EPS rigid mandrel.

General Composites Discussions Composites Talk
#1

Does anyone have any decent information on the use of EPS(expanded polystyrene) formed mandrels in the use of pressure molding composites parts in a billet mold? I have a couple products that I’m looking into moving towards a better prepeg/rigid mandrel and getting away from wet layup over an air inflated bladder due to inconsistencies in the final parts and overall wasted material.

I came across this website, http://www.swiftcarbon.com/design/ and at the bottom it briefly talks about the EPS molding system they use to form their structures.

While rigid rubber mandrels would be ideal in function, due to the shape of the part I don’t think it will be possible to extract the mandrel after the part has cured. An EPS mandrel could be hogged out and dissolved and any material stuck to the part could be dissolved if necessary.

I’m just curious if there are people here who have used this process and if they could provide some information like where to source materials, operating temps, etc. The process is intriguing to me and I’d like to give it a shot and see where it leads if nothing else.

Thanks!

-Adam

#2

I know of a paddle maker that uses XPS (for higher thermal stability) in prepreg parts, and alu moulds. Works perfectly, without any hassle. The XPS is slightly oversized, but the XPS is no match for the press used to close the mould…

#3

I believe they use a thin eps peice the shape of the mold but still inflate with a bladder, the eps piece is there to eliminate voids in small radius corners and help with compaction. So picture from inside to outside- inflatable bladder,eps support,layup.

#4

I was actually looking at XPS as well as that material is more consistent and I could CNC the mandrels with ease. But I’m not sure if EPS is available in a raw form(beads) where I could CNC a single mold that I could fill with the beads or pellets and some kind of binder that would allow me to rapidly replicate the mandrels with little fuss.

My only thought about having the mandrel oversize or the actual size of the mold cavity is how do you prevent the carbon material that wrapped around it from getting pinched in between the mold halves when it’s closed up. All the two part9or more) molds that I’ve created I’ve always had to lay up in the mold havels with stepped overlays, or undersize the layup over and expanding bladder.

This I can see as well, but just add complication I’d like to avoid if possible. The website describes the EPS expansion rate under heating in the autoclave and if it provides enough internal pressure to form their bike frames that in itself will be more than enough for my products which are nowhere near as stressed as that frame.

I guess i’ll just buy some block of EXP and EPS and see what happens during some test runs.

#5

Tossing a bit of EPS does not hurt financially.

The paddle maker had the XPS parts first routed (by hand, with a 20-head copying router). Later he switched to ordering them in the shape he wanted.

He applied prepreg to both mould halves, so catching fiber between the mould halves was no issue.

#6

I’m going to give this a whirl and see what happens. I’m most interested in knowing what temps I have to work with on the EPS to get it to expand but not burn up in flames and go form there.

Guess I’m gonna be baking some foam cookies this week.:smiley: