Advances In Additive Manufacturing Techniques Research Articles

Computational investigations for topology optimization of UAV and small-scale aircraft wings

This study was conducted under the 4R-UAV project. The project is funded by the Latvian Council of Science with the goal of creating an innovative, aerodynamically improved, environmentally friendly, zero waste, and zero emission UAV. For the Circular Aviation 4R (Reduce, Recycle, Reuse, Redesign) concept, this paper covers two Rs (Reduce and Redesign) aspects of the 4R-UAV project. Topology optimization of structures has gained enormous potential with the advances in additive manufacturing techniques. However, it is still challenging when it comes to conventional manufacturing. Aircraft/UAV wings are conventionally hollow structures and leave almost little or no space for further material removal. It becomes even more complicated when conventional manufacturing limitations are further imposed. Nevertheless, topology optimization is indeed an excellent way of reducing the mass of the structures by keeping the mechanical strength intact. This computational study attempts to implement topology optimization on a small-scale aircraft aluminum alloy wing as well as on a carbon composite UAV wing. In order to ensure the feasibility of not only additive manufacturing but also conventional manufacturing, controlled/limited topology optimization was applied only to the ribs of the wings. It was found that topology optimized wing ribs (aluminum and carbon composite) demonstrated a 20% mass reduction while up to 10% overall mass reduction of the wings was achieved. Moreover, after the topology optimization, the wings demonstrated improved mechanical characteristics and factor of safety. The knowledge learned from this study will be implemented for the topology optimization of the future small-scale 4R-UAV wings which will be mainly manufactured using additive manufacturing.

Optimized analytical approach for the detection of process-induced defects using acoustic emission during directed energy deposition process

Directed energy deposition (DED), an advanced additive manufacturing (AM) technique, facilitates the production of complex metallic and metal matrix composite structures. The DED process has continuously improved and offers numerous advantages for depositing high-quality coatings with excellent wear and corrosion resistance onto metallic surfaces. The dynamic nature of the process, however, introduces a significant risk of process-induced defects in manufactured parts. This study presents an optimized analytical approach using acoustic emission (AE) based defect detection technique to identify and quantify process-induced cracks during the DED process. The developed signal processing technique enabled the identification of actual AE events associated with cracking, distinguishing them from other disturbances. Experimental validation was conducted using manufactured parts that were longitudinally sectioned to determine the relationship of the crack location with the recorded acoustic signal. The demonstrated correlation of acoustic signatures with cracking illustrates the robustness of the AE technique to identify the process-induced cracking for quality assurance during the DED process.

Fused deposition modeling of Inconel 625 alloy: Effect of hot isostatic pressing on the microstructure and tensile properties

Inconel 625 alloy was fabricated using fused deposition modeling (FDM), an emerging advanced additive manufacturing (AM) technique. Subsequently, the effects of hot isostatic pressing (HIP) on its microstructure and mechanical properties were investigated. Notably, HIP treatment significantly reduced the defect density, resulting in enhanced tensile ductility.

Melt-electrowriting of 3D anatomically relevant scaffolds to recreate a pancreatic acinar unit in vitro

Melt-electrowriting (MEW) belongs to the group of advanced additive manufacturing techniques and consists of computer-aided design (CAD)-assisted polymer extrusion combined with a high-voltage supply to achieve deposition of polymeric fibers with diameters in the micrometric range (1 to 20 μm) similar to the size of natural extracellular matrix fibers. In this work, we exploit MEW to design and fabricate a three-dimensional (3D) model that resembles the morphology of the exocrine pancreatic functional unit without the need of supports, mandrels, or sacrificial materials. Optimized process parameters resulted in a MEW scaffold having regular fibers (19 ± 5 μm size) and an acinar cavity showing high shape fidelity. Then, human foreskin fibroblasts (HFF1) and human pancreatic ductal epithelial cells (HPDE), wild-type HPDE, and HPDE overexpressing KRAS oncogene were allowed to colonize the entire 3D structure and the acinar cavity. Thus, a physiologically relevant 3D model was created in vitro after 24 days using a co-culture protocol (14 days of HFF1 alone plus 10 days of HPDE and HFF1 co-culture). The effect of cell crosstalk within the MEW scaffolds was also assessed by monitoring HFF1 secretion of interleukin (IL)-6, a pro-inflammatory cytokine responsible for the inflammatory cascade occurring in pancreatic cancer. High levels of IL-6 were detected only when fibroblasts were co-cultured with the HPDE overexpressing KRAS. These findings confirmed that the MEW 3D in vitro model is able to recreate the characteristic hallmark of the pathological condition where cancer oncogenes mediate fibroblast activities.

