molding carbon fiber?

I started this thread on private message board, got some info, and I'll quote everything, because there's lots of good information, but I'm still looking for everyone's opinion. I've got NO experience w/ any of this, so any help's greatly appreciated.

Originally posted by -nick
anyone here ever layed their own cf? i'm about to jump into this project, for a new chassis, on my rc car, and have no idea if i'll even be able to pull it off, so looking for advice.

I found all the materials here (except for making the mold) here:
http://www.uscomposites.com/

I'm not sure what weight I should use.. there's 5.7, 11, and 19.7oz weights, but I don't know how thin I'll have to go to get the contours i want.. i'm guessing 5.7? also, it doesn't say how thick the material is. I'd like to do at least 3 layers, and at least 3mm thick. actually planning a cf layer, then a cf and kevlar layer, w/ another cf layer on top..

here's what I'm planning.. this is rough, as I'm not to hot w/ sweeps and lofts in solidworks just yet..

Originally posted by bigmak
I have extensive experience with CF (both wet layup and prepreg).

Do you have a vacuum pump and bag equipment?

Are you going to CNC a plug for that to be molded in? If you lay it up as shown you'll have the outer edge rough and not smooth.

Also, based on it being on an RC car I'd guess that's a small fucker. Working with carbon on a small scale like that is MUCH harder than you may think... I'm not good at it at all.

As for the weight of carbon you need, I'd need to see a model with dimensions, radii, etc.

3 layers of carbon is thin and isn't too strong.

Why the layer of carbon kevlar?

Btw, one of the things I've done.

Originally posted by -nick
I'm planning on somehow making a table, w/ a bag over it, then plugging a shopvac into the bottom, and then seal it w/ something..
can you put mold release on the inside of the bag, so after molding, it can be reused? I watched this series: http://youtube.com/watch?v=q_fKlDzemPY&feature=related
and saw his vacuum table dealy.. i read some tuts from google, and one guy put the cf and mold in a plastic bag, then vacuum'd the bag, and used a twist tie to seal it.. then just tore the bag off the part.. just like ziplock bags.

I'm planning on having the edge of the chassis on the mold either raised or lowered a bit, to make a ridge, so after it's hardened, i can dremel on the edge, and then run beads of ca around the edgs. i honestly don't know how many layers i'll need, that's why i'm asking lol. how thick is 3mm? this's eventually gonna be a 2 deck chassis, so it should be strong enough w/ 6mm of cf, and w/ the molded channel ;)
i just don't know how thick each layer is... but if i have to double, or triple the layers, that's fine..

kevlar/cf, because.. first layer will be cf.. i'll release from the mold, and make cutouts where the battery, center diff, servo, and reciever will sit.
then do a kevlar/cf layer, in orange and black. the second layer will then be recessed, so it'll lower cg of batteries (every mm counts :) ).

then, w/e other layers of straight cf on top, to finish. trim it all, and ca the edges.. the orange/black will be visible on the bottom of the chassis through the cutouts.

so the cf/kevlar is pretty much just for asthetics, but it should look dope.

i'll get dimensions in a minute. what type of cf was used on that car? nicely done btw. I hope starting this small will maybe not be easier (then again maybe), but should at least be less costly, if i fuck it all up.

Originally posted by bigmak
That's such a ghetto rigged vacuum system... the whole point is to use the vacuum to constantly pull the epoxy out. You also need batting for the epoxy to be pulled into. We have our own vacuum pump that we built years ago (looks like this but it's 120vac) and it works great. I can make up plans if you want to do it the right way.

You need to mold all of the carbon fiber at once. Doing multiple levels will not work well, you need proper adhesion between all layers and you can only do that by doing it all at once.

The carbon fiber used in that chassis is prepreg (preimpregnated carbon fiber). It was then autoclaved in the main General Dynamics helicopter autoclave. This year, we're doing exclusively wet layup as we don't have access to the autoclave.

You didn't answer one of my main questions though--what are you using for your plug? Are you machining something?

BTW--here are some pictures from the layup of that chassis.

This is the mold that we had machined (it's in two halves obviously). This picture shows it with a full gel coat after we fully sanded the mold down and filled any marks.



We laid up fiberglass on the mold to make the plug.



Picture of the fiberglass plug after it was removed from the mold. You can see how smooth the inside is cuz of the gel coat.



Here we're in the General Dynamics facility laying up the prepreg. This is much cleaner than wet layup (which you saw in the second picture) as the carbon fiber already has the epoxy in it. To keep it from setting up, the carbon fiber is stored in huge freezers kept well below 0 *F.



