Carbon fiber sheet

General Composites Discussions Composites Talk
#1

Hi All,

I need to make a large number of carbon fiber sheets with a glossy finish on both sides.
Can someone please advise what technique i can use to get two side glossy finish through vacuum bagging maybe?
I have seen examples of stacks sandwiched with two glass panels but i dont think this is an efficient method plus i would like my sheet to be structurally strong with a high carbon/resin ratio though not required for this project.
Has anyone been able to use a mylar sheet on top of your stack giving you a glossy finish on both sides, if so how have you gone about vacuum bagging without any flow media.

The next part of my question is more important. Well the truth is i need precision sheets exactly 2.5mm in thickness as there are going to be engraved and cut through CNC so any difference in thickness is going to mess up my entire CNC code every sheet i try.
so the question is how does one achieve the thickness he wants every single time i do a wet lay up or vacuum bagging. I know there are precision sheets in the market.
How do these guys achieve the thickness every single time?
Hopefully someone can help.
cheers

#2

Hi, the only way you can get what you want is a big press and pressing prepregs.

#3

Thank you, i kinda figured i would need equipment, but i also know of people making these sheets with everyday equipment… any other suggestions guys?

#4

You can’t do it with every day equipment and your exact tolerances. Even two sheets of 10mm glass will buckle and give you ± 0.5mm in an ideal case or even more.

#5

what if i settle for one side finish, can vacuum bagging stacks give me the thickness i require?

#6

Please check this video the largest sheet he created was around 4mm
https://www.youtube.com/watch?v=3uhR4jdFiS4&t=567s
So back to my original question is there some technique we can use to get both sides glossy through vacuum bagging, maybe apply a mylar sheet on top instead of peelply/breather
Would it work without flow media…? Someone who has done this already please help

#7

I have spoken about tolerance of a double sided finish. He has only one sided finish what is a total different world.
Also his toutorial has some mistakes/imperfections in setup. The bag should nit stretch, the brake zone should be on the part and the flow meter he ist using shows if you have a bag or not, but not if there is a small leak.
A one sided finish can be done by standard vacuum infusion with tolerances less then ± 0.2mm
And he mearsured only one spot of the panel.

#8

Consider using the wet-preg technique(wetting out your carbon on a piece of visquine, then covering it up with another piece of visquine, then draw your rectangles on the top layer,then cut them out and place on the glass)Remove the visquine of each layer! The trick is not to use too much resin. It would take eight layers of the carbon I use to achieve 2.5mm .You will need a vacuum pump. Envelope bag the whole thing. The parts will be very close in dimension especially if you use the same amount of resin on each batch. The Mylar or glass you use on top is called a caul plate. You still might have to clear coat the parts as pin holes at the weave might show.

#9

Also alternate between 90deg and 0deg to achieve a stiffer plate.

#10

dear ddcompound, im as you can tell, pretty new to the world of carbon fiber… you mention tolerances? what exactly do you mean? flexibility, structural strength?

i was only referring to thickness of the sheet, basically need to engrave into it, not cut through the sheet.

#11

Tolerances means the margin of error. So with a standard one-sided vacuum infusion, you can work out your cured sheet thickness within 0.2 of a mm (it could be ~0.2mm thicker, it could be ~0.2mm thinner). So your tolerance or margin of error is ±0.2mm.

This is why DD mentioned pre-preg in a press. It’s a controlled amount of resin with an equal consolidation pressure across the entire laminate, which makes it much more accurate.

So it sort of depends on how exact you need when you say exact. There’s a big difference between 2.500mm and 2.38mm!

#12

just the answer i was looking for, thank you hanaldo

#13

The big press has the advantage that the press plates do not flex. You can close the press to exact 2.500mm. And you have a finish on both sides.
If you only need one side finish and can live with some tolerance in thickness you can infuse you panel. The nice thing on infusion is that you get a perfect surface, a pressed panel will always have micro pinholes.

#14

Both sides gloss finish with no flow media , using resin infusion is possible:

#15

Hey can you please share what method and technique you use?

#16

Can you sandwich the carbon fiber between two sheets of glossy release liner and press it between two plates (or whatever type of mold you need for the shape you want)?

If your panels are flat, or relatively flat, you should be able to cure the cf between glossy release liners without any creasing. Just make sure to remove all trapped air first.

#17

I believe he’s just talking about the tolerance in the thickness… actual strength is a different issue… This sounds like it’s not structural?

Still a press and pre preg is the best bet, especially if do have tight tolerance requirements.

I’ve purchased gloss/gloss sheets from ACP before. They use pre preg and a press with some sort of gloss sheeting to give the finish. The ones i’ve used were pretty nice. Would be easier to just buy them rather than make a bunch of mistakes trying to figure out the process and wasting material? I guess it depends on how many and how long you plan to make them for? Having a press would be useful.

By the way, What are you making?