Vent Location Optimization Using Map-Based Exhaustive Search in Liquid Composite Molding Processes

Abstract

In liquid composite molding (LCM) processes, the resin is injected into the mold cavity, which contains preplaced reinforcement fabrics, through openings known as gates, while the displaced air leaves the mold through openings called vents. Under nominal conditions, the last points to fill are chosen as vent locations. However, due to imperfect preform cutting and placement, gaps and channels may form along the edges and curvatures in a mold, offering a path with less resistance for resin flow. The faster advance of resin through these gaps and channels, a common disturbance known as racetracking, will cause the last filled regions to vary, which complicates the vent selection process. In this study, probabilistic racetracking modeling is used to capture last-filled region distribution over the mold geometry. Success criteria for mold filling are defined in terms of dry spot tolerances, and vent fitness maps, which display potential vent locations, are created. Next, exhaustive search algorithm is coupled with vent fitness maps to determine optimal vent configurations. The map-based exhaustive search is demonstrated on three geometries and results are compared with existing combinatorial search results. The performance of the optimal vent configurations is evaluated in a virtual manufacturing environment. Sensitivity analyses are conducted to determine the influence of optimization parameters on the results.

Keywords:

• Liquid composite molding (LCM)
• Resin transfer molding (RTM)
• Mold design
• Vent optimization
• Map-based exhaustive search
• Fiber composites
• Resin flow

Acknowledgment

The financial support, provided by the Office of Naval Research (ONR) under Grant N000l4-97-C-0415 for the Advanced Materials Intelligent Processing Center at the University of Delaware, made this work possible.

Notes

^aNote that, the term last is not used in the chronological sense. It means the last region to fill in a contiguous dry area, after which the dry area disappears, regardless of the time scale.

^bCartesian product in set theory resembles outer multiplication operation in tensor notation, except that the operands are not actually multiplied in Cartesian product but are grouped together.

^cIn this study, as soon as a dry spot forms, it is recorded and the dynamics of the air bubble motion in the closed mold is ignored.

^d f maps elements of domain to real numbers R.

^ei.e., the air in the mold whose racetracking conditions match that scenario will not be drained successfully. Likewise, scenario i is filled means, the mold whose racetracking conditions match scenario i is successfully filled with resin.