat of carnauba paste wax, or perhaps a dipping coat of beeswax to achieve a smooth and more presentable surface to ease a final finish. Great I'ble, and I hope this information will help someone else.

DIY-Guy (author)PopsicleGhoul2015-03-02

Nice, quick, simple.
Does anyone know if dipping the styrofoam in wax will interfere with casting?
Perhaps a thin coat of wax would burn off during the casting process and still leave a very smooth face?

Dr_ain (author)DIY-Guy2015-03-02

I'll recommend you try coating your styrofoam in wax, and then give it a layer of plaster, it should make a very smooth surface.

tomatoskins (author)2015-02-27

This looks amazing! I've never done anything with casting before. Do you like lost foam or lost wax casting better?

thormj (author)tomatoskins2015-03-02

In general, lost wax is better for details because you can pack the part better/more completely (dip in plaster of paris, dust with sand, repeat 3x to make a "breaded model") -- the plaster results in an exceedingly fine/smooth surface. You have to bake it and support it with care, and be sure you have enough vents because the plaster is airtight at pouring speeds (you can mix extra stuff in that hopefully gives more of an airstone effect, but I haven't gotten there yet).

However, lost foam comes into its own when you get it right -- for a while, the auto manufacturers were doing lost foam casting on cylinders -- and when they got the foam, sand, etc right, they bragged that they only had to hone the cylinders (and no longer had to machine every block).

And lost foam is great for prototyping - no drying necessary if you're using sand (use a green sand formula)... you can even print it with a 3d printer (HIPS). I've done lost-PLA, but haven't gotten to lost-HIPS yet. PLA takes a long time to burn out. If you're doing this, get a 3doodler pen, and you can attach vents willy nilly (and the metal doesn't seem to want to go into the 0.3mm threads, so you don't end up with porcupine models) -- trapped air is the enemy!

As far as I know, lost wax is used more in the jewelery biz. You have to carve up your wax, cast it in plaster, and then melt out the wax in a furnace which also helps harden the mold. After it has cooled, you then use a centrifuge to help force the metal in to the void of the melted out wax.

I have used the Styrofoam method for larger items and had only ever done it with aluminium. It worked good, gut we also had proper sand for casting.

I would say both methods are different in my opinion of what I know

Dr_ain (author)tomatoskins2015-02-27

When it comes to casting, i'm pretty inexperienced, and have therefore never tried lost wax casting. But i think lost wax casting might gives better results...

The Green Gentleman (author)2015-03-02

I'm gonna go all armchair expert on you, but maybe someone can correct me with practical knowledge: motor oil instead of water to make sure the sand holds together, while avoiding possible BLEVE? Thoughts?

That, and like everyone else, I'm enamored with your bellows-powered forge. Super awesome!

snoopindaweb (author)2015-03-01

Where there's a will there is a way. Thank You. ~(:-})={>---- ]

clistul (author)2015-03-01

thats prety frickin cool

fburzaco (author)2015-03-01

Thank you, I'm excited about trying it out! :)

spylock (author)2015-03-01

Im with "thingy" you should do an able on the bellows.Also good job,never saw it done like that.

JoãoCruz (author)2015-03-01

you should dry your sand as much as possible, it looks like its not dry.

nice clean setup, well done :)

Dr_ain (author)JoãoCruz2015-03-01

Thank you :D
How should i dry the sand? By heating it, or waiting for the water to evaporate?

JoãoCruz (author)Dr_ain2015-03-01

the best way is by evaporation, small amounts at a time.

also you should try the lost wax method, you will get better results and its better to give form :)

wmistler (author)2015-03-01

I learned lost wax in high school. Since safety was unknown to me then, I took the technology home. I'd make my object out of wax, set it in plaster, lose the wax in Mom's oven, and fill it with lead melted with Dad's blowtorch. Yes it was a steamy explosive reaction. I'm really surprised I have all my fingers and eyes with the stuff I did in my youth.

kumiko (author)2015-03-01

Wow, that's amazing. I never knew such a technique existed before!

How do you cut the extra piece of metal from the top of the robot after casting?

Dr_ain (author)kumiko2015-03-01

I just used a hacksaw. It's important not to use electric tools for that, the aluminium might ruin the grinder.

thingy (author)2015-03-01

I'd be really interested to see how you constructed those bellows. Nice ible.

Dr_ain (author)thingy2015-03-01

I actually thought of making another bellows, if I ever do so, I'll make an instructable for you guys!

dschmidlkofer (author)2015-03-01

Consider yourself very lucky you did not have a serious accident because of the sand mix you used. Lost foam casting should be done with clean dry sand. When the foam burns it releases a large amount of gas that must go somewhere. With dry sand it can vent through the sand itself. Also your mix looked very wet, this moisture will flash to steam when the metal is poured in, adding to the amount of gas that must be vented. With the mix you used, the only place it can go is back up through the molten metal. Which could blow back in a shower of molten metal. Your sand-clay mix would be used for green sand casting. Where a pattern is used to make a mold from sand, then vents are cut in the mold to allow air and steam the sand to escape.

Dr_ain (author)dschmidlkofer2015-03-01

Thanks for informing me on that, I'll make vent holes next time.

matternat (author)dschmidlkofer2015-03-01

That is exactly what I was going to to say, people should do some research before they go play with molten aluminium. I love the bellow though.

Tommunbeig (author)2015-03-01

I still have a mat white painted block of aluminium that I cast in teaching practice.

It always raises a smile when you hand it to somebody new.

samuraijack (author)2015-02-27

i give it a thumbs up...

Dr_ain (author)samuraijack2015-02-27

Thanks :D

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