Novel approach to the production of fiber reinforced plastic composites by in situ foam core generation in resin transfer molding


Resin Transfer Molding (RTM) is a common process for the production of fiber-plastic composites in which a fiber reinforcement is positioned in a closed mold and impregnated by resin injection. The production of hollow components by RTM requires that the reinforcement structure placed in the mold is supported from the inside and consolidated against the mold contour during resin injection and curing. Typically, this is either realized by pressurized blow tubes or prefabricated, usually metallic, solid cores. However, all of these materials for creating the inner core have in common that they have to be prefabricated to the desired geometry in separate process steps and also involve increased handling effort during production. Moreover, the achievable geometry complexity is limited.

IVW is researching a novel process approach: A polyurethane foam core is generated in situ in the mold to form the inner core. For this purpose, reactive foam system is filled into the mold where it expands . The expanding foam core completes the preforming of the dry reinforcement structure and presses the laminate against the mold wall from the inside, similar to the bladder molding process. In this manner, the mold geometry can be formed accurately and high fiber volume contents can be achieved. After the foam system has cured, the resin system can be injected without opening the mold. The foam core remains in the part as part of a sandwich structure (Figure 1).

Although the foam core primarily plays a process supporing role in RTM-process, the sandwich structure also offers promising opportunities for function-enhancing properties such as improved acoustic and thermal properties, up to positive effects of foam bonding on the shear strength of the laminate. In total, these additional functionalities provide for more than compensating for the additional weight of the foam core introduced. Compared to conventional core materials, there is also great flexibility in shaping offered, since the foam expanses all-round and also complex geometries can be shaped. 

Current research work is addressing the process engineering challenges of this new approach. For example, the expanding foam must allow stable and uniform shaping and consolidation of the entire reinforcement structure, but must not excessively saturate the dry fiber structure in the process, as this would hinder the subsequent resin injection.



Alexander Faas, M.Sc.
Research Associate Dititalized Process & Material Development
Phone: +49 631 2017 434

RTM-process with in situ foam core generation

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