Injection Compression Molding of Long Glass Fiber Reinforced Polypropylene

A study has proven that by utilizing the injection compression molding (ICM) technique, mechanical properties of long-glass-fiber-reinforced polypropylene (LGFR-PP) are significantly enhanced compared to properties obtained employing standard injection molding (SIM). The ICM technique preserves the initial 11-mm long fiber glass lengths, allows lower injection pressures, reduces molded-in stresses, provides less warpage, and improves weldline strength. This study involved injection compression molding 1.5-mm and 3-mm thick plaques from 30%, 40% and 50% long-glass-fiber-reinforced PP, using SIM as the control. Tensile strength, flexural strength, and flexural modulus values, in both the flow and transverse direction, were generated on specimens cut out and machined from the respective plaques. Falling dart instrumented impact energies were also acquired. Greater benefits were realized at the thinner 1.5-mm substrate thickness. Falling weight impact energies were 25 to 45% higher. As part of the study, in-mold laminated ICM coverstock/substrate parts were produced for commercial applications development. By combining ICM with in-mold lamination, LGFR-PP materials allow automotive design engineers the capability to reduce part weight and cost by downgauging substrate thickness while maintaining high stiffness and impact strength.