Composite materials are manufactured in various industries using a range of processes, depending on the desired material specifications and the application it’s used for.
Choosing the most appropriate method for manufacturing your composite materials can lead to:
- Minimum manufacturing costs
- Short cycle times – increased production output
- Low labour costs
- Highest quality materials
- Minimal finishing requirements
- Optimal geometrical flexibility – shape and size complexity
- Optimal mechanical properties – tailored to desired specifications
Main Composite Manufacturing Processes
Resin and fibres are placed in an open mold, where they cure or harden while exposed to the air. Tooling cost for open molds is often inexpensive, making it possible to use this technique for prototype and short production runs. Below are the main open molding techniques:
In the filament winding method, fibre tows are drawn through a bath of liquid resin and wound onto a rotating cylindrical mandrel. This can be done in a variety of orientations and on multiple axes, creating a variety of shapes.
Filament winding is ideal for manufacturing hollow products such as pressure vessels, motor casings, pipes, stacks, and chemical storage tanks. It can produce materials of excellent structural strength and strict tolerances. Due to it being mostly computer-controlled, the labour cost is cheap.
In the wet lay-up method, woven or chopped strand fabric (the reinforcement) is laid into a mould. Then, the resin is applied and spread with a roller or brush. This is then left to cure at ambient temperatures for several hours. In cases where a special surface finish is required, a gel coat can be added to the mould before the reinforcement is placed into it.
The wet lay-up method (hand-applied or automated) is the most commonly used and least expensive method for manufacturing composites. It is ideal for low-volume products, such as boats, tubs and bespoke items. It can produce high-quality products with good production rates when applied by skilled workers.
In the wet spray-up method, a mixture of a resin and a catalyst is sprayed using a hand-held spray gun, onto a mould. The fibre is chopped into the resin stream as it is sprayed. The mixture is then left to cure at ambient temperatures.
The wet spray-up method is simple and quick. It is ideal for custom parts in low to medium volumes, such as baths, swimming pools, storage tanks. Its drawbacks are that it leads to a low fibre volume fraction with randomly oriented fibres.
In closed molding, fibers and resin cure inside a two-sided mold or within a vacuum bag. Closed molding processes are most times automated and require special equipment, so they’re mainly used in large production molds.
In pressure or compression moulding, the moulding materials are sandwiched between two matching moulds under intense pressure and heat until the part cures.
Pressure/compression moulding benefits from short cycle times, low labour costs, design flexibility and potential for automation. It is ideal for rapidly curing large quantities of complex fibreglass-reinforced polymer parts.
In the vacuum infusion method, dry layered pieces of fabric are laid in the mould, covered with a vacuum bag, and then sealed at the edges. Resin is pulled into the mould through a reservoir as the fabric is compacted under vacuum pressure. This ensures that there is no excess resin. This can lead to very high resin-to-glass ratios and excellent mechanical properties of the laminate.
Vacuum infusion is ideal for manufacturing large parts such as boat hulls, wind turbine blades or bridge structures. This process produces strong, lightweight laminates and offers substantial emissions reductions. In addition, it uses the same low-cost and requires minimal equipment.
Resin Transfer Moulding (RTM)
In the resin transfer moulding method, the dry fabric is laid into a mould, which is then closed and sealed with a heated press. The mould is then filled, to the point of complete impregnation, by pumping low-viscosity, catalysed resin into it under pressure and heat.
Resin transfer moulding is capable of producing complex parts with smooth finishes on all exposed surfaces, allowing any combination of materials and orientations, including 3-D reinforcements. It is ideal for mass production of 100 to 10,000 units/year. This process can be simple or highly automated, with quick cycle times. It however requires matched metal tooling.
In the pultrusion method, continuous strands of fibres are pulled through a resin bath before being pulled through steel moulds to form them into continuous shapes. It is then cut into its required length using an automated saw.
Pultrusion can be easily automated, as it is a continuous process, leading to strong materials at low labour costs. It is ideal for manufacturing materials with continuous shapes, such as beams, channels, pipes, tubing, fishing rods and golf club shafts.
Centrifugal casting consists of reinforcements and resins that are distributed against the inside of a rotating mold. Centrifugal force holds the fibers and resin in place until the material cures or hardens. Centrifugal casting is well-suited for producing structures with large diameters, such as pipes for oil and chemical industry installations and chemical storage tanks.
Cast Polymer Molding
Cast polymers are unique in the composites industry: they typically don’t have fiber reinforcement and are designed to meet the specific strength requirements of an application. Cast polymer molding is used to produce parts of any shape or size.
Gel Coated Cultured Stone Molding
Gel coat is tailored to outdoor composite use in demanding environments. Gel coat is a specialised resin that provides a cosmetic outer surface on a composite product to provide weatherability for outdoor products.
Many industries utilise modern composite materials beyond matrix manufacturing. Honeycomb/Sandwich panels are structures created by building up multiple layers of material, with the middle section containing a honeycomb plastic structure between two reinforced composite panels.
These panels are being utilised in an array of industries, from aerospace and aviation to e-mobility and motorsports.
Hunstman Epoxy Resins for Composite Material Manufacturing
A low-viscosity epoxy curing system that can be used in composite material manufacturing processes such as filament winding, pultrusion, pressure moulding and resin transfer moulding (RTM). It provides a long working time, good fibre impregnation properties, short cure cycles, easy processing and great mechanical properties. It has been used in applications ranging from pipelines to profiles.
A warm-curing, low-viscosity epoxy system that can be used in composite material manufacturing processes such as filament winding, vacuum infusion, resin transfer moulding (RTM) and wet lay-up. It provides high flexibility, adjustable reactivity on demand and low exothermic behaviour.
A cold-to-warm-curing, low-viscosity epoxy system that can be used in composite material manufacturing processes such as filament winding, vacuum infusion, resin transfer moulding (RTM) and wet lay-up. Hardener XB 3403 has a long pot life that makes it ideal for the assembly of large industrial parts. Its industrial applications have included wind turbine rotor blades and marine vessels.