moldless vacuum bagging carbon fiber bicycle frame

Using fillament wound carbon fiber tubing and prepreg carbon fiber plates as reinforcement gussets I was able to make a carbon fiber drivetrain chassis for a streamlined recumbent bicycle.
We tacked the mitered tubes and gussets together with super glue on a granite surface plate to ensure perfect allignment and then wrapped them with woven carbon fiber tape and fabric that had been wet out with Loctite/Hysol E-120hp aerospace grade epoxy. Then using a welded aluminum frame with traditional bagging film, breather, peel ply on both sides we were able to achieve 30 inches of vacuum and held it for 12 hours. the next video in the series shows the part after curing.

Category:

Science & Technology

Tags:

• vacuum
• bagging
• carbon
• fiber
• bicycle
• frame
• diy
• composites
• epoxy
• resin

[Mandersound]

Post curing can help in really solidifying the carbon epoxy matrix.

This is different than curing prepreg carbon though.

Trust me, Peel ply, breather, and batting is really needed to vacuum bag correctly.

If you remove one or more then you risk not getting all the air pockets out and then you don't get the vacuum type compression needed to get a good part out.

Our frame method is quite wasteful, this is very true. we now use a better method.

[Mandersound]

What pump did we use? a cheap second hand robinair 6.5cfm vacuum pump bought off ebay for $100 bucks, besides some fresh oil it has worked great for the last 3 years.

The mold for the shell was designed and made by Matt Weaver. The mold was sold to an Australian team who has produced several bikes from it. This one was shipped to us in MN and we have made lots of mods to it.

Baking the whole carbon shell is a good thing to do, It's sometimes called Post-curing.

[Mandersound]

Even with all that pressure, you can still screw things up. if you use too much resin then it has nowhere to go and it stays in the laminate and makes it heavier and actually weaker. If you use too little resin and don't get the resin into all the fibers before putting the bag around it it's not going to find a way into the fibers and your screwed again. The trick is to get just enough resin in there and make sure it's fully saturated and then the pressure compacts it.

[lucan316]

pre preg dude.

[Mandersound]

Dude, I hear ya! Wish I could get some for less than an arm or a leg. I used plain weave pre-preg for making flat plate re-enforcements. That stuff is incredible. I made a solar assisted curing oven for curing the flat prepreg plates. Might make a video for that too.

[Mandersound]

That is one of the reasons for using vacuum bagging. It applies very even pressure over the entire surface of the bag. when I used the bagging film directly over the tubing the film stretched to apply very even pressure over the joints. I used the aluminum plates to increase the pressure over a smaller area and to insure that the sides of the frame were very even. with a full vacuum that's 14 pounds for EVERY square inch. that's over 1,100 pounds of pressure for a 20x4 piece of aluminum!

[psyclistic]

@dragoneye360 Here's a tip from a rocket scientist: first of all, use pre-preg if you can. It's so much easier and yields a better product. Also, what's your budget, timeline, and tolerance requirements? You can make tooling for pretty cheap as long as you don't have really tight tolerance requirements. Try to design the places where your composite parts interface with loose tolerances (on the order of a tenth of an inch or more). Lastly, if you don't need the stiffness or strength...contd

[psyclistic]

@Mandersound "1,100 pounds of pressure"

At the risk of sounding dickish, the above phrase is nonsensical. A pound is a unit of force, not pressure. It's better just to speak of pressure in terms of psi because it non-dimensionalizes the value for parts of varying areas. How much compaction you are getting on your material is based on the pressure, not the overall force. Unless you're using a press that applies a certain amount of force, it makes more sense to talk in terms of "psi".

[psyclistic]

@geekfish You can put "peel ply" on the outside of the composite to give it a decent surface finish. It won't be as nice and shiny as a mold, but it will allow you to peel excess resin off the surface of the composite. I think that's right. Someone please correct me if I'm wrong.

[geekfish]

@Mandersound What is between the breether and the frame?

[geekfish]

@Mandersound What cloth are you using to cover the composite material?

[sexymgb]

When you used the bagging film directly over the tubing, did you have any trouble in releasing the film from the tubing? I'd really like to get rid of all the waste products - peel ply, breather film and batting.

[dragoneye360]

Did you produce the shell for the bike yourself too or was it done by someone else?

I'm a member of a collage solar car team and we are building a new car with a carbon fiber body.

Any pointers on how you formed the shell would be helpful. Our professor is telling us we have to bake the carbon fiber for it to cure.

[zackthegrind]

That frame for the bag is a waste of time, aluminum and bagging material. Make a bag put your part in and turn on the vacuum.