Beginner question - hand layup of carbon fiber

[oompaloompa]

Hello everyone. I'm new to the composites world but have great interest in the manufacture of carbon fiber parts. I was hoping to supplement my internet research and short amount of time experimenting, with some knowledge from the experts here. This is a hobby project for me, but I do have a BSME, so I'm not completely useless, I hope.

To start, I've been doing hand layups, mostly overlays (skimming/skinning) of some automotive interior parts from my car. I use an adhesive spray on the part, and gently attempt to wrap the part in 5.7 oz 2x2 3k carbon twill.

I've got some West 105 with the clear hardener, that I've been "painting" on with brushes. This works fine, except that the resin is so thin, it requires multiple coats (4-5) with wet sanding in between coats to help level it out. It is time consuming.

I've experimented with vacuum bagging (moldless) the setup to minimize the epoxy usage, save time, and compact the carbon twill for a nicer part. That results in wrinkles on the surface, depending on shape complexity, despite using peel ply, and two layers of breather. I end up sanding these down and adding a few layers of epoxy. Overall not bad, but not a perfect part either.

These parts are mostly one-shot parts, which is why I haven't made molds for them. Is there a better way to do this? Should I be thickening the epoxy to eliminate the extra coats? Skipping the bagging process unless I'm using molds?

Bonus question: I did make a urethane female mold of one part. It came out great, however the bag side came out pretty rough. Is it typical to make a silicone plug for that side if I need a nice surface? I think a two part mold (M-F) might be overkill.

Any thoughts are greatly appreciated, and thanks in advance.

Michael

 

[oompaloompa]

And pictures are always fun so here are a few:

hand layup parts -

http://i280.photobucket.com/albums/kk180/dynaspeed/carbon fiber/hand_layup.jpg

layup with expoxy, mesh showing through -

http://i280.photobucket.com/albums/kk180/dynaspeed/carbon fiber/hand_layup_epoxy.jpg

female mold -

http://i280.photobucket.com/albums/kk180/dynaspeed/carbon fiber/female_mold.jpg

vacuum bagging setup -

http://i280.photobucket.com/albums/kk180/dynaspeed/carbon fiber/vacuum_bagging.jpg

 

[Compositepro]

You are probably using way too much resin. 50% resin content by weight is more than enough. The fiber will soak-up the resin like a sponge. The goal is not to simply saturate the sponge but to compact the the sponge (fibers). This is done with a grooved roller or with a stiff bristled brush using a dabbing action. A grooved roller is far easier with large surfaces while a brush works better on smaller or highly contoured surfaces.

The ridges of a grooved roller will press the fibers down while squeezing excess resin and air bubbles back to the surface of the part in the grooved areas. This is how air is removed from the part. When the resin viscosity is very low it is easy to saturate the fibers but the fibers will quickly spring back up, so the surface looks dry. Do not add more resin. Roll the fibers down again periodically. As the resin builds in viscosity it will not be able to flow back into the fiber any longer, so then the fibers will be held down until complete cure of the resin. Getting this right takes practice.

Another method is put a plastic film over the part after it is saturated with resin. Then use a squeegee to sweep excess resin and air bubbles to the outside edges of the part. The plastic film will prevent air from being sucked back into the fibers so they cannot sponge up. The film will also give you a relatively smooth surface after cure.

Vacuum-bagging can also work very well to remove air bubbles and excess resin but requires more skill and materials. You would use a perforated film over the saturated part, then bleeder material to soak-up the excess resin and then perhaps more film and breather material, and then a vacuum bag. Use only 10 to 15 inches of mercury vacuum. The bleeder should not become completely saturated or you will still have excess resin in the part.

 

[Compositepro]

After seeing your pictures you do, indeed, have way too much resin. The way to get a really good surface finish is to clear coat it after it is cured and sanded.

 

[berkshire]

One of the problems with hand lay up of Carbon Fiber or Kevlar is that the fabric is lighter than the resin,with the result that the fabric wants to float on the resin surface.
The surface then looks dry, and the unknowing add more resin, the final result is a dry looking part floating on a sea of pure resin.
If you are using more than one layer of fabric, wet out the first layer, then apply the second layer without adding any more resin, simply roll or use a stippling action with a brush to pull the resin up from the first layer.Then go back and re submerge the fabric from time to time ,until the resin gets too thick to allow you to do that.
Good luck.
B.E.

 

[oompaloompa]

compositepro, thank you for your response. While I'm sure I am using way too much resin, the photos were taken after I wetted out a large part. I had extra resin in the cup and a wide brush handy. The resin started to kick, so I slathered it on the parts you see as quickly as possible. Normally, there isn't excess resin dripping from the part. But thanks for the idea of the roller and film. I will give that a try. Do you suggest keeping the film on until it cures, or at some point removing it? Hopefully that will help build the resin layer up over the exposed fibers faster.

On the vacuum formed parts I've tried, I used a layer of perforated peel ply, and two layers of breather. I like the results, for the most part, aside from the wrinkles I get. I suspect it is due to me pulling 29in Hg on the part, as opposed to the 10-15 you suggested. I will try that next. That should help with the carbon wrinkling. There is a lot of conflicting information out there about the proper vacuum required to mitigate pin holes and voids.

B.E. - Thanks for that suggestion. I will remember that the next time I do multiple layers.

I love learning about this stuff and would quit my job in a heartbeat if I knew I could pay the bills doing it. So a big thanks again to you guys.

Michael

 

[MikeHalloran]

Saran Wrap makes a nice compacting/ finishing film for hand layup.
Saran will stick to wet epoxy, but releases easily when the epoxy has cured.

Beware of wrinkles in laps in the film; the resin will bleed into them and make very sharp needles.



Mike Halloran
Pembroke Pines, FL, USA