Automated Fibre Placement with In-Situ Ultraviolet Curing and On-The-Fly Resin Impregnation

Abstract

Vehicle emissions contribute to up to one third of the world's air pollution [1]. Reducing vehicle weight is crucial to reducing these emissions. Composite materials offer high specific strength-to-weight ratios which make them ideal for lightweight applications; however, existing composite manufacturing is slow and expensive. Automated Fibre Placement (AFP) is a state-of-the-art composite manufacturing process but is limited by the low complexity of parts it can produce; the cost, size and speed of the actuation systems; expensive and sensitive material options; and numerous pre and post-processes required in order to complete a part. This research proposes a new and efficient composite manufacturing process that addresses these limitations by combining AFP technology with in-situ ultraviolet (UV) curing and on-the-fly fibre and resin impregnation (UVAFP). The body of this thesis focused on proving the process concept and building robust predictive models for the technology. It was proposed that reducing the size of the placement head would increase the capability of this technique to manufacture more complex parts. It was shown that by optimising the placement head clearance angle, placement head width and the compaction roller radius the minimum placement radius and arc length could be as small as 100mm and 90 degrees respectively. It was also demonstrated that industrial robots were sufficiently accurate and repeatable to act as placement articulators for AFP. The feed rate, path interpolation point filtering and spindle speed were optimised to achieve a path following accuracy of less than 0.042mm. By increasing the tension in the tow and compaction force, dry fibre tows were shown to be a suitably dimensionally stable replacement for expensive towpregs with minimal gaps and overlaps. Dry glass fibre tows and bulk vinylester resin impregnated on-the-fly was chosen as an inexpensive and versatile material system and consolidation approach for use in UVAFP. The material system was shown to have comparable mechanical properties to aluminium and steel but lighter with equivalent properties to composites manufactured by traditional techniques. Rapid impregnation times were demonstrated up to 2160 mm/sec. High intensity UV light curing eliminated the need for post process curing and shortened the cure time and increased layup speeds. When the UV light was applied in a ply-by-ply in-situ approach, the cure time was measured to decrease the current thermal cure cycle length by 43.75% and the degree-of-cure was increased by 1.3% (as measured indirectly by the interlaminar shear strength). By characterising the process parameters the effect on degree of cure and degradation could be controlled and predicted. A degree of cure in excess of 99% was achieved, providing equivalent material properties to traditional thermal cured composites while minimising peak exposure temperatures, thus reducing mass loss caused by thermo-oxidative degradation. UVAFP was demonstrated to be a viable composite manufacturing process capable of producing high quality components and addressing the limitations of current AFP systems. The technology was shown to address efficiency shortfalls and make composite manufacturing economical and accessible to vehicle manufacturers searching for manufacturing process solutions for lightweight. Show more