Has anyone tried casting or injecting foam into molds for lost foam casting?
I would like to be able to model in clay, create a mold from the model, and then use expandable foam or ? to make the pattern for lost foam casing. Just an idea to allow repeatable casting of complex parts.

i think it will leave to many pores

This is how the 'Big boys' do it. I've got a foam pattern of a meat grinder in my office. It's a full size replica of the thing, just add some sand and melted Ally and you'd have a meat grinder. You need a steel mold and some foam bead powder [for lack of the proper name]. You measure some of the powder out and add it to the steel mold and then hit it w/ live steam. The beads expand and fill the mold and after it cools a bit [ less than a minute I think] you can split the mold and pull the 'part'. The 'beading' of the foam part isn't so bad as it expands against the mold and gives a decent finished surface. It's not the same as when you cut into that beaded foam and its full of voids in the center. [Well, it is like that in the center, just not around the molded surface]

I've seen websites which supply the stuff for making duck decoy's and they sell the molds as well. Didn't find the site w/ just a quick search. I'll have to check into it at home. I might have the site in my favorites.

HTH
Jerry

are you refering to polystyrene. yes they use foamed polystyrene pellets (styrofoam is the trademarked name) and introduce a large amount of steam to their surface. within a mold they will expand when introduced to steam and expand to the point of saturation filling the mold completely. the surface is just as those foam products that are in items that are boxed new from the store, not that good as compared to a foam cut with hot wire cutter. it will work just won't be pretty. becareful though acetone, crazy glue, and some paints will melt it like there's no tomorrow.

http://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Polistirolo_faccia.jpg/799px-Polistirolo_faccia.jpg

Yup Schemo, thats exactly what I looks like. You can see the beading in the part surface but generally thats not an issue. I've seen a alum. head on a car w/ an exterior finish like that.. If you want a better finish, then either hot wire or the 'DOW' type blue foam is needed. I think the hot wire kinda melts off the surface and kinda smooth's it doesn't it? Sanding that junk [ the beaded stuff] doesn't seem to really work, its better w/ the Blue/pink stuff but.. whatever floats your boat I guess..

Jerry

yes, it will work just won't be as pretty. alot of car manufacturers use polystyrene since it's easy to work with.

blue or pink installation foam works best for a hot wire cutter. and regarding the hot wire cutter (cnc) one thing to remember is to take into account how much the wire will vaporize and adjust your design accordanly. the cut from a wire cutter is perfect. and well worth it.

http://www.buildyouridea.com/cnc/hblb/phase5/hot_wire_cnc3.jpg

The blue or pink will not evaporate and disipate in the sand as it is casted. The eps styro is better for this. The blue does do some neet things when melting. I have seen the top of the part beeing cast have an almost leather look to it because the styro. puddled at the top oif the mold and didn't evaporate.

The blue or pink will not evaporate and disipate in the sand as it is casted. The eps styro is better for this. The blue does do some neet things when melting. I have seen the top of the part beeing cast have an almost leather look to it because the styro. puddled at the top oif the mold and didn't evaporate.

was there proper ventalation? i never heard of that before, from my experience that foam always melts, stange

How hot was your pour? Typically for foam you have to pour hotter than for a green sand setup, correct?

Jerry

This was at a large foundary .I have not done it by myself. I was cnc cutting there runners they used to make the drive wheels for the case IH tractors that have the rubber tracks on all four wheels. While they said the blue foam would work it could have some of these problems. They had a vacumn set up on there vats and would burn the air as it came out during the pour.I had done some small things that they cast for me in blue foam and it had some of the leather look to it.

Hunters expand polystyrene in duck molds for decoys. They use closed and clamped molds and boil them in 55 gal drums...
Check it out:
http://ca.geocities.com/nbcc2@rogers.com/eps/epsdecoys.htm
You could use a lost wax process to make your molds,then do like the duck hunters to produce your foam positives. Seems like a lot of work, though, (when you could repeat your patterns in wax and use a lost wax / shell casting...)

There is quite a difference in the way that expanded polystyrene (eps) and extruded polystyrene (xeps) are manufactured.

http://www.dyplastproducts.com/newsletter/more_xpseps.htm

I've had mixed results in casting aluminum with both types. Can't conclusively blame the foam, though. Seems like everything has to be 'just right' when casting. Temperature, pour rate, proper venting, etc.

The extruded polystyrene does have a much smaller cell structure and will leave a better finish ( if everything else goes right) .

are you refering to polystyrene.

Love this site, there's another problem solved :)

I want to make a pattern for some axle boxes, basically a hollow cast iron cone. I was bogged down wondering what the heck to make them from and how to cut 15" tapers.

Now all I need is a 15" resistance wire and the foundry costs can only come down :)

I have used the blue foam and white styrofoam to make several castings in Al. I have had the foam's vapor flash (fire) and blow out chunks of liquid AL during the pour. Be carefull with new foams you have not used a lot.

I hack out the part close to size with the foam then mill it to size for a quick and cheap part.

My biggest home cast part was a bed for a horozontal mill weighing in at 22 lbs. It was done with a wooden pattern, petro sand and two people holding a bar hanging the crucible while I tipped it for the pour.

JIM

I've been looking into the same type of thing, and have found that there is a pourable marine foam that should do the trick. I havnt tried it yet but I believe this would be our best shot.

I've been looking into the same type of thing, and have found that there is a pourable marine foam that should do the trick. I havnt tried it yet but I believe this would be our best shot.