The prepreg finished in the plug. This is then placed in the autoclave where it is baked at high temperatures (450 *F +) and at very low pressures (close to vacuum).

Originally posted by -nick
oh plug... like cf mold from the mold lol.. sorry very new to this. i thought you meant a plug for vacuuming or s/t.. sry.
i'm doing a wet layup, for costs.. and i don't have access to an autoclave.. but prepreg does sound appealing lol.
is it possible to not make a fiberglass "plug"? like can't i just lay the cf right on top of a makeshift mold? like i'm planning on just carving foam for the center channel... and side pieces that curve up, and glueing it down to a flat board.. and just working off that.. will it not work well that way?
and fuck.. scratch the cf/kevlar then. I was hoping after first layer, i could cut out pockets.. it might not make it as strong doing the bottom layer seperate from all the rest, but it would still be possible correct? cause i could always do the first layer, and then just do 3mm of cf on top of the first layer, to retain the strength.

yeah i'd love plans for anything.. not really sure what's required..

[BrianG]

I really have nothing to offer as far as the how-to is concerned, but after all that work and expense of making a one-off, I wouldn't want to drive it! I would cry after landing from the first jump and scratching the bottom up.

Good luck and keep us posted on your progress!

[pb4ugo]

I don't have any advice for you on the mold. I'm using aluminum, but that would be nearly impossible for your rendering. You do have to remember that the finish of the mold will dictate the finish of the composite.

As far as vacuum bagging goes, the hot budget setup is to use a Foodsaver (or similar). A brand new one will cost less than $100, and they're available used in almost every flea market or swap meet for dirt cheap. They pull a good vacuum in a well sealed bag. Do a Google search for such, and you will pull up a couple excellent articles for using one. The articles are aimed at the model rocket crowd, but it all directly applies here.

[MetalMan]

I've been learning vacuum bagging from a RC cargo airplane team/research group, where we have a foam wing that we lay uni-directional carbon fiber and bi-directional fiberglass onto to increase strength (the 100" wing has to be able to support 40+ lbs).

If you want to reuse the mold, you'll have to wax it before each time CF is layed down. The wax needs to be rubbed in really well, as any minor chunks will show up on the finished product (like pb4ugo mentioned, the mold surface needs to be smooth).

The usage of a fabric ("batting") is to hold the excess epoxy, so it doesn't get into the vacuum pump.

That website linked to on the first post has thicknesses listed for the carbon fiber fabric:
http://www.uscomposites.com/carbonpage.html
The thickness you use I would think should depend on how many layers you want to do. The thinner the fabric (the lower the weight) the more layers you'll have to have. But I bet if you have too few layers, it won't be strong enough.

Actually designing the mold will be the hardest part IMO. I was thinking clay would work, but then I remembered that clay shrinks as the water in it evaporates. But if you could account for that shrinkage, then I suppose it'd work.

I want to try vacuum forming some CF or fiberglass as well, since I have access to mylar (vacuum bag material), fiberglass cloth, epoxy resin, a vacuum line, and the appropriate wax.

[lincpimp]

I have an automotive a/c vacum pump, it can pull a closed sytem down to 30" of mercury. Would that work? I think it is a 2.5 cfm. I would almost like to try this with fiberglass as I have years of experience in laying that up wet. Maybe I will make something, like a custom chassis or body or maybe a boat hull, any ideas what you guys would like to see?

real quick, i want to say i feel like an idiot for not seeing the thickness of the cf on that page :(

Originally Posted by lincpimp

I have an automotive a/c vacum pump, it can pull a closed sytem down to 30" of mercury. Would that work? I think it is a 2.5 cfm. I would almost like to try this with fiberglass as I have years of experience in laying that up wet. Maybe I will make something, like a custom chassis or body or maybe a boat hull, any ideas what you guys would like to see?

Boat Hull would be kick A$$

[pipeous]

A fellow rc'ers father showed me how to make carbon sheets. It was rather easy once he showed me. He had done fibreglass stuff and made boat hulls and such. It was always interesting going over for a chat and listen to him describe the methods and such. He explained a product he called peel and stick. it was a porous material for doing the inside of the hulls. they made a mould for the outside that used release wax and the inside this peel and stick stuff they squeeged the excess out. it left a rough finish inside though so you might not get the desired finish. I wish he still lived down the street so I could toss this thread at him to comment. he's retired and living up country now