raptor22

Just to introduce myself since I don't post to the forums much, I am an Aerospace Engineering student at SDSU. I don't post very often because I don't work on my car very often and i think that it's better to shut up and learn than spread misinformation.

However, I have been working with composites for close to eight years, and I am the "composites guy" for our our FSAE (open wheel racecar) and DBF (UAV) teams. During a recent "teaching" session for some teammates, I thought I'd take pics to post on here. Once you have all the materials, you will find that making composite parts is surprisingly easy. Its making molds for complex parts that is tough, but if your part doesn't need a mold you can skip that time consuming step.

All of the parts are going to be made from mirror-finish carbon plate we lay up ourselves.

The first step is gathering the materials for the plate, since most people don't have the proper tools/materials laying around.

First for the panel materials:

For the carbon, you can pick virtually any weave, but make sure it is bidirectional. I personally like 5.8 oz/sq. yd. twill weave, which is what we used. It makes a nice pattern when everything is said and done, is easy to wet out, and is fairly cheap. A yard of it is fine, because these panels are mainly cosmetic and you will only need one or two layers.

Next, you need a less expensive material to build bulk with, because a paper thin panel won't be strong regardless of the material. Fiberglass is fine and cheap; use 6 oz or heavier cloth. We used kevlar because of its low density and toughness, but it is much more expensive. Lastly, if you want the ultimate in strength-to-weight, you can use a foam core material like corecel or divinycell, but the resulting material will fracture more easily if abused.

The last material for the panel itself is a quality epoxy resin. Avoid the cheap polyester or vinylester resins like you would find at home depot, as they will provide a much weaker part and don't play well with carbon. My favorite is DMC's store brand, as it is affordable and the parts come out very stiff with a beautiful finish.

Now for the tools/support materials:

The biggest expenditure is a vacuum pump. Ready made systems are available for $150 and up, but you can easily build one yourself for FAR less than that. You can often find free fridge compressors at the dump to use as pumps, and then it's just a matter of getting a cheap vacuum gauge and bleeder valve to hook up to.

Next, its time for the consumables. You will need bagging material, mylars, parting wax, bagging tape, peel ply, and breather. You can get the good stuff or save yourself some money by using painters plastic and paper towels for the bagging material and breather, respectively.

Lastly, you will need some type of flat panel to stick into the bag and press the panel onto in order to insure that if comes out flat. We used MDF. Use whatever suits you best.

Pics of the equipment will go below.

--Alex

raptor22

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raptor22

First, for our carbon and kevlar. Both were found in cabinets in the FSAE workshop. The carbon is 5.8 oz twill weave, and the red fabric is a dyed kevlar and s-fiberglass hybrid.




Then for the epoxy. As stated, its the excellent DMC stuff, although any quality laminating epoxy will work.



Next for the bagging stuff. I don't have any pictures of the mylars because they are glassy smooth and transparent. The partall wax is very similar to carnuba car wax, although it's a bit softer and optimized to keep the epoxy from sticking to it. The next pic is of the vacuum pump setup they got a few years ago from ACP. This particular pump has a tank and switch rigged up so that it doesn't have to run constantly.

blwn rtr 89'

iTrader: (5)

please post more, i want to make several things this way. the fridge compressor is good, but did you have to wire it to a 220v?

gross polluter

How's AE treating you there? I'm torn between EE and AE. AE at sdsu was the first choice, but most I talked to never made it through, they said it was wayyyy harder than ME or EE.

thegoatc

you are just doing flat panels or are you doing molded parts with several contours.

raptor22

More pics!

I can only attach 5 pics at a time, so here are the rest of the bagging supplies.

The green plastic is what the top and bottom surface of the bag will be made from. This particular material is very stretchy and malleable, as it is specifically designed to be bagging material. Great for forming parts into molds, but not necessary for sheets like this.



This yellow roll is bagging tape. Kind of like strips of really sticky silly putty. It seals the edges of the bag and the spot where the tube enters the bag.



Next up are my only two pics of peel-ply and breather. The upper layer is peel-ply; a nylon material designed to allow epoxy to soak through it without sticking. The lower layer is breather; which can be any porous material. This "special made" stuff is just thick felt. Like I said, paper towels work fine in a pinch.



Lastly, i did manage to get a find a pic of the mylar. Its hard to see, but its the layer between the MDF and carbon. You can get this at lots of plastic places, and its reusable between bagging sessions. This particular material was purchased for bagging glass over foam wings, so its fairly thin at .010".




--Alex

2Fierce

iTrader: (7)

I'll be keeping an eye on this.

raptor22

Blwn Rtr: As you can see, we are using a store bought pump that has been in the team for at least 5 years IIRC. However, most people I know use a fridge pump or ebay GAST pump, and I never heard anything about 220V. One thing to remember is that the fridge pumps aren't designed for continuous running, so if you use a bleeder valve instead of a resovior like we have your pump may only last 15-20 parts. Oh well, its free, go get another.

