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3d food printing, extrusion, food waste, sustainability, dysphagia, hydrocolloids, Science, Manufactures, and TS1-2301

Food waste utilisation and zero waste approach are among the many ways of building a sustainable economy. Food waste as authentic edible food being accepted by the consumers still has many barriers to overcome. One tool to help in the valorisation of food waste to value-added products is three-dimensional food printing (3DFP). These products can lead to easier and greater acceptance of food waste by consumers, having familiar nature with respect to taste, texture and appearance as other consumables. In the present study, food ink recipes were formulated from spinach stems and kale stalks, the common green leafy vegetable wastes. These spinach and kale inks were then characterised on their rheological properties of shear thinning and yield stress. The inks were subjected to IDDSI tests meant for standardisation of soft foods for dysphagia patients. This paper demonstrates ways of converting vegetable wastes into edible diets that are aesthetically pleasing through 3DFP.

3d printing, additive manufacturing, cooperative robots, mobile robots, teams of robots, cooperative printing, Science, Manufactures, and TS1-2301

Additive manufacturing (AM) is a key enabler and technological pillar of the fourth industrial revolution (Industry 4.0) as it increases productivity and improves resource efficiency. However, current AM systems present some limitations in terms of fabrication time, versatility, and efficiency. The concept of teams of robots represents a novel approach for AM aiming to address these limitations. This review paper discusses the current state-of-the-art of the use of cooperative AM systems based on gantry systems, robotic arms, and mobile robots. The information flow, path planning and slicing strategies are discussed in detail, and several examples of the use of cooperative AM systems are provided. Finally, major research challenges and future perspectives are discussed.

miniaturisation, compliant mechanisms, customization, design automation, design synthesis, Science, Manufactures, and TS1-2301

Micro-additive manufacturing techniques have the potential to meet the demand for miniaturised functional components for minimally invasive surgical instruments. These techniques create monolithic, compliant mechanisms with micro-sized free-form structures that can be tailored to patient-specific surgical procedures. The automated design synthesis of the mechanisms using building blocks results in structures that are shape-programmable. This is achieved through an algorithmic-based computational workflow, which automatically converts user-specified 2D and 3D curves into discrete curve segments. The actuated motion of the mechanisms can be designed to move in a specific way, both forwardly and inversely. The mechanisms are manufactured using micro-laser powder bed fusion and hardenable stainless steel 17-4 PH. By carefully selecting the process parameters, it is possible to 3D-print micro-sized features such as a compliant beam thickness of 80 μm and an actuation hole of 100 μm. Both 2D planar curved mechanisms and 3D spatial curved mechanisms have been implemented and experimentally validated.

laser powder bed fusion, 3d-printing, automation, compliant mechanisms, design synthesis, design freedom, Science, Manufactures, and TS1-2301

Additive manufacturing (AM) facilitates the fabrication of compliant mechanisms through its free-form and design customisation capabilities. Specifically, the properties of kinetic mechanisms such as springs can be extended with regards to their inherent (non-)linear stiffness functions. This allows for the customisation of AM springs according to user preferences. By combining the design synthesis approach of building blocks with the structural optimisation approach for AM, it is possible to define and customise spring stiffness functionalities. The optimisation process employs an automated computational framework based on a genetic algorithm scheme, which has been demonstrated through randomised and reference case studies. This framework enables the attainment of linear, progressive (stiffening), and degressive (softening) stiffness curves. The manufacturability of the springs has been validated through laser powder bed fusion using stainless-steel material 17–4 PH (H900). The springs have resulted in an accuracy error of maximum 6.48% and precision error of maximum 5% through compression testing.

bainitic crossing nose, functionally graded material (fmg), laser directed energy deposition (l-ded), microstructure, wear and rolling contact fatigue (rcf) resistance, Science, Manufactures, and TS1-2301

In this paper, 20Mn2SiCrMo bainitic crossing noses were repaired by depositing 420SS, Stellite 6, 17-4PH and 18Ni300 alloys on the rail surfaces to form functionally graded materials (FGM) using laser directed energy deposition (L-DED) technology. As a result, only 18Ni300 deposit achieves an excellent strength-toughness combination, which possesses a yield strength of ∼1120 MPa together with an impact energy of ∼85.05 J, better than those of substrates (∼1071 MPa, ∼71.34 J). Besides, the wear and rolling contact fatigue (RCF) resistance of 20Mn2SiCrMo/18Ni300 FGM is enhanced to 2.7 and 23.6 times as much as those of substrates. Massive ultrafine nanoprecipitates and a small amount of austenite make 18Ni300 deposit strong enough as well as a certain work-hardenability, ensuring good wear resistance therein; the significant RCF resistance originates from the improved shakedown limit. Therefore, all findings reveal that 18Ni300 is the most promising depositing material for repairing bainitic crossing noses by L-DED.

additive manufacturing, sensor data fusion, thermal imaging, spatter monitoring, shape agnostic monitoring, porosity, Science, Manufactures, and TS1-2301

We developed and applied a novel approach for shape agnostic detection of multiscale flaws in laser powder bed fusion (LPBF) additive manufacturing using heterogenous in-situ sensor data. Flaws in LPBF range from porosity at the micro-scale (< 100 µm), layer related inconsistencies at the meso-scale (100 µm to 1 mm) and geometry-related flaws at the macroscale (> 1 mm). Existing data-driven models are primarily focused on detecting a specific type of LPBF flaw using signals from one type of sensor. Such approaches, which are trained on data from simple cuboid and cylindrical-shaped coupons, have met limited success when used for detecting multiscale flaws in complex LPBF parts. The objective of this work is to develop a heterogenous sensor data fusion approach capable of detecting multiscale flaws across different LPBF part geometries and build conditions. Accordingly, data from an infrared camera, spatter imaging camera, and optical powder bed imaging camera were acquired across separate builds with differing part geometries and orientations (Inconel 718). Spectral graph-based process signatures were extracted from this heterogeneous thermo-optical sensor data and used as inputs to simple machine learning models. The approach detected porosity, layer-level distortion, and geometry-related flaws with statistical fidelity exceeding 93% (F-score).

negative poisson’s ratio, triply periodic minimal surfaces, auxetic structure, bone implant, hip joint, Science, Manufactures, and TS1-2301

Based on the triply periodic minimal surface (TPMS), 3D auxetic structures are successfully implemented using a dual-period function. A series of shape-controllable, dual-period deformation functions are obtained by summarising the characteristics of periodic deformation functions and applying Bezier curve fitting methods. Then, with the geometry originating from the Schwarz primitive (P) of TPMS, the periodic shape transformation of TPMS is achieved using the dual-period deformation functions. The property (negative Poisson’s ratio) of the auxetic structure is investigated based on the control parameters (the TPMS c value, periodic function η, and deformation index γ). The auxetic structures can exhibit excellent 3D negative Poisson’s ratio properties, and the Poisson’s ratio can be effectively adjusted. Moreover, a heterostructure with positive and negative Poisson’s ratio structures is obtained and applied to a stem in the hip joint. The simulation proves that the heterostructure can effectively prevent the failure of the bone implant.

