LOST FOAM CASTING


This page has to do with LOST FOAM casting, and it's worth to the hobby foundry. The following is based on my experience as a patternmaker and the foundry work I've done at home. I want to see if it's possible to get an industrial quality lost foam casting, at home, and what work would be involved to get there.

Pros:
No pattern storage, pattern is burned out on casting.
No special sand requirements, silica sand can be bought at a local hardware store.
No major cash for tools, foam can be cut with just about anything.
Nothing more than a hot wire could be your only cutting tool.
Simple patterns can be made quickly, with little effort.

Cons:
One pattern one casting, if it doesn't work the first time you start all over again.
Surface finish is rough, if trying to cast without using lost foam sealer, of some kind.
Tools and equipment required to build an industrial type lost foam casting, can get expensive.
Complex patterns are difficult to make in the average home shop.
Minimal amount of detail can be put into a pattern, no fillets etc. without a lot of work.

The pros and cons are really meaningless, it all comes down to what you want to do with your casting and how you want them to look when your done. I'll try to explain the process I used to create the casting shown at the top of the page. In this case I'm building a venturi for a burner. Using a CNC mill to cut the pieces of the pattern then gluing them together. Other methods could be used but I chose this one for two reasons, because I can and using the cnc I can accuracy and details that would be missed if cut with a hotwire or other methods of cutting.

After cutting your pattern by whatever method you choose, you may have to glue the pieces together.
I use the spray on contact cement. I spray it on a piece of scrap, paper or other. Then wipe the matching
surfaces in the wet cement, let the cement tack and put together. In this case two pieces are already glued.
Then I'll glue the other pieces together, finishing by gluing the assembled piece into the just glued pieces.

This is the casting, I added nothing to the foam to improve the surface quality. I wanted to see how the casting
would look in it's unaltered state.
I made two patterns, one using the white beaded foam and one using the pink insulation foam. These are the 2 typical
foams used by the backyard foundryman. The beaded foam has a better finish just a lot of pits between the beads.
The pink foam is rough like sandpaper, some is caused by the grain size of the sand most is caused by the porosity
of the foam. Later I'll go through how I made the patterns, this will be done in the CNC PROGRAMMING page.

The following is a study in surface finish. I made a simple pattern and tried to duplicate what others have suggested to get a better surface finish. The test part is 5 sided one side is just foam, then a foam sealer used for model airplanes, another side uses white glue and the side opposite used spray glue, finally the last side used masking tape. In each case more care could have been taken to get a better surface finish, but I was just trying to get an idea of how the changes, in surface might look.

Sanded foam
no finish just sanded smooth.

Sealed foam
model airplane water based
foam sealer.
White glue
about 3 coats of glue. Dried
overnight before casting.
Spray glue
spray contact cement,
allowed to tack.
Masking tape
tape is just butted together.

I also tried the pink construction foam. You'll get a better overall finish with this foam. The only real problem I had with it is the piece I'm was making required a thin wall to be machined. The pink foam will move out of the way of the cutter, or be pulled into it depending on the cutter direction. This caused the thin area to be undercut. Overall the beaded foam, because it's more rigid, will probably make a more accurate pattern. The pink foam will give a better finish, but with a thin wall it's more likely to move when filling the mold with sand.

There's still a lot more to do, but my overall impression, so far, is that lost foam is not the best way to start out casting. You may get a casting that works, but the frustration level could be high, if trying to duplicate the results of a foundry specializing in lostfoam.

MORE TO FOLLOW AS TIME ALLOWS


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