Hi guys.

I ran into a bit of a problem today.

So i made e46 m3 hood. All good except for a little bulge (located in middle kevlar/cf "island on the right side o)n the top side (that i didnt notice untill todat when i took glued item from top mould) :/

After mild postcure (sun so max 50*C atm) it came out great so somwhere from that point to prior of bonding halves together this happend (inbetween i was only cutting vent holes).

Stack was as followed (top part) :
-245 2x2 cf
-600 2x2 cf
-200 cf/kevlar

All this time (apart from cutting & triming) paet was laying flat in mould to awoid any accidental damage in workshop. 

Halves arenow bonded and i can not seperate them again.

I was thinking of heating it gently locally with heat gun and then put so soft weight on and let it cool of (as atm TG is quite low...... plan was to let it full post cure bolted on the car and then sand it and get it clear coated). 

Any ideas how this happened and any alternative ways to solve it?

Thanks a lot

It's possible that putting the part in direct sunlight and letting it get to that sort of temperature quickly might have caused the blistering. Unless made with pre-preg at an initial elevated temperature then parts won't have a great tolerance to heat and using a heat gun to try and flatten things again might not work and could well make things look worse, unfortunately

Ideally, after an initial days or so curing at ambient temperature whilst still in the mould, curing at an elevated temperature with a slow and controlled ramp should be undertaken if greater heat tolerance is needed. All this without removing the part from the mould.

Of course, this would require an oven of the required size with facility to control the temperatures accurately.

Exposing the newly de-moulded part to temperatures of 50 degrees and up in direct sun is likely to lead to cosmetic issues, as would repeated exposure to high under bonnet temperatures without a controlled initial post-cure. 

Even a controlled ramp up to the maximum recommended heat for your resin system is likely to leave evidence of shrinkage across the part, but this could be sanded and finished after with clear coating.

Oh no!  I'm sorry that is no fun.  Can you tap on it and get a sense of how thick the delaminated part is?  If it is the top skin you may be able to re-inject it with resin and re-bond.  I have done this once with very small (.5mm or less) drilled into the intersection of the weave so it doesn't show (as much) and then bagged/weighted down with everything masked off except the spots that I drilled and injected with epoxy.  You could maybe do a similar trick with infusing through an array of tiny holes drilled through.  I have done this on non-cosmetic stuff and it makes a mess and you'd have to sand and clear the surface locally with primer.  Good luck!

Oh that's better I guess - delam in single skin parts is unnerving.  At least you could fill it in with clear and block it out.  Interested to know if the heat and re-shape works.  

I have had some issues in the past post-curing infused parts after removing the bag and so try to keep vacuum on through the post-cure.  Seems to help but never ran a control group - so may be solving a non-existent problem.  Have had people who know more than me about this suggest it as a best practice.  

And its not geometry related, shrinking laminate or some pressure from the bonded inside part?  I guess it would be symmetrical in theory. 

Nice looking part BTW!

Hi.

Thanks. It to a lot of time getting moulds ready

Yeah plan B is to fill it with clear coat and sand it out.

Pic of the whole hood is prior to bonding inner half (inner half is altered a bit as oem halves dont sit flush one on another so i added a little sloped area to awoid forcing parts into final place). 

Bonding faces were close to each other (max 1mm in some places).

Perhaps lack of vacuum during postcure was the problem that manifested it self later on.

Firts pic is of parts just put in place on top mould so no glue or weights yet.
Lower one is from fresh demoulded part.

Is there any chance there was a little bit of debris in the mould when you put it back into the mould? I've seen that happen before. Even a tiny piece of resin from the infusion mesh can cause dents like this on a freshly demoulded panel.

Unfortunately I don't think anything is really going to fix it so it isn't visible again. Even filling it with clear and blocking it flat again, that will look good in the reflection, but the carbon will still be distorted and will refract light differently to the carbon in the areas next to it. Your method is probably the best solution for the situation, but be very careful with heating it up, you don't want to get it too hot locally and cause more damage. I do feel it is unlikely to work, but it's worth a try.

Yeah it wont be perfect in any case. Ill post update in the next week or so.

Thanks for support