Polyester mould is incompatible with epoxy part?

General Composites Discussions Composites Talk
#1

Hello everyone.

I am trying to make a carbon fiber case with polyester mould.I post cured the moulds at 100 C degree to stand 90 C degree oven cure for 8 hours.And its a epoxy prepreg carbon fiber application.However the parts does not mate each other after demoulding.The parts fully cured.I will lose my mind because I have no idea where I go wrong.I checked the both moulds sizes after remove from oven.And they look fine.But the carbon fiber part lost its form.By the way the larger part seems lost form.Do you guys have any idea about this problem?Do I need to make epoxy mould?I attached a simple drawing to explain the problem.I hope its clear.

The size of the part
Top part 82 cm x 33 cm x 6cm
Bottom part 82 cm x 33 cm x 9 cm

https://ibb.co/fwYNUx

Thanks.

#2

100 degrees is a touch high for a polyester tool, do you know if it is specifically a high temperature capable tooling system? Most are at their max at about 85-90, so it wouldn’t be surprising if it warped a little bit at 100.

#3

Thanks for answer Hanaldo.I have asked a few time to manufacturer about HDT,The technician guy said that its a zero shrinkage and if I post cure at 105 C degree it will has 90 C degree HDT.But he did not this tolling system is a high temperature capable tooling system.I have a friend also he makes small prepreg carbon fiber parts with this tooling system moulds and he cures the parts at 100 C degree.its fine as he said.I am just wondering that is that possible to polyester moulds.Does polyester moulds lose their forms during cure and get back their forms when remove from oven?

#4

If the manufacturer says it can handle a 105C post cure then it should be fine at those temps.

How did you conduct the post cure then, what ramp rate did you use and did you leave the mould on the pattern or did you demould and post cure the mould on its own? Also how is the mould made, CSM or woven? How many layers and what weight fabrics?

#5

Hmmmm, just took another look at your image, I suspect it is less to do with the mould and more to do with the pre-preg part. What is your layup of the carbon part like, how did you lay it up? Can you show us a photo of the actual part?

#6

I added some pics to show the warped part.But the mould looks not warped like that.Something happens during cure at oven.I am not sure what is going on.

https://ibb.co/fWDAhH
https://ibb.co/igrwNH

#7

I post cured the moulds after fully cured overnıght at RT then @ 50 C Degree for 10 hours in the oven on the pattern.And then 3 hours @ 80 C degree + 3 hours 100 C degree without pattern.Ramp rate 10 C degree/hour.I made the moulds 8 layers CSM.1 layer 100 gr + 4 layers 300gr + 3 layers 450 gr.Finally the moulds look good after remove from oven.But part warped as shown the pics.

#8

I’m struggling with the pictures, I’m not sure what I’m looking at. Take some pictures of the whole part so we can tell what sort of geometry you’re working with.

There’s nothing wrong with your cure schedule or layup for the mould, so should be all good there. I suspect this will be something to do with stress across a flat section from an uneven layup, but hard to tell without seeing the whole picture, so to speak.

#9

Can’t really see from your pictures either
But you have 2 parts and ones good an ones bad ?
So simple elimination of the variables
Same mould construction ?
Same part construction ?
Same cure profile ?
We’re the parts cured in the same cook ?
Have you checked the heat distribution across your oven ?
Are your parts a tight fit in your oven ? Know someone who cooked two parts that were a tight fit in their oven at the same time.
Bottom item sat above the heaters and virtually blocked the air an heat flow to the second item
A polyester mould will “grow” during a cure cycle so if the mould enclosed the part you want to strip out hot before the mould cools and shrinks back onto the part

#10

I added some more photos.There is a gap stright bottom side.I hope its clear now.
Yes there 2 parts one is bad other is seems ok with tiny changes.But big part is awful as you can see added pics.Yes same moould construction.I put the owen at the same time right and same heating.I made the oven bymyself its a heater fan with ramp soak pid controller.But I can not say it is perfect heat circulation oven.its 145 cm x75cmx70cm oven.There are not too much room after put the molds into the oven but it seems ok.I am not sure.Do you think I need bigger oven?

https://ibb.co/iVqCWc

https://ibb.co/du7gPx

#11

Sounds like the carbon part may be an unbalanced layup.

For multiple layers the whole laminate should be like a mirror from the surfaces to the centre.

What is your part laminate? how many layers of what and which order?

#12

Its bottom part of the a hard case.The part has a good surface finish.It just warped.1 x 200gr twill prepreg cf + 1 x 100gr adhesive film + PVC core + 1 x 100gr adhesive film + 2 x 300gr UD prepreg cf.Its strange because the mould surface looks pretty straight, the only part warped.And only bigger part warped.The small part seems ok.

#13

Why use u/d in this application? What’s it giving you ??
Me ?
0-90 carbon
45 carbon
Film glue
Core
Film glue
45 carbon
0-90 carbon

#14

Yeh there it is. I’d say it’s that uni that is causing the issue. Or rather the fact that you’ve got an unbalanced layup, with only one layer of woven on the surface.

Rob’s layup is perfect, I would also do it the way he suggested.

#15

Sorry guys I have made a mistake when saying the layup orders.
1x200gr carbon fiber prepreg
1x300gr UD - 0
1X100GR film adhesive
PVC core
1x100gr film adhesive
1x300gr UD - 90
Is there still problem with my layup order?UD is giving me build a stronger and lightweight structure with less layer.At least I am hoping so.By the way, I just realized that there are blisters on the mould surface.One more thing how you explain big part is only 3 cm more depth than small part but same structure.But small part is ok.Not warped.

#16

Yes, your laminate needs to be the same on each side of the core.

Only as an example.

2 x 200g cloth
1 x 300g uni
film glue
pvc core
film glue
1 x 300g uni
2 x 200g cloth

Same orientation too, it’s called a balanced laminate and is literally a mirror each side of the laminate centre, with or without foam.

#17

Don’t know why your larger part warped an your smaller one didn’t but if I had to hazard a guess I would say you bridged your u/d in the corner
Either on the smaller part you didn’t bridge it or the shorter flange allowed the u/d to slide during
Larger part with the wider flange an there is more area to trap the u/d an it’s under tension an causes warpage?
Just a guess
Also wouldn’t use u/d as a bond face
Even with a film glue
Things stick LOTS better to cloth

#18

Thanks everyone.I changed the lamination order as you adviced.And it went perfect.I got the parts pretty straight now.But I have got another problem which surface quality is bad.I got too many gaps between layers and pinholes on the surface after remove from oven.I have no airleaks as I can see.And also I applied debulk to 1st. and 3rd.layers for 1 hour.I think problem couz of the pvc core material.So,I changed the lamination order and I just laid the 1st layer of 200gr twill prepreg carbon with peelply to get better surface.But I need your advice.How can I contunie to layup order to balanced lamination after cured 1 layer of cf prepreg? 300GR ud/Film Glue/3MM PVC Core/Film Glue/300gr UD/Twill?May I keep layup like this after cured 1st layer?Is there any problem with this?