Showing papers in "Additive manufacturing in 2022"
TL;DR: In this article , NiTiTa (2.5 at. % Ta) shape memory alloys (SMAs) were fabricated using commercialy available NiTi wire and Ta foil as the feedstock materials.
Abstract: Wire and arc additive manufacturing (WAAM) technology was used for the fabrication of NiTiTa (2.5 at. % Ta) shape memory alloys (SMAs) for the first time, using commercialy available NiTi wire and Ta foil as the feedstock materials. The addition of Ta significantly increased the phase transformation temperatures, leading to a room-temperature microstructure composed of both B19′ martensite and B2 austenite, and (Ti,Ta)2Ni precipitates distributed at the grain boundaries. Compared with the WAAM fabricated NiTi counterpart, the corrosion potential (Ecorr) of the NiTiTa material increased from − 0.55 to − 0.44 V, while the corrosion current density (Icorr) decreased from 1.90 × 10−6 to 4.2 × 10−7 A/cm2. The X-ray brightness increased from 19.6 to 56.4 %. These results indicate that the addition of Ta can enhance the corrosion resistance and X-ray visibility of NiTiTa parts. Furthermore, the WAAM fabricated NiTiTa material was able to retain a stable superelastic response under 10 loading-unloading cycles, highlighting the great potential application value in the biomedical field. Our work provides an innovative method for additively manufacturing NiTi-based multi-component SMAs through WAAM.
65 citations
TL;DR: In this article , the authors employ a systematic literature review method to identify, assess, and analyse published literature on additive manufacturing, including design for additive manufacturing (DfAM), material analytics, in situ monitoring and defect detection, property prediction and sustainability.
Abstract: Additive manufacturing (AM) is poised to bring a revolution due to its unique production paradigm. It offers the prospect of mass customization, flexible production, on-demand and decentralized manufacturing. However, a number of challenges stem from not only the complexity of manufacturing systems but the demand for increasingly complex and high-quality products, in terms of design principles, standardization and quality control. These challenges build up barriers to the widespread adoption of AM in the industry and the in-depth research of AM in academia. To tackle the challenges, machine learning (ML) technologies rise to play a critical role as they are able to provide effective ways to quality control, process optimization, modelling of complex systems, and energy management. Hence, this paper employs a systematic literature review method as it is a defined and methodical way of identifying, assessing, and analysing published literature. Then, a keyword co-occurrence and cluster analysis are employed for analysing relevant literature. Several aspects of AM, including Design for AM (DfAM), material analytics, in situ monitoring and defect detection, property prediction and sustainability, have been clustered and summarized to present state-of-the-art research in the scope of ML for AM. Finally, the challenges and opportunities of ML for AM are uncovered and discussed.
62 citations
TL;DR: In this article , a 3D printed square auxetic tubular lattice (SATL) structure was designed, fabricated and investigated, and their mechanical properties were examined by the finite element method and experiments.
Abstract: Novel 3D printed square auxetic tubular lattice (SATL) structures were designed, fabricated and investigated. Their mechanical properties were examined by the finite element method and experiments. The height and wall thickness show different effects on the mechanical properties of SATL structures. Compared with the circular auxetic tubular (CATL) structures, the SATL structure has a lower peak force under axial load. Under lateral load, the SATL structure has higher stiffness and specific energy absorption. Moreover, the auxetic effect of the proposed SATL structure is also obvious under lateral load. Then, numerical investigations of several improved SATL structures were carried out, the results show that the improved square auxetic tubular lattice (ISATL) structures have stronger energy absorption capacity under axial and lateral loads. Due to their unique structural design and excellent mechanical properties, the SATL structures and ISATL structures have great potential for applications in civil engineering, vehicle crashworthiness and protective infrastructure.
36 citations
TL;DR: In this article , the effects of interlayer laser shock peening (LSP) treatment, namely, an innovative laser hybrid additive manufacturing technology combined LDED with LSP, on microstructural evolution and mechanical performance of Ti6Al4V alloy were investigated.
Abstract: Laser-directed energy deposition (LDED) provides an attractive and cost-effective way to remanufacture high-value engineering components. However, the LDED manufactured (LDEDed) components are usually characterized by large columnar grains along the deposition direction, leading to mechanical anisotropy. Meanwhile, higher performance is usually required in the damaged regions. In this paper, the effects of interlayer laser shock peening (LSP) treatment, namely, an innovative laser hybrid additive manufacturing technology combined LDED with LSP, on microstructural evolution and mechanical performance of Ti6Al4V alloy were investigated. Particularly, the microstructural features between adjacent deposited layers were clarified using scanning electron microscope (SEM) and transmission electron microscopy (TEM) observations. The results indicated that the epitaxial growth of columnar grains caused by LDED was inhibited, and fine equiaxed grains were formed between deposited layers due to the recrystallization behavior. Besides, the microhardness and tensile property of the LDEDed specimen were significantly improved by the interlayer LSP treatment. Consequently, the laser hybrid additive manufacturing -generated dominant mechanism of the microstructural evolution and tensile property enhancement was revealed. • LSP was combined with LDED to realize the laser hybrid remanufacturing. • Epitaxial growth of columnar grains in the LDEDed specimen was inhibited by LSP. • The micro-hardness of the LDEDed specimen was significantly improved by LSP. • A good combination of UTS and ductility was achieved in the LDED-LSPed specimen. • The mechanism of the tensile property enhancement by LHAM was revealed.
