Fiberglass fabrication services include all types of services (e.g., design, repair and replacement) dealing with the use of fiberglass or fiberglass composites. A mineral fiber, fiberglass is used in many applications in both the industrial and commercial sectors. There are many variations of fiberglass with properties suitable for different functions. Examples include continuous fibers for electrical insulation, insulating wool for thermal and acoustic applications, and special-purpose products made of heat-resistant or lightweight materials.

Fiberglass Materials

Fiberglass is a reinforced polymer consisting of small glass fibers in a resin matrix. Fiber reinforcement significantly increases a resin’s tensile strength. A relatively high strength-to-weight ratio is the primary advantage of using fiberglass to construct parts. Other advantages include the simplicity of making complex and custom shapes and the ability to tailor products layer by layer.

Glass Fiber Production

The raw materials for fiberglass include a variety of natural minerals and chemicals. The major ingredients are silica sand, limestone, and soda ash, which must be carefully weighed in exact quantities and thoroughly mixed together. Once mixing is complete, the ingredients are melted in a furnace. The furnace is heated and then kept at a higher temperature than for normal glass making (about 2500°F) in order to form fibers. Once molten, the glass is transferred to bushings with fine orifices that allow the glass to pass through as fine filaments.

To create continuous strands for use as reinforcements in fiberglass plastics, multiple strands are caught up on a high-speed winder after passing through the bushing holes. The speed difference creates tension, which pulls out the filaments to form strands a fraction of the diameter of the orifices. Binder is added to allow the strands to be wound without breaking.

Resins

Fiberglass composites are made by adding glass fibers to a specific type of resin. There are two common types of resins used as the vehicle for making fiberglass: epoxy and polyester. Mold-making, molding, and laminating operations can be performed with either of these systems.

• Epoxy resins are higher performance and higher priced systems. They are used in weight critical, high strength, and dimensionally accurate (low shrinkage) applications.
• Polyester resins are styrene-based products used in all types of composite construction. They are less expensive, offer more corrosion resistance, and are more forgiving than epoxies.

Selecting Services

To select a fiberglass fabrication service, an industrial buyer must first determine which companies can meet the application’s requirements.. This selection guide is designed to help buyers with this process.

Capabilities

Select fiberglass fabrication services based upon their capabilities, which can include different types of services and production methods.

Service Types

Companies provide different types of services related to fiberglass fabrication. These include designing, modeling, prototyping, and testing.

• Designing services assist clients with design and production of fiberglass products. This can include any type of repair or part fabrication.
• Modeling services assist clients with any pre-production design and visualization aided by modeling. These services can provide scaled or to-size fiberglass models of a product in order for the client to make informed decisions about production.
• Prototyping services assist clients by producing low-quantity, pre-production pieces or parts used for testing and further design work and development.
• Testing or inspecting services assist the client by analyzing the quality of fiberglass parts constructed by the client or another service. The company’s fiberglass expertise can be utilized to assure the client that the product is effectively constructed and conforms to required design standards or regulations.

Production Methods

Production methods are ways in which companies can assist clients with the creation of fiberglass products. These include cutting, fabrication, laminating, machining, and molding.

• Cutting methods are used to cut and process fiberglass pieces out of larger stock shapes. Cutting of industrial parts is generally done using die cutting equipment.
• Fabrication involves bonding multiple fiberglass pieces into one unit. Services may implement structural putties, core bonding and bedding compounds, and fairing and filling compounds to join fiberglass parts.
• Laminating refers to the process of applying a thin protective coating of resin and reinforcement over a composite part. Laminating can be done to add strength, smooth out rough surfaces, or provide protection from corrosion or chemical attack.
• Machining uses tools to shape fiberglass materials by removing small amounts of material at a time. Certain types of fiberglass such as G10 (a high strength glass-epoxy laminate) may require special equipment for machining due to hardness.
• Molding is the process of constructing a part within a mold. Typically, precut reinforcement is placed one layer at a time into the mold and saturated with resin. When the part has achieved the desired thickness and orientation, it is left to cure. When it is removed from the mold, it will have the exact shape of the mold surface.

Molding Processes

Fiberglass molding itself can be performed via a number of processes.

Compression molding uses a slug of hard material which is pressed between two heated mold halves, usually with a vertical press. After being formed, the part is air-cooled. It is best suited for creating high-volumes of high-strength fiberglass.

Hand lay-up incorporates hand impregnating resins into fibers that have been formed into a woven, knitted, bonded, or stitched fabric. The method for applying the resin is usually by roller or brush. The material then cures at atmospheric pressure and temperature. Because this process allows for close control of material application, it is the method of choice for producing many fiberglass parts.

Spray up involves chopped fiber being fed into a catalyst resin and sprayed directly onto the mold by a hand-held gun. The material then cures at atmospheric pressure and temperature. Parts requiring large area coverage, moderate strength, and corrosion resistance are produced using this technique.

Resin transfer molding (RTM) involves dry fiberglass reinforcement being loaded into a closed mold. Resin is then injected into the mold to form the finished part. Because the material is completely enclosed within the mold in net or near-net shape, RTM offers superior surface finishes, close control of tolerances, and less material waste.

Sheet molding compound (SMC) is a process in which a layer of fiberglass material is sandwiched between two layers of thermoset polyester resin and extruded into flat sheets. The sheets are pressed into final form by heated molds. Tooling and piece part prices tend to be high.

Vacuum bag molding is a process in which a sheet of flexible transparent material (bag), bleeder cloth, and release film are placed over the lay-up on a mold and sealed on the edges. The vacuum is applied between the sheet and the lay-up, removing the trapped air. The part is then cured with temperature over time. This process is designed to maximize the fiber-resin ratio by “squeezing out” excess resin.

Figure 1 – Diagram of a typical bagged layup. Image Credit: Fibre Glast Developments Corp.

Vacuum forming begins with a thermoplastic sheet that is heated to form a drape and is then drawn over or into the mold, assisted by vacuum holes in the mold, to impart the desired shape of the part.

Figure 2 – Simple depiction of the vacuum forming process.

Vacuum assisted resin transfer molding (VARTM) is an infusion process where a vacuum draws a resin into a one-sided mold. A cover, or bag, is placed over the top of the resin to form a vacuum-tight seal, and then the vacuum is applied, drawing the resin into the mold.

Video depicting the creation of a part mold made from fiberglass.

References

Century Composites - Capabilities

Youtube - Fiberglass Vacuum Molding

Fibre Glast Developments Corporation - Vacuum Bagging, Figure 1