Introduction: Simple Methods for Molding Fiberglass and Carbon Fiber

By Making to learn
About: I'm a former bicycle industry designer turned professional jeweler. I like working with my hands and am happiest when I'm in the shop building my creations. If you need help with your project just let me know!

Here's a couple of low cost and quick procedures I use to manufacture simple parts using fiberglass and carbon fiber. While it's not the best method for producing parts that see structural loads (some form of consolidation like vacuum bagging/pressure molding to reduce internal voids should be used for that) or parts that need to have an extremely high finish leveI, I have molded everything from simple car parts to subwoofer enclosures to costuming/theatrical props using these methods.

Step 1: Materials

Clear packing tape
Blue foam insulation- available at many home improvement stores
Laminating resin- polyester resin and epoxy resin ( I use Bondo polyester resin for fiberglass and West Systems epoxy resin for carbon)
Acetone
Paint brushes- I use a short bristled brush, sometimes I just cut the bristles down to anywhere between 1/2' to 1" llength
Mold release paste wax-available from Aircraft Spruce- http://www.aircraftspruce.com
Woven fiberglass cloth and/or chopped strand mat- often called CSM
Woven carbon fiber cloth- available from Aircraft Spruce- http://www.aircraftspruce.com
3M Super 77 spray glue (optional)
Rubber gloves
Filtering mask

Please use proper safety equipment when working with resins and fibers. Carbon fibers are extremely sharp when cut and the use of resins and melting of foam can produce nasty vapors.

Step 2: Method #1- Creating a Mold and Pulling a Positve

I used this method to modify existing bodywork on a friend's Ralt R5 CSR Mazda race car. His new tire/wheel set up was causing the front tires to hit the existing bodywork so he modified it by cutting holes in the fenders and then bolting on some plates with spacers so the front tires would clear when the suspension was fully compressed. The modifications were pretty ugly and un aerodynamic (not to mention the tires would still rub on occasion) so he asked me to make new fender parts that could be grafted onto the existing bodywork so he wouldn't have to buy all new bodywork for the front of his racecar. I made these modifications several years ago so I don't have photos of the entire sequence so I did drawings to fill in the gaps.

The first thing I did was to figure out how much I wanted to raise the fender line and then cut a template to be used to cut the blue foam. The blue foam is then cut using a hot wire cutter and is placed on top of the existing fender to check the fit.

Next the foam is taped down to the fender using clear packing tape- the tape prevents the polyester resin from melting the foam when applying the fiberglass. I then made some vents for the new fender using some wood molding- this is hot glued in place on the taped foam.

The taped foam then gets a coating of mold release wax.

Now the fiberglass cloth is wetted with polyester resin and is applied over the foam. You can use woven fiberglass cloth or chopped strand mat for this. If you use CSM you have to use polyester resin- the polyester resin melts the styrene binder in the CSM. All epoxy resin will do is make a huge mess.

One trick I do when using woven cloth is I pre cut my cloth and stick it down on my pattern with some 3M Super77 spray cement and then wet the woven cloth out with resin using a short bristled paintbrush. If the cloth (or CSM) has to be applied in sections make sure the sections overlap by at least one inch.

Once the resin has cured you can pull the fiberglass mold from the foam pattern.

To mold a carbon fiber positive from the fiberglass mold you first apply a mold release wax to the fiberglass mold.

Then start wetting out the carbon cloth with resin and laying it inside the fiberglass mold. When wetting out the resin use a short bristled paintbrush and a "stippling" action to make sure the resin has fully penetrated the carbon cloth as is placed in the mold. I tend to use epoxy resin when laminating carbon cloth as it produces a much stiffer final product.

I usually apply layers of carbon cloth at alternating 45/90 degree positioning. This is because the woven carbon cloth only has stiffness in the direction of its fiber orientation.

Before the resin has fully cured you can trim the excess material around the edges of the mold with scissors- this is much harder to do later.

Once the resin has fully cured the part can be removed from the mold.

After the molding process was finished all I had to do was bond the new carbon sections onto the existing bodywork and blend it in with some filler.

Step 3: Method#2- Lost Foam Molding

I used this method to create an air duct for the oil cooler on a friend's Porsche GT5R racecar. This is a very quick and easy way to mold a hollow component or a part that has severe undercuts that would not alllow it to be molded in a single piece female mold.

The first step is to cut a pattern from blue insulation foam and wrap it with clear packing tape.

Next, cover the taped pattern with a mold release wax.

Now cover the pattern with woven fiberglass cloth and wet out the resin. Make sure to leave a section uncovered- this is where the foam will be melted.

After the resin has cured, melt out the foam by pouring acetone on the uncovered section (note that in drawing #4 it says kerosene- this is incorrect). Make sure you have a decent sized tray or bucket under your part- this will get messy! As the foam melts you can reach into your hollow part and pull out the packing tape and you are left with a hollow molding.

Step 4: Method#3- Using an Existing Item for a Mold

In this case I wanted to make a hidden subwoofer enclosure for my car by molding a fiberglass tub that sat inside the spare tire so I wouldn't lose any trunk space.

I first started by covering the inside of the spare tire wheel with clear packing tape and giving it a good coat of mold release wax.

Next I cut a large ring from MDF and placed it on top of the spare tire.

Then I started laying up my fiberglass ( I used CSM for this) into the taped spare tire. The fiberglass was applied so that it overlapped the upper surface of the MDF ring. This made the finished molded tub much stronger and made it much easier to remove from the spare tire after molding.

After the resin cured I cut another MDF ring to mount my subwoofer into and joined it to the MDF ring that was molded into the fiberglass tub. I used some sealant between the two rings and also screwed them together.

Then I drilled a hole in the hole in the MDF for my subwoofer wiring and applied sealant to it after I ran my wiring to the woofer. The last step was to bolt the subwoofer into place.

The volume of the molded tub turned out to be perfect for a 10" subwoofer and it sounds great without taking up additional trunk space- and I get to keep my spare tire!