35 citations
TL;DR: In this paper , a hybrid additive manufacturing (LAHAM) method was proposed to balance the element vaporization, microstructure uniformity, and mechanical properties of the Al-Zn-Mg-Cu alloy.
Abstract: A novel additive manufacturing followed by a hybrid process involving pulsed laser and tungsten inert gas (TIG) arc was proposed to balance the element vaporization, microstructure uniformity, and mechanical properties of the Al-Zn-Mg-Cu alloy. The amount of vaporized Zn in the laser-arc hybrid additive manufacturing (LAHAM) reduced by merely 2.5%, whereas the Zn vaporization loss of the WAAM specimens reached up to 8.3%. Compared with the grain sizes of specimen obtained via WAAM, those obtained via LAHAM decreased by approximately two times. The < 100 > texture in the LAHAM specimen was decreased significantly, due to the appearance of equiaxed grains and grain refinement. Furthermore, in contrast to WAAM specimen, the eutectics contained Al, Zn, Mg and Cu were evenly distributed in the LAHAM specimen, resulting in uniform element distribution. Nano-precipitates were dispersedly distributed within the grains in the LAHAM specimen, whereas they merely appeared around the grain boundaries in the WAAM specimen. Owing to microstructure changes, LAHAM improved the ultimate tensile strength and yield strength by up to 11.4% and 29.9%, as compared with WAAM. The substantial improvement in yield strength was primarily attributed to precipitation strengthening, instead of grain boundary strengthening or solid solution strengthening.
34 citations
TL;DR: In this article , different types of biomimetic porous structures seen in nature, many of which are composite structures, and categorise them are identified and illustrated their functions and shown how these porous structures have been mimicked for engineering applications.
Abstract: As a result of their mechanical characteristics, biological structures often provide inspiration for the development of high-performance mechanical structures. Nevertheless, traditional production processes are often incapable of precisely reproducing the intricate and exquisite nature of biological systems. Modern additive manufacturing techniques provide a pathway to the creation of materials with complex patterns that are inspired by biological processes. In this paper, we identify the different types of biomimetic porous structures seen in nature, many of which are composite structures, and categorise them. We also identify the natural species with porous structures and illustrate their functions. In addition, this review paper presents how these porous structures have been mimicked for engineering applications. Figures are shown to demonstrate the scale (meso, micro, and nano) at which the porous structures are emulated. As biological porous structures have been successfully mimicked into synthetic materials using additive manufacturing (AM), we classify the types of 3D printing with respect to impact loading applications and describe the various types of additive manufacturing processes used to manufacture biomimetic porous structures. This review paper will be of interest to academics looking to design innovative lightweight porous composite structures and use emerging technologies to investigate their energy absorption properties, which have a wide range of engineering applications.
34 citations
TL;DR: In this paper , the authors summarize the recent progresses on the characterization of microstructure, assessment of strengthening and damage mechanisms, evaluation of fracture and fatigue resistance, and attempts to build a primary comprehensive link between mechanical performance and micro-structure for the as built state.
Abstract: As important structural materials widely used in aerospace and automotive industries, aluminum alloys are perfect candidates for development of laser metal additive manufacturing (AM). Amongst AM aluminum alloys, laser powder bed fusion (LPBF) AlSi10Mg has received substantial attention due to its good printability and relatively low cost. Great efforts have been devoted to seek optimum process parameters that can enhance mechanical performance. However, a large scattering of material properties arises from the literature data, especially for the as built state, thus casting a shadow over further development of LPBF Al alloys. This review article aims to summarize the recent progresses on the characterization of microstructure, assessment of strengthening and damage mechanisms, evaluation of fracture and fatigue resistance, and attempts to build a primary comprehensive link between mechanical performance and microstructure for the as built state. Following the analysis of the state of the art, the review will finally provide an outlook on additional efforts needed to quantify the microstructure-property relation, based on which maximizing the potential of mechanical performance through optimizing microstructure may be achieved.
34 citations
TL;DR: In this article , the effects of different contaminations on the acoustic spectrum of wire and arc additive manufacturing (WAAM) were analyzed using the time and frequency domain techniques, namely, Power Spectral Density, and Short Time Fourier Transform.
