Browsing by Author "Williams, Stewart"

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    Achieving a columnar-to-equiaxed transition through dendrite twinning in high deposition rate additively manufactured titanium alloys
    (Springer, 2024-04-09) Davis, A. E.; Wainwright, J.; Sahu, V. K.; Dreelan, D.; Chen, Xin; Ding, Jialuo; Flint, T.; Williams, Stewart; Prangnell, P. B.
    The coarse β-grain structures typically found in titanium alloys like Ti–6Al–4V (wt pct, Ti64) and Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242), produced by high deposition rate additive manufacturing (AM) processes, are detrimental to mechanical performance. Certain modified processing conditions have been shown to lead to a more refined grain structure, which has generally been attributed to a change in the solidification conditions with respect to the experimental Hunt diagram proposed by Semiatin and Kobryn. It is shown that with Wire Arc AM (WAAM) increasing the wire feed speed (WFS) is effective in promoting a columnar-equiaxed transition (CET). Conversely, estimates of the dendrite-tip undercooling using the KGT model suggest that this will be too small for free nucleation without the addition of artificial nucleants, due to the very low solute partitioning in Ti alloys. It is also shown that it is difficult to promote a CET with plasma transferred arc WAAM as computational fluid dynamics (CFD) melt-pool simulations indicate that the solidification parameters remain within the columnar region on the Semiatin-Kobryn Hunt map, within the constraints of a stable process. However, a high fraction of twin boundaries was observed in the refined β-grain structures seen at high WFS. This has been attributed to departure of {001}β alignment from the direction of maximum thermal gradient, caused by the curvature of the fusion boundary, stimulating dendrite twinning during solidification. In addition, it is shown that increasing the WFS leads to a change in melt-pool geometry and a reduction of remelt depth, which promoted dendrite twinning and grain refinement.
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    Additive manufacturing of a functionally graded high entropy alloy using a hybrid powder-bed wire-based direct energy deposition approach
    (Elsevier, 2023-01-23) Lu, Yao; Wang, Jun; Williams, Stewart; Zhu, Lisong; Ding, Jialuo; Diao, Chenglei; Jiang, Zhengyi
    A functionally graded AlxCoCrFeNi high entropy alloy with a variation in Al concentration along the building direction was in-situ produced using a hybrid powder-bed wire-based direct energy deposition process. A continuous transition from a single FCC structure to a major BCC+minor FCC dual-phase structure was achieved, benefiting from the remelting and reheating process during the deposition. In the FCC→BCC transition zone, the dendritic core region is identified as an FCC matrix decorated by AlNi-rich ordered B2 precipitates. The interdendritic area shows B2 precipitating in the FeCr-rich disordered A2 matrix. Additionally, the interface between the two regions shows that the A2 phase and ordered Cr3Fe intermetallic phase precipitate at the B2 phase. The mechanical properties show a tendency for higher strength and hardening rate but lower plasticity corresponding to the areas with higher Al content. Through quantitative estimation of different strengthening mechanisms, the contribution from precipitation strengthening became increasingly apparent as Al content increased. Other strengthening modes, including solid solution and dislocations, also contribute to the total strength. This investigation realises a novel additive manufacturing method combining powder bed and wire feeding, which can produce a more convenient and cost-effective gradient material with a complex composition.
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    Automated interlayer wall height compensation for wire based directed energy deposition additive manufacturing
    (MDPI, 2023-10-16) Qin, Jian; Vives, Javier; Raja, Parthiban; Lasisi, Shakirudeen; Wang, Chong; Charrett, Thomas O. H.; Ding, Jialuo; Williams, Stewart; Hallam, Jonathan Mark; Tatam, Ralph P.
    Part quality monitoring and control in wire-based directed energy deposition additive manufacturing (w-DEDAM) processes has been garnering continuous interest from both the academic and industrial sectors. However, maintaining a consistent layer height and ensuring that the wall height aligns closely with the design, as depicted in computer-aided design (CAD) models, pose significant challenges. These challenges arise due to the uncertainties associated with the manufacturing process and the working environment, particularly with extended processing times. To achieve these goals in an industrial scenario, the deposition geometry must be measured with precision and efficiency throughout the part-building process. Moreover, it is essential to comprehend the changes in the interlayer deposition height based on various process parameters. This paper first examines the behaviour of interlayer deposition height when process parameters change within different wall regions, with a particular focus on the transition areas. In addition, this paper explores the potential of geometry monitoring information in implementing interlayer wall height compensation during w-DEDAM part-building. The in-process layer height was monitored using a coherent range-resolved interferometry (RRI) sensor, and the accuracy and efficiency of this measurement were carefully studied. Leveraging this information and understanding of deposition geometry, the control points of the process parameters were identified. Subsequently, appropriate and varied process parameters were applied to each wall region to gradually compensate for wall height. The wall height discrepancies were generally compensated for in two to three layers.
