Void reduction in autoclave processing of thermoset composites : Part 1: High pressure effects on void reduction

Industrial production of thermoset composite components usually involves the application of a vacuum bagging and autoclave pressure to minimize void percentage, usually to less than 5%. The application of vacuum bagging can be time consuming, with the actual vacuum application limited to a short interval during the curing process to avoid resin starvation. At the maximum vacuum achievable void reduction is only to about 10%, with a higher applied vacuum resulting in larger void diameters. This paper reports on the use of high pressure of up to 7000 kPa by means of an isostatic press, without vacuum application, to effectively reduce the void levels to below 3%. Void reduction occurred only above an initial pressurization level, at about 400 kPa, after which significant reduction was obtained until about 5000 kPa. Further pressurization reduced the void content only marginally. © 1992 Butterworth-Heinemann Ltd.