Making Molds for Rigid Urethane from Flexible 80A?

Hello all,

I’ve searched online and through forums on the issue of printing casting molds (not injection molds) with Flexible 80A. We’re casting 2-part resin rigid urethanes (not molten thermoplastic), and prefer to make one-part molds to diminish the amount of sanding we need to do.

Consequently, the mold needs to both be flexible enough to survive having the casting pried out (by hand) and durable enough to return to shape afterward. (We usually use Silpak tin mold silicon for this, but there are cases where printing the mold directly would save many labor hours). The mold wouldn’t need to last more than 5 or 10 castings.

There are a few references to things like this here on the forums, but most are old and none seem to be in relation to the Flexible 80A. I’ve heard the Flexibles are fairly new. We’re considering just buying a new tank and a bottle of the Flexible 80A and experimenting, but I’d like to first be able to at least give my bosses a “maybe” as to the question of if this will work.

this is quite interesting topic so I will be watching for more replies as well.

for now I only made hard printed molds out of STD Grey resin for softer urethane pour but also thinking about soft molds. for rigid resins
in any case I’m using Smooth-on mold release spray to prevent sticking and its working great


So, from doing a little more digging, it seems like the 50A is probably a better choice. We more specifically use MPFX mold silicone with a shoreness of 25A for our molds, so that will be a closer match for pliability.

We definitely use that mold release for a lot of applications. That stuff is great.

Have you done any more experimenting with printing molds to be used with rigid resins? Just curious what your results were?

So, I talked to a friend who has more experience here, and he said he tried using the Flexibles to make molds, and it was kind of a disaster. He said it didn’t matter what kind of mold release he used or how much, he could not get the castings to separate from the mold.

So, in short, the answer to my original question is a very bold “no,” you cannot use the Flexible resins as molds.

I also should give a shout out to smooth-on’s release compound. I;ve only used it for silicones but it’s good stuff (needs a vented place to spray on though)

I do tons of silicone from Tough 2000 molds, but not anything like what you’re seeking… yet.
I would think you might need to do an extra step and cast molds out of silicone (molds to make molds) and then cast your desired parts.

Well, that was why I presented the question, to find a way to avoid having to do that extra step. Making the silicone molds can take anywhere from an hour to days, depending on how complex the object is.

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