Autoclave Composite Moulding

Autoclave composite moulding is a similar to pressure-bag and vacuum-bag moulding but uses a high pressure chamber instead. This advanced composite process produces denser, void free mouldings because higher heat and pressure are used during curing. It is widely used in the aerospace industry to fabricate high strength/weight ratio parts from pre-impregnated high strength fibres for aircraft, spacecraft and missiles. Autoclaves are essentially heated pressure vessels usually equipped with vacuum systems into which the bagged lay-up on the mould is taken for the cure cycle. Curing pressures are generally in the range of 50 to 100 psi and cure cycles normally involve many hours. The method accommodates higher temperature matrix resins such as epoxies, having higher properties than conventional resins. Autoclave size limits part size.

A process using a two-sided mold set that forms both surfaces of the panel. On the lower side is a rigid mold and on the upper side is a flexible membrane made from silicone or an extruded polymer film such as nylon. Reinforcement materials can be placed manually or robotically. They include continuous fiber forms fashioned into textile constructions. Most often, they are pre-impregnated with the resin in the form of prepreg fabrics or unidirectional tapes. In some instances, a resin film is placed upon the lower mold and dry reinforcement is placed above. The upper mold is installed and vacuum is applied to the mold cavity. The assembly is placed into an autoclave pressure vessel. This process is generally performed at both elevated pressure and elevated temperature. The use of elevated pressure facilitates a high fiber volume fraction and low void content for maximum structural efficiency.

An alternative to the conventional autoclave process is a patented technique developed by the Australian CSIRO called ‘Quickstep’. Quickstep uses a unique, fluid filled, balanced pressure, floating mould technique, combined with vibration through the fluids to produce advanced fibre and glass reinforced composite components. The quickstep process produces composite structures having superior properties in a much faster time than conventional autoclave processes.