In-situ quality control of rtm preforms by the gas flow method

An in-situ method employing gas flow has been developed to determine the quality of fibrous preforms in the resin transfer molding (RTM) process prior to resin injection. This method quantifies defects resulting from fiber preform misplacement, accidental inclusions, preform surface density variation, etc. Local defects may cause permeability variations, which can result in defective part production and excessive part scrapping. Pressure profiles generated during steady state gas flow are affected by such variations. To determine the location and severity of a defect, a multivariate statistical approach is applied to compare measured and/or derived quantities, such as pressure and/or permeability, from a test preform to quantities obtained from known groups. The tested preform is then classified into a defect free (normal) group or any one of several groups associated with specific types of defects. The method was demonstrated by using a specially designed mold with multiple ports for gas injection and pressure measurement, and testing for various cases with and without defects.