Composite manufacturing methods range from highly manual processes to fully automated

Steps for Manufacturing in Composites

In any composite manufacturing process (fiber + resin), there are four essential steps, not always in this particular order which may be reduced to three depending on the type of material used.

• Impregnation: The resin, in liquid state, comes into contact with the fiber reinforcement and impregnates it. When using prepreg materials, this step is not required, as the fibers are already pre-impregnated.
• Lay-up: Placement of the fiber reinforcement onto the mold that defines the shape of the final part. Multiple layers can be stacked over the entire part or locally in specific areas to increase thickness and mechanical strength.
• Consolidation: Compaction of the different layers and removal of voids to prevent structural weaknesses in the final component.
• Curing: Activation of the chemical polymerization process, during which the resin transitions from a liquid to a solid state.

Once these fundamental steps are understood, the different manufacturing techniques used to produce composite parts can be examined.

Open Molding Processes

Wet Lay-Up (Hand Lay-Up)

A release agent or gel is first applied to the mold to prevent the part from sticking. Reinforcement mats or fabrics are then cut to size and placed on the mold surface, after which the resin is poured and spread evenly.

The simplest composite manufacturing method, accessible to virtually anyone, where fibers are manually impregnated with resin using basic tools.

Layers of reinforcement and resin are built up sequentially, using rollers to remove trapped air and excess resin. After curing at room temperature or under elevated temperature, the composite part is removed from the mold and prepared for further finishing operations.

Pros:

• Low tooling and equipment cost
• High process flexibility
• Suitable for large or custom parts

Cons:

• Strong dependence on operator skill
• Limited control over fiber-to-resin ratio
• Lower repeatability and longer cycle times

Spray-Up

Spray-up is a widely used technique for glass fiber parts that accelerates traditional wet lay-up by spraying chopped reinforcement fibers and liquid resin directly onto the mold surface. Layers are built up rapidly until the desired thickness is reached, and the process is often combined with gel coat application.

The process uses a spray gun equipped with a fiber chopper that cuts continuous glass fiber rovings into short lengths, typically between 25 and 75 mm, which are mixed with resin during spraying. This results in randomly oriented fibers that must be compacted by rolling, similar to hand lay-up.

Pros:

• Faster than traditional hand lay-up
• Widely used and effective for fiberglass parts
• Simple, well-understood process with easy operator training

Cons:

• Random fiber orientation limits mechanical performance
• High resin content and lower laminate quality compared to closed-mold processes
• Lower surface finish and dimensional control

Prepeg

Prepreg materials consist of fiber reinforcements that are pre-impregnated with a precisely controlled amount of resin during manufacturing. The resin is typically partially cured (B-stage), allowing the material to remain tacky and easy to handle until final curing.

Because impregnation is already completed, the manufacturing process focuses on lay-up, consolidation, and curing. Traditionally, prepregs are cured under heat and pressure in an autoclave, which enables excellent consolidation and very high laminate quality. However, in recent years, Out of Autoclave (OoA) prepregs have been developed to reduce processing cost and complexity.

Pre-impregnated fibers (prepregs) are a very common choice for high-performance applications.

Prepregs offer outstanding control over fiber-to-resin ratio and laminate consistency, making them a preferred choice for high-performance applications where repeatability, structural integrity, and surface quality are critical.

Pros:

• High laminate quality and repeatability
• Superior mechanical performance
• Excellent control of fiber-to-resin ratio

Cons:

• Higher material cost compared to dry fabrics
• Requires controlled storage and handling (typically refrigerated)
• Autoclave equipment often required, depending on prepreg type

Vacuum Infusion

This process, also known as Resin Infusion, is an open-mold method widely used in boat building and wind energy applications, as it enables the manufacture of very large parts with relatively precise fiber-to-resin ratios.

All reinforcement fabrics are first cut, positioned, and laid into the mold in a dry state, then sealed under a vacuum bag. Resin inlet lines are arranged and connected prior to sealing, creating a controlled resin delivery network. Once vacuum is applied, the pressure differential draws liquid resin through the inlet lines and distributes it across the dry reinforcement. Resin flow is guided by flow-assisting elements such as mesh layers, channels, or grooved core materials to ensure uniform impregnation.

