Browsing by Author "Pardal, Goncalo"
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Item Open Access 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, GoncaloA 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.Item Open Access Dissimilar metal joining of stainless steel and titanium using copper as transition metal(Springer, 2016-01) Pardal, Goncalo; Ganguly, Supriyo; Williams, Stewart W.; Vaja, JayJoining of stainless steel and titanium dissimilar metal combination has a specific interest in the nuclear industry. Due to the metallurgical incompatibility, it has been very difficult to produce reliable joints between these metals due to the formation of FeTi and Fe2Ti types of intermetallic compounds. The metallurgical incompatibility between both materials is enhanced by the time–temperature profile of the welding process used. Brittle intermetallics (IMCs) are formed during Fe–Ti welding (FeTi and Fe2Ti). The present study uses the low thermal heat input process cold metal transfer (CMT), when compared with conventional GMAW, to deposit a copper (Cu) bead between Ti and stainless steel. Cu is compatible with Fe, and it has a lower melting point than the two base materials. The welds were produced between AMS 4911L (Ti-6Al-4V) and AISI 316L stainless steel using a CuSi-3 welding wire. The joints produced revealed two IM layers located near the parent metals/weld interfaces. The hardness of these layers is higher than the remainder of the weld bead. Tensile tests were carried out with a maximum strength of 200 MPa, but the interfacial failure could not be avoided. Ti atomic migration was observed during experimental trials; however, the IMC formed are less brittle than FeTi, inducing higher mechanical properties.Item Open Access Effect of shielding conditions on bead profile and melting behaviour in laser powder bed fusion additive manufacturing(Elsevier, 2020-05-26) Caballero, Armando; Suder, Wojciech; Chen, Xin; Pardal, Goncalo; Williams, Stewart W.A series of experiments were performed using a 500 W continuous wave fibre laser on a single powder bed layer using different processing variables. The aim was to investigate the effect of different shielding conditions on melting behaviour and bead profile in laser powder bed fusion (PBF). Through high-speed imaging, it was found that under an argon atmosphere a strong plasma plume is generated from the meltpool. Laser beam-plasma plume interactions caused strong instabilities during melting, including laser wandering, track instability and continuous fluctuations between melting regimes (conduction and keyhole). Hence, it was not possible to control the profile of the melted tracks under this condition. By using a helium atmosphere, a smaller plasma was obtained, reducing the disruptions caused by laser-plasma interactions. This led to a stable melting regime that allowed control of the melt bead profile. This condition was used to study the effect of laser-material fundamental interaction parameters on the bead geometry in powder bed melting. It was found that during melting of single tracks, the dominant regime of melting is conduction for the range of parameters tested. Penetration and melt width were found to increase with increasing energy density. For longer interaction times, melt widths were found to be up to ten times the size of the beam diameter used. Fluid flow modelling showed that this is due to strong melt flow as consequence of surface tension gradients generated by very high temperature gradientsItem Open Access Experimental investigations on solid and metal-cored creep-resistant wires deposited under GMA and PTA-based wire arc additive manufacturing (WAAM)(Springer, 2025-01-01) Iqbal, Hambal; Pardal, Goncalo; Suder, Wojciech; Ascari, Alessandro; Fortunato, Alessandro; Liverani, Erica; Williams, Stewart W.; Neto, LeonorWire arc additive manufacturing (WAAM), also known as Arc-DED, possesses great potential for efficient production using various materials and wire types. This study utilized gas metal arc (GMA) and plasma transferred arc (PTA) variants of WAAM to deposit 2.25Cr-1Mo steel employing a metal-cored wire (MCW) and a solid wire counterpart having the same chemical composition for the comparative study. Initially, bead-on-plate trials were conducted with both WAAM processes and different shielding gas combinations in GMA-WAAM using the cored wire. The heat input versus deposition ratio was analysed to assess the heat input and the effects of shielding gases in GMA-WAAM. Arc behaviour was monitored with a process camera, and bead morphologies and dilutions were compared. Furthermore, test walls were deposited under the two WAAM processes and the shielding gas conditions, employing the cored and solid wire. Detailed microstructural study was conducted through optical microscopy, and hardness tests were performed to determine the mechanical properties. Energy dispersive X-ray spectroscopy (EDS) was used to examine the elemental composition and potential segregation in walls deposited with cored and solid wires. Results indicated