Composites materials are made by combining two materials where one of the materials is a reinforcement (fiber) and the other material is a matrix (resin). The combination of the fiber and matrix provide characteristics superior to either of the materials utilized alone. Examples of composite products in nature are wood, bamboo and bone, and an example of an early man-made manufactured composite is mud and straw which has been used for over 10,000 years.
Composite materials are very versatile and are utilized in a variety of applications. Composite parts provide superior strength, stiffness and light weight, and can be formed into any shape. An ideal applications are large complex-shaped structures such as fiberglass covers. Composite products are ideal in applications where high-performance is required such as aerospace, race cars, boating, sporting goods, and industrial applications. The most widely used composite material is fiberglass in polyester resin, which is commonly referred to as fiberglass. Fiberglass is lightweight, corrosion resistant, economical, easily processed, has good mechanical properties, and has over 50 years of history. It is the dominant material in industries such as boat building and corrosion equipment, and it plays a major role in industries such as architecture, automotive, medical, recreational and industrial equipment.
The typical composite materials can be made with fibers such as fiberglass, carbon fiber (graphite), Kevlar, quartz and polyester. The fibers come in veil mat, short fibers mat, woven cloth, unidirectional tape, biaxial cloth or triaxial cloth. The resins are typically thermal set resins such as polyester, vinyl ester, epoxy, polyurethane and phenolic. The resins start as a liquid and polymerize during the cure process and harden. The weight ratio of fibers to resin can range from 20% fibers to 80% resin to 70% fibers to 30% resin. Typically the higher fiber content provides even better strength and stiffness, and continuous fibers provide better strength and stiffness. The use of composite materials provides engineers the ability to tailor the combination of fibers and resin to meet design requirement, and perform better than standard materials.
Composites materials are replacing metals and plastics in many industries and composites are the material of choice for many new applications. Please see table 1 for a comparison of cost and properties of commercial grade composite materials to aluminum, steel and wood.
Open Mold Manufacturing process
The most common manufacturing process for fiberglass is the wet lay-up or chopper gun spray process using an open mold. The shape of the part is determined by the shape of the mold, and the mold surface is typically in contact with the exterior of the part. Mold release is first applied
to the mold to prevent the fiberglass part from adhering to the mold. Gel coat, which is pigmented resin, is applied to the mold to give the part color. Fiberglass and resin are then deposited onto the mold and the fiberglass is compressed by rollers, which evenly distributes the resin and removes air pockets. Multiple layers of fiberglass are deposited until the desired thickness is achieved. Once the resin is cured, the part is removed from the mold. Excess material is trimmed off, and the part is ready for paint and assembly. There are also closed mold processes for making fiberglass parts.