Pros:

• Suitable for large, complex parts (e.g., boat hulls, wind turbine blades)
• Good surface finish on the mold side
• Lower resin content and higher fiber volume fraction than other open-mold methods

Cons:

• More complex setup and planning than basic open-mold processes
• Requires careful control of materials, flow media, and resin viscosity
• Less suitable for very high-volume production compared to automated closed-mold methods

Resin infusion is often used to manufacture very large composite parts, such as boat hulls, where controlled resin flow and material consolidation are critical.

Closed Mold Processes

Resin Transfer Molding (RTM)

In RTM, mixed resin and catalyst are injected into a closed mold containing a dry fiber preform. This process produces components with good surface finish on both sides and allows precise control over fiber architecture, orientation, and laminate thickness, as defined by the mold cavity.

Schematic of a Resin Transfer Molding (RTM) process.

RTM supports a wide range of resin systems—including polyester, vinyl ester, epoxy, phenolic, and MMA—as well as reinforcements such as glass, carbon, aramid, or hybrid fibers. The process can be automated to increase production rates while reducing scrap, making it a common choice for industrial applications.

Pros:

• Good surface finish on both sides
• Tight dimensional tolerances and uniform thickness
• Ability to mold complex structural and hollow parts

Cons:

• Higher tooling cost than open-mold processes
• More complex process control
• Not ideal for very low or very high production volumes

Resin Transfer Molding Variants

HPRTM (High Pressure RTM) is a variant of the RTM process in which resin is injected at high pressure, enabling the production of parts with high structural quality, excellent repeatability, and very short production cycles.

LRTM (Light RTM) is another variant that uses very low resin injection pressures, significantly reducing tooling cost and complexity.

Compression Molding

Compression molding is a manufacturing process used with materials such as sheet molding compound (SMC), bulk molding compound (BMC), and thick molding compound (TMC). It employs heated metal molds installed in hydraulic presses and can be highly automated. The process offers significant design flexibility, allowing features such as inserts, ribs, and bosses, while achieving good surface finishes that reduce secondary finishing operations and labor costs.

During production, a measured charge of material is placed into a heated mold, which is then closed and compressed until curing is complete, typically within one to five minutes. The finished part is then removed. Tooling consists of durable heated metal molds, usually made of steel, which are highly durable but also relatively expensive.

Pros:

• Short cycle times and high productivity
• Low labor cost
• Good dimensional control

Cons:

• High tooling cost
• Limited design flexibility after tooling
• Part size and thickness limitations

Prepreg Compresion Molding

Prepreg Compression Molding (PCM) combines the material quality of prepregs with the productivity of compression molding. In this process, stacks of prepreg material are placed into a heated matched-metal mold, which is then closed under pressure to consolidate and cure the laminate in a single step.

The use of closed molds enables good surface finish on both sides, tight dimensional control, and short cycle times, making PCM well suited for medium- to high-volume production. Compared to autoclave-cured prepregs, PCM significantly reduces processing time while maintaining a high level of structural performance.

PCM is widely used in automotive and industrial applications where repeatability, productivity, and mechanical properties must be balanced with cost.

Pros:

• Short cycle times
• Good surface finish and dimensional accuracy
• Suitable for medium- to high-volume production

Cons:

• High tooling cost
• Limited flexibility once tooling is defined

Automated & Continous Systems

Pultrusion

Pultrusion is a continuous manufacturing process used to produce composite parts with a constant cross-section, such as beams, profiles, and structural elements.

In this process, continuous fibers are pulled through a resin bath or resin injection chamber to impregnate them, then guided through a heated die that defines the final shape and cures the resin. Once cured, the profile is continuously pulled and cut to length.

Pultrusion delivers excellent fiber alignment and high fiber volume content, resulting in strong, lightweight components produced with high efficiency and minimal material waste. It is commonly used for structural profiles in construction, infrastructure, and industrial applications.

