**4.5 Autoclave processing**

Autoclave processing is an advanced pressure-bag and the vacuum-bag molding process, and represents the production of composite materials uses denser molds without cavities because higher heat and pressure are used for curing. Autoclaves are essentially heated pressure vessels usually equipped with vacuum systems in which the packed layer on the mold is taken for the curing cycle. This method has wide usage, in the aerospace industry to fabricate high strength-to-weight ratio parts from impregnated high-strength fibers for aircraft, spacecraft, and missiles. The heating mechanism in the autoclave can be direct or indirect. Indirect heating systems have the heat source outside the autoclave and transfer heat into the working envelope by means of a heat exchanger. Direct heating systems have their heat source within the autoclave and aim to maximize the heat transfer from the elements to the pressure medium.
