Quality control for race tracking and shear in RTM preforms

Race tracking is a common phenomenon which occurs during resin transfer molding (RTM) and can result in overestimated permeability values for seated preforms. Accidental shearing of fabric preforms, an especially frequent mode of deformation for satin weave materials, may cause an underestimation of permeability for a preform. Either case could result in defective part production and costly part scrapping due to void formation. An in-situ gas flow method has been employed to quantify the permeability variation resulting from these occurrences, which are due to poor material preparation, mishandling, seating in the mold, etc. RTM quality control, which does not necessarily require online permeability estimation, is facilitated by a multivariate statistical analysis of the pressure data acquired during the gas flow method. This technique examines the pressure variations at accessible ports in the mold for a test preform compared against an established database of previously tested preforms. The degree of race tracking or angle of shear can be identified and corrective action prompted with this pre-injection technology. The feasibility of this method was demonstrated using a mold with multiple ports for gas injection and pressure measurement.