Single-step manufacturing of curved polypropylene composites using a unique sheet consolidation method

Many techniques have been developed over the past few decades to manufacture curved fibre reinforced thermoplastic composites. Long-fibre composite parts have been mostly manufactured by either compression moulding or thermoforming in two or more steps. No effort has been put into single-step manufacturing of long fibre curved thermoplastic composite parts. This work develops a manufacturing plan that has the ability to produce fairly strong curved thermoplastic composites in a single step. The production of composites according to this plan is expected to be significantly cheaper than the composites produced by compression moulding or thermoforming. In this research, curved composites were manufactured from flax reinforcements and polypropylene sheets using a unique manufacturing cycle, where the composites were formed and consolidated simultaneously. The optimum processing parameters and the fibre volume fraction were found to manufacture curved flax reinforced polypropylene composites with acceptable tensile and shear strengths. An experimental setup was used to monitor and record the applied vacuum pressure and temperature during the experiments. Shear and tensile strength of the manufactured composites was found. The consolidation quality of the manufactured composites was assessed by examining the composite specimens’ cross-sections under an optical microscope. The results showed that the tensile and shear strengths of the manufactured composites were dependent on the fibre volume fraction, transverse permeability of the fibre reinforcement and also the magnitude and method of application of compaction pressure. There were optimum fibre volume fractions with respect to tensile and shear strengths for each of the three fibre reinforcements used in this research. The shear and tensile strengths of the composites produced in this research are comparable to compression moulded or thermoformed parts.