Introduction to Prepregs
A prepreg consists of a reinforcement material (carbon, glass, etc.) in unidirectional or woven fabric form pre-impregnated at a pre-determined and controlled level with a resin matrix. Prepreg is a fully compounded, reactive system (no handling or mixing of potentially dangerous chemicals). Simply take it from the roll and laminate.
Prepregs are supplied with a controlled level of tack, meaning that plies can be easily and accurately positioned on the mould to give a high level of fibre orientation control without the risk of movement, fibre wash out or the development of resin rich areas during subsequent processing, all of which can lead to loss of performance.
The cure cycle is a process where the resin within the prepreg is changed from a liquid to a solid by the application of heat. There are a number of stages to this cycle.

 
Cure Temperature / Time
For each prepreg resin system there is a range of options for cure temperature/duration. There is also a minimum cure temperature. For each given cure temperature there will be a corresponding cure time. The oven/autoclave, component and tooling, should all reach and remain above the given cure temperature throughout the specified cure cycle.
Thermocouples are used to monitor the temperature of the component and tooling.
Heat Up Rate
The heat up rate dictates how quickly the component / tool is brought up to the cure temperature. This is governed by numerous factors; matrix viscosity and reaction rate,
thickness of laminate, and tool mass and conductivity. For highly reactive matrices and thick laminates the heat up rate will be low in order to avoid exothermic reactions.
Cooling Rate
The cooling rate is controlled in order to avoid sudden temperature drops that may induce high thermal stresses in the component.
Vacuum / Pressure
At specific times throughout the cure cycle, vacuum and pressure (autoclave only) are applied and removed.