A composite autoclave is a closed moulding tool/oven that uses pressurised steam to manufacture lightweight and strong composite materials. Autoclave curing creates a high-pressure environment through a heated cure cycle. It enables consistent polymer hardening and produces accurate results.
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The Autoclave Composite Manufacturing Process
The autoclave process for composites manufactures high-performance materials for the automotive and aerospace industries. Here is a step-by-step guide to the composite autoclave process:
1. Lay-up of Composite Materials
The first step involves laying up composite materials, such as carbon fibre. The material is often pre-impregnated with a resin system (prepregs), and these layers are placed over a mould in specific orientations to achieve the desired strength and stiffness.
2. Vacuum Bagging
Once the lay-up is complete, the materials and mould are covered with a sealed vacuum bag. When the vacuum is applied inside the bag, trapped air is removed, and resin bonds equally throughout the fibres.
3. Autoclave Curing
The sealed mould is placed inside the autoclave, a large, pressurised oven that applies heat and pressure to the composite material. The heat catalyses the curing of the resin, and the pressure helps compress the material, which supports bonding between the layers.
4. Temperature and Pressure Ramp-Up
The autoclave’s temperature and pressure gradually increase according to a specific ramp-up schedule. This controlled increase prevents the development of internal stresses within the material.
5. Holding Phase
Once the target temperature and pressure are reached, these conditions are maintained for some time. This holding phase allows the resin to fully cure and cross-link, forming a solid, durable matrix within the composite.
6. Cooling Phase
After the holding time, the autoclave is gradually cooled to room temperature while maintaining pressure to avoid warping or deforming the material.
7. Pressure Release and Unbagging
When the autoclave reaches room temperature, the pressure is carefully released. The vacuum bag is removed, and the composite part is extracted from the mould.
8. Post-Curing and Machining
Some composites may require a post-curing step outside the autoclave to achieve their final properties. Machining or other finishing processes are also applied to meet certain specifications.
9. Inspection and Quality Control
The final step involves thoroughly inspecting the composite part to ensure it meets design and quality specifications. Techniques such as ultrasonic testing, X-ray, or visual inspections are commonly used.
Pressure in a Composite Autoclave
The pressure in an autoclave typically ranges from 70 to 300psi, which is 5 to 20 times atmospheric pressure. However, two pressure parameters exist and can be altered depending on the results required. These include the externally applied autoclave pressure and the internal bag pressure.
Temperature of Composite Autoclave
For materials such as carbon fibre-reinforced plastics (CFRPs), the temperature in an autoclave is typically maintained between 120°C and 180°C. This activates the resin’s chemical hardeners and solidifies the matrix around reinforcing fibres. However, other materials, such as thermoplastic CFRP (CFRTP), may need processing temperatures up to 390°C. Fluctuations in temperature can lead to incomplete curing or defects, such as resin-rich or resin-poor areas, which may weaken the composite. Therefore, the temperature must be controlled carefully with advanced sensors and automated control systems.
Autoclave for Aerospace and Automotive
Autoclaves are used to manufacture aerospace and automotive components. Applying controlled heat and pressure allows manufacturers to produce incredibly strong, lightweight components such as aircraft fuselage panels and automotive chassis parts. This improves fuel efficiency, reduces emissions and enables more aerodynamic designs.
Conclusion – Autoclave for Composite Curing
Autoclave curing is an effective closed tooling method that combines heat and a pressurised stream to produce lightweight, strong composite materials. It catalyses the curing of the resin, compresses the material, and supports bonding between the layers. Temperature and pressure settings vary depending on the type of material being used and the required outcome.
Piran Advanced Composites has a high-spec aerospace composite autoclave with a 250°C operating pressure/temperature that produces complex, void-free carbon fibre components.
We also have state-of-the-art facilities capable of producing 20,000+ aircraft interiors annually, two clean rooms for the lay-up of contamination-free composites, a separate high-temperature curing oven, and the latest 3-axis and 5-axis CNC machines.
Contact our expert team to learn more about composite manufacturing and how our services can make your aerospace, space and automotive visions a reality.
