Additive Manufacturing Strategy Research Articles

Laser powder bed fusion in-situ alloying of W-Y alloy: Microstructure, mechanical properties and cracking suppression

The microcracks caused by impurity oxygen are recognized as one of the main challenges in additive manufacturing of tungsten. In this study, yttrium was incorporated into the tungsten matrix to suppress crack formation, and W-Y alloys with minimal cracks were successfully obtained by laser powder bed fusion (LPBF). It is found that during the LPBF process, yttrium combines with impurity oxygen to generate intergranular and intragranular precipitated particles in situ, which effectively suppress cracking behavior due to impurity oxygen. Furthermore, these intracrystalline nanoprecipitate are cubic Y2O3 particles that have formed a semi-coherent interface with the tungsten matrix. These dispersed particles significantly improved the mechanical properties of W-Y alloy. The results offer a corresponding strategy for crack suppression of tungsten alloys in laser additive manufacturing processes, and would provide a benificial additive manufacturing strategy to other refractory alloys.

Condition-based Predictive Maintenance as an Efficient Strategy for Industrializing Additive Manufacturing Technology

Objective: Traditional manufacturing has several issues to determine a general maintenance strategy. Additive Manufacturing (AM) is a special type of fabrication, which possesses different issues, especially uncertainty failure cases. This forms a big obstacle to becoming an industrialized production strategy. The objective of this work is to provide the most suitable maintenance strategy in order to reduce the likelihood of failure that can help in industrializing the AM technology. Methods: Among the different maintenance strategies, Predictive Maintenance (PdM) became widely treated in academia and industry. According to the methods used for detecting the failure signs, it can be classified into two types: Condition-Based Predictive Maintenance (CBPdM) and Statistical-Based Predictive Maintenance (SBPdM). The use of the last type highly depends on available and accessible data. However, CBPdM depends on only periodic or continuous condition monitoring tools for detecting the failure signs. Results: The existence of various types of failure cases yields to a big difficulty to predict failures. In addition, because of insufficient data, SBPdM cannot be selected as a suitable maintenance strategy for additive manufacturing. According to the presented examples, the CBPdM can be considered here as the best maintenance strategy for AM. Conclusion: CBPdM strategy is the best compromise between cost and applicability where there is not enough data. This selected maintenance approach represents an efficient tool in industrializing AM technology.

Ionically-crosslinked carboxymethyl chitosan scaffolds by additive manufacturing for antimicrobial wound dressing applications

Chitosan chemical functionalization is a powerful tool to provide novel materials for additive manufacturing strategies. The main aim of this study was the employment of computer-aided wet spinning (CAWS) for the first time to design and fabricate carboxymethyl chitosan (CMCS) scaffolds. For this purpose, the synthesis of a chitosan derivative with a high degree of O-substitution (1.07) and water soluble in a large pH range allowed the fabrication of scaffolds with a 3D interconnected porous structure. In particular, the developed scaffolds were composed of CMCS fibers with a small diameter (< 60 μm) and a hollow structure due to a fast non solvent-induced coagulation. Zn2+ ionotropic crosslinking endowed the CMCS scaffolds with stability in aqueous solutions, pH-sensitive water uptake capability, and antimicrobial activity against Escherichia coli and Staphylococcus aureus. In addition, post-printing functionalization through collagen grafting resulted in a decreased stiffness (1.6 ± 0.3 kPa) and a higher elongation at break (101 ± 9 %) of CMCS scaffolds, as well as in their improved ability to support in vitro fibroblast viability and wound healing process. The obtained results encourage therefore further investigation of the developed scaffolds as antimicrobial wound dressing hydrogels for skin regeneration.

Research on interface precision control strategy for additive manufacturing of coplanar sand laying with multi-material composite sand mold

Compared with the additive manufacturing of single sand material, it is more difficult to form multi-material composite sand mold. The paper focuses on the influence of sand laying process for the multi-material composite sand mold, explores the change rules in the quality of different curing agent content of composite sand mold, realizes the high quality and high precision sand laying of multi-material sand, and expands the application of composite sand mold in complex structure and high performance products.