Advances in Additive Manufacturing Techniques for Electrochemical Energy Storage

AbstractThe increasing adoption of additive manufacturing (AM), also known as 3D printing, is revolutionizing the production of wearable electronics and energy storage devices (ESD) such as batteries, supercapacitors, and fuel cells. This surge can be attributed to its outstanding process versatility, precise control over geometrical aspects, and potential to reduce costs and material waste. In this comprehensive review, major AM processes like inkjet printing, direct ink writing, fused deposition modeling, and selective laser sintering/melting along with possible configurations and architectures, are elaborately discussed for each bespoke ESD. The application of 3D‐printed energy storage devices in wearable electronics, Internet of Things (IoT)‐based devices, and electric vehicles are also mentioned in the review. The role of AM in facilitating the production of solid‐state batteries has also revolutionized the electric vehicle (EV) industry. Recent progress in the field of AM of energy systems with solid electrolytes and potential future directions such as 4D printing to incorporate stimuli‐responsive behavior in 3D‐printed materials, biomimetic design optimization, and additive manufacturing of ESD in a micro‐gravity environment have also been highlighted. Extensive research and continuous progress in this field are expected to enhance the longetivity, industrial scalability, and electrochemical performance of 3D‐printed energy storage devices in future.

Characterisation and thermochemical stability analysis of 3D printed porous ceria structures fabricated via composite extrusion Modelling

Composite Extrusion Modelling (CEM) is an advanced additive manufacturing technique that enables rapid, cost-effective production of complex, customisable designs. In this study, CEM 3D printing of porous ceria structures is reported for the first time. First, the ceramic injection molding (CIM) feedstock with thermoplastic properties was prepared and optimised in terms of its rheological properties to ensure good workability for the printing process at 140–150 °C. Subsequently, the thermoplastic feedstock was used to print porous ceria structures for thermochemical splitting. The feasibility of printing various porous structures with different dimensions, geometries, and macropore sizes was investigated, and the printing parameters: extrusion multiplier (EM), extrusion temperature (ET), nozzle velocity (NV), and layer thickness (LT), were optimised to prevent clogging of the printing nozzle and to achieve homogeneous overlap of the printed layers. The optimised printing parameters for ceria structures are EM 1.3, ET 150 °C, LT ∼ 0.13 mm, and NV 50 mm/s, which were determined by multiple response optimisation process. The sintered 3D-printed bars yielded relative densities of ≥ 98 % and a total microporosity of 0.29 %, measured with a Hg porosimeter. Thermogravimetric analysis (TGA) and cyclic stability experiments were performed on the printed porous ceria structures and showed stability over 100-redox cycles.

Three-Dimensional Printing, an Emerging Advanced Technique in Electrochemical Energy Storage and Conversion

Three-dimensional (3D) printing, as an advanced additive manufacturing technique, is emerging as a promising material-processing approach in the electrical energy storage and conversion field, e.g., electrocatalysis, secondary batteries and supercapacitors. Compared to traditional manufacturing techniques, 3D printing allows for more the precise control of electrochemical energy storage behaviors in delicately printed structures and reasonably designed porosity. Through 3D printing, it is possible to deeply analyze charge migration and catalytic behavior in electrocatalysis, enhance the energy density, cycle stability and safety of battery components, and revolutionize the way we design high-performance supercapacitors. Over the past few years, a significant amount of work has been completed on 3D printing to explore various high-performance energy-related materials. Although impressive strides have been made, challenges still exist and need to be overcome in order to meet the ever-increasing demand. In this review, the recent research progress and applications of 3D-printed electrocatalysis materials, battery components and supercapacitors are systematically presented. Perspectives on the prospects for this exciting field are also proposed with applicable discussion and analysis.

Research Progress of Bone Implant Additive Manufacturing

Bone implants are currently a solution for the treatment of large bone defects. The structural design and manufacture of complex bone tissue engineering scaffolds can be realized by using additive manufacturing technology. Advances in additive manufacturing techniques and the continued emergence of related materials provide different opportunities for new bone implant techniques to achieve the challenging requirements of proposed bone implants. The purpose of this review is to present the current status and analyze the advantages and disadvantages of various additive manufacturing for the manufacturing of bone implants. Five different manufacturing techniques (multilayer deposition forming, ink direct writing, laser melting, laser sintering, and light curing are reviewed.) and the currently required bone implants technology, and thus put forward the research and development direction of additive manufacturing suitable for bone implants.

