Investigation of a Two-Stage Injection Process to Reduce the Effects of In-Plane Resin Flow

This paper is a discussion of a manufacturing technique that reduces dependency on in-plane resin flow, allowing greatly reduced injection times, increased injected resin volume per port (reducing the number of ports required), and allows relatively higher fiber volume content. This method uses a two-stage injection process. The first stage injects resin into a vacuum evacuated “pool” outside of the plane of the fabric. Pressure is then applied outside of a flexible film, forcing resin into the fabric in the thickness direction. Since resin is not required to flow in the plane of the fabric, relatively high volumetric flow rates are possible during the injection stage. The hydrostatic pressure on the flexible film results in part-to-part and spatially consistent high volume content. This process has also shown to be less sensitive to fabric and manufacturing inconsistencies than traditional two-sided mold RTM, and has been used to successfully manufacture parts using difficult-to-RTM materials such as bonded fabrics. Drawbacks of this process include increased mold and process complexities, poor surface finish on one side of the part, and increased complexity of process tuning.