The polyurethane foam products are pourable, but you can't use them for the lost foam process. Polystyrene-based foams will burn away (relatively) cleanly; the polyurethane foams generate extremely toxic combustion products. Remember Bhopal? The people there were poisoned by the same chemicals generated when polyurethane is burned - isocyanates and hydrogen cyanide. Don't even think about burning this stuff...

Andrew Werby
www.computersculpture.com

PS: Look up the MSDS for the product you're contemplating, and see what it says about burning it.

Thanks for pointing that out. I was going down that road.
Is there any other pourable expandable foam that one could use other than polyurethane foam? I'm making molds for the positive plug on a 3d printer out of abs which I don't think will stand up to heat needed to expand polystyrene.
Another question...how much will plaster shrink if I were to build up enough plaster around the foam part, more than just dipping it, then disolve it out the polyurethane foam and pour aluminum with no foam in the mold?

Thanks for pointing that out. I was going down that road.

Is there any other pourable expandable foam that one could use other than polyurethane foam?

[Not that I know of.]

I'm making molds for the positive plug on a 3d printer out of abs which I don't think will stand up to heat needed to expand polystyrene.

[I think you're correct there...]

Another question...how much will plaster shrink if I were to build up enough plaster around the foam part, more than just dipping it, then disolve it out the polyurethane foam and pour aluminum with no foam in the mold?

[If you've got a 3d printer, why not make a positive model, take a rubber mold from it, cast wax into the mold, and treat the wax like a regular lost-wax part, casting it in aluminum via shell or investment casting? If you can't do this, any art foundry can. Also, some 3d printers (Perfactory, Solidscape) can produce models from a waxy material that can be burned out directly.

Trying to dissolve polyurethane foam out of plaster sounds like a nasty job to me; I certainly wouldn't want to be in the same room where that was going on (and PU is pretty resistant to most solvents; try getting it off your clothes sometime). Then you're left with plaster filled with solvent and PU; not something you'd want to pour metal into anyway. You're much better off relying on tried-and-true casting techniques than trying to invent new ones; people have been casting metals for thousands of years, and the processes, while they've improved somewhat, are basically the same as they ever were.
There are a few ways to do it right, and a whole lot of ways to do it wrong, with results ranging from bad castings to painful lingering death. Unless you're really an expert at this, I think you'll have better results by relying on people who are...]

I think there is some confusion with using foam. Most foam casting is by machining the foam to the part size needed, leaving a little extra foam where there are critical diminsions so it can be machined after casting. The foam is put in the mold box and sand rammed up around it to make the mold and the metal poured onto the foam, burning the foam away. The sand is the mold and will hold it's shape if properly tempered or petro bonded.

The foam machined to size because foam can be cut very fast and with almost no tool wear. Complicated shapes can be cast with no waisted metal. Think of milling out a custom L bracket. You end up with more chips than is left in your part.

I may be wrong but I have never seen foam burned out of a mold like wax has to be.

Most of the stuff I have read about as well as what I have cast with foam were peices starting at 1 pound and going up to engine blocks and cylinder heads. I don't think it would work as well with jewelry size parts unless you had a big sprue to force it in past the burning foam.

JIM

[If you've got a 3d printer, why not make a positive model, take a rubber mold from it, cast wax into the mold, and treat the wax like a regular lost-wax part, casting it in aluminum via shell or investment casting? If you can't do this, any art foundry can. Also, some 3d printers (Perfactory, Solidscape) can produce models from a waxy material that can be burned out directly.]
That sounds fine to me. How hot does the wax have to be to melt? Would it be too hot to pour into an abs mold? I'm trying to build an automobile intake manifold. I've already compensated for the aluminum shrinkage how much more would I have to compensate for the plaster shrinkage in the mold?
There's a couple reasons I'm not printing a positive, one the printer isn't big enough for the whole part, although I suppose I could print it in parts, two I only have access to an abs or a powder printer so a wax part isn't in the cards for me and I'm trying to do this on a budget to see if the part will even work. If it does I'll spend the money for propper tooling until then I'm going as cheap as I can.

Trying to dissolve polyurethane foam out of plaster sounds like a nasty job to me; I certainly wouldn't want to be in the same room where that was going on (and PU is pretty resistant to most solvents; try getting it off your clothes sometime). Then you're left with plaster filled with solvent and PU; not something you'd want to pour metal into anyway. You're much better off relying on tried-and-true casting techniques than trying to invent new ones; people have been casting metals for thousands of years, and the processes, while they've improved somewhat, are basically the same as they ever were.
There are a few ways to do it right, and a whole lot of ways to do it wrong, with results ranging from bad castings to painful lingering death. Unless you're really an expert at this, I think you'll have better results by relying on people who are...]

I agree, I don't want to mess around with any of that stuff, that's why I'm here asking questions. Part of my problem is I don't know enough to ask the right or relevant questions.
Thanks

One more question. I've modeled a mold to cast a foam plug in that will be produced on an abs 3d printer. What if I were to make the mold out of plaster? That is print a mold for the mold to expand foam into. I could expand polystyrene in it and go with the tried and true lfc techniques...right? I've attached a SolidWorks edrawing html file so you can see what I'm talking about.
Thanks

Any input or info about the dimensional stability of plaster? Does it shrink when it cures? If so is there a predictable rate of shrinkage? What would that be?
Thanks