Abstract: Additive Manufacturing (AM) processes allow the creation of complex parts with near net shapes. Wire and arc additive manufacturing (WAAM) is an AM process that can produce large metallic components with low material waste and high production rates. Typically, WAAM enables over 10-times the volumetric deposition rates of powder-based AM processes. However, the high depositions rates of WAAM require high heat input to melt the large volume of material, which in turn results in potential flaws such as pores, cracks, distortion, loss of mechanical properties and low dimensional accuracy. Hence, for practical implementation of the WAAM process in an industrial environment it is necessary to ensure flaw-free production. Accordingly, to guarantee the production-level scalability of WAAM it is fundamental to monitor and detect flaw formation during the process. The objective of this work is to characterize the effects of different contaminations on the acoustic spectrum of WAAM and lay the foundations for a microphone-based acoustic sensing approach for monitoring the quality of WAAM-fabricated parts. To realize this objective, WAAM parts were processed with deliberately introduced flaws, such as material contamination, and the acoustic signals were analyzed using the time and frequency domain techniques, namely, Power Spectral Density, and Short Time Fourier Transform. The signatures obtained were used to pinpoint the location of flaw formation. The results obtained in this study show that the effects of contamination in WAAM can be identified through the analysis of the acoustic spectrum of the process. • Acoustic monitoring of the WAAM process is performed. • Defect detection using acoustic signal is validated with CT scans. • Acoustic monitoring is a expedite and low-cost solution for defect detection during WAAM.
31 citations
TL;DR: In this paper , an efficient conductive nerve guidance conduit with three-dimensional continuous conductive network structure was constructed by prior powder design and laser additive manufacturing, where MXene was coated on poly-L-lactic acid (PLLA) particle surface by ultrasonic-assisted solution mixing and thus MXene enriched at interfacial regions among adjacent polymer particles to form continuous MXene conductive networks.
Abstract: Nerve guidance conduits with favorable electrical conductivity were highly desired in peripheral nerve repair since nerve was natural electro-active tissue. MXene was an appealing candidate in endowing polymeric guidance conduits with electrical conductivity, yet its superiority was extremely constrained by its discrete distribution, incapable forming contiguous conduction channels in matrix. Herein, an efficient conductive nerve guidance conduit with three-dimensional continuous conductive network structure was constructed by prior powder design and laser additive manufacturing. Specifically, MXene was coated on poly-L-lactic acid (PLLA) particle surface by ultrasonic-assisted solution mixing and thus MXene was enriched at interfacial regions among adjacent polymer particles to form continuous MXene conductive network. More ingeniously, benefiting from the unique shearing-free and confined-flowing forming characteristic of laser additive manufacturing, not only network structure was retained as well as MXene contact became more tightly, which provided a continuous channel for rapid charge transfer. Results demonstrated that the conduits with 3.5 vol% MXene exhibited a continuous conductive network structure, resulting in an excellent electrical conductivity of 4.53 S/m, which was in appropriate conductive range of nerve growth (1–10 S/m). Cell evaluation confirmed the conduits significantly promoted cell proliferation, differential and neurite outgrowth. Therefore, this work not only illustrated the feasibility of additive manufacturing in constructing conduits with three-dimensional continuous conductive network structure, but also created a powerful strategy for fabricating desirable conductive nerve guidance conduits.
28 citations
TL;DR: In this article , a review of recent achievements in additive manufacturing of functional optics including lens, optoelectronics, photonics, and metamaterials is presented, which covers the design scenarios, material selection, 3D printing strategies, and property evaluation.
Abstract: Various kinds of optical devices have been designed for unique functionality based on a deeper understanding of optical principles. Recently, the research of functional optics has become a hot topic due to their wide usage in diverse fields. However, the structural complexity and multi-material distribution of advanced optical devices far exceed the fabrication capability of traditional manufacturing techniques, which inevitably hinders the further development of functional optics for various promising applications. As a revolutionary advanced manufacturing technology, additive manufacturing (AM) has demonstrated its potential to produce multi-material, multi-scale and multi-functional optical devices for excellent performance in imaging, sensing, displaying, and light modulating. Here, recent achievements in additive manufacturing of functional optics including lens, optoelectronics, photonics, and metamaterials were reviewed. The investigation covers the design scenarios, material selection, 3D printing strategies, and property evaluation. Current challenges, prospective research topics, and future promising applications of 3D printing of next-generation functional optics are discussed at the end.
27 citations
TL;DR: In this article , the state-of-the-art printing of soft magnetic, hard magnetic, and electrically conductive materials was investigated to evaluate the maturity of each material type for integration into electrical machine (EM) construction.
Abstract: Metal additive manufacturing (AM) technology is maturing. Although currently slower and less reliable than traditional production methods, AM systems shine when producing parts with unconventional topologies or in small quantities. Like countless other research communities, the electrical machine (EM) research community has shifted considerable efforts towards integrating AM systems into the EM production cycle to implement more powerful and efficient topology optimized (TO) next-generation EMs. In this paper, the state-of-the-art printing of soft magnetic, hard magnetic, and electrically conductive materials was investigated to evaluate the maturity of each material type for integration into EM construction. The highest maturity was identified for AM pure copper, showing characteristics equivalent to commercial high purity copper. In contrast, AM permanent magnets were the least mature: suffering from low power density and limited magnetization capacities. Printed soft magnetic steels were characterized as halfway in-between: on one side showing equivalent DC magnetic properties to conventional non-oriented steels, but on the other – suffering from high eddy current losses in AC applications. Based on the study's findings, it would appear that the emergence of additively manufactured EMs is only a matter of time. We predict a dramatic increase in the printing of prototype TO components within the next few years, focusing most likely on TO machine windings, heat exchangers, and synchronous rotors.
TL;DR: In this paper , a novel depositing strategy by periodically alternating processing parameters is designed to partially preserve the equiaxed grains resulted from the columnar-to-equiaxing transition at the top of each deposited layer and, at the same time, to interrupt the epitaxial growth of columnar grains in AM titanium alloy.
Abstract: In metal additive manufacturing (AM), long columnar grains along the building direction due to highly directional thermal gradients often lead to a strong texture and severe anisotropy in mechanical properties of the deposits, which significantly impair part qualification and targeted applications. Here, a novel depositing strategy by periodically alternating processing parameters is designed to partially preserve the equiaxed grains resulted from the columnar-to-equiaxed transition at the top of each deposited layer and, at the same time, to interrupt the epitaxial growth of columnar grains in AM titanium alloy. With the help of the competitive growth of the new grains and the potential coarsening effect during subsequent thermal-cycles, a microstructure of full equiaxed prior-β grains in Ti6Al4V fabricated by laser directed energy deposition (DED) is finally obtained without either using any auxiliary equipment or adjusting alloy chemistry like previous researches. This further contributes to a superior mechanical property and a remarkable reduction on both the crystallographic textures and the property anisotropy.
TL;DR: In this paper , a multi-material additive manufacturing with multiple shape memory effect extends the shape transformation to quintuple complex shapes with accurate and local controllability under selective multi-stimuli.
Abstract: 4D printing of shape memory polymers (SMPs) endows the 3D printed structures with tunable shape-changing behavior and functionalities that opens up new avenues towards intelligent devices. Multiple-SMPs, specially, could memorize more than two shapes that have greatly extended the performance of 4D printed structures. However, the actuation to trigger the shape change of 4D printed multiple-SMPs is usually by direct heating to different temperatures. It hasn’t brought the full superiority of the programmability of multiple-SMPs with distinct responsive regions that could be sequentially and selectively actuated by various stimuli. Besides, the functionality of multi-material based additive manufacturing is another area that has not been fully developed. Herein, 4D printing of poly (D,L-lactide-co-trimethylene carbonate) (PLMC)/poly (trimethylene carbonate) (PTMC)/Fe3O4 multi-material with multiple shape-changing capabilities under sequential stimuli of remotely magnetic field and heat was achieved. At first, we optimized the composition of pure SMP to fine tune the multiple shape memory effect and quantitatively characterized the shape recovery by stepwise heating. Then with the addition of Fe3O4 nanoparticles, the multi-material distribution of 4D printed structure consisting of multiple-SMP and its nanocomposites was designed. The integration of multi-material additive manufacturing with multiple shape memory effect extends the shape transformation to quintuple complex shapes with accurate and local controllability under selective multi-stimuli. The 4D printed multiple-SMP and its nanocomposites with simultaneously thermo- and magnetic- responsive shape-changing capability also demonstrated excellent biocompatibility. This work thus offers a feasible and robust approach for 4D printing of multi-functional devices for broad applications in entertainment, robotics, biomedical field and beyond.
TL;DR: In this paper , the authors provide an overview of recent and future developments in 3D printing and materials in the branch of microfluidics fabrications, showing that the selection of the right materials together with the design freedom afforded by 3D printers will be the cornerstone for micro-fluidic development.
Abstract: During the last two decades, 3D printing technology has emerged as a valid alternative for producing microfluidic devices. 3D printing introduces new strategies to obtain high precision microfluidic parts without complex tooling and equipment, making the production of microfluidic devices cheaper, faster, and easier than conventional fabrication methods such as soft lithography. Among the main 3D techniques used for this purpose, fused filament manufacturing (FFF), inkjet 3D printing (i3Dp) and vat polymerization (VP) are of the greatest interest since they are well-established techniques in the field and are cost-affordable both in equipment and material. However, there are still some barriers in terms of technology and materials to overtake for definitively establishing 3D printing as a truly microfluidic production method. For example, the level of resolution and precision of 3D printed microfluidic parts still does not reach the level of conventional fabrication techniques, and, from a materialistic point of view, few materials present the desired characteristics (e.g., biocompatibility, optical transparency, and mechanical properties) for target areas such as medicine, analytical chemistry, and pharmaceuticals. This review intends to evaluate and analyze the current state of polymeric 3D printing techniques and materials to manufacture microfluidic chips. The article will show and discuss the latest innovations, materials, and applications of such 3D printed microstructures. The focus of this review is to provide an overview of recent and future developments in 3D printing and materials in the branch of microfluidics fabrications, showing that the selection of the right materials together with the design freedom afforded by 3D printing will be the cornerstone for microfluidic development.