Sawtooth scanning strategy for additive manufacturing

PurposeThis study aims to improve the acceleration in the additive manufacturing (AM) process. AM tools, such as extrusion heads, jets, electric arcs, lasers and electron beams (EB), experience negligible forces. However, their speeds are limited by the positioning systems. In addition, a thin tool must travel several kilometers in tiny motions with several turns while realizing the AM part. Hence, acceleration is a more significant limiting factor than the velocity or precision for all except EB.Design/methodology/approachThe sawtooth (ST) scanning strategy presented in this paper minimizes the time by combining three motion features: zigzag scan, 45º or 135º rotation for successive layers in G00 to avoid the CNC interpolation, and modifying these movements along 45º or 135º into sawtooth to halve the turns.FindingsSawtooth effectiveness is tested using an in-house developed Sand AM (SaAM) apparatus based on the laser–powder bed fusion AM technique. For a simple rectangle layer, the sawtooth achieved a path length reduction of 0.19%–1.49% and reduced the overall time by 3.508–4.889 times, proving that sawtooth uses increased acceleration more effectively than the other three scans. The complex layer study reduced calculated time by 69.80%–139.96% and manufacturing time by 47.35%–86.85%. Sawtooth samples also exhibited less dimensional variation (0.88%) than zigzag 45° (12.94%) along the build direction.Research limitations/implicationsSawtooth is limited to flying optics AM process.Originality/valueDevelopment of scanning strategy for flying optics AM process to reduce the warpage by improving the acceleration.

Surface functionalization of binder jetted steels through super-solidus liquid phase sintering and electro-spark deposition

This study proposed a surface functionalization strategy for porous binder jet additive manufacturing (BJAM) steels. The methodology involves a sequential process of super-solidus liquid phase sintering (SLPS) followed by electro-spark deposition (ESD). SLPS with varying liquid fractions was used to modify the initial surface quality of BJAM steels, creating a range of surface roughness and bulk porosity. The ability of ESD to address substrate surface roughness and porosity variation was investigated using lower (Inconel 625) and higher (WC-Co) melting point coating materials. The results revealed a clear correlation between substrate surfaces and the surface finish, uniformity, and thickness of ESD deposits. Inconel 625, with its lower melting point, showcased an infiltration behavior and high tolerance to substrate conditions. Conversely, achieving high-quality WC-Co coating necessitated prior SLPS treatment to attain substrates with minimal roughness and sub-surface porosity. This investigation provides insights into optimizing surface modifications for porous BJAM metal parts, considering different coating materials and their compatibility with substrate conditions.

Influence of Si3N4 fillers and pyrolysis profile on the microstructure of additively manufactured silicon carbonitride ceramics derived from polyvinylsilazane

ABSTRACT In this work, various methods were used to improve the printability of a photocurable polyvinylsilazane resin filled with silicon nitride particles for digital light processing. The developed resin was used as a preceramic polymer for polymer-to-ceramic conversion. The pyrolysis-induced structural changes of the additively manufactured objects were evaluated by comparing samples with different thicknesses, filler amounts and heating profiles. The printed green body retained its original geometry better and showed fewer cracks due to the addition of silicon nitride particles to the resin. Based on the thermally induced changes in a polyvinylsilazane resin system, a customized heating profile for the pyrolysis process was developed, which contributed to the reduction of pores and cracks while the average pyrolysis heating rate remained relatively high. This work provides insight into the pyrolysis of additively manufactured preceramic polymer green bodies and highlights various strategies for additive manufacturing of polymer-derived ceramics.

Electrohydrodynamic Direct-Writing Micro/Nanofibrous Architectures: Principle, Materials, and Biomedical Applications.

Electrohydrodynamic (EHD) direct-writing has recently gained attention as a highly promising additive manufacturing strategy for fabricating intricate micro/nanoscale architectures. This technique is particularly well-suited for mimicking the extracellular matrix (ECM) present in biological tissue, which serves a vital function in facilitating cell colonization, migration, and growth. The integration of EHD direct-writing with other techniques has been employed to enhance the biological performance of scaffolds, and significant advancements have been made in the development of tailored scaffold architectures and constituents to meet the specific requirements of various biomedical applications. Here, a comprehensive overview of EHD direct-writing is provided, including its underlying principles, demonstrated materials systems, and biomedical applications. A brief chronology of EHD direct-writing is provided, along with an examination of the observed phenomena that occur during the printing process. The impact of biomaterial selection and architectural topographic cues on biological performance is also highlighted. Finally, the major limitations associated with EHD direct-writing are discussed.

