There are three main types of composite manufacturing processes: Hand Lamination, Vacuum Infusion and Pre-Preg.
Hand laminating is when fibre reinforcements are placed by hand in an open mould and resin is applied with a brush or roller.
Gel coat is first applied to the mould and once cured sufficiently, fibreglass reinforcement is placed by hand on the mould. The base resin is mixed with the catalyst and applied by pouring and brushing. Further layers of fibreglass reinforcement are added to build desired thickness.
Hand lamination is the most straightforward composites moulding process, which offers a wide range of part sizes, low cost tooling, and simple processing.
- Low cost
- High production runs
- Higher risk of voids
- Fibre/Resin ratio cannot be controlled easily due to the resin being applied by hand resulting in parts being heavy
Vacuum Infusion is when resin is pushed into the mould under a pressure vacuum to allow even distribution.
Fibre reinforcements are placed in a mould and then covered with a plastic membrane to create the vacuum seal. When the resin is drawn into the mould, the fibre reinforcement is compacted and there is no room for excess resin waste.
Vacuum infusion is suitable to mould very large structures and produces parts with a uniform degree of strength, while being lightweight.
- High fibre content laminates can be obtained with very low void content
- Rapid manufacturing route
- Improved health and safety, and environmental control due to enclosure of resin
- Possible labour reductions
- Both surfaces of the component have a moulded surface
- Matched tooling is expensive, and heavy in order to withstand pressures.
- Component size limited by above
Pre-preg is a ready-made material where the fibre reinforcement has been impregnated with a thermoset matrix at manufacture. As the matrix is partially cured to allow for easy handling, the pre-preg therefore requires cold storage to prevent complete curing.
The manufacturing process begins with the pre-preg material being placed on the mould and then covered by a plastic vacuum bag. The job is then put in an autoclave under a vacuum. The autoclave applies both heat and external pressure, which adds to the force of the vacuum. The pre-preg material is completely cured from the heat of the autoclave.
The vacuum from within the bag eliminates voids and forces excess resin from the reinforcement. The addition of pressure from the autoclave provides high fibre concentration and a better adhesion between layers of sandwich construction.
- Resin/hardener levels and the resin content are controlled by the materials manufacturer
- Superior fibre placement control
- High fibre content and low void content readily achieved
- Resin chemistry can be optimised for mechanical and thermal performance
- Potential for automation and labour saving
- Additional materials costs
- Additional cost of autoclaves, ovens etc
- Material must be stored and transported frozen