Development of wire and arc additive manufacture for large scale application for the energy industry.

Wire + arc additive manufacture (WAAM), as the most discussed tool in manufacturing, can complement the design of a fully optimised structure through multi-material deposition and incorporation of geometric design features not possible by traditional manufacturing technologies. Despite all the progress made in WAAM, detail studies on the implication of WAAM parameters on the structural integrity of steel-built components in both machined and as-built condition, and their fracture mechanics properties are largely unknown. To effectively and economically commercialise WAAM, the integrity and reliability of built components under specific loading conditions must be assured. In these studies, the properties of steel components built with WAAM were determined, and the possible methods to improve strength, fatigue performance, and fracture toughness, by tailored deposition of different wire grades, through the modification of the build surface from rolling, and through the addition of cold wire during deposition were determined. The results were presented through mechanical test data (tensile properties, hardness, Charpy and fracture toughness, and fatigue crack growth rate and fatigue life results, along with microstructural analysis (electron microscopy of fractured surfaces, EBSD, XRD, and optical microscopy), and the surface topography of the WAAM build, as characterised by the surface waviness. The studies showed that WAAM process parameters are responsible for the fatigue initiation of WAAM as-deposited (ASD) structures and that reduction of SW by process parameter optimisation and the use of side rolling will improve the fatigue life of ASD WAAM components. The possible cause of variability in fracture toughness in the WAAM steel deposits is the hardening and softening regions in the layer bands caused by the variation in peak temperature and cooling rates of the adjacent layer in the building direction. The addition of cold wire into the melt pool mop-up the excess heat, controlled the surface morphology and improved the mechanical properties and the deposition rate. In this study, a deposition rate of 6.27kg/hr was achieved. In conclusion, low carbon and high strength steel wires will be suitable for making bespoke components with WAAM application for large scale energy manufacturing, and WAAM mild steel components could be used in the as-deposited condition for engineering application when rolling is applied to reduce its SW.