Product Design Optimization Strategies for Metal Additive Manufacturing in Aerospace Applications

Product Design Optimization Strategies for Metal Additive Manufacturing in Aerospace Applications

A shape-performance synergistic strategy for design and additive manufacturing of continuous fiber reinforced transfemoral prosthetic socket

A shape-performance synergistic design and additive manufacturing strategy was developed for the transfemoral prosthetic sockets (TPS) to fulfill the demands of customized geometry and long-term load bearing. The 3D printing path of the continuous fiber reinforced polymer composites (CFRPC) was generated by reversing the milling path of subtractive manufacturing. The mechanical properties of the 3D printed CFRPC samples were investigated as a foundation, and the customized fiber trajectories were designed based on the analyzed stress pattern of the TPS in daily gait. The CFRPC TPS with weight of 28 % less than those made by pure resin had a safety factor larger than 3 and passed the fatigue testing of 3 million cycles. The design and additive manufacturing strategy developed in this study was also applicable for other parts with freeform surfaces.

A novel additive manufacturing strategy with high hydrogen production for ordered-porous stainless steel catalyst support

This paper proposes to improve hydrogen production performance of ordered-porous stainless steel by increasing its forming structure parameters. Firstly, selective laser melting additive manufacturing of ordered-porous stainless steel is carried out through designed orthogonal experiment table, to obtain its forming structure parameters under different manufacturing process parameters. Then, different forming structure parameters of ordered-porous stainless steel are converted into a comprehensive index by grey relation theory, which is grey relational degree (GRD). When powder thickness, scanning speed, scanning space and laser power are 30 μm, 800 mm/s, 90 μm and 60 W, respectively, the highest GRD of 0.930 is obtained, when those are 40 μm, 1200 mm/s, 70 μm and 60 W, respectively, the lowest GRD of 0.410 is gained. Finally, catalyst bonding strength and hydrogen production performance of the ordered-porous stainless steels with the above GRDs are verified. It is found that the ordered-porous stainless steel with the highest GRD has higher catalyst bonding strength and higher hydrogen production performance. When 12 mL/h injection rate of methanol–water solution and 250 ℃ reaction temperature are used, CH3OH conversion, H2 flowing rate and CO selectivity of the above ordered-porous stainless steel are 64.3%, 0.396 mol/h and 6.75%, respectively.

Additively-manufactured Mg wire-reinforced PLDL-matrix composites for biomedical applications

Coupons of a medical grade PLDL polymer matrix uniaxially reinforced with a 15% volume fraction of Mg wires have been manufactured by fused filament fabrication for the first time. Two different types of Mg wires, without and with a surface treatment by plasma electrolytic oxidation were used. Both composite materials were subjected to degradation in phosphate buffer solution over a 3-week period, and their degradation and deformation micromechanisms were analysed in detail. Additionally, the materials were subjected to extensive mechanical testing under various loading conditions, and the interface strength was also analysed. It was found that the presence of the Mg wires improves the mechanical behaviour and accelerates the corrosion rate of the composite with respect that of the polymer matrix and these properties can be further tailored through the surface-modification of Mg wires by plasma electrolytic oxidation. The additive manufacturing strategy presented opens the path to fabricate multimaterial implants and scaffolds with complex shape and tailored properties provided by biodegradable polymers reinforced with either Mg and Zn particles and/or wires.

Deepening the synergistic role of additive manufacturing and computational strategies in jewellery

This study investigates the synergy between additive manufacturing (AM) technologies and computational design strategies in jewellery and how that synergy can be successfully exploited to extend innovation in that field further. A case study called Ecdysis, a bioinspired jewellery collection, is presented. A dedicated computational algorithm has been developed and is described in detail. This algorithm allows for the exploitation of the shape and functional complexity dimensions allowed by AM and the control of the printability of the generated concept. Shape and functional complexity are exploited to mimic the beauty and dynamism of snakes’ slithering mechanism. At the same time, starting from the developed algorithm, multiple digital models and physical prototypes have been fabricated, leveraging material extrusion, vat photopolymerisation, and powder bed fusion processes. This further development step of the collection thus confirms the versatility of both the proposed approach and AM technologies for jewellery. Therefore, the paper demonstrates how unique wearing experiences can be created and how uniqueness can be simultaneously preserved and democratised in jewellery by deepening the synergy between AM technologies and computational strategies.