terahertz, metamaterials, 3d printing, mortise and tenon structures, reconfigurable multi-functional, Science, Manufactures, and TS1-2301

The emergence of metamaterial has provided an unprecedented ability to manipulate electromagnetic waves, especially in the terahertz band where there is a lack of natural response materials. However, most metamaterials are fixed single function due to the fixed structure at the beginning of design. The paper reports a reconfigurable multi-functional terahertz metamaterial with variable structures based on mortise and tenon mechanism. And a hybrid 3D printing method based on FDM and E-jet is proposed to fabricate the metamaterials, which simplifies the processing process, improves the speed, and reduces the cost compared to traditional semiconductor processing methods. Through flexible mortise and tenon connections, the metamaterial can achieve: (1) narrowband transmission and broadband absorption; (2) perfect reflection; (3) narrowband reflection and broadband absorption. Relying on ingenious design and processing, the multi-functional metamaterials are expected to be widely used in fields such as electromagnetic shielding, radar stealth, communication and so on.

design workflow, scaffolds, patient-specific, 3d printing, generative design, voronoi, scaffold-guided bone regeneration, Science, Manufactures, and TS1-2301

A streamlined design workflow that facilitates the efficient design and manufacture of patient-specific scaffolds independently applied by the surgical team has been recognised as a key step in a holistic approach towards the envisioned routine clinical translation of scaffold-guided bone regeneration (SGBR). A modular design workflow was developed to semi-automatically fill defect cavities, ensure patient specificity and ideal surgical scaffold insertion for a given surgical approach, add fixation points to secure the scaffolds to the host bone and generate scaffold based on Voronoi, periodic lattice and triply periodic minimal surface pore architectures. The adopted functional representation modelling technique produces models free from 3D printing mesh errors. It was applied to a clinical case of a complicated femoral bone defect. All models were free from mesh errors and the patient-specific fit and unobstructive insertion were validated via digital inspection and physical investigation by way of 3D printed prototypes. The real-time responsiveness of the workflow to user input allows the designer to receive real-time feedback from the surgeon, which is associated with reducing the time to finalise a patient-specific scaffold design. In summary, an efficient workflow was developed that substantially facilitates routine clinical implementation of SGBR through its ability to streamline the design of 3D printed scaffolds.

zirconium alloy, zr-4, additive manufacturing, laser powder bed fusion, annealing, Science, Manufactures, and TS1-2301

Zirconium (Zr) alloys are widely used in nuclear energy because of their excellent mechanical properties and low thermal neutron absorption cross-section. This work investigated the printability, microstructure, and mechanical properties of Zr-4 alloy additively manufactured by laser powder bed fusion (LPBF) for the first time. The effect of annealing temperature on the microstructural and the mechanical property evolution of the printed Zr-4 alloy was studied. The results exhibited that the Zr-4 alloy with a high relative density of 99.77% was obtained using optimised printing parameters. With an increase in the annealing temperature, the formed α phase of the Zr-4 alloy changed from an acicular shape to a coarse-twisted shape, and finally to an equiaxed shape. Such microstructure change endowed the alloy with a high compressive strength of 2130 MPa and compressive strain of 36%. When the annealing temperature exceeded 700°C, Zrx(Fe2Cr) compounds were precipitated, strengthening the alloy by pinning effect. These findings provide valuable guidance for the manufacture of geometrically complex Zr alloy parts for nuclear power applications.

wire and arc additive manufacturing (waam), recursive bead profile, multi-bead overlapping model, axisymmetric drop shape analysis (adsa), surface topography, Science, Manufactures, and TS1-2301

Dimension prediction of robotic wire and arc additive manufacturing (WAAM) part is fundamentally dependent on the modelling accuracy of single-bead profile and its subsequent overlapping ones. Current multi-bead overlapping models are still not capable of describing the flatten valley area of WAAM parts. This paper proposes a new recursive model, based on coordinate transformation and axisymmetric drop shape analysis (ADSA), to predict multi-bead overlapping profiles. First, a single-bead profile model for WAAM is established based on ADSA, followed by detailed description of conventional and proposed modified recursive ADSA profile model. The properties of developed recursive ADSA model are then investigated to reveal the effects of overlapping ratio and single-bead aspect ratio. Finally, multi-bead overlapping deposition experiment is carried out to validate the model feasibility. The results show that the modified recursive ADSA model is more accurate than the conventional one for its better accountability of valley areas. It is also indicated that the modified recursive ADSA model is suitable for the robotic WAAM process. The research outcome is beneficial to improving the forming accuracy of WAAM parts and geometry prediction of other additive manufactured products.

al-sc alloys, heat treatment, laser powder bed fusion (lpbf), strengthening mechanism, Science, Manufactures, and TS1-2301

According to the material nature, aluminium alloys are widely applied in aerospace, construction and automotive applications due to their characteristics, such as lightweight, good formability and good corrosion resistance. Among the aluminium alloys, scalmalloy (Al-4.49Mg-0.71Sc-0.51Mn-0.27Zr-0.07Fe-0.03Si alloy) was developed to overcome the hot crack issue during the laser powder bed fusion (LPBF) process. Hence, the degree of lightweight can be further improved by introducing this high-specific strength material with a structure of the lightweight design. However, the strengthening mechanism of the heat-treated 3D printed scalmalloy has not been sufficiently explored. In this study, the synergistic effect of the strengthening mechanisms is explored through detailed microstructure analysis. The grain size, size and spacing of the precipitate and coherent phase contribute to the strengthening of scalmalloy. Through the observation of the microstructure feature, the theoretical strength of the heat-treated 3D printed scalmalloy can thus be calculated by three strengthening mechanisms and match the experimental results perfectly.

mechanical alloying, selective laser melting, amorphous/crystalline, zn60zr40 alloys, mechanical properties, Science, Manufactures, and TS1-2301

In the present study, mechanical alloying (MA) was employed for synthesising non-equilibrium Zn60Zr40 amorphous powders, and then consolidated into amorphous/crystalline Zn60Zr40 alloys using selective laser melting (SLM). The results showed that the MA process destabilised the atomic periodicity of Zn and Zr powders and induced crystalline-to-amorphous transformation due to atomic size mismatch and negative heat of mixing. Moreover, the amorphisation trend of as-milled powders was intensified with increasing milling time and attained almost fully amorphous structure after 30 h of milling. During SLM, the ultra-high cooling rate restricted the long-range atomic diffusion of the amorphous powders and enabled successful survival of amorphous phase, leading to amorphous/crystalline Zn60Zr40 alloys. The alloys exhibited a maximum compressive yield strength and microhardness of 160.9 ± 9.1 MPa and 3.73 ± 0.8 GPa, respectively. These findings demonstrated that the developed MA-SLM process might be a promising strategy for the preparation of amorphous/crystalline alloys with superior properties.

