Introduction to Composite (Fiberglass) Molding and Manufacturing
The process of composites manufacturing consists of combining a fiber reinforcement and polymer resin in a mold and forming a shape. This basic process can produce a wide range of products from aircraft to transportation components, or boats to chemical resistant equipment. Depending on the component size, complexity, specifications and production volume there are a number of composite molding processes that are employed to produce a wide range of products.
In the world of plastics there are two major types of materials broadly characterized by thermoplastic resins and thermoset resins. Thermoplastic materials make up a large portion of the common plastics that surround us in everyday life. These materials are solid at room temperature and are heated to a "liquid" state, formed in a mold, then cooled back into a solid in the form of an object. If subsequently heated the thermoplastic material will again become a liquid.
With thermoset resins a chemical reaction takes place called polymerization. These resins are in liquid form at room temperature and with the addition of a curing agent convert from a liquid to a solid. Once cured, or polymerized, a thermoset resin cannot be converted back to a liquid; the process is irreversible. In manufacturing composites a number of types and formulations of resins are available. The most widely used polymers include; polyester resin, vinyl ester resin and epoxy resin.
The term composites literally means "to put together", that is to combine different materials. In this case the thermoset resin is combined with a fiber material known as a reinforcement. The fiber reinforces the resin matrix. So the fiber provides the strength and the polymer resin holds the fiber together and provides the product shape. There are numerous combinations of resin and fiber that enable composites to provide specific properties and meet end-user requirements. The most commonly used fiber reinforcements include; glass fiber (fiberglass), carbon fiber, and aramid fiber also known as Kevlar®. The most common combination is fiberglass reinforced polyester which is often referred to simply as fiberglass (e.g. That is a nice fiberglass boat.).
The selection of composites materials and manufacturing process is keyed to the required finished product properties, the rate of production, and the cost factors for an individual product. These manufacturing options include two major production methods; Open Molding and Closed Molding. With open molding technology the polymer resin is exposed to the atmosphere during the forming and curing process. As implied with closed molding, the process takes place inside a mold cavity where the materials are not exposed to the atmosphere.