Browsing by Author "Marinelli, Gianrocco"

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    Development of Wire + Arc additive manufacture for the production of large-scale unalloyed tungsten components
    (Elsevier, 2019-05-11) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.
    The manufacturing of refractory-metals components presents some limitations induced by the materials' characteristic low-temperature brittleness and high susceptibility to oxidation. Powder metallurgy is typically the manufacturing process of choice. Recently, Wire + Arc Additive Manufacture has proven capable to produce fully-dense large-scale metal parts at relatively low cost, by using high-quality wire as feedstock. In this study, this technique has been used for the production of large-scale tungsten linear structures. The orientation of the wire feeding has been studied and optimised to obtain defect-free tungsten deposits. In particular, front wire feeding eliminated the occurrence of pores and micro-cracks, when compared to side wire feeding. The microstructure, the occurrence of defects and their relationship with the deposition process have also been discussed. Despite the repetitive thermal cycles and the inherent brittleness of the material, the as-deposited structures were free from internal cracks and the layer dimensions were stable during the entire deposition process. This enabled the production of a relatively large-scale component, with the dimension of 210 × 75 × 12 mm. This study has demonstrated that Wire + Arc Additive Manufacture can be used to produce large-scale parts in unalloyed tungsten by complete fusion, presenting a potential alternative to the powder metallurgy manufacturing route.
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    Effect of shielding gas composition and welding speed on autogenous welds of unalloyed tungsten plates
    (Elsevier, 2019-07-30) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.
    Tungsten usually exhibits poor weldability and marked brittleness at room temperature. This causes tungsten welds to be affected by the evolution of cracks along the weld bead, which can be eliminated by using a pre-heating step to reduce thermal straining. In this study, based on the tungsten inert gas welding process, a working envelope, focussed on varying welding speed and five different shielding gas mixtures of argon and helium, has been defined with the view of producing crack-free autogenous welds. The bead appearance and the microstructure of the different welds were correlated to the welding parameters, whose main effects have been analysed. Welding defects such as humping occurred when using gas mixtures with relatively low content of helium, and when using relatively high welding speeds. Crack-free autogenous welds have been produced without pre-heating when using a high content of helium and relatively low welding speeds. Thus, this study has demonstrated that a helium-rich shielding gas is required for welding thick tungsten plates. Moreover, the low thermal shock induced by the process, coupled with the purity of the tungsten plates used, strongly contributed to avoid the occurrence of any crack.
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    Functionally graded structures of refractory metals by Wire Arc Additive Manufacturing
    (Maney Publishing, 2019-03-11) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.; Lewtas, Heather; Hancock, David
    Functionally graded components are usually preferred for severe and critical service conditions, thanks to the possibility of achieving different complementary material properties within the same structure. Wire + Arc Additive Manufacturing is an emerging technology which lends itself well to the production of sound graded structures. In this study, an integral structure of two functional gradients, namely tantalum to molybdenum, and molybdenum to tungsten, was successfully deposited. A linear gradient was observed in both composition and hardness. Microstructure, elemental composition and hardness were characterised as a function of position, and discussed. The study demonstrates that WAAM has the potential to successfully deposit functionally graded structures of refractory metals, obtaining controlled properties
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    Grain refinement in an unalloyed tantalum structure by combining Wire+Arc additive manufacturing and vertical cold rolling
    (Elsevier, 2019-12-26) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.
    Components manufactured via Wire + Arc Additive Manufacturing are usually characterised by large columnar grains. This can be mitigated by introducing in-process cold rolling; in fact, the associated local plastic deformation leads to a reduction of distortion and residual stresses, and to microstructural refinement. In this research, inter-pass rolling was applied with a load of 50 kN to a tantalum linear structure to assess rolling’s effectiveness in changing the grain structure from columnar to equiaxed, as well as in refining the grain size. An average grain size of 650 μm has been obtained after five cycles of inter-pass rolling and deposition. When the deformed layer was reheated during the subsequent deposition, recrystallisation occurred, leading to the growth of new strain-free equiaxed grains. The depth of the refined region has been characterised and correlated to the hardness profile developed after rolling. Furthermore, a random texture was formed after rolling, which should contribute to obtaining isotropic mechanical properties. Wire + Arc Additive Manufacture demonstrated the ability to deposit sound refractory metal components and the possibility to improve the microstructure when coupled with cold inter-pass rolling.