invar 36 alloy, laser powder bed fusion, high cycle fatigue, microstructures, defects, Science, Manufactures, and TS1-2301

The Invar 36 alloy was additively manufactured by laser powder bed fusion (PBF-LB), and systematical observations and experiments for microstructure, defects, metallography, especially high cycle fatigue behaviour and fractography were conducted. Inadequate laser energy density results in hardly overlapping melting traces, generating numerous defects. Accordingly, the fabricated Invar 36 alloy presents an inferior high cycle fatigue life, as it failures from the rapid aggregation of the defects. In contrast, an adequate laser energy density remarkably enlarges the overlapping between adjacent melting traces. The large molten pools with steady boundaries are beneficially to generate favourable microstructures and low porosity. Consequently, the Invar 36 alloy shows superior high cycle fatigue life, completely generated from small crack propagation, long crack propagation and final fracture stages. Above experimental results and analysis primarily link up the PBF-LB process, microstructures (defects) and high cycle fatigue performance for PBF-LB Invar 36 alloy.

4d printing, additive manufacturing, energy absorption, shape memory materials, recoverability, crashworthiness performance, Science, Manufactures, and TS1-2301

The emergence of 4D printing from additive manufacturing has opened new frontiers in crashworthiness application. Energy-absorbing structures with fixed geometrical shapes and irreversible deformation stages can be programmed such that after mild or extreme deformation, their initial shapes, properties and functionalities can be recovered with time when actuated by external stimuli. This survey delves into the recently-accelerated progress of shape memory/recovery energy-absorbing metamaterials (EAMM) and energy-absorbing smart/intelligent structures (EASS). First, the introduction gives some fundamental concepts of metamaterials and their application to energy-absorbing structures. Next, some common 3D printing technologies that have led to 4D printed EAMM and EASS are succinctly described. Shape memory materials, their functional properties and recovery process, are then discussed. Finally, various recoverable/reversible energy absorbers with their future challenges and perspectives, are presented. With well-tailored 4D printed EAMM and EASS, reusability with minimal maintenance and higher energy absorption capacity can be retained.

laser powder bed fusion, overhang, downskin, high-speed thermal imaging, homography, parameter optimization, Science, Manufactures, and TS1-2301

One of the most revolutionary aspects of Laser Powder Bed Fusion (LPBF) is to be able to lift the design constraints from conventional manufacturing. However, as a rule of thumb, any surfaces lower than 45° with respect to the horizontal plane would still require sacrificial supports in order to complete the printing. Fundamentally, it is unclear whether it is feasible to print a 1st layer 0° overhang nor how the print parameters for the 1st layer can be optimised. This research demonstrates that large 1st layer 0° overhangs can be printed with a coverage above 90%. For the first time, the parameter space of laser power, scan speed and hatch spacing for the 1st layer has been simultaneously explored efficiently. The use of the rate of change of the mushy zone is proposed for the parameter selection instead of the average melt pool temperature. Adaptive Parameter 28 (AP28: 250W_4000 mm/s_50 µm) is the best choice. Several surface morphological phenomena are discussed. The core parameter (285W_960 mm/s_110 µm) causes severe balling and its mechanism is revealed. The average melt pool temperature of the 1st layer by the core parameter is lower than that of the bulk. The ramifications beyond the 1st layer are also illustrated.

hybrid rocket engine, additive manufacturing/three-dimensional printing, breathable blade, composite fuel grain, mechanical and combustion properties, porous structure, Science, Manufactures, and TS1-2301

Hybrid rocket engines suffer from the restricted mechanical properties and low regression rates of current polymeric fuel grains. We propose a three-dimensional printed aluminium (Al) nested composite fuel grain with millimetre-scale lattice pores (referred to as Al-L). In this study, breathable Al blades with micrometer-scale interconnected pores (Al-B) and blades combining millimetre-scale and micrometer-scale pores (Al-B&L) are designed. The formation mechanisms, characteristics, and effects of the breathable blades are analysed in simulations, micro-computed tomography, and cyclic compression tests. The mechanical properties of the composite fuel grains are investigated numerically and in compression tests. Al-B has the highest Young’s modulus at more than 15 times that of a paraffin-based fuel grain and Al-B&L has the highest yield stress at 4 times that of the paraffin-based fuel grain. Referring to combustion properties, the regression rates of the Al-B and Al-B&L grains are respectively 63.3% and 58.2% greater than the regression rate of the paraffin-based fuel grain.

wire arc additive manufacturing, mg-gd-y-zr alloy, heat treatment, microstructure evolution, mechanical properties, Science, Manufactures, and TS1-2301

A detailed and systematic investigation on the effect post heat treatment has on the microstructure evolution and the resultant mechanical properties of the wire arc additive manufacturing processed Mg-5.9Gd-2.8Y-0.7Zr alloy is conducted in this work. The microstructure of the as-built sample is composed mainly of fine equiaxed α-Mg grain and Mg24(Gd, Y)5 phase. The solution heat treatment (400°C × 1 h) has relatively little effect on grain size, but it can effectively reduce the content of the Mg24(Gd, Y)5 phase, which leads to a significantly improved elongation with slightly decreased strength. Further ageing heat treatment at 200°C induces prismatic βʹ precipitates formation and does not influence other phases and grain size. The samples directly following the peak ageing heat treatment process demonstrate the best tensile properties with yield strength of 227 ± 9 MPa, ultimate tensile strength of 350 ± 4 MPa and elongation of 5.5 ± 0.6%.

multi-photon photopolymerisation, laser direct writing, order of absorption, tunable wavelength, group delay dispersion, resolution bridges, Science, Manufactures, and TS1-2301

Multiphoton photopolymerisation (MPP), also known as 3D nanoprinting, was studied using a wavelength-tunable femtosecond laser. The possibility of using any colour of the spectrum from 500 to 1200 nm with a fixed pulse width of 100 fs revealed an interplay of photophysical mechanisms more delicate than just two-photon photopolymerisation. An effective order of absorption, i.e. the X-photon absorption, as well as optimal exposure conditions were assessed for photosensitised and pure SZ2080$^{{\rm TM}}$ pre-polymer. The tunability of wavelength greatly influenced the dynamic fabrication window (DFW), optimised conditions resulting in a 10-fold increase. Furthermore, a non-trivial energy deposition by X-photon absorption was noted with an onset of a strong lateral size increase at longer wavelengths and can be understood as due to reaching epsilon-near-zero conditions. Such a control over the voxel aspect ratio and, consequently, the photopolymerised volume, may boost 3D nanoprinting efficiency. Overall, the results reveal wavelength being an important degree of freedom to tailor the MPP process and, if optimised, benefiting broad applications in areas of micro-optics, nanophotonic devices, metamaterials and tissue engineering.

additive manufacturing, cellular materials, lattice structures, metamaterials, fused filament fabrication, Science, Manufactures, and TS1-2301

One of the areas that have benefited the most from the advent of additive manufacturing is the development of customized cellular materials, scaffolds and lattices. Although these different groups of materials are typically considered separately, they can be categorized as mechanical metamaterials. Among the different additive manufacturing techniques, perhaps the most popular is that of Fused Filament Fabrication. Numerous works have been reported in the literature in which this fabrication technique has been used to produce such materials. Inspired by the increasing volume of work dealing with the subject, we present a review of the manufacturing and characterization of cellular and lattice-based mechanical metamaterials using Fused Filament Fabrication. An overview of the topologies, their effective mechanical properties and intrinsic manufacturing aspects are presented. The methods for failure analysis at different scales are also discussed. Finally, studies comparing the production of mechanical metamaterials using Fused Filament Fabrication and other additive manufacturing techniques are presented, in addition to recommendations and current trends in the production of these structures by Fused Filament Fabrication.

cationic photoinitiators, photopolymerisation, photopolymerisation kinetics, 3d printing, photo-cured composites, photoinitiating systems, Science, Manufactures, and TS1-2301

In this article, the application of 10 new amino-m-terphenyls in 3D-VAT printing was described. New compounds have specially designed D-π-A structure, where the central phenyl ring with nitrile and amino groups is the acceptor and the modifiable amino group is donor. Such design eliminates problem with acid scavenging and guaranteed desire properties and photoactivity as well as it allows further development of such system for 3D-VAT printing. Efficient excitation with intramolecular charge transfer provides excellent absorption and electrochemical properties, which can be tuned by modification of the amino group. The design allows photoinitiation of free radical, hybrid and especially cationic polymerisation even at 455 nm with more than 70% of monomer conversion. Such properties allow to use the developed compounds as efficient visible light photoinitiators for 3D printing of nanocomposite materials. The terphenyls can efficiently cure resins containing CuO and Al2O3 nano additives leading to high-resolution 3D prints.

titanium, β-tricalcium phosphate, direct ink writing, composite porous scaffold, Science, Manufactures, and TS1-2301

A Ti/β-TCP composite porous scaffold with a hierarchical pore structure composed of 3D printed interconnected macroscopic pores and sintered microscopic pores was prepared by direct ink writing (DIW) 3D printing technology. This method can control the extrusion of composite ink at room temperature and produce a 3D scaffold using layer-by-layer deposition. We studied the effects of the β-TCP powder particle size, β-TCP/Ti powder ratio and solid loading on the rheological properties of the ink and optimised the DIW printing process parameters. After sintering, the compressive strength and elastic modulus of the composite scaffold reached 45 MPa and 1 GPa, which is close to the strength of human cancellous bone. The cell culture experiment confirmed that the composite scaffold had better biological properties than the pure titanium scaffold. The composite scaffold has satisfactory mechanical and biological properties, meeting the requirements for orthopaedic implants.

robotic system, grid-stiffened shell structure, continuous fibre-reinforced polymer additive manufacturing, surface conformal toolpath, Science, Manufactures, and TS1-2301

The advents in continuous fibre-reinforced polymer additive manufacturing (CFRP-AM) present unprecedented opportunities for the rapid development of next-generation high-performance composites with selectively and spatially distributed reinforcement. However, the widely adopted 3-degree-of-freedom motion configuration in current CFRP-AM systems hinders the exploration of composite structures with non-planar fibre layouts. This work presents a novel conformal CFRP-AM system to fabricate grid-stiffened shell structures leveraging its multi-DoF motion to pattern spatial features. The system integrates a 6-axis robot with an optimally designed co-extrusion module and operates through a design-to-manufacturing workflow. The proposed workflow includes three steps: system calibration, conformal toolpath generation, and process implementation. The conformal toolpath generation is a surface-mapping-based method that allows a simultaneous exploration of various geometric designs and their toolpaths. Experimental comparisons were made between parts fabricated by different processes, i.e., planar and conformal based, with different toolpaths, i.e., shells filled with zigzag and arc-offset patterns, and with various geometric designs, i.e., stiffener ribs with different crossline angles. The results manifest that the proposed system can significantly improve the compression strength and stiffness of grid-stiffened shell structures. Meanwhile, the additional design freedom on process and structure opens up a new possibility to customise their mechanical performance.

vat photopolymerization (vpp), superamphiphobic interface, rapid moulding, Science, Manufactures, and TS1-2301

Vat photopolymerization (VPP) is one of the convenient methods to create high-precision parts; however, due to the significant adhesion between the cured layer of the photopolymer resin and the release film, the currently prevalent VPP equipment is less productive and thus challenging in achieving production on a large scale. To tackle the issues above, a facile method is utilised to produce a transparent film capable of effectively resisting the photopolymer resin. Such film is achieved by incorporating micron-nanometre layered rough features and low surface energy materials onto the surface of quartz glass. It allows innovative applications in speedy VPP processes, achieving a printing speed of up to 323 mm/h in an LCD (Liquid Crystal Display) 3D printer while maintaining sound accuracy, exceptional durability and fair applicability, thanks to the features of the prepared film. The presented approach provides new perspectives into the production and application of VPP technology.

al–mn–mg–sc–zr alloy, laser powder bed fusion, fabrication rate, layer thickness, high strength, Science, Manufactures, and TS1-2301

The high cost of laser powder bed fusion (LPBF) fabricated high-strength Sc containing aluminium alloy hinders its applications. To reduce the cost, we reported a LPBF fabricated strong and ductile Al–Mn–Mg–Sc–Zr alloy using large layer thicknesses to improve the fabrication efficiency on coarse powder particles. A high relative density exceeding 99.2% was achieved at layer thicknesses up to 120 μm. In post-process heat-treated specimens, the yield strength only had a slight 6% decrease from layer thickness of 30 to 120 μm; such a decrease in strength was attributed to the larger grain size resulted from the adopted larger layer thickness. The fabricated sample at layer thickness of 120 μm still exhibited high tensile yield strength of 472 MPa and fracture strain of ∼10%. This work showed a successful application of improving the LPBF fabrication efficiency of high-strength Al–Mn–Mg–Sc–Zr alloy using large layer thickness in LPBF process.

direct laser writing, photopolymerization, multi-photon polymerisation, femtosecond projection, nanoscale 3d printing, Science, Manufactures, and TS1-2301

Large and deterministic 3D structures with nanoscale features and porosities are valuable for various applications but are challenging to print due to the proximity effects that lead to the merging of adjacently printed features. Here, this challenge has been overcome by minimising the proximity effects in projection two-photon lithography (P-TPL), which is a high-throughput photopolymerization-based 3D printing technique. Through empirical studies and physics-based computational models, it is demonstrated that the proximity effects arise from distinct optical and chemical sources. Processing conditions that individually minimise these sources have been identified. These insights have been leveraged to generate an interspersing P-TPL technique capable of rapidly printing 3D structures with features smaller than 300 nm, pores finer than 700 nm, and at rates greater than 0.5 mm2/s per layer. As interspersing P-TPL is up to 50 times faster than conventional point-scanning TPL, it can enable the scalable printing of nanoporous 3D structures.

laser powder bed fusion, crystal-inspired structure, hybrid lattice structure, mechanical property, structural feature sensitivity, Science, Manufactures, and TS1-2301

Node-strengthened hybrid structures with lower relative density inspired by solid solution strengthening mechanism, namely the edge center interstitial lattice (ECIL) structures and vertex node substitutional lattice (VNSL) structures were designed and fabricated by laser powder bed fusion (LPBF). The geometric feature-dependent defects distribution, the intense microstructure sensitivity as well as the node size effect on the mechanical response were investigated. The microstructure sensitivity induced by geometric feature was found to be related to the different supporting condition and distinctive thermal history. ECIL-1.5 structure possessed the highest plateau stress of 1.79 MPa and the largest crush force efficiency of 59.1%, which increased by 59.8% and 15.2% compared to the initial face centre cubic with z-struts (FCCZ)structure. VNSL-1.5 exhibited the greatest specific energy absorption of 14.6 J/g, demonstrating the highest strengthening efficiency was achieved at the critical sphere diameter to strut thickness (Sph-strut) ratio of 3. This method further improved lightweight efficiency, indicating the inherent strengthening mechanism of crystal materials could guide the design of metamaterials.

gas flow direction, laser powder bed fusion, crystallographic orientation, scan strategy, thermal conductivity, Science, Manufactures, and TS1-2301

This study demonstrated that the gas flow direction in the laser beam powder bed fusion (PBF-LB) significantly affects the crystallographic texture evolved in the products. The effect on texture is attributed to the difference in the melt pool depth, which depends on gas flow direction. The melt pool was shallower when the laser scanning and gas flow directions were parallel than when they were perpendicular. This phenomenon should be of particular concern when applying Scan Strategy_XY wherein the laser was scanned with a 90° rotation in each layer, which is often used in PBF-LB. The asymmetry in the melt pool depth generated by laser scanning in the x- and y-directions can lead to unintended variations in the crystallographic texture. The gas phase would interact with a part being manufactured immediately beneath the gas and affect the crystallographic feature of the product.

tensile test, miniature specimens, additive manufacturing, local mechanical properties, Science, Manufactures, and TS1-2301

The various process-specific differences in techniques compared to traditional techniques can produce significantly different mechanical behaviour in additively manufactured (AM) parts compared to traditional bulk counterparts. Components produced by AM are built layer by layer via localised melting. Therefore, both location- and orientation-dependent properties can be expected. Since many AM parts take advantage of the design and topology freedom provided by AM, properties characterisation with the use of standard specimens is not always possible, requiring the use of small-sized specimen techniques. In the current paper, three AM-produced IN-718, Ti-6Al-4V and H13 parts using electron beam powder bed fusion and laser powder bed fusion are evaluated. Local mechanical properties have been assessed with the use of mini-tensile tests that were developed for cases where limited amounts of material are available. The results obtained demonstrate the ability to measure location- and orientation-dependent properties in AM components using such approaches and highlight that additional work by the AM community remains in order to determine the source(s) of such differences.

vat photopolymerisation, smart materials, laser ablation in liquids, feni, magnetic nanoparticles, millirobots, Science, Manufactures, and TS1-2301

Masked stereolithography printing can be used to produce functionalised magneto-responsive polymer structures. Magnetic filler additivation of the photopolymer enables the production of powerful and fast soft robotics. However, current approaches require high filler concentrations, reducing the mechanical properties and compromising the processability. In this study, FeNi nanoparticles were added to a photopolymer to take advantage of their soft magnetic response and high magnetisation. Field-assisted printing gives rise to magnetic anisotropy by arranging laser-synthesised FeNi nanoparticles into uniaxial magnetic strands of up to 500 μm length. Favoured by the small size and even distribution of the nanoparticles, only 0.02 wt% are needed to detect magnetic responsivity. Thus, the impact on the mechanical property is reduced while facilitating the control over the composite magnetic properties. The practical feasibility of the composites is demonstrated by actuating gripper and impeller structures which offer possibilities in applications like drug delivery and tissue engineering.

laser powder bed fusion, spark plasma sintering, niti alloys, superelasticity, healing crack, Science, Manufactures, and TS1-2301

The pursuit of enhancing NiTi superelasticity through laser powder bed fusion (L-PBF) and [001] texture creation poses a challenge due to increased susceptibility to hot cracking in the resulting microstructure with columnar grains. This limitation restricts NiTi's application and contributes to material waste. To overcome this, we introduce a pioneering approach: utilising spark plasma sintering (SPS) to heal directional cracks in [001] textured L-PBF NiTi shape memory alloy. Diffusion bonding and oxygen utilisation for Ti2NiOx formation was found to successfully heal the cracks. SPS enhances mechanical properties, superelasticity at higher temperatures, and two-way shape memory strain during thermomechanical cycling. This work provides an alternative solution for healing cracks in L-PBF parts, enabling the sustainable reuse of cracked materials. By implementing SPS, this approach effectively addresses hot cracking limitations, expanding the application potential of L-PBF NiTi parts while improving their functional and mechanical properties.

additive manufacturing, laser powder bed fusion, aluminium alloys, fe, strengthening mechanisms, Science, Manufactures, and TS1-2301

Achieving superior mechanical properties of Al alloys with high content of Fe impurities is very challenging. Here, a feasible method was applied to accommodate high Fe content (∼2.2 wt.%) and obtain superior strength in an Al–5Mg2Si–2Mg–2Fe alloy by using additive manufacturing. Heterogeneous distribution of Fe, including a high number density of α-Al12(Fe,Mn)3Si particles distributed at the melting pool boundary and excessive Fe segregated along the cell boundaries that divided by Mg2Si eutectics, was verified as the beneficial factor for the alloy design and strength enhancement. In addition to the heterogeneous grains that contain fine cells, the interactions between dislocations and coherent Mg2Si eutectics and the α-Al12(Fe,Mn)3Si particles played an important role in improving the mechanical properties. This work represents a breakthrough in recycling high-strength Al alloys with extremely high Fe doping for green industrial application through additive manufacturing.

high-entropy alloying, cracking inhibition, laser additive manufacture, d019 precipitates, post-aging treatment, Science, Manufactures, and TS1-2301

Developing high-performance high-entropy alloys (HEAs) fabricated by laser additive manufacturing (LAM) is the pursuit of the metallic community. In the present work, we designed a series of [(Al6-xNbx)-(FeCoNi)12]Cr3 HEA compositions using a high-entropy alloying strategy based on a cluster-plus-glue-atom model. And their thin-wall-sharped bulks were fabricated by LAM and post-aging treatment. The effects of cracking inhibition and microstructure evolution on the tensile properties were researched in detail. The results show that as the Nb substitutes for Al atoms, the cracking behaviour is ameliorated, ascribed to the tiny Laves phase refined the dendrite spacings and back-filled in the inter-dendritic liquid film. Also, introducing Nb atoms improves the strength but deteriorates the ductility. Significantly, the Nb4 HEA possesses the best tensile-property combination (i.e. σs ∼ 419.2 MPa, σb ∼ 787.4 MPa, and δ ∼ 15.5%) with a strain mechanism of dislocation slip mode. After post-aging for 72 h, the microstructure comprises fully recrystallized equiaxed FCC grains and many tiny needle-like D019 precipitates, leading to high strength and sufficient ductility (i.e. σ0.2 ∼ 535.9 MPa, σb ∼820 MPa and δ value of 8.9%). These findings provide a new paradigm for the LAM of crack-free HEAs with excellent mechanical properties.

alsi10mg, laser powder bed fusion (lpbf), thermal stability, deformation-free recrystallisation (dfrx), Science, Manufactures, and TS1-2301

Laser powder bed fused (LPBFed) AlSi10Mg is recognised for its superior mechanical properties. However, its thermal stability has never been justified. Herein, we exposed as-built AlSi10Mg to different temperatures (200–500°C) for only 3 min to evaluate its thermal stability. Results showed that LPBFed AlSi10Mg had relatively low thermal stability. Only 3 min of thermal exposure at 200°C would deteriorate its tensile strength dramatically. Microstructural analysis revealed that with increasing thermal input, as-built AlSi10Mg exhibited a microstructural evolution similar to annealing of cold-worked metals, namely recovery, recrystallisation followed by grain-growth. The excessive energy stored in as-built microstructure due to fast cooling during LPBF was deduced as the driving force for this phenomenon. Therefore, such microstructural change was at the expense of dislocations stored in the as-built material, which in turn caused deterioration in tensile strength. The present findings may provide guidance for the application of LPBFed AlSi10Mg.

laser-directed energy deposition, niti, ni4ti3, martensitic transformation, precipitation behaviour, Science, Manufactures, and TS1-2301

In this study, we report an unconventional precipitation and martensitic transformation behaviour of directly aged Ni-rich NiTi alloys fabricated via laser-directed energy deposition (LDED). Ni4Ti3 particles precipitate uniformly under all ageing conditions and no traditional multiple-step martensitic transformations are observed. We conclude this unique behaviour to the intrinsic characteristics of the LDED technique, which are metastable microstructures and high residual stresses. On the one hand, these features make grain boundaries no longer a fevered location for precipitation and, on the other hand, significantly suppress the martensitic transformation when ageing at low temperatures (300°C/400°C). As the aging temperature increase (500°C), residual stresses release significantly, accompanied by the growth of Ni4Ti3 precipitates from several nanometres to 452 ± 181 nm with increased interparticle spacing. At the same time, reverse martensitic transformations change from two-step (B19′ → R → B2) to single-step (B19′ → B2).

3d printing, bayesian optimisation, convolutional neural network, supercapacitor, Science, Manufactures, and TS1-2301

A convolutional neural network (CNN) guided Bayesian optimisation framework is introduced to strategically maximise the surface to volume ratio of 3D printed lattice supercapacitors. We applied Bayesian optimisation on printing parameters to exploit regions where uniform and narrow lines are printed. A line shape classifying CNN model guided the optimiser’s search space to straight-line printed regions, minimising optimisation time and cost. An automatic scoring method allowed each iteration to be conducted within two minutes with accurate and precise measurements. The optimisation process has been demonstrated with graphene oxide (GO) and poly(3,4-ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) inks. The results were compared to the parameters that follow the conventional methodologies of direct ink writing (DIW) 3D printing. For each printed line of GO and PEDOT:PSS inks, irregularities decreased by 61.8% and 18.9% and average widths decreased by 39.0% and 28.6%. PEDOT:PSS lattice supercapacitor printed using optimised result showed a 151.0% increase in specific capacitance.

mechanical properties, optimisation, pha, phbh, Science, Manufactures, and TS1-2301

The crystallisation process of polyhydroxyalkanoates (PHA) polymers plays a key role on final properties of manufactured parts due to most PHA are highly sensitive to physical aging which leads to embrittlement. The secondary crystallisation associated with the aging process can be partially controlled by the cooling process during manufacturing or, even, by heat treatments such as annealing. A critical parameter in additive manufacturing is the difficulty to achieve good adhesion of the material to the printing bed. The bed temperature plays a key role on PHBH crystallisation, which leads to shrinkage having a negative effect on polymer-to-bed adhesion. In this work, a study of the effect of different processing parameters such as the printing temperature, the bed temperature, the cooling conditions, as well as raster direction on the final properties of PHBH 3D-printed parts is carried out.

additive manufacturing, preceramic polymer, digital light processing, shape transformation, composites, Science, Manufactures, and TS1-2301

It remains challenging to broaden the application fields of ceramics, largely because the hardness and brittleness of ceramics mean that they cannot undergo shape reconfiguration. In this study, we developed an ultraviolet light-curable preceramic polymer slurry, and this slurry was used for digital light processing printing of flexible green parts in designed shapes. These parts were subsequently transformed into complex structures by an assisted secondary molding strategy that enabled the morphology of their green and pyrolyzed forms to be well controlled. The collapse of bulk pyrolyzed parts was avoided by impregnating their precursors with silicon nitride (Si3N4) particles. The effects of different proportions of Si3N4 on the weight loss, shrinkage, density, porosity, and mechanical properties of the pyrolyzed composites were investigated, and the bending strength and Vickers hardness of the composites with 10 wt.% Si3N4 were found to be 130.61 ± 16.01 MPa and 6.43 ± 0.12 GPa, respectively.

bipolar plate, active screen plasma nitriding, laser powder bed fusion, 316l stainless steel, Science, Manufactures, and TS1-2301

Laser powder bed fusion (LPBF) is capable to process complex flow field structures on 316L stainless steel (316L SS) bipolar plates, which is promising to improve the performance of proton exchange membrane fuel cell (PEMFC). However, insufficient corrosion resistance and relatively high interfacial contact resistance (ICR) hinder the widespread of LPBF-processed 316L SS bipolar plates. In this work, active screen plasma nitriding (ASPN) was used to modify 316L SSs fabricated by the LPBF process and forging, respectively. Results showed that the nitrided layer of LPBF-processed 316L SS (2000 mm/s, 300 W) exhibited the highest surface nitrogen concentration, thickest nitrided layer and highest average hardness. The ICR values decreased significantly after ASPN treatment. The corrosion current of nitrided LPBF-processed 316L SS (2000 mm/s, 300 W) was much lower than that of the nitrided forged 316L SS. By comparing multiscale microstructures between LPBF-processed and forged 316L SS, the ASPN mechanism of LPBF-processed 316L SS was proposed.

functionally graded material, laser directed energy deposition, acoustic emission, optical emission spectroscopy, artificial intelligence, Science, Manufactures, and TS1-2301

Laser directed energy deposition (L-DED) allows the production of multi-materials and functionally graded material (FGM) parts. But for commercialisation, process and quality monitoring of parts is required. For the first time, a novel monitoring method for chemical composition and process regimes of FGMs is proposed using a cost-effective acoustic emission (AE) (microphone) and optical emission spectroscopy (OES) sensors. Four chemical compositions (100%Ti, 58%Ti42%Nb, 37%Ti63%Nb, and 100% Nb) and two process parameters (475 W – 1'400 mm/min and 175 W – 2'000 mm/min) were selected, leading to four regimes/quality (conduction mode, partial, minor, medium, and severe lack of fusion pores). The signals were classified using seven mainstream artificial intelligence algorithms. The main conclusions are twofold. First, microphones are unsuitable candidates for monitoring the laser-material interaction during L-DED. The acoustic waves generated by the laser-material interaction are shielded by high gas flow surrounding it and so are either highly disturbed or does not reach the microphone. Conversely, OES are suitable candidates as the classification accuracies are higher than 90% for most category and machine learning algorithms, even after drastic feature reduction. Considering the wide range of chemical composition and quality, our proposed methods using OES have high industrialised potentials for them during L-DED FGM.

laser printing, laser sintering, conformal printing, silver nanoparticles inks, flexible electronics, Science, Manufactures, and TS1-2301

The laser induced forward transfer and sintering of metal nanoparticle inks has been proven a key enabling technology for flexible electronics. Nevertheless, many challenges concerning the conformal processing of non-planar substrates incorporating thermally sensitive layers are yet to be addressed. In this work, we study the behaviour of conformal laser printing of silver nanoparticle inks on patterned samples comprising sensitive underlying structures, by correlating the laser sintering powers employed to the undesired effects on the adjacent interfaces. The latter include demanding surface topographies with periodic patterns and micro-components exhibiting aspect ratio in the nano to 100-micron scale. We investigate the contribution of crucial processing parameters, such as the per pulse energy, repetition rate and the pulse to pulse spatial and temporal overlap to the overall result. The demonstrated results validate the versatility of laser processing which can offer application specific solutions on different use cases involving multilayered and multimaterial electronics.

additive manufacturing, multi-material, ceramic, laser powder bed fusion, computational fluid dynamics, Science, Manufactures, and TS1-2301

Experiments on Laser powder bed fusion (LPBF) of powdered Ti on Al2O3 substrate were conducted and the interface formation was studied using a multi-material fluid dynamics model. Results show that the melt pool is relatively shallow, with relatively flat interlayer interface under LPBF’s conduction mode. In this condition, a thin sheath of molten Al2O3 forms and acts as a lubricating film for the molten Ti, leading to Rayleigh instability due to high flow inertia. Keyhole formation penetrates the Al2O3 substrate, resulting in a wavy interlayer interface. The recoil pressure from the keyhole and overall melt inertia are suppressed by the highly viscous molten Al2O3, thereby improving single-track melt pool stability. However, the thermal expansion coefficient difference between Ti and Al2O3 led to the formation of transverse cracks. Achieving a defect-free metal-on-ceramic single track remains a challenge, despite this study serving as a guide for melt track and interface control.

meltpool monitoring, laser powder bed fusion, additive manufacturing, scan strategy, hot spots detection, porosity, process monitoring, near-infrared sensors, Science, Manufactures, and TS1-2301

In-situ co-axial meltpool monitoring has become a popular tool for digitising the laser powder bed fusion (L-PBF) process , providing baseline data for certification. Each layer produces an image where the pixel position represents the laser coordinates and the pixel intensity denotes the sensor response. The 3D image stacks represent the infrared emission during the manufacturing of the physical component. However, interpreting monitoring data remains a challenge. To address this issue, this study evaluates the performance of a near-infrared photodiode in detecting typical geometrical features such as porosity and overhanging structures ranging from the micro-to-meso scale. Monitoring data is highly sensitive to heat accumulation around overhanging structures and can quantify dross formation based on hotspots. Cold spots, which represent a lack of fusion porosity at scan track intersections, can indicate a probability of defect formation. However, the sensitivity and predictive value of monitoring data for porosity are low due to the healing of defects in subsequent layers. Local process variables, such as the scan strategy and part orientation, significantly influence dross and hot spot formation. This study shows the potential of NIR photodiodes in deriving metrics for in-line certification of L-PBF components, leading to improved process control and quality assurance.

multi jet fusion, polyamide 12 matrix, polyimide fibres, fibre-reinforced polymer composites, annealing, Science, Manufactures, and TS1-2301

Multi Jet Fusion (MJF) has attracted extensive attention because of its ability to print support-free complex structures. However, the mechanical properties of MJF-printed polymer parts are still unsatisfactory for certain industrial requirements. Herein, by leveraging the fibre reinforcement effect and high specific strength of polyimide (PI) fibres, this work developed PI/polyamide 12 (PA12) composites with largely enhanced mechanical performance via MJF. Specifically, the tensile strength and modulus were increased by 43% and 42%, and the flexural strength and modulus were improved by 39% and 46%, respectively, compared to those of the neat PA12 parts. Furthermore, the incorporation of lightweight PI fibres endowed the composites with high specific tensile strength (67.60 kN·m/kg) and specific flexural strength (93.70 kN·m/kg), which are superior to those of MJF-printed PA12 composites reinforced with other fibres. This work provides new insights into enhancing the mechanical performance of lightweight parts printed by MJF and other powder-based techniques.