Pros:

• Continuous, highly efficient production
• Excellent fiber alignment and mechanical performance
• Low labor cost and minimal waste 

Cons:

• Limited to constant cross-section parts
• High initial tooling cost
• Low geometric flexibility

Filament Winding

In this method, continuous fibers (such as glass, carbon, or aramid), impregnated with resin, are wound under tension onto a rotating mandrel in a controlled geometric pattern. Fiber orientation is selected based on load requirements, enabling the production of strong, lightweight hollow structures such as pipes, tanks, and pressure vessels.

Once the required thickness is achieved, the laminate is cured on the mandrel using heat, and the finished part is either removed or left with a permanent liner. The process is highly automated, offering excellent precision, repeatability, and high fiber volume content, making it ideal for structural and pressure-related applications.

Pros:

• Excellent mechanical performance for cylindrical and axisymmetric parts
• Highly automated and repeatable
• Efficient material usage compared to alternative processes

Cons:

• Limited geometric flexibility
• Mandrel removal can be complex
• Surface finish often requires secondary operations

Automated Fiber Placement (AFP)

Automated Fiber Placement (AFP) is used to produce lightweight, high-strength structures, particularly for aerospace and high-performance industrial applications. It uses pre-impregnated fiber tows, typically carbon/epoxy, which are automatically placed onto complex molds or mandrels with high accuracy.

The use of robotic tools enables high precision and repeatability.

During the process, multiple narrow tows are heated, compacted, and laid down by a robotic head in predefined orientations such as 0°, ±45°, and 90°, building the laminate layer by layer. AFP offers high precision, excellent material efficiency, and the ability to manufacture complex geometries, making it suitable for structural components where performance and repeatability are critical.

Pros:

• High precision and repeatability
• High level of automation
• Ability to manufacture complex geometries

Cons:

• Very high equipment cost
• High programming and setup complexity
• Expensive raw materials

Composites manufacturing methods comparison

TL;DR

Composite parts are made by combining fibers and resin through different manufacturing processes, all of which follow the same basic steps: impregnation, lay-up, consolidation, and curing (with impregnation omitted for prepregs). Each process offers a different balance between cost, complexity, quality, automation, and production volume.

• Open-mold processes (Wet Lay-Up, Spray-Up, Vacuum Infusion) are low-cost and flexible but have lower repeatability and quality control.
• Closed-mold processes (RTM, LRTM, HPRTM, Compression Molding) provide better surface finish, dimensional accuracy, and structural performance at higher tooling cost.
• Automated processes (Filament Winding, AFP) deliver the highest performance and repeatability but require significant investment and are best suited for specific geometries or high-performance applications.

There is no single “best” process—the optimal choice depends on part geometry, mechanical requirements, production volume, cost targets, and level of automation required.

The post Manufacturing Methods in Composites appeared first on Managing Composites.

As with any sport, the competition to be the best leads to innovation everywhere possible, and as all composite lovers already know, carbon fiber can always help with that!

The first all carbon fiber commercially available production scale bicycle was the iconic Kestrel 4000, which was released in 1986. Before that, the utilization of carbon fibers by the cycling industry was limited to CFRP tubes glued to aluminum lugs.

1989 saw the start of the carbon fiber revolution in the Tour de France. Metal bikes continued to feature in the tour for a further decade but with dwindling success. The last Tour won on a steel bike took place in 1994, and the last non carbon fiber bike (this time made of aluminum), won the competition in 1998.

Carbon fiber composites allowed for further weight advantages and more aerodynamically shapes that weren’t possible with metals!

The post The first production carbon fiber bicycle appeared first on Managing Composites.

Siemens Gamesa celebrated the delivery of green energy from the world’s first turbine equipped with the company’s composite RecyclableBlades. The first commercial installation of recyclable wind turbine technology recently took place at RWE’s Kaskasi offshore wind power project in Germany, marking what is said to be a turning point in the long-term sustainability of offshore wind power.