a lower heat input when using cored wire and variable heat input due to shielding gases. A bainitic/martensitic microstructure was observed in test walls deposited with cored and solid wires with comparable microstructural features. The PTA process produced higher hardness than GMA, and solid wire exhibited slightly higher hardness than cored wire. Selection of shielding gas also influenced the hardness. Finally, the EDS maps and elemental study revealed comparable results for both wires. The results show good performance and outcome for cored wire.Item Open Access Fabrication of functionalised surfaces on gum metal (Ti-30Nb) using micromachining(euspen, 2019-06-30) Hawi, Sara; Dickins, Andrew; Pardal, Goncalo; Giusca, Claudiu; Pearce, Oliver; Goel, SauravStructured surfaces are attracting deep interest, as they allow tailoring the functionality via changes in the surface topography. Applications for these surfaces range greatly, including, optical surfaces for antireflective surfaces, thermal structures to assist in heat dispersion and anti-fouling surfaces to reduce micro-organisms from adhering to components. Gum metal is a relatively newer kind of beta titanium alloy that has earmarked its place as the next generation Ortheopedic implant material. In a timely effort, this work investigated the generation of micron level structured surfaces on Gum metal (Ti-30Nb – a beta titanium alloy) to explore micromilling as the robust scalable process to achieve low dimensional surfaces in titanium alloy. During micromilling, the feedrate, spindle speed, axial depth of cut and tool step over were varied to optimise these parameters for achieving superior quality of machining.Item Open Access In-process mechanical working of additive manufactured Rene 41(American Society of Mechanical Engineers, 2023-01-18) James, William Sean; Ganguly, Supriyo; Pardal, GoncaloIn developing the wire + arc additive manufacturing (WAAM) process for creep resistant alloys for defence applications, structures were built from nickel-based superalloy Rene 41 (RE41). The performance of the additive manufactured alloy was analysed for applications including components used in high-speed flight environments, where external structures could reach service temperatures of up to 1000 K. As a single use system with relatively short flight times of < 1 hour, components will be highly stressed to minimise structural mass. In this paper, three wall structures were deposited using a plasma transferred arc process, in a layer-by-layer manner where each layer was mechanically worked by machine hammer peening directly after deposition. With a constant impact frequency, three different travel speeds for the peening tool were used for each wall structure. To understand the most effective cold working parameters, samples were tested and analysed for their mechanical properties and microstructural characteristics after aging treatment. Samples were tested at room temperature and compared with results of both non-worked heat-treated AM material and wrought data obtained from literature review.Item Open Access Investigation of dissimilar metal welds by energy-resolved neutron imaging(International Union of Crystallography, 2016-06-09) Tresmin, Anton S.; Ganguly, Supriyo; Meco, Sonia; Pardal, Goncalo; Shinohara, Takenao; Feller, BruceA nondestructive study of the internal structure and compositional gradient of dissimilar metal-alloy welds through energy-resolved neutron imaging is described in this paper. The ability of neutrons to penetrate thick metal objects (up to several cm) provides a unique possibility to examine samples which are opaque to other conventional techniques. The presence of Bragg edges in the measured neutron transmission spectra can be used to characterize the internal residual strain within the samples and some microstructural features, e.g. texture within the grains, while neutron resonance absorption provides the possibility to map the degree of uniformity in mixing of the participating alloys and intermetallic formation within the welds. In addition, voids and other defects can be revealed by the variation of neutron attenuation across the samples. This paper demonstrates the potential of neutron energy-resolved imaging to measure all these characteristics simultaneously in a single experiment with sub-mm spatial resolution. Two dissimilar alloy welds are used in this study: Al autogenously laser welded to steel, and Ti gas metal arc welded (GMAW) to stainless steel using Cu as a filler alloy. The cold metal transfer variant of the GMAW process was used in joining the Ti to the stainless steel in order to minimize the heat input. The distributions of the lattice parameter and texture variation in these welds as well as the presence of voids and defects in the melt region are mapped across the welds. The depth of the thermal front in the Al–steel weld is clearly resolved and could be used to optimize the welding process. A highly textured structure is revealed in the Ti to stainless steel joint where copper was used as a filler wire. The