Lower Temp Carbon Prepreg Oven Cure Process?

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#1

Hi All,
I’m having wrinkling with my carbon prepreg laminates. I was wondering if I changed my process if it would help. Currently, I’m using apcm uni prepregs that cure at 200F for 1 hour. After vacuum bagging my part (8-10layers of 150gsm over substrate) allowing to sit under vacuum for 1hr to assure consolidation, I ramp up 3 degrees per minute to temp, dwell for 1.5hrs, then ramp down and cool. I’m using silicone “glove molds” as pressure intensifiers, that have helped quite a bit, but still have some wrinkling at the seams.

I was thinking, if I lower my cure temp and find the proper dwell for cure, could this “in theory” help with the wrinkling? Would the lower temp and longer cook somehow make a difference as it changes the reaction or slows the gel stage so the carbon doesn’t start to bunch? I know I have to do some experimenting, but wondering if someone here has done this before and has any insight.

Always appreciate the help. Thanks in advance for the responses.

#2

whats your tooling made from?

#3

Do you have any pictures of the problem areas?

Lower temp means higer viscosity. I am not familiar with the prepreg you are using, does it have a lot of flow?

You might need to extend your vacuum period, or find a way to quickly get air away from the layers (a thermoplastic scrim could help) if you start using prepregs with less flow. (keep in mind that lower flow means more risk of voids)

#4

The curing profile will have a very small effect maybe on wrinkles - Ive never really had a problem where the curing profile was a contributor to them. The only instance I could think on where it possibly makes a difference is if the resin viscosity isn’t sufficiently low to enable inter laminar slippage – this could be a good thing or a bad thing and maybe even make wrinkles worse if they slip in the wrong way! But I think this is only a minor factor compared to lay-up procedures such as not putting the fibres down properly, lack of debulking, etc.
What shapes, plies and tooling material are you using?

#5

Ramp rate seems fine btw. Some of the low temp pre-pregs I use dwell around 75 degrees (15-20 lower than yours)

#6

That’s quite a few layers without an autoclave. Even if you can get the wrinkling out I would be surprised if there weren’t internal voids.

But barring that- have you tried heating up the laminate slightly before debulking to reduce viscosity?

#7

That’s quite a few layers without an autoclave. Even if you can get the wrinkling out I would be surprised if there weren’t internal voids.

But barring that- have you tried heating up the laminate slightly before debulking to reduce viscosity?

#8

10 layers at a time is crazy also using an autoclave.
You need to make a debulk on the first layer, then another one each three layers.

#9

Guys,
Thanks for all the advice. My tooling is a higher temp carbon. I’m building tube to tube bicycles, and though I have a pretty good product(structurally sound and almost wrinkle free), I’m still getting a ridge where the bags seams meet. From what I hear, I need to spend more time with my layup process and debulking as opposed to changing my oven cycle.
Thanks for the help.
-Michael

#10

When laying up some plies together, the air can’t flow thorough them and it’ll keep inside the laminate.

If any radius, when compacting the laminate, the thickness will be reduced and the radius of the external plies will change, and you`ll have an excess of clothe that will origin the wrinckle.

That’s why debulcking is used. Normally each three layers, to minimize risks…