Tuesday, January 24, 2012

How to laminate carbon fiber to plywood

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In our Belite ultralight aircraft, we occasionally make and use a carbon fiber / plywood laminate.  This makes a very nice looking and strong panel, yet is very thin.   It is capable of holding a lot of load when suspended across a frame, for instance, a seat bottom.  (Double sided applications would probably be used with other cores than thin plywood.)

I recently made some of this magic thin carbon fiber / plywood.  I documented the production steps so you can see how we do it.

In order to do this, we'll use some thick beveled glass, tacky tape, a vacuum pump and some vacuum tubing, bagging film, peel & ply film, fluffy cloth padding, epoxy, and of course, -- carbon fiber and plywood.

Let's start with a nice sheet of beveled plate glass.  We've cleaned it thoroughly (I mean it, thoroughly!!!) and have lined the edges with tacky tape.  It has been waxed, then the glass has been sprayed with film release, and I've run some plastic vacuum tubing along one edge, secured with tacky tape as well.

Warning:  carbon fiber and epoxy and glass can be nasty stuff -- always use breathing protection, along with protective gloves.  Use these instructions, as always, at your own risk.

Let's get going...

Plate glass, cleaned and prepared for use.

Mold release, special wax, and tacky tape

Vacuum tubing, with notches cut into it every few inches

Generic vacuum pump, attached to tubing. 

Closeup of tacky tape in corner, holding vacuum tube down

I connected the bagging film to the tacky tape on one side, then flipped it back over the edge of the table:

Bag Film attached to tacky tape on one side, then flopped over side of table.

Second strip of tacky tape, along with peel ply film placed to tape

We don't use fancy carbon fiber, just inexpensive industrial 3K weight and plain weave.  The number of layers is dependent on the application.  For seat bottoms, 2 layers work well.

Carbon Fiber cloth (3K, plain weave) doubled over to correct size
The plywood used is birch, 1/8".   The size I am making here is 2' x 4'.  The glass must be completely clean, completely dry.

Plywood, 1/8", 2' x 4' size

Carbon Fiber (doubled) placed over dry plywood.

Now I mix up some epoxy.  We use West Systems, with 'slow' or 'fast' depending on the temperature of ths shop, along with my patience.  How much epoxy?  Enough to thoroughly wet the carbon fiber cloth and leave puddles of epoxy; you'll have to figure it out as you try this process.  I pour it on the cloth and move it around, gently, with a small paint brush.  I am careful not to disturb the orientation of the carbon fiber as I brush in the epoxy.  It will drag with the brush very easily, and is a pain to move back to a square orientation.

A bunch of wet epoxy on the carbon fiber / plywood sandwich
After doing that, I flip the peel ply over the wet carbon fiber and careful work out any problems with the film.

Peel ply flipped onto wet epoxy.

Now I take some puffy cloth and put two layers on top of the peel film.  It's purpose is to allow epoxy to squeeze up through the peel ply and into the puffy cloth.  (Puffy cloth == high fill, non woven polyester)

Two layers of puffy cloth over the peel film
Note that I I doubled it up even more at the edge near the vacuum tube.  This helps ensure that epoxy will not wick into the vacuum tube, but will fill into the cloth first.

More Puffy Cloth near vacuum tubing
Removing the covering from the tacky tape all around, I then pull the bagging film over everything.  This is hard to do, because the film tends to stick with creases, which makes it hard to get a good vacuum seal.  It's easier to do if someone helps you pull the film tight.

Bagging film pulled over the entire assembly.
The vacuum pump is then turned on.  You can see it suck the bagging film down almost immediately.

This is how it looks after a few minutes.  The epoxy is being sucked through the peel ply, into the puffy cloth.

The film had a couple of leaks.  I fixed them with blobs of tacky tape.

At this point, I left the vacuum pump on and left the whole thing setting and curing.  When I came in the next morning, I removed the green bagging film.  It was easy to do; it didn't stick to anything.  All of the epoxy below is fully cured:

Bagging film removed, revealing cured epoxy throughout puffy cloth

The peel and ply will pull right off the carbon fiber assembly.  Here's how it looks, as it is peeled off.  This is where things get really cool:

Removing the peel ply and excess cured epoxy

Closeup of carbon fiber, note white dots (from peel & ply holes)

The assembly easily lifted off the glass.  If it's difficult, a shot of compressed air under one corner can make it easy as well.

The carbon fiber / plywood is nearly ready to use

And then all I have to do is trim off the edges using a band saw.  Here's the finished panel, ready to use:

Carbon Fiber bonded to plywood

I hope you found this helpful!

-- James Wiebe, 2011 EAA August Raspet recipient


dan izvernariu said...

Hello! I`m Dan Izvernariu from Wellington NZL...i looking for a job in CFRP. I have 5 years full time aeronautics composites executions ; im technician i work for O.G.M.A. Industria Aeronautica de Portugal Europe in FCO (fabrication) for: NH90, Marin Lokheed C190, F16, Pilatus and Dassault. Items gr. 1 and 3 importance quality and resistence . I have statement of my works emited by OGMA and i real interest for a job.
Sample: Panels upper, lower/ Beads/ flaps/ door batery/ interior and exterior pannels/ ...many others
Work with:
fibre glasses/ carbon texture/ kevlar ...
If do you want to contact me pls. note my mail:
perfectcircleissquare.usa@gmail.com or my mobile phone : 0212602449.
Thank you! Dan

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