limited diffusion of Ti into the weld region is also verified by the resonance absorption.Item Open Access Laser spot welding of laser textured steel to aluminium(Elsevier, 2017-03) Pardal, Goncalo; Meco, Sonia; Dunn, Andrew; Williams, Stewart W.; Ganguly, Supriyo; Hand, Duncan P.; Wlodarczyk, Krystian L.Laser welding of dissimilar metals (steel and aluminium) was investigated with the aim to increase the maximum tensile shear load of the Fe-Al joints. The increase was achieved by texturing the surface of steel prior to the laser spot welding process which was performed in a lap-joint configuration with the steel positioned on top of the aluminium and with a texture faced down to the aluminium surface. This configuration enabled an increase of the bonding area of the joints, because the molten aluminium filled in the gaps of the texture, without the need of increasing the process energy which typically leads to the growth of the intermetallic compounds. Different textures (containing hexagonally arranged craters, parallel lines, grid and spiral patterns) were tested with different laser welding parameters. The Fe-Al joints obtained with the textured steel were found to have up to 25% higher maximum tensile-shear load than the joints obtained with the untextured steel.Item Open Access Laser stabilization of GMAW additive manufacturing of Ti-6Al-4V components(Elsevier, 2019-04-26) Pardal, Goncalo; Martina, Filomeno; Williams, Stewart W.GMAW (Gas Metal Arc Welding) of titanium is not currently used in industry due to the high levels of spatter generation, the wandering of the welding arc and the consequent waviness of the weld bead. This paper reports on the use of laser welding in conduction mode to stabilize the CMT (Cold Metal Transfer), a low heat input GMAW process. The stabilization and reshaping of Ti-6Al-4 V weld beads was verified for laser hybrid GMAW bead on plate deposition. The laser beam was defocused, used in conduction mode, and was positioned concentric with the welding wire and the welding arc (CMT). Finally, the results obtained for bead-on-plate welding were applied to an additively manufactured structure, in which a laser-hybrid stabilized sample was built and then evaluated against CMT-only sample. This work reveals that laser can be used to stabilize the welding process, improve the weld-bead shape of single and multiple layer depositions and increase the deposition rate of additive manufacture of Ti-6Al-4 V from1.7 kg/h to 2.0 kg/h.Item Open Access Microstructure and mechanical properties of Inconel 718 and Inconel 625 produced through the wire + arc additive manufacturing process(NATO, 2022-03-05) James, William Sean; Ganguly, Supriyo; Pardal, GoncaloIn developing the wire + arc additive manufacturing (WAAM) process for heat and creep resistant alloys, structures were built from nickel-based superalloys Inconel 718 (IN718) and Inconel 625 (IN625). In this paper, wall structures were deposited in both superalloys, using a plasma transferred arc process. The microstructure was analysed optically and under SEM; both alloys revealed typical dendritic structure with long columnar grains, with little variation between the alloys. The findings suggest that the structures included significant segregation of alloying elements, with potential intermetallic phases e.g. Laves phases and δ-phases also found across the alloys, which showed significantly more segregation of Nb and Mo at the grain boundaries and inter-dendritic regions. The alloys also underwent room temperature mechanical testing, in addition to this IN625 specimens were tested after a solutionising and ageing treatment. Hardness measurements indicated that in general the WAAM process has the effect of increasing material hardness by approximately 10 %, when compared to wrought alloy in a solutionised state. In IN625 the heat-treated specimens showed an increase in hardness of around 6 %, when compared with its as-deposited condition. Elongation in IN625 showed much greater values. Overall, IN718 showed a greater strength with less elongation than IN625. A comparison between both alloys and their stated maximum UTS and YS values from literature revealed that WAAM built IN718 and IN625 in its as-deposited condition can achieve just over half the maximum achievable UTS, with no post-process treatment. The heat-treatment process tested in IN625 marginally reduced the gap in UTS performance by 3.5 %.Item Open Access New phenomenological model for comparison of lasers with different temporal outputs(Springer, 2022-04-06) Coroado, Julio; Williams, Stewart W.; Suder, Wojciech; Ganguly, Supriyo; Meco, Sonia; Pardal, GoncaloLaser welding is distinguished by low heat input, low distortion, high travel speeds and accuracy. Traditional high-power pulsed wave (PW) lasers are being replaced by high-frequency low-pulse energy fibre lasers. However, as these lasers operate at very high frequencies, near continuous wave (CW) operation, it is not clear the benefit of such frequencies in comparison to CW lasers for micro-welding. In this project, two