Browsing by Author "Jones, Christopher A."

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    Defect minimisation in vacuum assisted plaster mould investment casting through simulation of high value aluminium alloy components
    (Springer, 2023-02-09) Pagone, Emanuele; Jones, Christopher A.; Forde, John; Shaw, William; Jolly, Mark R.; Salonitis, Konstantinos
    Vacuum-assisted plaster mould investment casting is one of the best available processes to manufacture ultra-high complexity castings for the aerospace and defence sectors. In light of the emerging cross-sectoral manufacturing industry digitalisation, process simulation appears as a very important tool to improve casting yield, reduce metallurgical scrap, and reduce lead time to new product introduction. Considering the unique aspects and the level of customisation of the process system, this work will present a Computational Fluid Dynamics-based simulation tool with bespoke settings (that include thermophysical properties). Optimal fill and solidification parameters are identified for a representative geometry able to describe a variety of very complex, high-value aluminium alloy components through an iterative process.
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    Effect of crack-like defects on the fracture behaviour of Wire + Arc additively manufactured nickel-base Alloy 718
    (Elsevier, 2020-09-11) Seow, Cui Er; Zhang, Jie; Coules, Harry E.; Wu, Guiyi; Jones, Christopher A.; Ding, Jialuo; Williams, Stewart W.
    The fabrication of large components using a high deposition rate, near-net shape process like Wire + Arc Additive Manufacturing (WAAM) is a promising option for many industries, due to the potential for reduction in material wastage and shorter lead times in comparison to conventional methods. Specialist materials like nickel-base superalloys, which are typically used in high temperature and corrosive environments, are particularly attractive options due to their high raw material costs. Although nickel-base Alloy 718 seems well suited to the process due to its good weldability, process-induced defects can arise from unfavourable deposition conditions and elimination of these defects may not always be possible. In WAAM Alloy 718 deposited under such conditions, crack-like defects with planar morphology and hot cracking characteristics were observed. These defects were observable using conventional non-destructive testing techniques and displayed directionality relating to the deposition path. The fracture behaviour of WAAM Alloy 718 containing these defects was “semi-stable” – a mixture of fracture instability and stable crack extension. The apparent fracture toughness of WAAM Alloy 718 containing these defects was found to be anisotropic, which can be attributed to the interaction of the notched crack with pre-existing defects. WAAM Alloy 718 displayed an apparent fracture toughness comparable to that of wrought Alloy 718 when notched perpendicular to the defects; but only half that of wrought when notched parallel to the defects. Therefore, careful consideration of defect orientation and their effects on mechanical properties is important in assessing the fitness-for-service of WAAM Alloy 718
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    An experimental characterization of thermophysical properties of a porous ceramic shell used in the investment casting process
    (Springer, 2020-02-12) Jones, Christopher A.; Jolly, Mark R.; Jarfors, A. E. W.; Irwin, M.
    This study presents the results of an investigation that characterises the thermophysical properties of an investment casting mould, comprising of a Zirconium dioxide/Cobalt aluminate prime slurry and a fused Silica/fibre reinforced backup slurry. Growing prevalence of successful computer simulations within the foundry industry enables defects that emerge during the casting process to become increasingly predictable, providing cost-effective alternatives to trial castings. The viability of these simulations as predictors is heavily dependent upon the facilitation of accurate material property data, as attained through this investigation. Differential scanning calorimetry (DSC) and laser flash analysis (LFA) were utilized to determine the specific heat capacity and thermal diffusivity, respectively. These values, in combination with the material density and linear coefficient of thermal expansion, have been used to determine the thermal conductivity of the mould. With the aim of verifying these parameters, initial studies in Flow-3D® simulation software have been performed to determine the constraints needed to reduce variability in simulation parameters. Due to the diversity of casting moulds used throughout the industry, ensuring the material database is kept as comprehensively populated as possible is a crucial undertaking.
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    A mathematical examination of the impact of mould transparency to infrared radiation on solidification during the investment casting process
    (IOP Publishing, 2023-06-18) Jones, Christopher A.; Jarfors, A. E. W.; Rogers, Edith; Vrethed, P.; Silva, P.; Jolly, Mark R.
    Investment casting is a highly dynamic process during which multiple competing physical phenomena are at work. Those seeking to understand and simulate such processes computationally are confronted with a considerable task, balancing accuracy with efficiency. Approximations and models based on well-understood and documented fundamental physics are powerful tools in a modeller's arsenal. Driven by observed discrepancies between experimental thermocouple measurements and simulation predictions of casting temperatures, this work explores the additional alloy cooling mechanism of mould transparency to infrared radiation, targeting a new mathematical approximation applicable in such situations. Direct attenuation, scattering from coarse sand, sand distribution in the mould and material temperatures play a role in the extent of radiation transparency that must be considered. From this model, estimation of the additional cooling rate resulting from expected mould transparency can be determined and applied as a corrective measure to computation fluid dynamics (CFD) simulation results that do not capture this phenomenon.
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    A verification of thermophysical properties of a porous ceramic investment casting mould using commercial computational fluid dynamics software
    (IOP Publishing, 2020-06-12) Jones, Christopher A.; Jolly, Mark R.; Jarfors, A. E. W.; Irwin, M.; Svenningsson, R.; Steggo, J.; Eriksson, J.
    Defects in cast metals remain a common problem in many areas of the foundry industry, particularly in the investment casting of large area, thin-walled components for aerospace applications. During previous research, the thermophysical properties, density and porosity of a fibre reinforced ceramic investment casting mould were determined using several experimental techniques. Without verification, these experimental results remain nothing more than educated guesswork. The purpose of this study is to verify previous results and to more fully characterise the ceramic mould material with complementary measurements. A commercially available computational fluid dynamic (CFD) simulation package, Flow-3D®, was used in conjunction with a full-scale Ni-superalloy (IN718) casting to assess the accuracy of these results. By placing thermocouples strategically across the mould thickness, temperature profiles were determined and compared directly to predicted profiles extracted from the simulation by a custom-written Python script