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**molding carbon fiber? -** 02.04.2008, 07:02 PM

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.

Quote:

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..

Quote:

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.

Quote:

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.

Quote:

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).

Quote:

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..