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    Collaborative robotic wire + arc additive manufacture and sensor-enabled in-process ultrasonic non-destructive evaluation
    (MDPI, 2022-05-31) Zimermann, Rastislav; Mohseni, Ehsan; Vasilev, Momchil; Loukas, Charalampos; Vithanage, Randika K. W.; MacLeod, Charles N.; Lines, David; Javadi, Yashar; Espirindio E Silva, Misael Pimentel; Fitzpatrick, Stephen; Halavage, Steven; Mckegney, Scott; Pierce, Stephen Gareth; Williams, Stewart; Dingv, Jialuo
    The demand for cost-efficient manufacturing of complex metal components has driven research for metal Additive Manufacturing (AM) such as Wire + Arc Additive Manufacturing (WAAM). WAAM enables automated, time- and material-efficient manufacturing of metal parts. To strengthen these benefits, the demand for robotically deployed in-process Non-Destructive Evaluation (NDE) has risen, aiming to replace current manually deployed inspection techniques after completion of the part. This work presents a synchronized multi-robot WAAM and NDE cell aiming to achieve (1) defect detection in-process, (2) enable possible in-process repair and (3) prevent costly scrappage or rework of completed defective builds. The deployment of the NDE during a deposition process is achieved through real-time position control of robots based on sensor input. A novel high-temperature capable, dry-coupled phased array ultrasound transducer (PAUT) roller-probe device is used for the NDE inspection. The dry-coupled sensor is tailored for coupling with an as-built high-temperature WAAM surface at an applied force and speed. The demonstration of the novel ultrasound in-process defect detection approach, presented in this paper, was performed on a titanium WAAM straight sample containing an intentionally embedded tungsten tube reflectors with an internal diameter of 1.0 mm. The ultrasound data were acquired after a pre-specified layer, in-process, employing the Full Matrix Capture (FMC) technique for subsequent post-processing using the adaptive Total Focusing Method (TFM) imaging algorithm assisted by a surface reconstruction algorithm based on the Synthetic Aperture Focusing Technique (SAFT). The presented results show a sufficient signal-to-noise ratio. Therefore, a potential for early defect detection is achieved, directly strengthening the benefits of the AM process by enabling a possible in-process repair.
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    Comparison of continuous and pulsed wave lasers in keyhole welding of stainless‑steel to aluminium
    (Springer, 2021-10-31) Coroado, Julio; Ganguly, Supriyo; Williams, Stewart; Suder, Wojciech; Meco, Sonia; Pardal, Goncalo
    A continuous wave (CW) and a nanosecond pulsed wave (PW) lasers were used to join 1-mm thick sheets of SS304L (SS) austenitic stainless-steel to AA5251 (Al) aluminium alloy in an overlap joint configuration. The weld shape (penetration depth and width), intermetallic compounds concentration, weld quality (cracking and porosity) and mechanical strength were correlated with the process energy and compared between each laser temporal mode. Successful CW joints were produced with the SS sheet on top of the Al, but the opposite configuration revealed to be impossible for the range of parameters tested. The PW joints were successful with the Al sheet on top of SS, but all the joints cracked at the interface when the opposite configuration was used. The mechanical tests showed that even though it is possible to achieve higher tensile shear load in CW welds due to the larger bonding area, the tensile shear strength revealed to be almost 5 × higher for PW welds at similar applied energy.
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    Comparison of microstructure refinement in wire-arc additively manufactured Ti–6Al–2Sn–4Zr–2Mo–0.1Si and Ti–6Al–4V built with inter-pass deformation
    (Springer, 2022-09-22) Davis, Alec E.; Caballero Ramos, Armando; Biswal, Romali; Williams, Stewart; Prangnell, P. B.
