Experimental analysis and numerical modeling of flow channel effects in resin transfer molding

Composite manufacturing by Liquid Composite Molding (LCM) processes such as Resin Transfer Molding involve the impregnation of a net-shape fiber reinforcing preform inside a mold cavity by a polymeric resin. The success of the process and part manufacture depends on the complete impregnation of the dry fiber preform. Race tracking refers to the common phenomenon occurring near corners, bends, airgaps and other geometrical complexities Involving sharp curvatures within a mold cavity creating fiber free and highly porous regions. These regions provide paths of low flow resistance to the resin filling the mold, and may drastically affect now front advancement, injection and mold pressures. While racetracking has traditionally been viewed as an unwanted effect, pre-determined racetracking due to now channels can be used to enhance the mold filling process. Advantages obtained through controlled use of racetracking include, reduction of injection and mold pressures required to fill a mold, for constant flow rate injection, or shorter mold filling times for constant pressure injection. Flow channels may also allow for the resin to be channeled to areas of the mold that need to be filled early in the process. Modeling and integration of the flaw channel effects in the available LCM now simulations based on Darcian flow equations require the determination of equivalent permeabilities to define the resistance to now through well-defined now channels. These permeabilities can then be applied directly within existing LCM flow simulations. The present work: experimentally investigates mold filling during resin transfer molding in the presence of now channels within a simple mold configuration. Experimental flow front and pressure data measurements are employed to experimentally validate and demonstrate the positive effect of flow channels. Transient now progression and pressure data obtained during the experiments are employed to investigate and validate the analytical predictions of equivalent permeability for a rectangular flow channel. Both experimental data and numerical simulations are presented to validate and characterize the equivalent permeability model and approach, while demonstrating the role of now channels in reducing the injection and mold pressures and redistributing the flow.