Void content analysis and processing issues to minimize defects in liquid composite molding

This investigation aims to study the impact of key process parameters dealing with the resin impregnation of fibrous reinforcements used in Liquid Composite Molding (LCM). The process parameters are the flow front velocity, the inlet mold pressure and the bleeding flow rate. The experimental setup consists of a computer‐assisted injection system and a Resin Transfer Molding (RTM) mold that allows monitoring the progression of the flow front and study the effects of resin bleeding and applying post‐fill resin pressure during cure (also known as “mold packing”). Three sets of RTM injections were carried out with a vinyl ester resin and a bidirectional 0°/90° E‐glass noncrimp fabrics under (1) constant injection pressure, (2) constant injection flow rate, and (3) bleeding as well as mold packing after filling. The quality of injected parts was evaluated by standard void content analysis based on ASTM burn‐off (D2734) tests. The experimental results are consistent with published data and with predictions of the optimal impregnation velocity obtained from capillary rise tests. This study also shows that the impregnation of fibrous reinforcements in LCM can be improved through various injection strategies, namely monitoring of the flow front velocity and specific post‐filling procedures. POLYM. COMPOS., 40:109–120, 2019.