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How do we create a composite fairing?*
1. The first step of any process is to create a plan. Assuming you have access to programs like ProE or Solidworks, you can create a rendered model of you bike. Unless you are doing extensive finite element analysis on your bike, the 3-D modeling step is not really required.
2. Once the planning phase has finished, creation begins. A mold must be made so carbon fiber can be infused into a frame. Tooling foam is a standard mold-making material due to its high density and the ease with which we can shape it.
The picture on the left shows the foam structure of the blue shocker fairing. The wood is a support structure and the yellow blocks are blocks of tooling foam. On the lower right is the beginning of the speed racer foam mold. Looking closely, you can see that there are layers of foam on top of one another in a rough outline of the finished product.
The figure below depicts the sanded result of figure 3. The smooth surface is now ready for a sealant coat, (we use Durotec products) which will be followed by more sanding, and a few more layers of sealant. The final product is seen in figure 5.
The final product is meant to be completely smooth. Any imperfections will transfer to the mold, where removing them is practically impossible.
The next step in the fairing creation process is to make the mold. The mold is made of fiberglass. These glass fibers are sold in rolls, and can be bought online. The fiberglass will be infused to create the mold. The infusion process is the art of using a vacuum bag and a vacuum to force the resin (the stiffening agent) into the fibers. The process for infusing fiberglass is primarily the same for infusing carbon fiber, so we will go over them together.
To infuse something, you will need:
Items 2-9 can be purchased at Stephenson Pattern Supply
We will assume that you already have a mold. (If you are making the mold, the glass fibers will be layered on the sealed foam). The next step is the most confusing.
The fiber you are using will most likely have one direction. All of the fibers will be oriented i one direction. If you layer the fibers onto the mold like this, your resulting structure will be unstable because the fibers naturally want to bend. To prevent this, you must cut layers into different directions as shown in the figure. Place C on the mold and then place D on top of C. A will then go on top of B (like they are pictured) and then AB will lay on top of CD (you can use small amounts of spray tac (available at
Stephenson Pattern Supply) to hold the layers together.
You now have C-D-A-B layered together. Next do the same thing in reverse so you have C-D-A-B-B-A-D-C. This will ensure maximum rigidity and a sound structure.
You now have your fibers on your mold. The next step is the bagging process. You will take the plastic you bought and lay it out over the structure. Allow plenty of extra room for pleats and then cut it. (The final length should be 1.5 times the actual length of the structure). The figure on the left shows the bagging of the seat for the blue shocker. The pink lining around the edges is the tacky tape, which creates an air-proof seal.
Next you must assemble the resin flow components. The CX-1000 will distribute the resin. You must NOT place the CX-1000 on your fiber. There must be a layer of Peel ply between them so the CX-1000 can be removed and disposed of. Be certain to line all entrances and exits with lots of tacky tape. Fold a piece of peel ply in half and place spiral tubing in the fold. This will be your exit point. Place the free edges of the peel ply on the fiber so the resin can flow out.
Please note that the amount of spiral tubing and the amount of CX-1000 should be determined by the size and dimension of your piece. That is what makes the infusion process more art than science. You will need to practice a few times with trash pieces to get the hang of it.
Connect the spiral tubing to the whole tubing and run a line to the sump. This will catch any excess resin. Run another line from the sump to your vacuum pump (use a compressor hose). Use a broad clamp to seal off the feed tube. Turn the vacuum on to test the system. If you find you are leaking, check along the bag entrances.
When there are no more leaks, you are ready to infuse. To calculate the amount of resin you need, take the volume of the fiber (a precise measuring device would be helpful at this point) and divide by 2. This is the amount of resin you will need. (We assume that the resin-less carbon fiber is ~ 50% free space.) Mix with the appropriate amount of hardener when you are ready to infuse.
One of the most important things to consider when infusing is the time limit. After the hardener is mixed with the resin, the clock starts ticking. Resin will harden along the tubes and along the leading edges. To keep this from hindering you, remember these things:
Every resin has its own viscosity. For infusion purposes, your viscosity should be no higher than 400 cps. It is very important to keep in mind that the viscosity rating is for a certain temperature. You can decrease your viscosity by using electric blankets as a heating source. Keep your feed tube as short as possible, and above all, make sure you have enough entry and exit points. As stated before, the last item is a matter of practice, so try some infusions at least once or twice on different sized pieces.
Consult your resin to see the cure time. After it has cured, de-bag it (be careful of sharp edges) and enjoy your finished piece.
*We assume no responsibility for your actions, even those prompted by this article. Proper safety precautions should be observed at all times. Consult the MSDS of the components for specific instructions.
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