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    Increasing the speed of automated ultrasonic inspection of as-built additive manufacturing components by the adoption of virtual source aperture
    (Elsevier, 2022-06-15) Zimermann, Rastislav; Mohseni, Ehsan; Vithanage, Randika K. W.; Lines, David; Foster, Euan; Macleod, Charles N.; Pierce, Stephen Gareth; Marinelli, Gianrocco; Williams, Stewart; Ding, Jialuo
    Wire + Arc Additive Manufacture (WAAM) is an economical manufacturing technique to build components. To maintain the commercial and technical benefits, inspection is desired at each layer of the build. New conformable phased array roller-probes offer the potential to inspect the as-built sample in-process or on completion. A challenge with such inspections is the refraction of the ultrasonic waves at multiple interfaces. The Synthetic Aperture Focusing Technique (SAFT) and Total Focusing Method (TFM), combined with Full Matrix Capture (FMC) acquisition enabled imaging through the as-built WAAM surface. However, single-element firings, associated with FMC are a limiting factor due to the lower energy at transmission, while the high number of firings and subsequent larger data size negatively affect inspection speed. This work introduces the concept of Virtual Source Aperture (VSA) for ultrasonic roller-probe inspection, through modelling of VSA on custom-designed calibration WAAM block. The concept is then demonstrated on a mock as-built WAAM sample inspection with reference defects. The results demonstrate that a markedly lower number of transmissions are required to match the performance of the FMC counterpart while increasing the energy levels. Moreover, an almost 50% reduction in the data size enabled a doubling of the inspection speed.
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    Microstructure and thermal properties of unalloyed tungsten deposited by Wire + Arc Additive Manufacture
    (Elsevier, 2019-05-01) Marinelli, Gianrocco; Martina, Filomeno; Lewtas, Heather; Hancock, David; Mehraban, Shahin; Lavery, Nicholas; Ganguly, Supriyo; Williams, Stewart W.
    Tungsten is considered as one of the most promising materials for nuclear fusion reactor chamber applications. Wire + Arc Additive Manufacture has already demonstrated the ability to deposit defect-free large-scale tungsten structures, with considerable deposition rates. In this study, the microstructure of the as-deposited and heat-treated material has been characterized; it featured mainly large elongated grains for both conditions. The heat treatment at 1273 K for 6 h had a negligible effect on microstructure and on thermal diffusivity. Furthermore, the linear coefficient of thermal expansion was in the range of 4.5 × 10−6 μm m−1 K−1 to 6.8 × 10−6 μm m−1 K−1; the density of the deposit was as high as 99.4% of the theoretical tungsten density; the thermal diffusivity and the thermal conductivity were measured and calculated, respectively, and seen to decrease considerably in the temperature range between 300 K and 1300 K, for both testing conditions. These results showed that Wire + Arc Additive Manufacture can be considered as a suitable technology for the production of tungsten components for the nuclear sector.
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    Microstructure, hardness and mechanical properties of two different unalloyed tantalum wires deposited via wire + arc additive manufacture
    (Elsevier, 2019-05-30) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.
    An innovative way of producing large-scale unalloyed tantalum parts, based on the Wire + Arc Additive Manufacturing process, has been developed in this study. Two different unalloyed tantalum wires have been used to deposit 200-mm-long structures in tantalum. The effect of the wire chemistry on microstructure, hardness, porosity, mechanical properties and strain localisation has been investigated. The deposits showed high integrity and excellent mechanical properties, with yield strength, ultimate tensile strength and elongation as high as 234 MPa, 261 MPa, and 36%, respectively. Indeed, yield strength was higher than commercially available tantalum, even though, in this study, the grains were large and had a high aspect ratio. Wire + Arc Additive Manufacture has clearly shown the potential to produce tantalum components with relatively low cost and reduced lead time, thus offering a new robust and viable manufacturing route.
