Hey all,
I’m working on a project that has all of the engineers in my department stumped and we are all searching for answers.
We have a part that we are molding in Nylon and are getting varying shrinkage rates, enough that we are now looking at making a set of core/cavity inserts for our mold for the 3rd time.

The Nylon we are using is a pure/prime/virgin batch that has a listed shrinkage rate of .020” per inch. I designed our first iteration using that in mind and the parts came out way too big. I measured all the parts and found that they actually had a shrinkage of around .009”/inch.
We turned around and remade the mold again using this new shrinkage rate, however now the parts are showing only a .005”/in shrinkage.
This most recent batch used the exact same batch of material, use the same machine settings/parameters in terms of cycle time, temp, etc. We are scratching our heads and grasping at straws trying to determine the source for this variance in shrinkage rates.

This uses Nylene 4114. We dried it over a 24 hour period prior to each use.

Has anybody run into something similar or does anyone have a potential cause?

I appreciate any of your support,
Thanks