AE has been good so far. It is true that AE is the hardest, but if you really enjoy the material its not bad.

the goat: This project is just flat panels. Making complex shapes requires that you make a plug....then polish and wax wax wax....then make the mold. then polish and wax wax wax. and wax some more. Then make the part. You could easily have 100+ hours into it if you want a professional quality finish. I may do a separate writeup on mold making at a later date.

We have done that for body panels and airplane parts, but thats too much work for one part that will still look nice with a flat sheet and some innovation. Especially since the Porsche guys wanted flat stock for their 911 dashes.

We are using the same techniques that we would use to make parts from a mold, but the mold is a flat piece of mylar instead of a complex female surface.

--Alex

raptor22

Here is how the whole thing is going to go together. If you have a mold you can replace the mdf and mylars with a polished female mold surface. I was forced to rock my badass paint skills for this one to make sure I got the message across. Sorry about that, but I wanted to go over what everything does before the pictures.

The MDF is just there as a flat and stable surface for the bag to smash everything onto.

The mylars are non-stick and extremely glossy. They provide a barrier between the MDF and the layup to make sure it all releases properly and produces that mirror finish we all love so much.

The peel ply and the breather act as a team to serve in two capacities.

The primary one is that the breather provides a porous material for the vacuum to pull air through, ensuring a nice even vacuum across the bag. In this case, the peel ply acts as a non-stick surface to keep the epoxy from bonding the part and breather together. This pressure aids the finish and produces the fiber compaction that makes bagged parts stronger than atmospheric parts.

The secondary role of the two is that excess epoxy gets squeezed through the peel-ply and soaked up by the breather, making a lighter part and adding further to the strength.

--Alex

raptor22

Now we get to the good part. Actually laying up the part.

Start by cutting out a piece of bagging plastic that will be about 4" or more wider than your mdf on all sides. Lay that on your work surface and put bagging tape around the edge, leaving the paper backing on and trying as hard as you possibly can to avoid wrinkles. No bag is perfectly leak-free, but if you halfass it you will be kicking yourself while you try to track down all those leaks that keep you from pulling a decent vacuum.

Then lay down your mdf on that plastic, and put a piece of mylar over that. Put at least two coats of wax down on the mylar. You can usually get away without the wax, but surface imperfections may make the layup stick, and its cheap insurance.



Lay your first piece of carbon down on the waxed mylar. Mix up some epoxy and pour in on. Make ABSOLUTELY sure you mix the resin and hardner well and in the right proportions. If you don't your part will come out like the bagging tape you just put down. Well, probably not that bad, but it will be soft and tacky.



Use a squeegee to get it worked in nicely; dry spots mean pinholes and ugly parts. You can then roll it with a wood or aluminum roller. It makes the resin mroe uniformly distributed, but its not strictly necessary.



Then, blot the excess resin off with paper towels. You shouldn't see any pools of resin when you are done. Rinse and repeat for the remaining panels.

raptor22

Finally, lay down peel-ply over all of the layup and breather over the whole bag area. Wrap some bagging tape around the vacuum tube where it will enter the bag and push it down onto the bagging tape on the edges of the bag. Make sure that the tube end is surrounded by breather so that no plastic gets sucked onto the tip to clog it up.

then, but your second piece of bagging material over the first. Once again, be careful to avoid wrinkles. Its harder on the top, but do your best. Then push down on the tape through the bagging material to ensure a good seal.

It should look like this.

raptor22

If you did it right, you get a beautiful production-quality sheet of carbon. Here are some pics of a piece I cut from "the big sheet."

As you can see, its glass smooth and very shiny. I can see myself in it. This is with zero treatment of any kind. No waxing, polishing, or clearcoating.

If you had all the bagging materials handy you could do a very large sheet for about $80.

--Alex

j0rd4n

wow, very impressive. looks like you could do an oem hood replacement with cf (for those who want a cf hood without all the vents that most will have) for fairly cheap (relatively speaking)

classicauto

iTrader: (3)

Good info and good job!

TheDarkRacer

sooooo nice, You should make some CF rx7 badges. Shoudn't be too hard right? hehe....

raptor22

Thanks for the comments. Getting a finish like this on a hood requires a mold. It'smuch easier with the stock hood because you can use it as your positive, but you still need to go through the cost of making a mold that size. That's a lot of tooling resin.

If you don't want the shiny finish you can use the hood itself as a positive mold, but then you could expect to get a matte finish that requires painting.

What do you mean by a rx-7 "badge"? I might be convinced to do some custom work for a paintball gun

--Alex

phoenix7

good job. Now, when are you gonna make a whole dash?