Key factors affecting permeability measurement in the vacuum infusion molding process

The composites industry, under increased environmental constraints, is seeking to shift from existing open mold manufacturing processes for composite parts. A promising manufacturing technology known as the vacuum infusion molding process is gaining acceptance among composite-parts manufacturers since it involves low tooling cost and allows complete elimination of volatile organic compounds (VOC). The process is similar to the resin transfer molding process; however, in the vacuum infusion technique, a polymeric film, often referred to as vacuum bag, replaces the stiff mold cover. The film is sealed against the lower half of the mold, at the periphery. Air expelled from the mold cavity results in the compaction of the reinforcement by the atmospheric pressure present on the outer side of the polymeric film. Finally, resin impregnates the mold cavity, usually through a resin distribution channel. The process is mainly developed for large-scale structures, where material cost is an important parameter and users cannot afford any production pitfalls. Among process parameters that affect resin flow in the vacuum infusion molding process is the permeability of the reinforcement stack, which has to be measured and evaluated taking into consideration the requirements of the process. A possible approach is the definition of a parameter that defines the maximum infused length, and this parameter will take into account the structure of the reinforcement, the resin viscosity, the fiber volume fraction and inlet geometry.