lasers, one in high-frequency PW and another in CW are operated at the same conditions, including average power, average peak power, spot size and travel speed, and the differences in material response are investigated. It has been shown that frequency is one of the important parameters that affect the heat loss between individual pulses, referred to as inter-pulse losses. At low frequency, the PW laser provided lower melting efficiency and higher penetration efficiency than CW. On the other hand, at high frequency, the PW resulted in lower melting and penetration efficiency than CW. In addition, a new definition of interaction time has been proposed to capture conduction losses by travel speed and heat inter-pulse losses due to periodic lack of laser power. This allows a like-for-like comparison of CW and PW lasers and can be used to predict penetration depth with processing parameters.Item Open Access A performance comparison of additive manufactured creep-resistant superalloys(Taylor and Francis, 2023-03-13) James, William Sean; Ganguly, Supriyo; Pardal, GoncaloCreep-resistant nickel, cobalt based superalloys, selected for a high-speed flight application, deposited using Wire + Arc Additive Manufacturing (WAAM), was reported. Three different alloys, Haynes 188, Inconel 718, and Rene 41, were deposited, and tested for their high-temperature tensile properties, and the results compared with wrought data. The alloys were tested from ambient temperature to 1000°C in their as-deposited condition and after undergoing industry standard age-hardening and solutionising heat-treatments, to down select the best performing alloy under two different processing conditions. The mechanical strength of the alloys fell short of the maximum achievable in wrought condition. Precipitation-strengthened alloys, Inconel 718 and Rene 41 were found to have underperformed the most significantly, whereas solid-solution-strengthened Haynes 188 suffered the least due to WAAM.Item Open Access Selection and performance of AM superalloys for high-speed flight environments(Springer, 2022-09-01) James, William S.; Ganguly, Supriyo; Pardal, GoncaloIn developing the Wire + Arc Additive Manufacturing (WAAM) process for the manufacture of components used in high-speed flight environments, a selection process for suitable alloys was devised. Using material properties from literature sources, creep-resistant alloys were down-selected based on the requirement for service in a high temperature, high stress environment and the need for an alloy suitable for manufacture using the WAAM process. Down-selected alloys, Inconel 718 (IN718), Rene 41 (RE41), Haynes 188 (H188) and Inconel 625 (IN625), were deposited by a plasma transferred arc WAAM process in an oxygen-controlled environment. Wall structures were built, and samples extracted for mechanical testing. The performance of as-deposited material was then compared against the wrought literature data. Tensile testing at room temperature revealed a performance mismatch, in comparison with wrought literature data, for precipitation strengthened IN718 & RE41; however, this performance mismatch was less significant for solution strengthened H188 and IN625. Results revealed that the AM material did not meet the wrought strength with performance varying depending on each alloy’s strengthening mechanism. Results illustrate the need for further processing to return the mechanical performance to wrought values.Item Open Access Selection of parameters in nanosecond pulsed wave laser micro-welding(Springer, 2021-05-31) Coroado, Julio; Ganguly, Supriyo; Suder, Wojciech; Williams, Stewart; Meco, Sonia; Pardal, GoncaloThe digital control of the latest nanosecond pulsed wave (PW) fibre lasers allows very high flexibility in controlling the application of the total energy to a workpiece, which brings several advantages to the joining process. By choosing different pulse shapes in different spatial profiles, it is possible to apply low energy per pulse with high precision and accuracy resulting in lower heat input. Since the energy of each pulse is insufficient to generate melting, these lasers operate at very high pulse repetition frequencies near continuous wave (CW) regime. Nevertheless, the peak powers of PW lasers are much higher than CW. In this research, the effect of peak power, pulse energy, pulse width, pulse repetition frequency and duty cycle has been studied. The experimental work was conducted in bead on plate of austenitic stainless steel to investigate the effect of laser on the weld geometry, i.e. depth of penetration and width. An empirical model, previously established for CW mode, which enables the achievement of a particular penetration depth independent of the beam diameter, was redesigned and tested for PW mode. The “pulse power factor model” allows the laser user to select a weld profile that meets certain quality and productivity requirements independent of the laser system. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of different system parameters by keeping a constant trade-off between pulse power factor and interaction time.Item Open Access Selection of processing parameters in laser microwelding. Part 1: Continuous wave (CW) mode(Old City Publishing, 2020-07-01) Coroado, J.; Ganguly, Supriyo; Suder, Wojciech; Williams, Stewart; Martins Meco, Sonia; Pardal, GoncaloA phenomenological model which specifies the penetration depth and width of the fusion zone in laser microjoining can be a very useful tool in achieving the required welding parameters for a desired application. In this study the power factor model, previously established and validated in macrowelding, has been tested in fibre laser microwelding, enabling achievement of a particular weld independently of a laser system. Differ-ent weld profiles in aluminium and stainless steel were correlated with various combinations of parameters for a wide range of beam diameters. It has been shown that the same penetration depth can be achieved with different weld profiles. A similar trend, as previously found in macrow-elding, has been confirmed in microwelding. It was demonstrated that the depth of penetration can be kept constant independently of the laser sys-tem until certain limit of beam size.Item Open Access Tandem Metal Inert Gas process for high productivity Wire Arc Additive Manufacturing in stainless steel(Elsevier, 2018-11-19) Martina, Filomeno; Ding, Jialuo; Williams, Stewart W.; Caballero, Armando; Pardal, Goncalo; Quintino, LuísaThis study investigates the feasibility of achieving high deposition rate using wire + arc additive manufacturing in stainless steel to reduce lead time and cost of manufacturing. The pulse MIG welding technique with a tandem torch was used for depositing martensitic stainless steel 17-4 PH. The mechanical and metallurgical properties of the manufactured component were analysed to evaluate the limitations and the extent to which the rate of deposition reaches a maximum without any failure or defect being evident in the manufactured component. Deposition rate of 9.5 kg/hr was achieved. The hardness was matched for the as deposited condition.Item Open Access Thermal fluid dynamics of the effect of filler wire on deposition rate and bead formation intending plasma arc-based DED(Elsevier, 2023-10-22) Chen, Xin; Wang, Chong; Ding, Jialuo; Qu, Rongdong; Wang, Yipeng; Pardal, Goncalo; Williams, StewartThe influence of filler wire configuration, such as size and geometry, on the deposition rate (DR) and bead formation, has been studied in wire arc-based directed energy deposition (WADED), but the fundamental physics underlying its effect on wire melting and melt pool dynamics remains unclear. In this paper, a series of plasma arc-based DED (plasma-DED) experiments were conducted to investigate the impact of five different filler wire configurations on DR and bead dimensions. The coupling behaviours of wire melting, metal transfer and melt pool dynamics under the five filler wire configurations were also simulated numerically using the authors' recently developed wire-feeding model. The calculated wire melting and bead cross-sections are consistent with the experimental images and measurements. The results demonstrate that the filler wire significantly affects the highest DR by altering wire melting and metal transfer behaviours through changes in arc energy absorption. The filler wire with a rhombus geometry which is closer to a Gaussian-like arc distribution than the flat wire was shown to get higher DR and more stable metal transfer. Furthermore, different filler wire configurations lead to distinct melt pool behaviours, including temperature distribution and flow velocity, due to various metal transfer behaviours and arc shading effects. This study sheds light on the fundamental physics underlying the impact of filler wire on wire melting and bead formation for the first time. The methods and findings can guide improving DR and controlling bead shape in the plasma-DED process.Item Open Access Wire + Arc Additive Manufacturing(Maney (Taylor and Francis), 2016-02) Williams, Stewart W.; Martina, Filomeno; Addison, Adrian C.; Ding, Jialuo; Pardal, Goncalo; Colegrove, Paul A.Depositing large components (>10 kg) in titanium, aluminium, steel and other metals is possible using Wire + Arc Additive Manufacturing. This technology adopts arc welding tools and wire as feedstock for additive manufacturing purposes. High deposition rates, low material and equipment costs, and good structural integrity make Wire+Arc Additive Manufacturing a suitable candidate for replacing the current method of manufacturing from solid billets or large forgings, especially with regards to low and medium complexity parts. A variety of components have been successfully manufactured with this process, including Ti–6Al–4V spars and landing gear assemblies, aluminium wing ribs, steel wind tunnel models and cones. Strategies on how to manage residual stress, improve mechanical properties and eliminate defects such as porosity are suggested. Finally, the benefits of non-destructive testing, online monitoring and in situ machining are discussed.