Using Tooling Foams

General Composites Discussions Composites Talk
#1

I am planning to make a short-run mold (not pattern) from tooling foam. I’ve only worked with alum molds for this kind of part before, so am unsure of how to finish the foam. So my questions are two parts:

The Foam
With the foam being the mold, is something in the 40-48# range necessary (like RenShape 460)? When is it appropriate to use something lighter/cheaper like 15# sign foam instead? This will not be oven cured.

The Finish
I have read some threads about finishing with a paint/sealer, but it seems like having a harder tooling gel-coat would be necessary. Duratec primer would be easier to polish, but will it hold up as a mold surface. What do other people use? Is a different surface suitable depending on the foam density?

The mold does have deep contours, but only a dozen parts will be pulled from it.

#2

Duratec surface primer holds up really well as a tooling surface. It’s as tough as the regular polyester tooling gelcoat that I’ve got here. I’ve used it as a tooling gelcoat when I’ve been in a grind, and I’ve used it to resurface a couple of my other moulds. Works great. You would easily get a dozen parts from it before the surface starts to deteriorate.

#3

Hanaldo - thanks for the input. Duratec primer is much more convenient for us, so that’s good to know. Do you use it on a certain density of tooling board?

#4

I’ve used both the heavier, like 70lb, and lighter, say 15lb, foams.

they both work fine. They’re both a bit fragile and can scratch, but workable. The heavier is more durable and will give a nicer surface.

To seal use a sealer like something from chemtrend. I think typically 3-5 coats. The sealer will give the surface a smoother finish. Of course you’ll want to sand the molds to the desired smoothness after machining.

Just beware when you make a part using the foam… if you make some thing, like say a spar, it’s good to leave one side open or at least not to layup end to end. If you leave some area out of part, then this makes detooling much easier as the difference in CTE from the foam to the carbon can lock some parts in. Be sure you have sufficient draft, or use a multiple part mold.

after sealing, release with freekote.

The molds work well and you can definitely get a good number of parts out of them. if you’re just making 1 or 2 parts, you might also consider something like MDF. I don’t know what the CTE is of mdf, but I do know that some companies use it for tooling.

#5

Do you really think that the Duratec surfacing primer is as good as a traditional gel coat, hardness-wise? I think it is much more easy to scratch it than a traditional filled gelcoat. Most of my experience is with the duratec ‘easy sand’ primer, but I wouldn’t rely on the traditional primer either from my few experiences using it. I wouldn’t even trust the duratec vinylester top coat that I use to finish plugs/patterns as a production mold surface when a traditional gelcoat is available as an alternative. The duratec products are definitely easier to apply, but the ones that I’ve used are all quite soft and easy to scratch compared to a gelcoat resin.

#6

craj, I also think surfacing primer is softer than traditional gel coat…but both seem much harder than just a sealed Ren (say 450) surface. But that seems to be a common practice.

sammy, when you say just seal the surface and then apply mold release, is the surface as durable as a typical gelcoat mold surface? I am picturing sealing with this product that Freeman recommends.

#7

That product is sanding lacquer, which is good stuff and may be ok. Not sure what the temp rating is on it?

Freeman also carries chem-trend sealer: https://www.freemansupply.com/Chemlease15SealerE.htm

And the sealer just seals porosity on a mold. You would use it on a gelcoated/surface coated or uncoated carbon/glass mold, metal mold, or foam mold. The sealer gives a good smooth surface free of porosity.

Then you apply the release. I’ve also used molds with no sealer, just release as well. So like anything, it varies.

But the durability of the mold depends on the material, not the sealer. The foam molds are obviously less durable than a composite mold, but very usable. They can scratch or ding, but so can a composite mold.