Long term dimensional stability of engineering resins

Hi, im interested in using one of the engineering resins, either durable or tough to make production parts.
They are low volume, small in size and a real pain to CNC from Delrin or Acetal copolymer.
I was wondering if anyone had any experience with their own printed parts and if they change dimensions over time? These will be hidden from sun light and not experience extreme temperature or humidity. In most cases, they will be in a normal indoor environment, however they should not shrink or expand very much for at least 25 years.
(I know the resins are new but I am hoping someone has some advice)
Formlabs official response to me was that “I should do my own testing as they did not have that data”.


Formlabs will obviously not guarantee a 25 years lifespan, and really no one will with SLA resins as the technology isn’t much older than that (less than 35 years since the original patent).

That being said, fully cured photo polymers are pretty stable and should not out-gas or change characteristics much. We use Tough for small productions parts, one which is submitted to light and slow temperature cycles (20-50°C) with little force applied to it, and another which is submitted to a significant amount of force (for a plastic component) in pure compression and we’ve been doing this for almost two years without issues.

Could you cast these hard-to-machine parts out of a polyurethane or epoxy resin that is advertised to be stable for 25+ years? You could print the positives and/or molds, at least.

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Will the parts be under any sort of load / strain?

There is some creep, over time. I made a replacement bracket for a keyboard tray out of Tough v1 and it stretched quite a bit after few days installed. I did a new one in Standard resin and it’s kept it’s dimensions much better (it’s been in service several years now). Note the part is under a moderate amount of force, and there have been significant improvements between Tough v1 and the current Tough v4. Regardless, last time I checked Formlabs doesn’t recommend Tough for static loads, and it’s still (in my opinion) nothing like a practical replacement for ABS.

I’ve been really impressed with Rigid, especially for chunky parts. I have a variety of brackets printed in Rigid which have been hanging for several months, again under load, and I haven’t yet noticed any significant deformation. If you want to minimize long-term creep, that would be my go-to. Note it’s not recommended for moving parts that will rub against each other. It’s also one of the most brittle resins (we tried using it for small models but tiny bits broke off too easily compared to Tough).

I’m told Grey Pro was engineered to minimize creep over time, so it might be worth a look as well.

I haven’t used Durable. While I hear it has the best impact resistance (great for stuff you’ll drop) and resists wear and tear, I don’t think it’s optimized for dimensional stability over time if your parts are under any sort of constant load.

I’ve come to think of the Formlabs resins as a spectrum of stiffness / brittleness vs. flexibility / droopiness. That’s an oversimplification that will probably make some of the engineers groan but it works for me.

Here’s a brief summary of the engineering resins: https://support.formlabs.com/s/topic/0TO1Y000006mfNrWAI/engineering-resins

If you go here, then click any of the links under Engineering Resins, it tells you in more detail which applications are recommended / discouraged for each: https://support.formlabs.com/s/topic/0TO1Y000006mfMdWAI/materials

The interactive chart at the bottom of this page might be helpful:

A blog post discussing various metrics referred to in the chart:

Hope this helps.