Composite Manufacturing Techniques
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Matched die compression moulding of thermoset, showing high temperature press and polished aluminium mould tool
Thermoset composites
Thermoset composite are cured by applying heat and pressure, this accelerates the chemical reaction which sets the polymer.
There are a large number of manufacturing methods for composites many of which are suited to specific types of components manufacture. At C2 Composites we process thermoset composites by
- Matched die compression moulding
- Bladder moulding
Matched die compression moulding -- (Top of page)
Matched die uses a closed mould tool in aluminium or steel which produces a component with a controlled mould face on both sides. Prepreg. is cut to the required shape and multiple layers are laid up in the tool. Each layer has a pre-specified fibre direction to optimise stiffness and other characteristics. The closed mould tool is then placed in a high temperature press which applies heat and pressure to the composite.
Thermoset component
produced by bladder
moulding process
Bladder moulding -- (Top of page)
Bladder moulding utilises a single mould cavity that produces a single controlled surface. The pressure is applied via compressed air onto a flexible membrane in contact with the composite. This manufacturing method has cheaper tooling costs and can produce parts with undercuts or re-entrant surfaces. The heat is provided through an integrated tool heating system.
Thermoplastic missile fin designed for ultimate strength at extreme temperature
Table of available polymers / fibres
Thermoplastic composites
Thermoplastic composites become pliable when hot and become hard when cold, and can be processed very rapidly making them ideal for high speed automation. At C2 Composites we offer two methods which are fully automated to provide low cost manufacture.
- Thermoplastic stamping
- Thermoplastic winding
Thermoplastic stamping -- (Top of page)
Thermoplastic stamping requires preconsolidated thermoplastic composite to be heated to just below the melt temperature. Then, whilst hot, the material is transported over a mould tool (male or female) and a high speed press forms the composite into the tool. As the composite cools, the shape is locked in, retaining all the characteristics of strength, stiffness and impact resistance. For simple shapes, one half of the tool may be low cost rubber which deforms to fit the mould. In more complex shapes, matched metal tooling is used. Tooling is produced in house using computer controlled milling equipment.
Stamped parts usually have a constant thickness because the thermoplastic composite materials are supplied as a flat pre-consolidated board or a single thickness flexible comingled fabric (the fibres are mixed with filaments of polymer). The strength and stiffness of the final component is determined by the composition of the thermoplastic material. The fibre orientation and the polymer matrix can be controlled to provide the precise characteristics of stiffness, strength, aesthetics and cost.
This manufacturing method is ideal for high volume runs where the basic shape is relatively simple. The startup costs for dedicated automated production equipment are higher than equivalent thermoset application, but this is quickly offset by the high production rate and very low labour requirements.
This method yields consistently high quality parts with excellent surface finish, which can be further machined or bonded together as required.
Close-up of winding head, showing tape being wound over thin steel mandrel
Range of tubes and pressure vessels produced by thermoplastic winding.
Thermoplastic winding -- (Top of page)
Thermoplastic composites are available as continuous filaments embedded in a polymer. In this form the composite can be wound to form cylindrical components.
As winding proceeds, the tape is locally heated to its melt point which allows it to fuse with adjacent material. Further consolidation is achieved by pressure rollers at the point of contact.
Physical properties of the finished part are largely determined by the fibre orientation and the matrix polymer.
C2 Composites use thermoplastic winding to achieve very high levels of pre-stress in tubes and pressure vessels. Composite stresses during winding in excess of 900MPa (130Ksi) have been used. Some typical applications include
- magnet retention on very high speed electric motors,
- pre-stressed liner tubes and gun barrels,
- very high pressure vessels (700MPa /100,000psi) operating in temperature ranges up to 250°C.
Composite insert moulding (CIM)-- (Top of page)
Advanced thermoplastic composites can be combined with conventional thermoplastic injection moulding to provide hybrid components. This gives the best of both worlds with the excellent formability of injection moulding plus increased strength from continuous fibre thermoplastic. The strength of an injection moulding can be increased many fold simply by incorporating a fibre insert. This technique can be used especially to reinforce key points of maximum load, or to reduce the component profile.
This method is ideally suited to high volume manufacture. The continuous fibre insert is produced using fully automatic equipment which is subsequently fed into the injection moulding process, producing a component which looks the same but is significantly stronger.
As both parts are thermoplastic full part re-cycling is achievable
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