Experimental study of flexible injection to manufacture parts of strong curvature

Abstract

Flexible injection (FI) is a new process for the manufacture of high performance composites, which consists of injecting a thermosetting resin through a fibrous reinforcement contained in the lower chamber of a double cavity mold. Resin is injected in the lower cavity, which is sealed by a membrane, and then a compaction fluid is injected in the upper chamber to compress the reinforcement. This new composite manufacturing technique, which allows a limited and controlled deformation of the flexible membrane during processing, was shown to be very effective in reducing filling times in the case of planar or slightly curved geometries. In the present study, flexible injection is applied to strongly curved parts, namely here a composite rectangular panel with two 90° corners. After setting up an experimental procedure to produce the stair-shaped components out of fiberglass and vinylester resin, longitudinal cross-sections of the parts are analyzed to assess the quality of the final product in both the flat and curved zones. This characterization method allows detecting manufacturing defects such as thickness gradients or resin-rich zones. Such defects are likely to induce geometrical deformations of the component and may decrease its mechanical performance. Therefore they ought to be minimized to improve the overall quality of the part. Modifications of the manufacturing procedure are proposed in this article to decrease the importance of process-induced defaults and improve the performance of the flexible injection. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers