The applications of Additive Manufacturing (AM) have been grown up rapidly in various industries in the past few decades. Among them, aerospace has been attracted more attention due to heavy ...investment of the principal aviation companies for developing the AM industrial applications. However, many studies have been going on to make it more versatile and safer technology and require making development in novel materials, technologies, process design, and cost efficiency. As a matter of fact, AM has a great potential to make a revolution in the global parts manufacturing and distribution while offering less complexity, lower cost, and energy consumption, and very highly customization. The current paper aims to review the last updates on AM technologies, material issues, post-processes, and design aspects, particularly in the aviation industry. Moreover, the AM process is investigated economically including various cost models, spare part digitalization and environmental consequences. This review would be helpfully applied in both academia and industry as well.
Directed energy high deposition-rate additive manufacturing processes involve a larger melt pool diameter (∼5–10 mm) and layer height (1–2 mm) than powder bed technologies, which generally leads to ...greater microstructural heterogeneity and more severe Heat Affected Zone (HAZ) banding. While HAZ banding has been widely reported in AM, in this study the banding features seen in samples produced by Wire-Arc Additive Manufacturing (WAAM) have been more rigorously quantified than previously possible, using statistically reliable compositional and, purpose developed, microstructure analysis mapping tools, which has provided new insight into their nature and mechanisms of formation. In addition to HAZ banding, a segregation layer has also been discovered at the fusion boundary from each melt track. This transient segregation layer and the weak coring seen, for the first time in the AM deposits, can be attributed to the lower partition coefficient of Fe in titanium, as well as limited V and Al segregation. The detailed microstructure evolution occurring in the HAZ bands has been revisited, based on new evidence, and is shown to involve both dark and white etching bands. The lower temperature dark etching region is caused not just by an increase in the α lamellar spacing due to coarsening, but also by greater chemical partitioning with temperature rise. In addition, it is shown by thermal simulation that the thin white band occurs on re-heating to just below the β transus temperature, which is shifted upwards owing to the high heating rate in AM. This white band is associated with a morphological change to a fine α lamellar colony morphology, which exhibits less solute partitioning. The mechanisms involved are discussed. The rapid coarsening that occurs in the range of the β approach curve is attributed to interface migration from β re-growth, rather than conventional surface tension driven effects, whereas the fine colony microstructure is proposed to be caused by colony nucleation, in subsequent cooling, on a low volume fraction of residual α.
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Many additively manufactured (AM) materials have properties that are inferior to their wrought counterparts, which impedes industrial implementation of the technology. Bulk deformation methods, such ...as rolling, applied in-process during AM can provide significant benefits including reducing residual stresses and distortion, and grain refinement. The latter is particularly beneficial for titanium alloys where the normally seen large prior β grains are converted to a fine equiaxed structure – giving isotropic mechanical properties that can be better than the wrought material. The technique is also beneficial for aluminium alloys where it enables a dramatic reduction in porosity and improved ductility.
The past few decades have seen substantial growth in Additive Manufacturing (AM) technologies. However, this growth has mainly been process-driven. The evolution of engineering design to take ...advantage of the possibilities afforded by AM and to manage the constraints associated with the technology has lagged behind. This paper presents the major opportunities, constraints, and economic considerations for Design for Additive Manufacturing. It explores issues related to design and redesign for direct and indirect AM production. It also highlights key industrial applications, outlines future challenges, and identifies promising directions for research and the exploitation of AM's full potential in industry.
•Elimination of distortion through the application of rolling after deposition.•Reduced residual stresses – particularly adjacent to the baseplate.•Grain refinement when the rolled material was ...reheated by the subsequent deposition pass.•A simple analytical model for predicting the residual stress and distortion in AM parts.
Parts manufactured by Wire and Arc Additive Manufacture (WAAM) can have significant residual stress and distortion, as well as large grain sizes. To overcome these problems, each layer on a linearly deposited steel WAAM part was rolled with either a ‘profiled’ roller, which had a similar shape to the deposited layer, or a ‘slotted’ roller, in which a groove prevented lateral deformation. Both rollers reduced the distortion and surface roughness, but the slotted roller proved more effective – eliminating the distortion. The residual stresses in the rolled WAAM parts were measured and were lower than those in the unrolled control specimen – particularly adjacent to the baseplate. Rolling also induced additional grain refinement when the rolled material was reheated during the subsequent deposition pass. The application of rolling may be a key technology for enabling implementation of WAAM on large-scale structures.
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.
Wire Arc-Based Additive manufacturing is a high deposition rate process suitable for building large-scale aerospace components. However, the larger heat source can cause greater microstructural ...heterogeneity and, in particular, a coarse columnar ß grain structure. The effect of the subsequent related transformation microstructure heterogeneity on the mechanical behaviour is investigated, in both standard WAAM materials and samples subjected to inter-pass rolling, which leads to substantial ß grain refinement and texture randomisation. Full-field strain maps were produced by digital image correlation, using tensile samples loaded in different orientations. When loaded normal to the columnar grain structure, it is shown that the coarse ß grains lead to a highly heterogeneous deformation distribution, which is linked the presence of dominant hard and soft α variants in texture colonies within each parent ß grain. ß grain refinement through the application of inter-pass rolling was found to be very effective at homogenising the strain localisation for all test orientations.
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.
The uncertainty surrounding the fracture behaviour of CMT-WAAM deposited steel, in terms of crack tip condition (J and CTOD) needed to cause crack tip extension, has made this manufacturing technique ...unpopular to date. Fracture toughness parameters are crucial in the structural integrity assessment of components and structures in various industries for assessing the suitability of a manufacturing process and material. In the offshore wind industry, the EN-GJS-400-18-LT ductile cast grade for the mainframe and hub has lower fracture toughness resistance for its high strength grade. Its high weight level affects the Eigen frequency of the tower and imposes high installation cost incurred from heavy lifting equipment usage. Poor fracture toughness is currently a challenge for wind turbine manufacturers in the quest for a cleaner and cheaper energy in the form of offshore wind. In this study, CMT-WAAM is used in depositing steel components with an oscillatory and single pass deposition strategy. The effects of microstructural variation, as a result of layer by layer deposition and the layer band spacing, on the fracture resistance in the build and welding direction was shown here. The fracture mechanics and failure mode of the WAAM deposited parts were investigated. The microstructural variation, again as a result of the layer by layer deposition and the layer band spacing, are the key parameters that control the fracture toughness of WAAM steel. Anisotropic behaviour in the Jq values was observed between both fracture orientations. The constructive transformation mechanism of the WAAM oscillatory process made way for intragranular nucleation of acicular ferrite on the Ti containing inclusion, thereby improving the toughness of the ER70S-6 deposit with a unique microstructure and Jq value of 640kJ/m2 .
Anisotropic dependence of fracture resistance of cold metal transfer wire + arc additive manufactured (CMT-WAAM) structural steel components of high strength low alloy (HSLA) steel. Display omitted
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