Process influence in the combined compaction and back-injection process for manufacturing of self-reinforced composites

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In an extrusion process, high-strength fibers or tapes can be produced. A combination of melt deformation and solid state drawing results in highly anisotropic properties, with up to 5 or 6 times higher strength and stiffness, in direction of orientation, than the conventional injection-molded samples. These properties are used for the production of self-reinforced composites. The fibers or tapes are first processed into textiles. Subsequently they are stacked in several layers and are consolidated to a self-reinforced composite system in a hot compaction process. The aim of this research project is to investigate the necessary fundamentals in order to be able to assess the process influences during a combined hot compaction and back-injection process to produce composites. This process enables the production of self-reinforced composites by means of a simultaneous consolidation and back-injection molding process in one tool. In the back-injected areas the stacked textiles are consolidated by the injection pressure of the polymer melt only. The microstructure of the self-reinforced material, which is directly related to the mechanical properties, is highly influenced by the inflowing melt. By means of this temperature sensitivity, self-reinforced composites can be graded, which means the implementation of local different mechanical properties, due to different process settings. This can be used to produce components with different stiffness in defined areas, only caused by the different process control, while material is chemically identical. Thus, monomaterial systems are produced which consist of consolidated textiles and an injection molded component of the same polymer. This results in excellent recycling properties.Within this research project, the influence of the combined compaction and injection molding process on the microstructures of the material, the warpage of the specimen, the adhesion between the melt and the composite, the mechanical properties of the composite and the local pressure and temperature levels along the flowpath are investigated, with and without a thermal grading of the self-reinforced composites. The local conditions are finally summarized in a describing model. This is intended to form the base for the understanding of the process and the construction of components produced by this manufacturing process.