TL;DR: In this paper , the cracks in DED Hastelloy X were confirmed to be solidification cracking based on extensive observations of the inner crack surface and fracture surface, and the origins of the cracking were mainly attributed to thermal stress/strain level, grain boundary (GB) characteristics (GB misorientation and GB density), and micro-alloy elements.
Abstract: Metal additive manufacturing (AM) offers promising potential in the production of components with geometric complex or customized structure and outstanding properties, but severe defect like cracking remains a significant concern. The debate has long prevailed as to the mechanisms that lead to cracking in AM parts of some nickel-based superalloys like Hastelloy X. In this study, we investigated the underlying cracking mechanism of Hastelloy X fabricated via directed energy deposition (DED). The cracks in DED Hastelloy X were confirmed to be solidification cracking based on extensive observations of the inner crack surface and fracture surface. The origins of the solidification cracking were mainly attributed to thermal stress/strain level, grain boundary (GB) characteristics (GB misorientation and GB density), and micro-alloy elements. Our results showed that the plastic strain rate during the terminal stage of solidification is one of the most critical factors affecting cracking susceptibility when AM processing conditions change. We found that the fraction of S-HAGB (crack susceptible - high angle grain boundaries) is another critical factor in affecting cracking susceptibility. More than 75% of cracks occurred preferentially in the range of GB angles of 25°–45° (defined as S-HAGB) owing to its high GB energy rather than high GB misorientation angle. Besides, GB density could affect the cracking susceptibility by adjusting the thermal stress/strain level and S-HAGB fraction. Micro-segregation of C and Mo is a necessary condition for solidification cracking in DED Hastelloy X, which promotes the formation of low-melting liquid films. These new insights gained from this study could be used to instruct the preparation of crack-free metals and alloys during AM.
TL;DR: In this paper , ultrasonic frequency pulsed variable polarity TIG (TIG-TIG) arc heat source was employed to fabricate WAAM 2024 aluminum alloy thin-wall structures.
Abstract: Ultrasonic frequency pulsed variable polarity TIG and conventional variable polarity TIG arc heat source were employed to fabricate WAAM 2024 aluminum alloy thin-wall structures. Heat treatment procedure was conducted to process the components. The microstructure, porosity and mechanical properties were comparatively investigated to reveal the effects of ultrasonic frequency pulsed arc on the properties of WAAM aluminum alloys. With ultrasonic frequency pulsed arc, the grain was refined, and the porosity was significantly reduced. The micro hardness and its uniformity increased. Ultrasonic frequency pulsed arc can particularly increase the vertical tensile properties of heat-treated components and improve property isotropy. The refined grains and lower porosity in WAAM aluminum alloy structure with ultrasonic frequency pulsed arc were the reasons for property and isotropy improvement.
TL;DR: In this paper , a 3D X-ray micro-tomography technique was used to investigate the hot cracking behavior of 2195 Al-Li alloys fabricated by LPBF process.
Abstract: Al-Li alloys printed by laser powder bed fusion (LPBF) have huge potential for industrial application due to their remarkable advantages. However, the high hot cracking susceptibility (HCS) due to the addition of Li is still a key restraining factor for their rapid development towards such industrial application. Here in this report, hot cracking behaviour of 2195 Al-Li alloys fabricated by LPBF process was investigated by a three-dimensional (3D) X-ray micro-tomography technique. The relationship between the microstructural evolution and the high HCS was established to reveal the hot cracking mechanism for the first time. Observations by X-ray tomography showed large, interconnected cracks with a 3D reticular structure in the printed samples, extending layer by layer from the lamellar cracks in the previous single tracks along the building direction. Contributions to hot cracking were found to origin from the stable liquid film and the stress concentration. The segregation between the Al6CuLi3 and α-Al matrix contributed to the Al-Cu eutectics along the high-angle grain boundaries in form of intergranular liquid films. Furthermore, it was found that the interfacial layer (intradendritic liquid film) between the Al2Cu and the adjacent LiAlSi or AlCuMgAg exhibited the reduced micro-crack resistance in the interior of the grains. It was pointed out on the basis of the calculation that the higher stability of the intergranular liquid film led to a higher HCS at the grain boundaries as compared to that in the interior of the grains. Furthermore, high internal residual tensile stress provided the driving force for the crack initiation and propagation. In summary, this work contains a practical guide to optimize the powder composition and processing steps of high-quality Al-Li alloys produced by LPBF.
TL;DR: In this paper , a new type of tubular lattice architecture was designed by rolling up planar lattice structures with a negative Poisson's ratio, and then fabricated samples using a material jetting 3D printing technique.
