Abstract
The present article introduces a dimensionless number devised to assist composite engineers in the fabrication of continuous fiber composites by Liquid Composite Molding (LCM), i.e., by injecting a liquid polymer resin through a fibrous reinforcement contained in a closed mold. This dimensionless number is calculated by integrating the ratio of the injection pressure to the liquid viscosity over the cavity filling time. It is hereby called the “injectability number” and provides an evaluation of the difficulty to inject a liquid into a porous material for a given part geometry, permeability distribution, and position of the inlet gate. The theoretical aspects behind this new concept are analyzed in Part I of the article, which demonstrates the invariance of the injectability number with respect to process parameters like constant and varying injection pressure or flow rate. Part I also details how process engineers can use the injectability number to address challenges in composite fabrication, such as process selection, mold design, and parameter optimization. Thanks to the injectability number, the optimal position of the inlet gate can be assessed and injection parameters scaled to speed up mold design. Part II of the article completes the demonstration of the novel concept by applying it to a series of LCM process examples of increasing complexity.
Highlights
Manufacturing processes of continuous fiber composites by liquid polymer injection through fibrous reinforcements contained in a mold cavity may be grouped under the general name of Liquid Composite Molding (LCM) [1,2]
The polymer resin can be injected through a fibrous preform contained in a closed and rigid mold such as in Resin Transfer Molding (RTM)
It can be as well infused under vacuum in an open cavity covered by a plastic film or a flexible membrane such as in Vacuum Assisted Resin Infusion (VARI)
Summary
Manufacturing processes of continuous fiber composites by liquid polymer injection through fibrous reinforcements contained in a mold cavity may be grouped under the general name of Liquid Composite Molding (LCM) [1,2]. For large and complex parts fabricated in heated molds, optimal mold design and selection of injection parameters based on numerical simulations remain very time-consuming. This number connects the primary process parameters It is defined by a time integral of the ratio of the injection pressure to the resin viscosity, and represents an invariant of Darcy’s law, the mathematical model commonly used to describe flows through porous media [12]. This article shows how the injectability number can offer a simple quantitative way to evaluate the industrial feasibility of LCM processes It can assist in designing the mold and setting up a proper injection strategy. Critical issues such as the maximum length of the liquid flow path or limitations for large or thick composite parts have not been comprehensively addressed yet to provide guidelines to end-users
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