Need Help!- Vacu forming EPS foam

[Trimakas]

Anyone have any luck forming eps foam? My idea is to layer formed abs over the foam.. I wonder if I could thermomould it or how to shape it
Thanks

[keebler303]

I have no direct experience but I would think it would turn into a huge mess once you heated it up. You would also lose some of the loftiness as it would tend to deflate when you heated it and moved it around. Most folks wire cut or machine foam.

Matt

[AMCjeepCJ]

There is nothing particularly hard about forming EPS, if you build a reinforced mold that can handle a little pressure and steam, you can dump the "prepopped" bb's in there and mold them. We build EPS molds along with the steam chests and core vents, etc. and there is very little in the way of difficulty in producing the parts on a small scale if you research it a little bit.

If you are strictly talking about reheating EPS and forming it like you would a plastic sheet, I don't see that happening but I could be wrong... I say go for it and let us know how it works!

[Belaruz]

Originally Posted by AMCjeepCJ There is nothing particularly hard about forming EPS, if you build a reinforced mold that can handle a little pressure and steam, you can dump the "prepopped" bb's in there and mold them. We build EPS molds along with the steam chests and core vents, etc. and there is very little in the way of difficulty in producing the parts on a small scale if you research it a little bit. If you are strictly talking about reheating EPS and forming it like you would a plastic sheet, I don't see that happening but I could be wrong... I say go for it and let us know how it works!

That seems interesting to me, would you please confirm if I have understood you correctly and explain a bit further?

Is it this type of foam that you can mold in the way you talk about?

And you just pack pack those pellets, which you still can see the shape of in a factory made board, into a mold and heat it with steam?

From what I have read I have understood that you can buy those expanded pellets from some suppliers.

Does the steam need to be superheated?

How precise shapes can you create molding it this way? If you mold something like the picture below, a rod with a diameter of 40mm with a groove with a width of 3mm, would the corner where the groove begin to cut into the rod be sharp?

[AMCjeepCJ]

Yup, that is exapanded poly styrene...

You can buy them prepopped or in granular form, our customer buys it in granular form by the freightcar load.

You don't need to "pack" them in, they are normally gravity fed into the mold out of a tube.

You got me on the steam question, I do not know the exact temps required for the different thicknesses and materials BUT a quick call to the supplier would fix that for you.

As for precision, that is a tough one to answer because it depends on the density of foam you are molding. You can get up to four pound density relatively easily and the higher the density, the better tolerance the part seems to hold. Our customer is pretty well known for having extremely high density products and holding abnormally tight tolerances in the industry. I cannot say "how" it is done since it a trade secret of his but I can tell you it isn't difficult if you experiment with it and keep your mold tolerances tight along with a good handle on your shrink factor.

Another thing worth noting is that the higher density you produce, the easier it is to machine and the 3.5-5.0 density will mill with a HSS endmill fantastic in a milling center.

The whole trick in a nutshell is taking detailed setup notes and only changing one variable at a time. Keep track of the contraction rates (shrink) and eliminate as much variability as possible, there is no reason you cannot mold extremely close on your parts, not the same as injection molded pieces but very close none the less.

As for your part, are you asking if you could mold a solid part exactly like that? Absolutely, but if you are asking if you can mold one with thin walls, no... You'd need too much draft to eject the part and would be better off wire cutting in that case.

[AMCjeepCJ]

Yes, you can get a fairly sharp corner but not dead sharp...

[Belaruz]

Originally Posted by AMCjeepCJ Yup, that is exapanded poly styrene... You can buy them prepopped or in granular form, our customer buys it in granular form by the freightcar load. You don't need to "pack" them in, they are normally gravity fed into the mold out of a tube. You got me on the steam question, I do not know the exact temps required for the different thicknesses and materials BUT a quick call to the supplier would fix that for you. As for precision, that is a tough one to answer because it depends on the density of foam you are molding. You can get up to four pound density relatively easily and the higher the density, the better tolerance the part seems to hold. Our customer is pretty well known for having extremely high density products and holding abnormally tight tolerances in the industry. I cannot say "how" it is done since it a trade secret of his but I can tell you it isn't difficult if you experiment with it and keep your mold tolerances tight along with a good handle on your shrink factor. Another thing worth noting is that the higher density you produce, the easier it is to machine and the 3.5-5.0 density will mill with a HSS endmill fantastic in a milling center. The whole trick in a nutshell is taking detailed setup notes and only changing one variable at a time. Keep track of the contraction rates (shrink) and eliminate as much variability as possible, there is no reason you cannot mold extremely close on your parts, not the same as injection molded pieces but very close none the less. As for your part, are you asking if you could mold a solid part exactly like that? Absolutely, but if you are asking if you can mold one with thin walls, no... You'd need too much draft to eject the part and would be better off wire cutting in that case.

Originally Posted by AMCjeepCJ Yes, you can get a fairly sharp corner but not dead sharp...

Thank you for your answers, this does certainly seem worth looking into.

I do understand that a hollow shape as the one in my picture wouldn't be possible to make but I used it just as an example of the groove's placement.

The groove would easily be wire cut so that's probably easier to do that way and then there isn't any corner that need to be dead sharp.

I live in northern Europe, in Sweden, and CNC hot wire cutters aren't that easily available here. I have been thinking about building one but haven't gotten to it yet.

The part I would like to make is part of the leading edge on a model airplane and I need rather large quantities, I could easily use more than 200 if my club-mates also wants their made this way. That amount is a bit tedious to wire cut manually so I'm looking for improvements.

Since it's a part for the leading edge it is tapered towards one end. That would surely make it easier to extract from the mold. While wire cutting manually it's a problem on the other hand, since it causes problem if you fail to manage to keep the movement even on the differently sized ends.

Just a week ago or a little less I was watching videos on youtube and found several sets of equipment like this,

link

link

, I thought that equipment also made the expansion of the foam but now I guess that's the type of equipment that you make molds for, that's filled with pre-expanded pellets.

Originally Posted by Trimakas Anyone have any luck forming eps foam? My idea is to layer formed abs over the foam.. I wonder if I could thermomould it or how to shape it Thanks

To the OP, I apologies if you think I have taken this off-topic but I thought this method could be of public interest.

While browsing youtube I found a video of a machine that does something similar to what you want at least.

Link

Link

Vacuum forming thin sheets of EPS. But it's using rather large radiuses compared to the thickness of the foam, if you can't do that too your application might not be possible.