MANUFACTURING OF COMPOSITES - EuCIA · MANUFACTURING OF COMPOSITES ... The RTM method is used in...
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MANUFACTURING OF COMPOSITES Composites manufacturing processes can be divided into “open” and “close” moulding technologies, which are briefly illustrated below. OPEN MOULD TECHNOLOGIES Hand lay-up In hand lay-up, the necessary amount of reinforcing material is laid out in the female mould in the desired directions. The reinforcing material is impregnated with the polymer by spreading a liquid mixture of resin and curing agent/hardener using a brush or roll or by injecting. Finally, a roll is used to ensure that the reinforcing material is properly impregnated. Small-batch products, such as large boats or architectural structures, are often manufactured this way. When aiming at improved quality, the mould can be covered with a flexible film and a vacuum can be created under the film, whereby the air pressure ensures impregnation and the formation of a tight structure. This vacuum bagging is used for manufacturing car parts, for example. High fibre content, in excess of 50% of the volume, is attained with hand lay-up and almost all different fibres can be used, usually as woven rovings or chopped strand mats. The chopped stand mat is a reinforcement made of short or continuous fibres that are not woven but bound together with glue. Prepreg lamination Airplane and sports car industries are using an advanced version of hand lay-up, where pre-impregnated reinforcements, i.e., prepregs, are laid up in the mould in a clean room. These prepregs are stored in a freezer so that hardening/curing does not happen during storage and prepregs stay adhesive-like at room temperature. a vacuum bagging is used after the prepregs are laid up and the mould is taken to an autoclave where the part is hardened, often with pressure as high as 6 bar and temperature of 120– 180°C. Pregpreg lamination can be automated, which enables fast, efficient and reproducible lamination process to manufacture larger parts which cannot be produced by hand lay-up. Spray lay-up The most affordable way of manufacturing composites in an open mould is spray lay-up lamination where the resin and chopped fibre strands are sprayed to the mould. The length of the fibres is usually under 25mm, and the fibre content remains low, approximately 30% of volume. Spray lay-up is used for manufacturing small boats and bathtubs, for instance, where the mould is a vacuum-shaped acrylic shell, the visible surface of the bathtub. Filament winding A third example of the open mould technology is filament winding, where the fibrous reinforcing material is impregnated by pulling it through a resin bath and winding the impregnated fibres around a rotating mould called mandrel. In this way various tanks are made for the construction and chemical industries as well as for the liquid fuel of space rockets. Fiches Eucia V3.indd 5 14/09/17 10:54
Transcript of MANUFACTURING OF COMPOSITES - EuCIA · MANUFACTURING OF COMPOSITES ... The RTM method is used in...
MANUFACTURING OF COMPOSITES
Composites manufacturing processes can be divided into “open” and “close” moulding technologies, which are briefly illustrated below.
OPEN MOULD TECHNOLOGIES
Hand lay-up
In hand lay-up, the necessary amount of reinforcing material is laid out in the female mould in the desired directions. The reinforcing material is impregnated with the polymer by spreading a liquid mixture of resin and curing agent/hardener using a brush or roll or by injecting. Finally, a roll is used to ensure that the reinforcing material is properly impregnated. Small-batch products, such as large boats or architectural structures, are often manufactured this way. When aiming at improved quality, the mould can be covered with a flexible film and a vacuum can be created under the film, whereby the air pressure ensures impregnation and the formation of a tight structure. This vacuum bagging is used for manufacturing car parts, for example. High fibre content, in excess of 50% of the volume, is attained with hand lay-up and almost all different fibres can be used, usually as woven rovings or chopped strand mats. The chopped stand mat is a reinforcement made of short or continuous fibres that are not woven but bound together with glue.
Prepreg lamination
Airplane and sports car industries are using an advanced version of hand lay-up, where pre-impregnated reinforcements, i.e., prepregs, are laid up in the mould in a clean room. These prepregs are stored in a freezer so that hardening/curing does not happen during storage and prepregs stay adhesive-like at room temperature. a vacuum bagging is used after the prepregs are laid up and the mould is taken to an autoclave where the part is hardened, often with pressure as high as 6 bar and temperature of 120–180°C. Pregpreg lamination can be automated, which enables fast, efficient and reproducible lamination process to manufacture larger parts which cannot be produced by hand lay-up.
Spray lay-up
The most affordable way of manufacturing composites in an open mould is spray lay-up lamination where the resin and chopped fibre strands are sprayed to the mould. The length of the fibres is usually under 25mm, and the fibre content remains low, approximately 30% of volume. Spray lay-up is used for manufacturing small boats and bathtubs, for instance, where the mould is a vacuum-shaped acrylic shell, the visible surface of the bathtub.
Filament winding
A third example of the open mould technology is filament winding, where the fibrous reinforcing material is impregnated by pulling it through a resin bath and winding the impregnated fibres around a rotating mould called mandrel. In this way various tanks are made for the construction and chemical industries as well as for the liquid fuel of space rockets.
Fiches Eucia V3.indd 5 14/09/17 10:54
CLOSED MOULD TECHNOLOGIES
Vacuum infusion
Vacuum infusion (VI) resembles hand lay-up the reinforcing material is laid up in the mould and then vacuum bagging is applied. The difference is that the resin is taken to the mould after vacuum bagging, via a hose, sucked by vacuum. This technology is cleaner and safer than hand lay-up and often produces better composite properties. RTM
Resin transfer moulding (RTM) resembles the injection moulding of thermoplastics. In this technology, liquid resin is pressure-injected between metallic mould parts. Before the resin is injected and the mould is closed, the reinforcing material have been laid up in the mould. The RTM method can be used for manufacturing bigger/larger batches than hand lay-up or vacuum infusion, but the size of the products is limited because of the requirements of the moulds and injection units. The RTM method is used in manufacturing bus body parts or tractor parts, for instance.
Compression moulding
In compression moulding a compound made of resin pre-mixed with chopped fibre strands is introduced into a mould and compressed, so that the mass flows to fill the cavity. The curing of the resin is activated by contact to the heated mould walls. The method is used for manufacturing the chassis of medicinal devices or electric devices that are intended for demanding applications.
Pultrusion
In pultrusion the fibres are impregnated by pulling them through a resin bath and by hardening/curing the impregnated fibres in a heated mould. The process is continuous, with the impregnated reinforcing material continuously entering the machine and the hardened profile having the shape of the mould’s cross section continuously exiting. This method is used in the manufacture of a large variety of products, from skiing poles to the large side panels in buses. The continuous profile is cut into pieces of the desired length during the manufacturing process.
The level of automation in composite production increases continuously, and almost all stages of composite production from lamination to curing/hardening and machining to finishing and inspection can be automated, particularly with larger batch sizes. With modern methods it is relatively easy to inspect and repair composite products.
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