    The titanium alloy Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242) has been deposited for the first time by a directed energy deposition process using a wire and arc system—i.e., wire-arc additive manufacturing (WAAM)—with and without inter-pass machine hammer peening, and its microstructure investigated and compared to the more commonly used alloy Ti–6Al–4V (Ti64). The application of inter-pass machine hammer peening—where each added layer was deformed before deposition—successfully refined the strongly textured, coarse, columnar β-grain structure that is commonly seen in α + β titanium alloys, producing a finer equiaxed grain structure with a near-random α texture. The average grain diameter and texture strength decreased with the peening pitch. When Ti6242 was deposited under identical conditions to Ti64, by switching the alloy feed wire in-situ, the refined β-grain size decreased across the alloy-to-alloy transition reaching on average 25 pct less in Ti6242 than in Ti64. A similar 25 pct scale reduction was also found in the Ti6242 α-lath transformation microstructure. This comparatively greater microstructure refinement in Ti6242 was attributed to the dissimilar alloying elements present in the two materials; specifically, molybdenum, which has a lower diffusivity than vanadium and led to slower β-grain growth during reheating as well as a finer transformation microstructure.
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    Compression behaviour of wire+ arc additive manufactured structures
    (MDPI, 2021-05-27) Abbaszadeh, Masoud; Ventzke, Volker; Neto, Leonor; Riekehr, Stefan; Martina, Filomeno; Kashaev, Nikolai; Hönnige, Jan; Williams, Stewart; Klusemann, Benjamin
    Increasing demand for producing large-scale metal components via additive manufacturing requires relatively high building rate processes, such as wire + arc additive manufacturing (WAAM). For the industrial implementation of this technology, a throughout understanding of material behaviour is needed. In the present work, structures of Ti-6Al-4V, AA2319 and S355JR steel fabricated by means of WAAM were investigated and compared with respect to their mechanical and microstructural properties, in particular under compression loading. The microstructure of WAAM specimens is assessed by scanning electron microscopy, electron back-scatter diffraction, and optical microscopy. In Ti-6Al-4V, the results show that the presence of the basal and prismatic crystal planes in normal direction lead to an anisotropic behaviour under compression. Although AA2319 shows initially an isotropic plastic behaviour, the directional porosity distribution leads to an anisotropic behaviour at final stages of the compression tests before failure. In S355JR steel, isotropic mechanical behaviour is observed due to the presence of a relatively homogeneous microstructure. Microhardness is related to grain morphology variations, where higher hardness near the inter-layer grain boundaries for Ti-6Al-4V and AA2319 as well as within the refined regions in S355JR steel is observed. In summary, this study analyzes and compares the behaviour of three different materials fabricated by WAAM under compression loading, an important loading condition in mechanical post-processing techniques of WAAM structures, such as rolling. In this regard, the data can also be utilized for future modelling activities in this direction.
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    Computationally efficient models of high pressure rolling for wire arc additively manufactured components
    (MDPI, 2021-01-04) Gornyakov, Valeriy; Sun, Yongle; Ding, Jialuo; Williams, Stewart
    High pressure multi-layer rolling is an effective method to reduce residual stress and distortion in metallic components built by wire arc additive manufacturing (WAAM). However, the mechanisms of the reduction in residual stress and distortion during multi-layer rolling are not well understood. Conventional finite element models for rolling are highly inefficient, hindering the simulation of multi-layer rolling for large WAAM components. This study aims to identify the most suitable modelling technique for finite element analysis of large WAAM component rolling. Four efficient rolling models were developed, and their efficiency and accuracy were compared with reference to a conventional large-scale rolling model (i.e., control model) for a WAAM built wall. A short-length transient model with fewer elements than the control model was developed to reduce computational time. Accurate predictions of stress and strain and a reduction in computational time by 96.5% were achieved using the short-length model when an implicit method for numerical solution was employed, while similar efficiency but less accurate prediction was obtained when an explicit solution method was adopted. A Eulerian steady-state model was also developed, which was slightly less efficient (95.91% reduction in computational time) but was much less accurate due to unrealistic representation of rolling process. The applicability of a 2D rolling model was also examined and it was found that the 2D model is highly efficient (99.52% time reduction) but less predictive due to the 2D simplification. This study also shows that the rigid roller adopted in the models is beneficial for improving efficiency without sacrificing accuracy
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    Control of meltpool shape in laser welding
    (Springer, 2024-03-05) Suder, Wojciech; Chen, Xin; Rico Sierra, David; Chen, Guangyu; Wainwright, James; Rajamudili, Kuladeep; Rodrigues Pardal, Goncalo; Williams, Stewart
