Hello, I've searched the forums, but haven't found this.  If I want to properly post-cure a resin-infusion CF part, in-mould, will the fiberglass mould be ok for post-curing?  I'm concerned about thermal expansion differences between the fiberglass mould and the CF part creating distortion and also about damaging the mould with the higher temperatures.

Is this only an issue if using high-temp epoxy resins?

Is everything ok as long as I use the same epoxy for mould and part?

I'm hoping that I don't have to make moulds out of CF just to get a good match for post-curing. 

If high temps in post-curing are an issue, what are the problems with post-curing without the mould and what are some techniques for dealing with these?


Thank you!!

Steven

I think that as long as the part is still not released then post curing should be fine. If so then it will post cure to the shape of your mould. The only risk I see is if the mould were long, skinny or flat then it might bow a little due to the different material expansions.



I build pre preg carbon parts from fglass moulds all the time. The moulds expand with the oven cure and so the carbon cures when the mould is expanded and I end up with parts that are slightly bigger. When the moulds cool the parts self release as the mould shrinks back to it's original size and carbon part remains the expanded size. This self releasing will only happen with larger parts. The difference is about 1mm per metre.

The scenario I get does not apply to your job but it is still interesting to understand all the possibilities. I even wonder if using fglass moulds and the pre preg oven process can make stronger carbon parts due to the fact that the expanding mould will pull and pre tension the carbon fibres as it cures??

Thanks for the reply.  That "rule-of-thumb" about 1mm per meter of expansion is good to know.  Is this what you get when post-curing a low temperature epoxy resin like IN-2?

After re-reading my original post, I think I should be more precise about my questions.  I have 4 basic questions:

1.  Can a typical fiberglass mould, like one made with Uni-Mould, be used for in-mould post-curing of CF parts - with respect to warping and with respect to the temperature limits of the mould?  Based on your answer (Fasta), I think that question is answered. Yes, with the caveat that there is this 1mm per m expansion that must be considered.  This will mostly make a difference on larger parts.

2. Can a typical fiberglass mould be used for post-curing parts made with high or very-high temperature epoxy?  From what I've been able to determine, the typical epoxy used in making moulds (like the Uni-Mould Tooling Resin) have a Tg of about 90C.  So, it would seem that these moulds would not be able to withstand the higher post-curing temperatures needed for high or very-high temperature epoxies.

3.  If I plan to use high temp epoxy for parts, does that mean I should use high temp epoxy for the moulds?  It seems logical and would address the Tg limit for the mould, however, the question of thermal expansion at the higher elevated temperatures becomes a question.  Will I see enough difference in thermal expansion between the glass laminate of the mould and the CF laminate of the part in post-curing to cause problems like warping?

4.  Can high temperature post-curing be done outside of the mould and, if so, what problems can arise and what techniques can help reduce these problems?

Thank you for any advice.

If using glass for your mold (+high Tg resin), what I would try is to lay the fabrics on the particular orientation that avoid or reduces the expansion. The expansion should be mainly on the longer side direction. (lay fabric diagonal +/- 45 to that direction. Avoid fabrics aligned. The longer the fabric, the bigger expansion (linear variation) This may help.