The majority of high performance composite structures are manufactured in autoclaves. To cut costs, especially in the aerospace industry, methods to manufacture composites out of autoclave (OOA) are interesting to the industry. However, todays' OOA-methods require new materials in the manufacturing process. This research project aims to present a method that could use conventional materials in OOA-manufacturing.


The use of composite materials for aerospace structures has seen a high increase in recent years, and is still growing. However, the manufacturing of composites remains very costly since it requires equipment investments, such as an autoclave. As a result, there is high interest in Out of Autoclave (OOA) manufacturing to cut costs. But the absence of additional compaction pressure from an autoclave is of major concern. Especially for large and complex shape parts, the limited compaction pressure in OOA processing can produce higher void content levels and cause consolidation issues. Semi-impregnated fiber plies and new formulated resin systems were developed to be used with OOA as solutions to reduce the voids content. However the use of these new materials requires a huge amount of experimental tests to validate their use in the aerospace industry.


This project, within innovative OOA, aims to show a method that does not require the use of new materials in OOA manufacturing. 

Partners and funding

Partners: RISE SICOMP, Oxeon

Financing: Vinnova


Out-of-autoclave (OOA) manufacturing technology represents a great cost saving opportunity by eliminating the purchasing and service costs associated with autoclaves. Nevertheless, the reduction of pressure compared with an autoclave makes it difficult to achieve proper quality related to porosity. High porosity levels have been observed when traditional prepregs are used to produce OOA laminates due to entrapped air. New prepregs were developed to be used with OOA. However, the use of new materials is expensive due to the experimental validation needed. In this study, an innovative OOA method was developed which does not require the use of a special designed OOA material.

The new innovative OOA method reduces the void content effectively and ILSS showed characteristics comparable to a conventional laminate. The method is preferably used to reduce manufacturing cost; or for larger laminates that will not fit into an existing autoclave; or as a method where an autoclave is not available.

By using a thin air evacuation layer between the plies of conventional prepreg the voids content was significantly reduced. C-scan and microscopy were used to measure the voids content. Interlaminar shear stress (ILSS) tests were used to investigate the effect on mechanical properties.

The ILSS tests show promising results, comparable ta the reference laminate, suggesting that the addition af the thin air evacuation layer does not have any detrimental effects.