Casting expanding foam

Anyone ever try to cast expanding foam to make fins? Once removed from the mold it could be vacuum bagged, either glass or composits.

I think for limited runs maybe the mold could be made of thick MDF coated with poly and a release agent.

With a cnc you could make quite complex foils.

I don't know if this is even possible.

See attachment for my quick idea.

Having only limited experence with expanding foams in nose cone applications, but a good bit in casing of other products, I can't see attemping to cast fins unless you are a production house. Making the original plug fin to make the molds, Setting up the mold blocks, casting the molds, trimming and finishing the molds, running and remaking the molds to eliminate bubble traps etc....... Sorry Orbital I can't see this for making a few fins, WAY to much work. I think you'd be better looking at the MDF as the fin material and bagging it with carbon fibre etc. Unless you are thinking of running 20 to 30 sets of fins or maybe some (8 to 10 sets) of huge fins, then the mold idea may be worth the time.
OBTW If you were making large fins it would seem more effective and efficent to use foamcore as the fin core material with a 1/64th aircraft ply skin, as strong but lighter than what you are proposing.
my 2 cents worth

I realize it would be a lot of work. But I think it would be fun too.



Just curious if anyone had tried..

Hey, I say go for it. If you think it would be a fun project, why not? If the foam doesn't work maybe you can use the molds with hobby resin?

Robert Dehate used a method kind of like this to make the fins for his L3 project. He made a Form then filled it with expanding foam. He then glassed over it all. I am sorry if you are a member of this forum Robert and wanted to post this, I wasnt sure if Robert was a member.

I am not sure what the website it. It used to be on the NSL website but it has been taken down. Does anyone know the URL...Doug...somebody!?!

I found the page

https://www.geocities.com/rdh82000/L3/

Ryan:
your link shows some foam filled wood fins not what orbital was talking about at all. but after looking at the site i question if the foam was even necessary in that application. Those fins could have been stood on with just the glassing.

O okay, I just thought the two seemed related

Okay.. Sounds like it's to much trouble..

How about this???

Use some type of ridged foam, cnc a slot in the back side first to accept a material for fin mounting. Flip the foam over. You will need some type of registration marks so the slot is aligned correctly. Cnc the outside surface of the fins, glue both sides together. Then either cover with glass or composite.

This will eliminate molding issues/headaches.

This may not work either. Who knows.

Attached image illustrates my suggestion.

If I had a CNC mill at my disposal, I would use it to cut fins directly, not create a mold. even if you wanted to make a short "production" run.