Thermoformage d'un composite a fibres continues polypropylene/fibres de verre

Thermoforming of several unconsolidated commingled continuous glass fiber/polypropylene fabric composites has been studied using the stamp forming and rubber-forming process. For these manufacturing processes, unconsolidated fabric plies are heated in a convection oven and then rapidly transferred to the press where they are thermoformed to achieve simultaneously consolidation and conformation to the mold shape. Thermoforming of unconsolidated fabric offers a great potential for cost reduction compared to thermoforming of consolidated fabric since the separate consolidation step (prior to molding) is not required.; In the first part of this study, the stamp forming process of two unconsolidated fabrics was studied for a simple flat plate. For the materials studied, similar flexural properties were obtained for parts produced by stamp forming unconsolidated fabric and for plates produced by compression molding. For both materials, optimal properties were obtained for a forming pressure of 3 MPa. This pressure had to be applied before the temperature of the fabric felt below values comprise between 160 and 170°C. To obtain the maximal flexural properties, the pressure should be maintained until the crystallization is completed. Results also showed that the flexural strength and modulus vary approximately linearly with the void content.; In the second part of this study, thermoforming of unconsolidated fabrics was studied using the rubber-forming process. A mold with a bath-shape cavity was chosen so that several deformation mechanisms occur, like in the production of a realistic part. Results showed once again that a forming pressure of 3 MPa is necessary to obtain the optimal flexural properties. This forming pressure has to be applied before the temperature of the fabric felt below a temperature comprise between 190 and 200°C to obtain optimal properties while avoiding matrix cracking in the matrix rich area located at the apex of the molded parts. By opposition to what was obtain for the simple flat part, a discontinuity is observed in the flexural modulus vs. void content curves. This difference was attributed to the occurrence of several deformation mechanisms during molding.; In the last part of this study, the formability of several consolidated and unconsolidated fabric were compared for two different mold shapes. Results showed that a minimal forming temperature of 215°C is required to achieve conformation to the mold shape. Experiments also revealed that increasing the punch hardness, varying the fabric orientation and increasing the number of vents could lead to reduction of the pressure necessary to achieve conformation to the mold shape. (Abstract shortened by UMI.)...