Closed-loop flow control approaches for VARTM
Date
2005
Authors
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Publisher
University of Delaware
Abstract
VARTM (Vacuum Assisted Resin Transfer Molding) is a liquid composites manufacturing process that offers numerous advantages over other processes because of the low tooling costs and the manufacturing benefits for large structures. During the infusion of resin into a closed mold that contains a preform in VARTM process, resin flow is often affected by the inherent variations in permeability resulting from the part design as well as the variability associated with the mold lay-up. Current injection methods used for VARTM provide very limited control of the resin flow within the mold; this can result in part defects including dry (unfilled) regions and voids. A definite need exists to continue to improve the part quality especially to eliminate the dry spots and voids. Improved control of resin flow appears possible with several approaches including the development of a multi-segment resin injection line that provides real time modifications to the resin flow front. ☐ The overall goal of this study is to demonstrate practical control strategies for VARTM that provide control of the resin flow within the mold. The potential benefits of this capability are significant. Control of the flow will reduce the presence of voids in finished parts thus decreasing the number of rejected parts. Current manufacturing methods minimize void formation by extending the injection time to promote full mold infusion; better control of the resin flow will reduce the need for extended infusion times thus increasing production efficiency. ☐ To improve process controllability during VARTM, a new and innovative resin injection line was designed and tested. The injection line, which consists of individual segments each independently operated, allows for the control of resin flow to different locations within the mold. Simulation of different smart injection line configurations for various mold geometries and determination of the relationship between line segment configuration and controllable mold region is studied. Performance of a prototype smart line is quantified with a laboratory size mold used to demonstrate the potential value and benefits of this approach. Specific performance metrics, including resin flow front controllability, total injection time and void formation are used to compare this approach to conventional VARTM injection methods. Computer-based closed loop controller strategies are designed that use point sensors to feedback resin flow front location and a real time adaptive control algorithm to provide the best smart injection line configuration at various instants of filling process to steer the resin to all parts of the mold thereby eliminating the formation of dry spots and voids. An experimental evaluation and exploration of the capabilities of the new active control approaches towards making VARTM a smarter process is provided.