“We’ve brought the Siemens Gamesa RecyclableBlade technology to market in only 10 months: from launch in September 2021 to installation at RWE’s Kaskasi project in July 2022. The RecyclableBlade technology was developed in Aalborg, Denmark, the blades were manufactured in Hull, U.K. and the nacelles were produced in and installed from Cuxhaven, Germany” Marc Becker, CEO of the Siemens Gamesa Offshore Business Unit, says. “This is impressive and underlines the pace at which we all need to move to provide enough generating capacity to combat the global climate emergency. This milestone marks a significant contribution to Siemens Gamesa’s target of having fully recyclable turbines by 2040. With RecyclableBlade available for our customers, we can create a virtuous circular economy.«

https://www.compositesworld.com/news/siemens-gamesa-recyclableblades-installed-at-rwe-offshore-wind-farm

Definitely a step in the right direction!

Swedish company Trelleborg has launched low-friction thermoplastic composite bearings!

Trelleborg Sealing Solutions launched its latest lightweight thermoplastic composite bearing, the HiMod Advanced Composite Bearing Plus, an enhanced dual-layer bearing with a low-friction modified polyetheretherketone (PEEK) layer that reduces friction and increases wear performance for use in bearing, wear ring and bushing applications.

Manufactured using Trelleborg’s patented automated fiber placement (AFP) technology, a thin low-friction liner is bonded to the inner diameters and can be added to the outer diameters of the bearing to create a high-quality solution for use in a wide range of industries. According to the company, HiMod Advanced Composite Bearing Plus will not seize or gall, unlike metal bearings, to reduce the likelihood of pump damage in chemical processing applications, has a low coefficient of friction and can withstand extreme temperature ranges.

The company says the bearings can operate from a low temperature of -156ºC to +274ºC and are capable of continuous service even when wet, with nearly zero water absorption. Unlike other non-metal bearings, Trelleborg’s solution reportedly doesn’t crack or swell in extreme conditions, making them reliable for a wide range of applications.

Interested to know more about this project? Check out this link:

https://www.compositesworld.com/news/trelleborg-launches-low-friction-thermoplastic-composite-bearing

Now, let’s talk about the usage of carbon fiber composites in the marine industry:

Carbon fiber composite hydrofoils to enable “world’s fastest” electric ferry!

The Candela P-12 Shuttle is a hydrofoiling electric ferry set to hit the waters of Stockholm, Sweden, next year. Marine technology company Candela claims the ferry will be the world’s fastest, longest-range and most energy-efficient electric ship yet. The Candela P-12 Shuttle is expected to reduce emissions and slash commuting times, and will shuttle up to 30 passengers at a time between the suburb of Ekerö and the city center. With a speed of up to 30 knots and a range of up to 50 nautical miles per charge, the shuttle is expected to travel faster — and more energy efficiently — than the diesel-powered bus and subway lines currently servicing the city.

Candela says the key to the boat’s high speed and long range will be the ferry’s three carbon fiber/epoxy composite wings that extend from under the hull. These active hydrofoils enable the ship to lift itself above the water, decreasing drag.

The P-12 Shuttle features carbon fiber/epoxy wings, hull, deck, inner structures, foil struts and rudder built via resin infusion. The foil system that actuates the foils and holds them in place is made from sheet metal. According to Mikael Mahlberg, communications and PR manager at Candela, the decision to use carbon fiber for most of the boat’s main components was lightness — the overall result is a roughly 30% lighter boat compared to a glass fiber version. “[This weight reduction] means we can fly longer and with heavier loads», Mahlberg says.

https://www.compositesworld.com/articles/carbon-fiber-composite-hydrofoils-to-enable-worlds-fastest-electric-ferry

Our last story covers the usage of composite materials in the eVTOL industry:

Horizon Aicraft completes the construction of composites intensive 50%-scale prototype eVTOL aircraft!

Horizon Aircraft Inc., an advanced aerospace engineering company, has announced that it has successfully completed the construction of its 50%-scale “Cavorite X5” electric vehicle takeoff and landing (eVTOL) prototype. Jason O’Neill, Horizon Aircraft chief operating officer (COO), told CW that the hybrid-electric aircraft could not have been built without its advanced composites team led by Kirk Creelman.

