Fiberglass mold

I’m trying make a fiberglass mold from a plug printed with clear v2, it’s hollow with 2mm wall thickness. Never done fiberglass, I hear the resin gets hot enough to melt plastic. Will clear v2 hold up to the heat?

How hot is hot? After 180 F the Clear 2 will get very pliable. There is a high temp resin that might be better for what you want.
I make molds directly from the clear 2 here with silicone and organic rubber for zamak and pewter items. They do hold up enough to make a good mold 325 f under 25 tons for one hour but the masters are usually junk after and will just crumble. Mold cavities do come out great.
If your considering making multiple parts in fiberglass then you may want to make a silicone rubber master and a good mold release.

FIberglass resin might get into the >150ºF range when curing.

i wish i could use silicone for a mold, but im trying to make a hollow carbon fiber part out of a 2 part female mold. Im going to use an internal bladder that will put pressure on the mold, i think silicone might distort while under pressure.

ok, i think i will use the spray foam stuff from home depot to fill the void and add needed stiffness.

By fiberglass and resin, I’m assuming you mean polyester resin? If you are worried about heat, use a laminating epoxy with a longer work time and you should see less exotherm (self generated heat) than polyester. You will also have a more dimensionally stable mold using epoxy. Leave polyester to boats and bathtubs. Also, using polyester for carbon parts is also a no-no in the composites world. Epoxy all the way. You will want to make sure your pattern is released extremely well. At a minimum, 6-8 coats of a good paste wax and a nice coat of PVA.

I’ll leave it to the Formlabs gang for final, but molding fiberglass can be any temp you want when you crank up the catalyst. Just a function of cure time and thickness of the mold. Have noticed some of the resins to be somewhat heat sensitive. Epoxy, Vinylester, Polyester? There is “tropical” mix for slow epoxy cure, and staying below 1.5%MEK slows the cure for the non epoxy resins. Yeah, needed a fire extinguisher once. Completely controllable process… just get the ingredients right.

Definitely agree epoxy is the proper choice for carbon. Also set up a heated post cure chamber to get things tightened up.

Thanks for the input guys, yes I’m using high temp tooling epoxy, I want to use preprogrammed carbon fiber.

We paint the hulls black and it gets to 165 or so just from solar. These are 60ft things so not real sure on scale factors, but heat is heat. And epoxy is by far the best option with carbon.

Also would recommend infusion techniques as carbon is wicked hard to see when the fabric is fully wet out with carbon. Prepreg takes care of that, but post cure is critical. Not sure if autoclave is completely necessary… out of my pay grade.

Just a quick note to mention that I have been using the high temp resin to print molds that then go into a vacuum bag and oven, using prepreg carbon fiber. It took me several tries to get the mold right, the high temp material is fairly brittle.

Sounds interesting, Any pics or your moulds if possible, I was thinking of this same but adding some ribs like you would on an injection moulded part…

I read in yor post that you are going to use prepreg. Most readily available prepregs will have a cure temp higher than the standard resins.

If you are planning on a blow mold (air bladder) I would think that high temp resin would be a little too expensive because of how thick it will need to be.

You’ll want to print a mold for your tool and cast that in a good tooling resin (aluminum filled works best for me). BJB, Alumilite, and Smooth-on all have these. Cast tools have always lasted longer for me compared to printed tools.

So after much experimentation/struggling with the high temp resin for prepreg carbon fiber molds, I have gone from the thick and heavy end of the mold design spectrum to basically just printing a veneer type of mold that is disposable.

I know that’s the opposite of normal mold making advice, but the high temp material is so very brittle that I’ve cracked it each time the mold cooled down on both the thick and heavy molds and the thin ones, and one size in between. I think it’s residual stress from the cured carbon fiber… So now I layup my part on a dummy mold that I printed in the tough material, and then transfer it to the veneer type high temp mold for vacuum bagging and curing (-70 psi vacuum and 250 deg F temp). My parts are pretty small so I can do this for about $10 worth of resin per disposable mold. De-molding has also proven very difficult with the high temp material, even after hand sanding at 600 grit and a full 10 coats of high temp release compound. All that said, I have been getting excellent compaction and decent dimensional tolerance with it at the end of the day. I’ll put some pics up later this week

De-molding has also proven very difficult

Are you using any kind of mold release?

yep. May need to try another type tho

With the high temp you will need to cure for an extended period. It will have an amber tint to the material when fully cured. If the interior of the material is a little green it can weep to the surface when heated and cause issues.

I’ve had to cure thin walled parts for 5 hours to get things fully cured.