Abstract: Tubular lattice structures have gained tremendous attention due to their lightweight and excellent mechanical properties. In this work, we designed a new type of tubular lattice architecture by rolling up planar lattice structures with a negative Poisson’s ratio, and then fabricated samples using a material jetting 3D printing technique. We investigated their bending behavior under large deformation using a combined experimental and numerical approach. It was found that the proposed auxetic tubular lattice (ATL) structure exhibits a more compliant behavior, and the ductility increased by up to 85.4% compared to that of a conventional diamond tubular lattice (DTL) structure. Meanwhile, the ATL structure is characterized by a local bending behavior due to the auxetic effect, while the DTL structure is featured with global bending mode. Finite element simulations further reveal that the stress on the ATL structure distributes locally around the indenter. In contrast, stress on the DTL structure distributes much more uniformly across the span. As such, the ATL structures exhibit excellent global stability compared to the DTL structure. Our parametric study shows that bending stiffness, maximum load, and ductility of the proposed ATL structure are mainly controlled by beam depth, due to its large exponential contribution to the moment of inertia. Increasing beam depth leads to a more desirable ductility than increasing beam thickness. The beam amplitude and tubular curvature have minor effects on the bending performance compared to other geometric parameters. The findings reported in this work can guide designing and optimizing mechanically robust tubular lattice metamaterials for applications in tissue engineering, biomedical devices, and robotics engineering.
TL;DR: In this paper , the productivity of 3D printed geopolymers has been analyzed from various perspectives of input variables and response measures, including rheological, physical and mechanical characteristics.
Abstract: The latest trends of sustainability have introduced environmentally friendly materials and green technologies in the construction sector. However, these materials and technologies are not fully adopted due to certain limitations in their practical applications. In this concern, extensive research has been conducted on the geopolymer materials and additive manufacturing technologies for construction sector in the last decade. The application of geopolymers in 3D printing was first introduced in 2016 which has provided a state of the art sustainable dimension to the construction industry. Reasonable investigations have been conducted in this direction in the recent few years. The focus of this study is to provide an in-depth analysis of the productivity of 3D printed geopolymers. The productivity of 3D printed geopolymers of the previous research is categorized into rheological, physical and mechanical characteristics. Effects of distinct variables including minerals, activators, reinforcement, printing and post-processing have been analyzed on the fresh and hardened properties. This review provides an extract for the productivity from the recent studies to present a complete picture from various perspectives of input variables and response measures. Based on the critical analysis and findings, this review study offers a future direction for the current research field to ensure the practical applications of 3D printed geopolymers in the construction industry.
TL;DR: In this article , a hybrid 3D printing and foaming process is developed, which involves simultaneous 3D print and foam-filling of closed-cell lattice structures on an open-source fused filament fabrication (FFF) 3D printer.
Abstract: This work studies the novel concept of multi-material additive manufacturing by filling closed-cell lattice structures with secondary material. Filling closed cells incorporate new functional properties that unfilled or open-cell lattice structures cannot otherwise achieve. Filled closed cells also prevent materials from escaping the cellular cavity that can prove advantageous while combining dissimilar materials. For this, a hybrid 3D printing and foaming process is developed, which involves simultaneous 3D printing and foam-filling of closed-cell lattice structures on an open-source fused filament fabrication (FFF) 3D printer. This hybrid system targets direct digital manufacturing (DDM) by combining two separate processes into a single process, eliminating post-process operations. Here, the global closed-cell sea-urchin (SU) lattice structure is 3D printed with thermoplastic polyurethane (TPU), and the secondary functional material filled in the lattice structures is polyurethane (PU) foam. The load vs. deformation responses of the composite of PU foam and TPU lattice structures has shown higher stiffness, energy dissipation, and damping characteristics which otherwise could not have been achieved by the lattice structure alone. Possible applications for these could be protective equipment, shoe midsoles, and other energy absorbing and damping devices.
TL;DR: In this article , high speed impacting tests are systematically conducted on a split Hopkinson pressure bar device to investigate the strain rate and temperature dependence of dynamic compressive properties of Ti-6Al-4 V (TC4) fabricated by selective laser melting (SLM).
Abstract: In this study, high speed impacting tests are systematically conducted on a split Hopkinson pressure bar device to investigate the strain rate and temperature dependence of dynamic compressive properties of Ti-6Al-4 V (TC4) fabricated by selective laser melting (SLM), the ranges of strain rate and temperature are 2000–6000/s and 25–650 ℃, respectively. The results reveal that the yield strength and ultimate compressive strength of the SLM-TC4 alloy increase with the increasing strain rate and the decreasing temperature, showing obvious strain rate and temperature sensitivities. The high speed impacting load intensifies the texture of the SLM-TC4 alloy significantly. Adiabatic shear band (ASB) is more likely to evolve at higher temperatures and strain rates, submicron equiaxed grains formed in the ASB and the surrounding area are mainly ascribed to the combination of dynamic recrystallization, deformation-induced twinning and transverse α-lath splitting. Within the ASB, grains with {0001} pole orientation are rotated by approximately 45° with respect to the shear direction, indicating that the recrystallized grains are able to reorient themselves to accommodate to the shear deformation. The findings in this work provide a theoretical basis to understand the deformation behavior and mechanism of SLM-TC4 alloy under impacting loads, thus is helpful to widen the application of SLM technique and products.
TL;DR: In this article , the main methods of GPs additive manufacturing based on material extrusion and powder-based printing processes are considered and their features, advantages, and limitations are scrutinized.
