Improvements in Liquid Composite Moulding through Assessment of Process Parameters

Abstract

Liquid Composite Moulding (LCM) describes a family of manufacturing processes utilised for the manufacture of fibre reinforced plastics. With a large number of variables and process parameters requiring active measurement and control, achieving high quality simultaneously with low cost and variability has proven an elusive target for LCM processes. Although the effects of many parameters and variables have been studied and understood, others have received little attention. As a result process robustness and consistency often do not reach levels desired, resulting in part defects. This thesis focuses on the study of key process and environmental parameters for LCM techniques, and the introduction of non-destructive measurement methods to allow for improvements in both quality and consistency. Concerning vacuum assisted resin infusion, reviews of prior literature have shown that limited research had been undertaken on the effects of infusion methodology, resin dissolved gas content, and the effects of pre-cure environmental moisture. These topics were investigated in detail, with infusion methodology, resin dissolved gas saturation state, and resin moisture content all being found to have significant impacts on the manufacturing process and final part quality. The knowledge gained was utilised to develop a high performance infusion manufacturing methodology that matched or exceeded some physical and mechanical properties of the autoclave cured prepreg against it was benchmarked, including fibre volume fraction, modulus, and compressive strength. Concerning Resin Transfer Moulding (RTM), the effects of preforming temperature and thickness were investigated in detail, with preforming thickness being found to significantly affect preform properties and subsequent RTM mould filling behaviour. Over compaction of preforms, and the subsequent reduction in compaction resistance and through-thickness permeability resulted in a dynamic compaction of the preform by the fluid pressure, substantially increasing filling rates with no effect on final laminate mechanical strength. Additionally, localised flow acceleration through over compaction of regions of the preform was achieved without significant impacts on laminate strength. Based on these findings, a series of experiments concerning the non-destructive testing of carbon preforms were performed to determine the ability of non-destructive imaging techniques to identify variability and defects (presence, severity) within textile structures. Through the evaluation of a series of carbon preforms with a range of features, a thorough understanding of the ability of radiography and active thermography to act as quality and process control tools in the preform production process chain has been developed.