Crowley, D., Ward, C., and Potter, K., "A Status of Acceptance Criteria and Process Requirements in Advanced Composites Manufacturing, and Whether They are Fit for Purpose," SAE Technical Paper 2013-01-2144, 2013, doi:10.4271/2013-01-2144.
Composite materials have seen, and will continue to see, increased usage, particularly in the realms of automotive and aerospace where increasingly tight emissions standards call for lighter weight structures. These structures will also have to be made at a lower cost than previous iterations, particularly for mainstream automotive concerns. The production of composite panels is a complex, multi-step process consisting of a number of interactions. Variability is present within the raw materials and throughout the production process.Quality is intrinsically linked to both production rate and cost. Fewer defective parts means fewer concessions and less scrap, thus presenting a cost saving. Present defect rates are relatively high for composites when compared to metallic structures. Quality in composites also does not assume defect-free conditions, but rather acceptable levels of features and variations which occur during production.Acceptance criteria are established to specify what is defective and what is not. They were analysed to determine their fitness for purpose. The criteria were separated by measurement and process step. This enabled analysis of which measurements were carried out and when. Comparing them to an established defects knowledgebase highlighted why these were done.Many of the acceptance criteria were suitable for the task of avoiding defects, particularly during cure. However, for some major defect types, such as bridging and wrinkling, the acceptance criteria lacked definition and acceptable limits.Suggestions were made as to how to make the criteria fit for purpose, these include: removing ambiguity, imposing testable limits and streamlining documentation.