Abstract: This paper analyzes the current development of additive manufacturing (AM) technologies exploiting geopolymers (GPs) as promising green and sustainable 3D printable aluminosilicate inorganic materials. Material design and processing strategies to achieve or enhance three-dimensional printability of various geopolymer systems are summarized. The main methods of GPs additive manufacturing based on material extrusion and powder-based printing processes are considered. Their features, advantages, and limitations are scrutinized. There is presented a brief description and a principle of operation of the varieties of 3D printers, with whose help these fabrication approaches are implemented. Fresh and hardened state properties of 3D printed GPs are discussed in detail from the point of view of chemical reactions and structural transformations occurring in the material. The areas and specific examples of the application of advanced printable geopolymer materials and products are surveyed. The main current challenges, perspectives and directions of future work required to improve this technology have been delineated.
TL;DR: In this paper , a novel high strength Zr/Sc/Hf-modified Al-Mn-Mg alloy with a good L-PBF processability is investigated, which exhibits a heterogeneous microstructure featuring a bi-modal grain structure with coarse columnar and fine equiaxed grains and heterogeneously distributed nanometer and submicrometer-sized cuboid-shaped primary Al3(Sc,Zr,Hf) particles.
Abstract: Laser Powder Bed Fusion (L-PBF) provides great advantages in creating supersaturated solid solutions due to its intrinsic ultrafast cooling and high solidification rate, which is particularly desired for enhanced solid solution strengthening and precipitation strengthening. In the present work, a novel high strength Zr/Sc/Hf-modified Al-Mn-Mg alloy with a good L-PBF processability is investigated. The as-built alloy exhibits a heterogeneous microstructure featuring a bi-modal grain structure with coarse columnar and fine equiaxed grains and heterogeneously distributed nanometer and submicrometer-sized cuboid-shaped primary Al3(Sc,Zr,Hf) particles. The Al3(Sc,Zr,Hf) phase, exhibiting a homogeneous elemental distribution of Zr, Sc, and Hf, adopts a cubic L12 structure with a lattice parameter of 0.4044 ± 0.009 nm, showing a good coherency with α-Al. Additionally, the rapid L-PBF solidification enables the formation of submicrometer-sized elongated and globular primary Al6Mn and a supersaturated Al matrix with a high dislocation density. This results in a good combination of strength (yield strength of 438 ± 3 MPa and ultimate tensile strength of 504 ± 2 MPa) and ductility (elongation at fracture of 10.9 ± 1.4 %), with a moderate work hardening strength of 113 ± 12 MPa. Direct-ageing at 325 °C for 10 h promotes the formation of a large amount of rod-shaped Al6Mn precipitates and a few spherical Al3(Sc,Zr,Hf) nanoprecipitates. The heat treatment increases the hardness from 166 ± 2 HV in as-built condition to 173 ± 4 HV and enhances the tensile strength (yield strength of 487 ± 2 MPa and ultimate tensile strength of 542 ± 3 MPa) but slightly reduces the ductility to 7.4 ± 0.7 %. The high strength was achieved by the synergistic effect of grain boundary strengthening, solid solution strengthening, and Orowan strengthening mechanisms.
TL;DR: In this article , a global continuous toolpath optimization for both solid and partial infill designs in large format additive manufacturing (LFAM) is presented, where outward contour and double offset schemes are used to generate smooth curves as the primary volume-filling paths; the remaining unfilled areas are covered by extending zigzag lines from the closest contours.
Abstract: Large format additive manufacturing (LFAM) has witnessed rapid development in recent years and facilitated digital fabrications of geometrically intricate structures. However, there has been limited research on toolpath optimization tailored for LFAM. This paper presents a novel framework to generate a globally continuous toolpath for both solid and partial infill designs in LFAM. For solid infill, outward contour and double offset schemes are used to generate smooth curves as the primary volume-filling paths; the remaining unfilled areas are covered by extending zigzag lines from the closest contours. Subsequently, a contour layer-wise connection is carried out based on the depth-first-search algorithm to formulate a globally continuous path. A post-processing step is also presented to optimize the coverage and curvature of the toolpath design. The concept is extended for partial infill settings by trimming and joining rectangular grid lines. Compared with other state-of-the-art methods in the literature, the proposed algorithm is superior in delivering better print quality, fewer sharp turns, and enhanced fabrication efficiency. Finally, two interesting experiments demonstrate how LFAM of topology optimized structures can benefit from the proposed continuous toolpath: topology optimized table printed from thermoplastic polyurethane (TPU) and topology optimized chair printed from 3D concrete printing (3DCP).
TL;DR: In this paper , a large number of recent publications presented tensile property improvements of fused filament fabrication (FFF) printed parts in longitudinal and transverse directions covering material development, post-treatment, and process modification.