    In laser welding, the achievement of high productivity and precision is a relatively easy task; however, it is not always obvious how to achieve sound welds without defects. The localised laser energy promotes narrow meltpools with steep thermal gradients, additionally agitated by the vapour plume, which can potentially lead to many instabilities and defects. In the past years, there have been many techniques demonstrated on how to improve the quality and tolerance of laser welding, such as wobble welding or hybrid processes, but to utilise the full potential of lasers, we need to understand how to tailor the laser energy to meet the process and material requirements. Understanding and controlling the melt flow is one of the most important aspects in laser welding. In this work, the outcome of an extensive research programme focused on the understanding of meltpool dynamics and control of bead shape in laser welding is discussed. The results of instrumented experimentation, supported by computational fluid dynamic modelling, give insight into the fundamental aspects of meltpool formation, flow direction, feedstock melting and the likelihood of defect formation in the material upon laser interaction. The work contributes to a better understanding of the existing processes, as well as the development of a new range of process regimes with higher process stability, improved efficiency and higher productivity than standard laser welding. Several examples including ultra-stable keyhole welding and wobble welding and a highly efficient laser wire melting are demonstrated. In addition, the authors present a new welding process, derived from a new concept of the meltpool flow and shape control by dynamic beam shaping. The new process has proven to have many potential advantages in welding, cladding and repair applications.
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    Data for paper entitled "Laser stabilization of GMAW additive manufacturing of Ti-6Al-4V components"
    (Cranfield University, 2019-05-09 12:07) Rodrigues Pardal, Goncalo; Martina, Filomeno; Williams, Stewart
    Data used in paper "Laser stabilization of GMAW additive manufacturing of Ti-6Al-4V components"
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    Data for the paper "residual stress and texture control in Ti-6Al-4V wire + arc additively manufactured intersections by stress relief and rolling"
    (Cranfield University, 2018-05-02 13:58) roman Hönnige, Jan; Ganguly, Supriyo; Colegrove, Paul; Williams, Stewart; Lik Lee, Tung; Fitzpatrick, Michael; Ahmed, Bilal
    Data supporting the paper: "residual stress and texture control in Ti-6Al-4V wire + arc additively manufactured intersections by stress relief and rolling".
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    Data supporting "A novel cold wire gas metal arc (CW-GMA) process for high productivity additive manufacturing"
    (Cranfield University, 2023-06-30 11:53) Wang, Chong; Wang, Jun; Bento, João; Ding, Jialuo; Rodrigues Pardal, Goncalo; Chen, Guangyu; Qin, Jian; Suder, Wojciech; Williams, Stewart
    This is a supplementary figure, showing the experimental setup for building the large-scale component with the CW-GMA process: (a) experiment setup, and (b) monitors for thermal camera and process camera.
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    Data supporting: 'Modelling and optimising hybrid process of wire arc additive manufacturing and high-pressure rolling'
    (Cranfield University, 2022-10-04 10:54) Gornyakov, Valeriy; Sun, Yongle; Ding, Jialuo; Williams, Stewart
    Figure 7 Predicted distortion of the WAAM part after deactivation of clamps . Figure 8 Longitudinal RS distributions along the vertical path in the symmetry plane for the full-length mechanical models after clamps deactivation, compared to experimental measurements [5]. The flat roller (a) and slotted roller (b) were used in the rolling simulations, and the full-length model was based on the solution mapped from the steady-state region of the reduced-length WAAM + IL rolling model Figure 10 Concurrent evolution of temperature and longitudinal stress (a), as well as the longitudinal PS (b), in the layer 6 during WAAM deposition of layers 6-8 in conjunction with IL rolling using the flat roller. The data were collected at the top of layer 6 in the inspection plane and the rolling phases are highlighted in the yellow shaded areas. Figure 11 Concurrent evolution of temperature and longitudinal stress (a), as well as longitudinal PS (b), in the layer 6 during WAAM deposition of layers 9-11 in conjunction with IL rolling using the flat roller. The data were collected at the top of layer 6 in the inspection plane and the rolling phases are highlighted in the yellow shaded areas. Figure 12 Concurrent evolution of temperature and longitudinal stress (a), as well as longitudinal PS (b), in the layer 6 during WAAM deposition of layers 12-14 in conjunction with IL rolling using the flat roller. The data were collected at the top of layer 6 in the inspection plane and the rolling phases are highlighted in the yellow shaded areas. Figure 13 Concurrent evolution of the longitudinal PS and stress in the layer 9 during WAAM deposition of layers 9-16 in conjunction with IL rolling using the slotted roller. The data were collected at the top of layer 9 in the inspection plane (the slotted roller started rolling on layer 6) and the rolling phases are highlighted in the yellow shaded areas. Figure 18 Evolution of longitudinal PS in the layer 6 during WAAM deposition and stacked 4L rolling with flat roller. The rolling phases are highlighted in the yellow shaded areas.