Sustainability in Electromagnetic Metamaterials: Synthesis, Applications, and Future Directions with Challenges

This paper is about sustainable Electromagnetic Metamaterials (EM-MM), which are a new class of artificial materials with unique electromagnetic properties that cannot be found in nature. These materials are made from discrete micro and nanoscale objects which resonate, allowing for precise control over how they interact with electromagnetic waves, and hence, leading to unheard of functionalities. Thus the need for sustainable synthesis methods for EM-MM has become paramount to mitigate the quantity of resources associated with conventional fabrication techniques. Renewable resources like biopolymers that mimic natural patterns are examples of the sustainable use of bio based synthetic material pathways. This may guarantee sustainability through fabricating additive manufacturing strategies, especially 3D printing innovation where fabric statement is controlled only as required, diminishing waste. With all this recycling and up cycling offer opportunities for development and cost reduction while reducing the natural impacts related to sustainability. There are several different domains have benefited from the application of EM MM, for example solar energy harvesting offer potential for sustainable power generation, imaging uses met material lenses which have superior resolution and sensitivity, while in telecommunications met material antennas ensure to transmit and get signals more successfully. But there are still a few issues that still need to be resolved in electromagnetic met materials. Future directions include the research of incorporating a plan of new types of electromagnetic composites with upgraded qualities and sustainable synthesis strategies. Applications of technology require to overcome practical challenges such as integration, toughness, and cost-effectiveness while assessing societal implications, financial, and social affects. For the sustainable advancement of metamaterials in order to deal with major societal concerns, minimizing their natural impressions requires collaboration and moral concerns.

Designing liquid metal microstructures through directed material extrusion additive manufacturing

Material extrusion (MEX) of soft, multifunctional composites consisting of liquid metal (LM) droplets can enable highly tailored properties for a range of applications from soft robotics to stretchable electronics. However, an understanding of how LM ink rheology and print process parameters can reconfigure LM droplet shape during MEX processing for in-situ control of properties and function is currently limited. Herein, the material (ink viscosity, and LM droplet size) and process (nozzle velocity, height from print bed, and extrusion rate) parameters are determined which control LM microstructure during MEX of these composites. The interplay and interdependence of these parameters is evaluated and nearly spherical LM droplets are transformed into highly elongated ellipsoidal shapes with an average aspect ratio of 12.4 by systematically tuning each individual parameter. Material and process relationships are established for the LM ink which show that an ink viscosity threshold should be fulfilled to program the LM microstructure from spherical to an ellipsoidal shape during MEX. Additionally, the thin oxide layer on the LM droplets is found to play a unique and critical role in the reconfiguration and retention of droplet shape. Finally, two quantitative design maps based on material and process parameters are presented to guide MEX additive manufacturing strategies for tuning liquid droplet architecture in LM-polymer inks. The insights gained from this study enable informed design of materials and manufacturing to control microstructure of emerging multifunctional soft composites.

Optimal after-sales service offering strategy: Additive manufacturing, traditional manufacturing, or hybrid?

In this study, we investigate the effects of additive manufacturing (also known as 3D printing) on the optimal after-sales service offering strategy. A service offering strategy should be selected on the basis of not only its characteristics but also customers’ decisions influenced by the associated costs of each strategy. Two supply chain structures are examined in this study: one in which the service provider is vertically integrated and the other in which an outside agent is involved to adopt additive manufacturing. We find that when the nonavailability cost (associated with traditional manufacturing) is moderate compared to the unreliability cost (associated with additive manufacturing), the service provider should adopt the hybrid strategy that offers both additively and traditionally manufactured parts; otherwise, the pure additive manufacturing or traditional manufacturing strategy dominates when the nonavailability cost is high or low respectively. This key finding is robust in that it holds for both the short-term and long-term problems and is irrelevant to whether the service provider is vertically integrated. In addition, our results indicate that the endogenous service level has different impacts on the equilibrium in the two examined supply chains. Finally, we reveal that allowing an outside agent to adopt additive manufacturing is profitable when the service provider adopts the hybrid strategy in both the investigated supply chain structures; otherwise, deterring the entry of the outside agent is the unique equilibrium for the service provider.