Abstract: Fused Filament Fabrication (FFF) is a rapidly growing and widely used 3D printing process with many practical applications thanks to its superior advantages such as ease of handling, cost-efficiency, and ability to fabricate complex structures with reduced waste and shorter production time. However, the mechanical property deficiency and related anisotropy with respect to build direction of FFF printed parts is still one of the most crucial challenges due to inherent process limitations and material properties, resulting in internal defects in printed structures. This review article offers researchers and users in the FFF community guidance to evaluate and determine impactful methods for manufacturing polymer printed parts with required mechanical strength for a wide range of end-use applications. The paper categorizes, evaluates, and compares a large number of recent publications presenting tensile property improvements of FFF printed parts in longitudinal and transverse directions covering material development, post-treatment, and process modification. Moreover, reported tensile test results are normalised via a calculated improvement efficiency index, and fundamental mechanisms responsible for strength improvements are highlighted. The advantages of and remaining concerns for the respective approaches are then discussed and compared via their respective improvement efficiency indices, thereby highlighting the impact of the proposed evaluation approach. • Process improvement approaches were categorized, compared, and evaluated to improve tensile performance in both longitudinal and transverse directions of FFF printed parts, covering material development, post-treatment, and process modification. • The respective fundamental mechanisms for strength improvements of each process improvement category were described comprehensively. • Tensile test results are normalised via a calculated improvement efficiency index to evaluate the efficiency of different process improvement approaches. • Guidance was provided to researchers and users to evaluate and determine impactful methods for manufacturing FFF printed parts with high mechanical strength requirements.
TL;DR: In this paper , the additive manufacturing (AM) technique is used to condense the problem associated with the manufacturing of complex body parts with near-net shape dimensions using magnesium material.
Abstract: Materials like, stainless steel, titanium, magnesium-based alloys, cobalt-based alloys are used as suitable materials for biomedical implants. Magnesium and its alloys are highly used as a suitable metal for the present-day biomedical implants because of its increased ability to get mixed in the human bodily fluids, eliminating the shortcomings like stress shielding effect, metal toxicity over a certain period of utilization, second surgery caused by other metal implants. The bioabsorbable and bioresorbable properties, mechanical strength, excellent osteogenic properties, degradation, and dissolving property of the magnesium alloys are the unique characteristics that make it a suitable choice for bio-degradable bone replacements. Fabrication of complex geometry implants through conventional manufacturing techniques stands challenging. The introduction of the additive manufacturing (AM) technique condenses the problem associated with the manufacturing of complex body parts with near-net shape dimensions using magnesium material. Manufacturing of such bio-medical components with comprehensive improved properties related to microstructure, mechanical property, design constraint through AM process requires a detailed and thorough understanding of the process and material. The current review article highlights the above said particulars and issues related to AM of Magnesium components. Various AM procedures involved in the Mg bio-implant fabrication, mechanical and metallurgical property improvement, and various challenges involved in handling Mg powders are discussed. Lastly, the opportunities and future scope of the AM process of Mg implants are highlighted.
TL;DR: In this paper , a bi-directional evolutionary structural optimization (BESO) framework was proposed to solve the manufacturing constraints of 3D concrete printing (3DCP) and topology optimization.
Abstract: The integration between 3D concrete printing (3DCP) and topology optimization (TO) enables the fabrication of structurally efficient components without expensive formwork and intensive labor. However, manufacturing constraints of 3DCP are impeding the integration between the two fields, and there has been limited research on this topic. In this paper, we address various manufacturing constraints of 3DCP within the bi-directional evolutionary structural optimization (BESO) framework. Firstly, a layer-wise sensitivity scheme is proposed to generate self-supporting designs in the user-defined print direction. Secondly, a novel continuous extrusion constraint is implemented to facilitate the continuous printing operation of the design. Thirdly, the anisotropy of the 3DCP process is simulated during optimization by employing a transverse isotropic material model. Fourthly, domain segmentation is introduced to facilitate modular construction, and each partitioned segment can be assigned with its favorable print direction. Finally, the algorithm's feasibility is demonstrated by constructing a topology optimized chair.
TL;DR: In this paper , powder injection molding (PIM) binder compositions for the material extrusion (MEX) additive manufacturing of zirconia parts were evaluated in a ring-on-ring setup.
Abstract: The aim of this study is the evaluation of powder injection molding (PIM) binder compositions for the material extrusion (MEX) additive manufacturing of zirconia parts. Four commercial PIM binder compositions were selected and mixed with 45 vol% of yttria-stabilized zirconia powder. Due to the brittle characteristic of the obtained ceramic feedstocks, a screw based pellet printing head was used for printing dense zirconia structures. To compare 3D printing performance, additionally a commercially available zirconia filament was used in this study. Application of PIM binder compositions was limited either due to phase separation during processing, poor printing performance or delamination during solvent debinding. Only one of the PIM based feedstock compositions could be successfully printed, debound and sintered. A ring-on-ring setup was used to investigate the equibiaxial flexural strength after sintering for both pellet and filament printed disks. For benchmarking, cold isostatic pressed (CIP) ceramic discs were fabricated by commercial, ready-to-press, zirconia powder. The ring-on-ring results showed a low Weibull modulus (3