elastomer, carbon fibres, mechanical properties, additive manufacturing, Science, Manufactures, and TS1-2301

Mechanical dependence of 3D-printed thermoplastic polyurethane (TPU) reinforced with continuous carbon fibres (CCFs) on the selected printing conditions was investigated. The melt-extrusion-based 3D-printing (ME3DP) method was employed to fabricate specimens, of which the dependence of tensile, flexural and cryo-impact properties on layer thickness, printing speed and layer number was evaluated. Results showed that the printed TPU reinforced with raw CCFs revealed an over five-fold increase in tensile yield stress with the occurrence of necking phenomenon whereas those reinforced with preimpregnated CCFs (PCCFs) displayed brittle fracture which was also confirmed by the impact testing. The flexural strength and modulus of the printed CCFs/TPU were greatly raised over that of TPU and the PCCFs provided a much more enhancement. Both the increased yield stress and flexural strength implied an improved capacity for dynamic load bearing. Finally, the structure–property relationship was established via interface microstructure detection and simulation.

additive manufacturing, acoustics, defect detection, sensor, Science, Manufactures, and TS1-2301

In additive manufacturing of metals, numerous techniques have been employed to sense print defects. Among these, acoustic-based sensing has the advantage of low cost and shows the most potential to identify both external and internal defects as an in-situ monitoring system. Using acoustic signals, researchers have broadly investigated non-machine learning and machine learning-based approaches to identify defects like balling, micro defects, lack of fusion pores, keyhole pores, cracks, and porosity. While most of these works have shown promising results for laser-based AM systems, few have explored how acoustic signals can be used effectively for Wire Arc Additive Manufacturing (WAAM) defect detection. This paper proposes a methodology to construct machine learning (ML)-based models on identifying geometrically defective bead segments using acoustic signals during the WAAM process. Geometrically defective bead segment or geometric defect is a defect that causes voids in the final printed part due to incomplete fusion between two non-uniform overlapping bead segments. Such a defect is currently not explored in the literature. The proposed methodology uses a novel dataset labeling approach to identify good and bad bead segments based on an optimal threshold of the range of mean curvature. Furthermore, the methodology targets defective bead segments based on acoustic feature inputs like Principal Components (PC) or Mel Frequency Cepstral Coefficients (MFCC). To understand the resulting performance of the defect identification models constructed based on the proposed methodology, experiments are performed and tested on a variety of ML models (KNN, SVM, RF, NN, and CNN) based on the Inconel 718 material. The results show that the combinatorics of two acoustic input features and five ML models can be able to identify geometrically defective segments accurately with F1 score that ranges from 80% to 85%.

metal additive manufacturing, additive manufacturing, topology optimisation, aerospace, automotive, medical, Science, Manufactures, and TS1-2301

Metal additive manufacturing is gaining immense research attention. Some of these research efforts are associated with physics, statistical, or artificial intelligence-driven process modelling and optimisation, structure–property characterisation, structural design optimisation, or equipment enhancements for cost reduction and faster throughputs. In this review, the focus is drawn on the utilisation of topology optimisation for structural design in metal additive manufacturing. First, the symbiotic relationship between topology optimisation and metal additive manufacturing in aerospace, medical, automotive, and other industries is investigated. Second, support structure design by topology optimisation for thermal-based powder-bed processes is discussed. Third, the introduction of capabilities to limit manufacturing constraints and generate porous features in topology optimisation is examined. Fourth, emerging efforts to adopt artificial intelligence models are examined. Finally, some open-source and commercial software with capabilities for topology optimisation and metal additive manufacturing are explored. This study considers the challenges faced while providing perceptions on future research directions.

4d printing, high flexibility, anisotropic magnetic property, digital light processing, smart manufacturing, Science, Manufactures, and TS1-2301

Flexible anisotropic soft-magnetic composite (FASMC) presents superior magnetic properties in one or more specified directions, showing great potential in the application of microwave absorption, soft robots, and other smart sensors/actuators. However, the fabrication of FASMC using additive manufacturing is challenging due to a trade-off between magnetic properties of the composites enhanced by iron particles and printability during printing. Here, we developed a 4D printing scheme using flexible soft-magnetic photosensitive resin consisting of flexible long-chin acrylic resin monomer and soft magnetic iron particles. Multiple complex structures with good spatial resolution of ∼170 μm were fabricated using magnetic field-assisted digital light processing (MF-DLP). Directional magnetic field was applied during printing, enabling the fabrication of FASMC with strong anisotropic magnetic properties. FASMC with high CIP (carbonyl iron powder, CIP) concentration of up to 45 wt.% was fabricated with excellent tensile strength and elongation up to 460%. Strong anisotropic magnetic properties were demonstrated through a series of stimuli-response testing such as large deformation, anti-deflection, controlled motion, variable stiffness metamaterial, and array assembly, under external magnetic field. This study demonstrates the feasibility and potential of MF-DLP technique for fabrication of FASMC, shedding light on the design and fabrication of next-generation sensors and actuators.

laser powder bed fusion, bulk metallic glasses, composites, microstructure, mechanical properties, Science, Manufactures, and TS1-2301

In this work, a new design principle, i.e. doping with refractory metal particles with a low diffusion rate to prevent the formation of cracks and to improve the mechanical properties of bulk metallic glass (BMG) composites, was put forward. It was proven that crack-free and dense Mo(p)/Cu47Zr47Al6 BMG composites with enhanced mechanical properties can be produced via LPBF. The dislocations generated in the Mo particles can release thermal stress, thereby inhibiting the formation of thermal-cracks. The fracture patterns of Mo particles show that they can delay rapid of crack expansion, thereby improving the inherent strength and toughness of the material.

additive manufacturing, discrete element method, fiber-reinforced polymer composite, fiber orientation, fiber homogeneity, Science, Manufactures, and TS1-2301

The packing characteristics of fiber/polymer powder in powder bed fusion additive manufacturing exhibit a high correlation with the mechanical behaviours of printed composite parts such as homogeneity and anisotropy. A discrete element model has been developed to investigate the packing characteristics of glass fiber/polyamide 12 (PA12) powder, which include fiber orientations, fiber homogeneity, and packing density. The predicted probability distributions of fiber orientations in the powder bed are comparable with those measured in glass fiber–reinforced PA12 composites printed via multi jet fusion. Three types of fibers with different length distributions are adopted to study the effects of the fiber length distribution on their packing characteristics. The simulation results reveal that a large average fiber length is beneficial to fiber alignment in the powder spreading direction but lowers the fiber homogeneity and packing density of the powder bed. Furthermore, varying the fiber length can provide an effective way to regulate fiber orientations in the powder packing process, which would help achieve satisfactory anisotropic mechanical properties for composite parts.