Dissolution of mega-voids in resin transfer molding

Resin transfer molding (RTM) is a common composite manufacturing process. Voids are a common defect encountered in RTM components. A new type of void, the 'Mega-Void', has been identified and addressed by this research. To produce acceptable RTM components requires that the mega-void be eliminated either through prevention or through dissolution. The latter is the topic of this research. Three process parameters affecting mega-void dissolution are researched; 1) Preform/mold vacuum , 2) Resin degas, and 3) Resin curing pressure. To address preform/mold vacuum, analytical and empirical investigations were carried out. Results show that the preform can take-up and retain water. Additional analytical investigations show that gas flow within the preform is molecular in nature. The consequence of this finding is that the removal of moisture and gases from the preform is difficult. Confirming experiments were carried out showing a significant difference between gas pressures within the mold and the gas pressure external to the mold. The resin degas and resin curing pressure parameters were studied by researching the solubility of air in epoxy. An experimental apparatus was designed and fabricated wherein a sample of resin could be subjected to a specified level of vacuum for degassing. Subsequently, a measured amount of air was introduced into the resin sample and the combination pressurized to a controlled pressure. The resin and air were then monitored over time to observe the shrinkage of the air pocket as the air was absorbed by the resin. The experimental results show the pressure of residual air and the resin dissolution pressure both significantly affect the absorption of the air pocket. Higher levels of resin degassing are shown to provide a small benefit to gas dissolution. As a final research effort, composite panels were fabricated using a blind injection setup where a single mold port is used for evacuation and resin injection. In this way, the starting size of the mega-void is fixed and equal to the mold free volume. The three processing parameters were varied in order to show the dissolution of mega-voids when the appropriate parameters are use