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    A modular path planning solution for Wire + Arc Additive Manufacturing
    (Elsevier, 2019-05-11) Michel, Florent; Lockett, Helen L.; Ding, Jialuo; Martina, Filomeno; Marinelli, Gianrocco; Williams, Stewart W.
    Wire + Arc Additive Manufacturing (WAAM) has proven its capability to build medium to large metallic parts thanks to its high-rate deposition and its potentially unlimited build volume. Moreover, the low-cost equipment and the ability to deposit various metals make WAAM a strong candidate to become a standard industrial process. However, like all Additive Manufacturing (AM) technologies, the key to manufacturing suitable parts lies in the generation of an optimised path that guarantees a uniform defect-free deposition. Most AM technologies have been able to use traditional path strategies derived from CNC machining, but the specificities inherent to the arc deposition make the use of those solutions unreliable across a variety of topologies. Nevertheless, studies have shown that superior results can be achieved by using a feature-based design approach, but developing a path strategy for each new geometry would be a very time-consuming task. Therefore, this paper introduces the Modular Path Planning (MPP) solution that aims to incorporate the modularity of feature-based design into the traditional layer-by-layer strategy. By dividing each layer into individual deposition sections, this method allows users to adapt the path planning to the targeted geometry allowing the construction of a wide variety of complex geometries. This paper also proposes a software implementation that limits user interventions and reduces user inputs to basic CAD modelling operations. Moreover, the MPP has been compared to a traditional path planning solution and used to build a complex part for industry.
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    Wire and arc additive manufacture of tungsten and tantalum
    (2018-05) Marinelli, Gianrocco; Ganguly, Supriyo; Williams, Stewart W.
    The advent of the next industrial revolution is clearly represented by the constant maturation of additive manufacturing. Wire + Arc Additive Manufacturing (WAAM) is a novel technique suitable for the deposition of medium to large scale components. This study was focused on investigating the WAAM process for the deposition of refractory metals, such as tungsten and tantalum. Generally, this class of metals is characterised by intrinsic low-temperature brittleness, poor weldability and a high susceptibility to oxidation over a large temperature range. For unalloyed tungsten, the process parameters to produce defect-free autogenous welds were found by varying the shielding gas composition and the welding speed. This represents a fundamental study for the WAAM deposition of tungsten, which has been reported to be markedly influenced by the wire feeding orientation. In particular, wire side feeding produced a large amount of spatter which resulted in an enhanced presence of structural defects within the structure deposited. The occurrence of defects was eliminated when employing wire front feeding. The characteristic microstructure of tungsten was investigated resulting to be composed of two specular arrays of large columnar grains meeting at the centre of the structure. The thermal conductivity and thermal diffusivity of as-deposited and annealed tungsten structures were observed to considerably decrease over the temperature range analysed. 200-mm-long structures in pure tantalum have been also deposited using two wires with different oxygen content. The tantalum structures can be deposited with high integrity and excellent mechanical properties. Superior yield strength was achieved for the WAAM deposited material compared to commercially available tantalum, even though the grains in the WAAM material were larger and had a high aspect ratio. The typical columnar grains of the tantalum deposits were refined into an equiaxed microstructure when additional cold-working was implemented to the deposition process. This led to obtaining a microstructure with an average grain size of 650 μm and completely random texture. Furthermore, two functionally graded structures were produced within the same built using tantalum, molybdenum and tungsten achieving a regular compositional and hardness gradient. The results of this study have shown that WAAM is able to produce refractory metal components with relatively low cost, exploiting the characteristic freedom of 3D printing and the opportunity of obtaining optimised properties, offering a solid alternative manufacture route to powder metallurgy.