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    Data supporting: 'Multi-Energy Source (MES) Configuration for Bead Shape Control in Wire-based Directed Energy Deposition (w-DED)'
    (Cranfield University, 2022-08-31 15:42) Chen, Guangyu; Suder, Wojciech; Williams, Stewart; Ding, Jialuo; Wang, Chong
    Video shows the the dynamic changing of the melt pool and highspeed scanning motion of the laser beam.
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    Data supporting: 'Split anode calorimetry for plasma arc energy density measurement with laser calibration'
    (Cranfield University, 2022-11-23 15:46) Chen, Guangyu; Williams, Stewart; Ding, Jialuo; Suder, Wojciech; Wang, Yipeng
    Video shows the accelarated thermal image when the laser beam traveled acrossed the copper anodes interface.
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    Data supporting: 'Strain controlled fatigue behaviour of wire + arc additive manufactured Ti-6Al-4V'
    (Cranfield University, 2023-03-07 19:02) Khadar Syed, Abdul; Williams, Stewart
    This paper investigates the strain controlled fatigue and cyclic deformation behaviour of a wire + arc additive manufactured Ti-6Al-4V alloy in the as-built condition. Higher local heat input used to build the material exhibited a coarser parent columnar β grain structure along with a coarser transformation microstructure compared to other additive manufactured Ti-6Al-4V. Test specimens were manufactured in horizontal and vertical orientations with respect to the deposited layers. Property isotropy was observed at lower applied strain values. When the strain amplitude was above 0.6%, the vertical samples, where the loading axis was in parallel with the parent columnar β grains, showed marginally higher fatigue strength owing to larger plastic deformation. Moreover, higher cyclic softening ratio by a factor of two was measured in the vertical samples when the strain amplitude was above 0.6%. No porosity defects were found in the material. Cracks were initiated from α lath due to cyclic slip localisation.
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    Data supporting: 'Wire based plasma arc and laser hybrid additive manufacture of Ti-6Al-4V'
    (Cranfield University, 2022-11-23 16:47) Wang, Chong; Suder, Wojciech; Ding, Jialuo; Williams, Stewart
    These are two supplementary videos for Fig 5, showing different configurations for wire based PTA-laser hybrid additive manufacturing process.
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    Data Underpinning "Weld-Bonded Stainless Steel to Carbon Fibre-Reinforced Plastic Joints"
    (Cranfield University, 2017-09-07 15:26) Colegrove, Paul; Joesbury, Adam; Ayre, David; Van Rymenant, Patrick; Ganguly, Supriyo; Williams, Stewart
    Figures for article entitled "Weld-Bonded Stainless Steel to Carbon Fibre-Reinforced Plastic Joints"
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    Data: Automated interlayer wall height compensation for wire based directed energy deposition additive manufacturing
    (Cranfield University, 2024-05-08 16:28) Qin, Jian; Vives, Javier; Rajan, Parthiban; Lasisi, Shakirudeen; Wang, Chong; Charrett, Tom; Ding, Jialuo; Williams, Stewart; Hallam, Jonathan; Tatam, Ralph
    Experimental dataset to support the publication. The data includes all the test and measurement records for the experiment.
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    Data: Effect of machine hammer peening conditions on β grain refinement of additively manufactured Ti-6Al-4V
    (Cranfield University, 2023-11-14 11:37) Machado Santos Carvalho Neto, Leonor; Williams, Stewart; Davis, Alec; Kennedy, Jacob
    The data in this folder is a table with the average grain size according to variations of parameters studied. This information is given in the paper as a graphical representation and is here described to support any further studies.