Horizon’s approach and technology enables the five-seat aircraft to fly 98% of its mission in a low-drag configuration like a traditional aircraft. Flying most of the time as a normal aircraft is also safer and should make the aircraft easier to certify than radical new eVTOL designs, the company believes. The full-scale aircraft will also be powered by a hybrid-electric system that can recharge the battery array in-flight while providing additional system redundancy. Comprehensive testing of this 50%-scale aircraft will reduce technical risk moving forward as Horizon continues development of its full-scale aircraft.

“With a 22-foot wingspan, 15 feet in length and capable of speeds over 250 kilometers per hour, this 50%-scale prototype is an impressive aircraft,” Brandon Robinson, CEO of Horizon Aircraft, says. “Furthermore, it will yield valuable information that will help to reduce technical risk as we move forward with detailed design of our full-scale aircraft.”

https://www.compositesworld.com/news/horizon-aircraft-completes-construction-of-composites-intensive-50-scale-prototype-evtol-aircraft

The post August’s Top Composite News! appeared first on Managing Composites.

AIMPLAS recently reported that it has made progress in regards to the EU-funded RECOTRANS project, which focuses on integrating unconventional manufacturing technologies to obtain cost-effective recyclable multi-material composites suitable for the transport sector at high production rates.

In particular, new thermoplastic composites have been developed through the integration of microwaves and laser welding. It has been demonstrated that microwaves can be used to optimize the curing process of composites in resin transfer moulding (RTM) and pultrusion, which reduces the energy consumed, shortens manufacturing times and helps produce better quality parts.

It has also been shown that laser technology can be used to obtain stable joints between the composite and metal, thus making it possible to eliminate riveted joints, which typically increase structural weight. Finally, studies were carried out on the recyclability of the thermoplastic composite by using it to manufacture a new part.

AIMPLAS says these results were validated through the manufacture of three life-size demonstration samples using various either carbon or glass fiber reinforcement and a thermoplastic acrylic resin, and one demo sample from the recycling material:

• A glass fiber-reinforced thermoplastic rear suspension system for a truck cab, manufactured by integrating microwaves into the RTM process; the composite-metal joint employed laser welding.
• Carbon fiber-reinforced thermoplastic automotive door panel, manufactured via microwave integration with C-RTM.
• Glass fiber-reinforced thermoplastic interior panel for the rail industry manufactured by using microwaves in the pultrusion process.

The joint between the composite and metal parts was made using laser welding. In addition, the recyclability of the materials was validated by manufacturing a demo sample of a car door handle made of 50% recycled material.

The post Recotrans Project by AIMPLAS appeared first on Managing Composites.

Spray-up is another alternative for open mould wet lay-up processes. It helps to automate the application of the matrix resin and reinforcement fibre layers, thereby reducing the time period required in the manual lay-up procedure.

As shown in this picture, in a spray-up process, chopped fibres, together with the liquid matrix resin, are sprayed onto an open mould surface until the desired thickness of the composite lamination is obtained by successive layers. Spray-up may also be used in applying the gel coat to the mould surface beforehand lay-up and spray-up processes.

The equipment necessary in the spray-up process includes a spray gun, a glass fibre chopper attachment and a pumping system. The chopper attachment delivers continuous roving and cuts them into short fibres.

Generally, chopped fibres have a length of between 25 and 75 mm, and they are added to the matrix resin stream as it exits the spray gun nozzle. This type of mixing leads to random orientation of the fibres in the layer, whereas in hand lay-up fibres may be oriented.

After the application of the catalysed resin mixture and chopped fibres through the spray gun onto the open mould surface, rolling will be necessary to compact the laminate as in hand lay-up.

Manufacturers use hand rollers or automated rolling systems. Usually, hand rolling is adequate for smaller parts, whereas automated rolling systems are preferred for larger parts with flat surfaces.

Bibliographical Reference:

Handbook of Composite Fabrication – Page 59

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