Abstract

Compression resin transfer moulding (CRTM) can help to reduce costs and increase the productivity of composite parts in the automotive industry. This process is suited for fast production of high quality parts, but a number of parameters must be precisely characterised and well controlled during the process. This work describes the CRTM manufacturing process of a real sports car bonnet. Resin and carbon fibre reinforcement have been characterised (viscosity, permeability), and this information has been used to perform numerical simulations to optimise the process parameters in order to reduce the cycle time. The heating cycle has also been optimised and the possible implementation of an induction heating system has been analysed. Once the process parameters have been defined, the mould has been manufactured and bonnet prototypes have been manufactured. This work has been carried out within the framework of the project ADVANCRTM.

Abstract

In this work the feasability of the monitoring system, composed of flow-rate and injection pressure sensors, in addition to the pressure sensors integrated in the mold, is demonstrated to determine the optimal process window of the CRTM (Compression Resin Transfer Molding). The sensors of the injector allow monitoring of the injection phase, while the pressure sensors integrated in the mold allow the phases of the compression and the curing to be followed. In order to relate the pressure sensor variations with the curing phase, an electric current sensor has been used. The increase of the resistance, associated with the beginning of curing, corresponds in time with the pressure drop, which in turn is justified by the contraction generated during curing. This pressure drop reaches a horizontal asymptote which corresponds to a conversion rate of 40%. Based on this behavior of the pressure sensor, it is possible to determine the minimum time for the demoulding of each of the pieces. Finally, the system has been used to monitor the manufacturing of prototypes with curing temperatures between 80-120 ºC, and it has been confirmed that the sensors identify the parts that are inside the process window and those that are not.

Abstract

Muchas industrias, como la del automovil están haciendo un gran esfuerzo para reducir costes y aumentar la productividad de los procesos de fabricación de composites. Aunque todas estas tecnologías aún están emergiendo, parece que los procesos de Moldeo de Compuestos por Vía Líquida (LCM) en los que hay una fase de compresión, como el Moldeo de impregnación  por Compresión (WCM) o el Moldeo por Transferencia de Resina de Compresión (CRTM), son los mejor posicionados. En estos casos, dado que la preforma de fibra impregnada se comprime durante el proceso, es imprescindible conocer el comportamiento de compresión de estos materiales para seleccionar y optimizar el proceso de fabricación mediante herramientas de simulación.

Cuando se trata del proceso de compresión, se ha considerado que las preformas presentan un comportamiento elástico-lineal. Sin embargo, las últimas publicaciones han demostrado que este comportamiento es principalmente viscoelástico.

En este trabajo se ha caracterizado la relajación de un Non-Crimp Fabric (NCF) impregnado de 50k, bajo presión, para 3 velocidades de compresión diferentes. Para ello, el comportamiento viscoelástico se ha descrito mediante modelos fraccionarios, que en comparación con los modelos clásicos exponenciales, son capaces de reproducir correctamente la relajación del material durante la fase de máxima compresión