Fiberglass molding
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Fiberglass molding is a process in which fiberglass reinforced resin plastics are formed into useful shapes.
[edit] Making a mold
The plug or buck is required first to make a mold. This will be like an original part that is to be copied, but usually slightly bigger to account for the shrinkage of the mold.
First the plug must be waxed with mold release wax. Depending on the desired surface, PVA (Poly Vinyl Acetate) may be sprayed on as an additional mold release agent. However, this will reduce the smoothness of the mold's finish.
Once the plug has its release agent applied, gelcoat is sprayed onto the plug. Gelcoat is a pigmented resin without reinforcement. Tooling gelcoat is used for its harder, more durable finish.
Molds are usually made from the same fiberglass the part is made from. A mold should be 5 times thicker than the part being made. For instance, if a part is made from two layers of 1.5 ounce mat, then the mold should be 10 layers of 1.5 ounce mat. Layers of fiberglass will be applied, and tooling resin is added for bonding the fiberglass layers together. Special rollers are rolled over the wet laminate to drive out air bubbles.
Once the final layers of fiberglass are applied to the mold and allowed to set up, wedges are driven between the plug and the mold to separate the two. Once released you have a negative image of the original part.
Advanced techniques like RTM use two mold halves. The second mold half is made by building the product thickness up in the bottom mold with calibrated wax sheets, and then laminating the top mold half over that.
[edit] Making a part
The making of a part is the reverse of making a mold. Release agent is applied to the mold. The mold will be sprayed with gelcoat in the desired color of the part, then layers of fiberglass are built up to the desired thickness. Once complete and cured, wedges are used to separate the part from the mold.