Effective Strategies for Electron Beam Additive Manufacturing of Graded Metal Interfaces between Stainless Steel and Vanadium

This work examines the feasibility of joining two dissimilar metals, vanadium (V) and wrought Nitronic 40 stainless steel, through electron beam additive manufacturing (EBAM). Depositing V on Nitronic 40 led to mixed results with some builds exhibiting microcracking and other builds exhibiting severe cracking resulting in delamination. These build failures are thought to be caused by a large coefficient of thermal expansion (CTE) mismatch and solubility issues, demonstrating the challenges associated with this material combination. The large melting temperature discrepancy between Nitronic 40 and V was thought to exacerbate the issues with CTE mismatch and solubility. Four strategies could be employed by EBAM to mitigate the observed issues to successfully deposit V on Nitronic 40: (1) adjust wire feed speed, (2) use dual wire feeders, (3) use different wire feedstocks to control composition, and (4) create a transition layer known as buttering to accommodate CTE mismatch.

Integrating Melt Electrowriting and Fused Deposition Modeling to Fabricate Hybrid Scaffolds Supportive of Accelerated Bone Regeneration.

Emerging additive manufacturing (AM) strategies can enable the engineering of hierarchal scaffold structures for guiding tissue regeneration. Here, the advantages of two AM approaches, melt electrowriting (MEW) and fused deposition modelling (FDM), are leveraged and integrated to fabricate hybrid scaffolds for large bone defect healing. MEW is used to fabricate a microfibrous core to guide bone healing, while FDM is used to fabricate a stiff outer shell for mechanical support, with constructs being coated with pro-osteogenic calcium phosphate (CaP) nano-needles. Compared to MEW scaffolds alone, hybrid scaffolds prevent soft tissue collapse into the defect region and support increased vascularization and higher levels of new bone formation 12 weeks post-implantation. In an additional group, hybrid scaffolds are also functionalized with BMP2 via binding to the CaP coating, which further accelerates healing and facilitates the complete bridging of defects after 12 weeks. Histological analyses demonstrate that such scaffolds support the formation of well-defined annular bone, with an open medullary cavity, smooth periosteal surface, and no evidence of abnormal ectopic bone formation. These results demonstrate the potential of integrating different AM approaches for the development of regenerative biomaterials, and in particular, demonstrate the enhanced bone healing outcomes possible with hybrid MEW-FDM constructs.

Alloying strategies for additive manufacturing of Ti6Al4V based alloys, composites and functionally graded materials: Microstructure and phase evolution of intra and inter-layer

The further developments of additive manufacturing (AM) provides a possibility for Ti6Al4V and its functionally graded materials (FGMs), but limits further applications due to its low ductility, low microhardness and poor wear resistance. The key lies in the presence of microstructures such as epitaxial columnar β-grain orientation and heterogeneous phase distribution in AM Ti6Al4V, as well as the interfacial bonding problems (intermetallic phases, delamination, cracking) in AM Ti6Al4V FGMs. In order to address these fundamental intra and inter-layer problems, firstly the microstructure and phase evolution process of AM Ti6Al4V columnar-to-equiaxed transformation (CET) promoted by some alloying strategies was summarized in this paper according to alloying elements and reinforcing particle types. Subsequently, controlled changes in the composition and microstructure of AM Ti6Al4V FGMs were achieved by adding interlayers/introducing gradient interfaces, and the metallurgical reactions and phase transformation mechanisms that inhibit the formation of intermetallic compounds and interfacial defects were explored. Finally, the difficulties and future research directions for alloying strategies to achieve high strength and ductility of AM Ti6Al4V were presented. This review aims to improve the reliability of AM Ti6Al4V and its FGMs for applications in critical load-bearing structures through in-situ alloying and multi-material for the microstructure design of AM Ti6Al4V.

Strategies for wire arc additive manufacturing of thin walls and overhangs

Strategies for wire arc additive manufacturing of thin walls and overhangs