A comparison of droplet deposition modelling, fused filament fabrication, and injection moulding for the production of oral dosage forms containing hydrochlorothiazide

Additive manufacturing (AM) possesses a transformative potential to revolutionize personalized medicine fabrication. Fused filament fabrication (FFF), an advanced AM technique, enables the development of tailored medicines with customizable dosages and controlled release properties. Nevertheless, filament prerequisites impose material limitations and present considerable challenges, necessitating a comprehensive evaluation of mechanical, rheological, and thermal characteristics to circumvent complications during the FFF process. Droplet deposition modeling (DDM), an innovative AM approach derived from injection molding (IM) technology, processes granulate feedstock to facilitate the production of personalized medicines. This study delves into the effects of FFF, DDM, and IM techniques on the release profiles of Hydrochlorothiazide, a widely employed drug for hypertension and edema treatment. By varying infill density, the investigation assesses the manufactured tablets using DDM and FFF methods. Our findings show that tablets made with FFF and DDM with identical infill densities had distinct microstructures, resulting in variable drug release profiles. Decreasing the infill densities resulted in higher sample porosity, leading to an accelerated drug release rate. A comparative analysis of drug release profiles from DDM and IM fabricated tablets demonstrated notable differences, despite DDM's origins in injection molding technology. This comprehensive study underscores the significance of not only infill densities but also the choice of manufacturing technique, as both factors can profoundly influence drug release profiles. By shedding light on these considerations, the research contributes to the ongoing advancement of personalized medicine through additive manufacturing technologies.

Critical Feature and Seawater Testing of Cross-Flow Rotor Components Fabricated with Additive Manufacturing

Cross-flow tidal turbines are an attractive option for powering remote or off-grid applications because of their simplicity as compared to axial-flow turbines. For instance, when oriented vertically, they harvest power from any current direction with a single degree of freedom and no yaw mechanism. Additive manufacturing (AM) offers an opportunity to print parts out of a wide variety of materials that can result in components that are lighter, stronger and/or less expensive to produce than with traditional manufacturing techniques. When coupled with cross-flow turbine rotors, which require critical features (blade-strut, strut-shaft connections) to be both structurally stiff and hydrodynamically shaped, which can be challenging for typical fabrication processes, AM offers the ability to do both well. This paper describes work on the feasibility of using advanced AM techniques to fabricate small cross-flow turbine rotors for applications at sea and near remote coastal communities.
 AM materials were categorized into 3 classes – plastics, metals, and ceramics – and reviewed for suitability based on a set of engineering requirements and criteria related to turbine characteristics, material properties, and AM process capabilities. Two plastics and two metals were selected to undergo further testing: Essentium CF25, CarbonX Ult 9085, Titanium Ti-6Al-4V, and Inconel 718. Testing is conducted in three phases: the first is a long-term, 5-month submersion test in the seawater tanks at PNNL-Sequim to study corrosion, water uptake, and biofouling potential; in the second, materials are tensile tested on a load frame to find their failure parameters to compare to material standards; the third test is a fatigue test consisting of cyclically loading test parts with a known force on the order of that exerted on rotor blades in a 1.5 m/s current flow. These tests are designed to discern the suitability of AM materials since their properties from 3D printing processes are known to vary from published parameters. The test samples undergoing submersion testing will be tension tested and compared to control samples not subjected to extended seawater immersion. For fatigue life testing, a small rotor is expected to complete 100 million cycles over the course of a year-long lifespan, but for the case herein is restricted to 1 million for a preliminary performance evaluation. The first 10k cycles are run on an MTS 312.21 load frame at a rate of 0.2 Hz, with the remaining on a custom-built cyclic-deflection test rig at 0.8 Hz.

Experimental Investigations on Wear and Mechanical Properties of Post Heat Treated Am 17-4 PH SS Parts

Abstract: Selective laser melting (SLM) is an advanced additive manufacturing (AM) technique which constructs 3D objects by melting powder materials in a laser, layer by layer, according to a computer-aided design (CAD) model. SLM is utilized to create products from a variety of materials, with qualities equivalent to benchmarked conventionally manufactured components. Because of these qualities, 17-4PH stainless steel is a suitable material for a diverse range of industrial applications, including structural parts in the aerospace, chemical and petrochemical sectors. The specimens using 17-4PH stainless steel powder were successfully manufactured by optimizing the parameters using SLM process. The as built specimens were heat treated using two different cooling rates. Present research paper evaluates and compares the microstructure, wear behavior and tensile strength of the finished additively manufactured specimens with as built, post heat treated and wrought specimens.

Melt electrowritten scaffolds containing fluorescent nanodiamonds for improved mechanical properties and degradation monitoring

Biocompatible fluorescent nanodiamonds (FNDs) were introduced into polycaprolactone (PCL) – the golden standard material in melt electrowriting (MEW). MEW is an advanced additive manufacturing technique capable of depositing high-resolution micrometric fibres. Due to the high printing precision, MEW finds growing interest in tissue engineering applications. Here, we introduced fluorescent nanodiamonds (FNDs) into polycaprolactone prior to printing to fabricate scaffolds for biomedical applications with improved mechanical properties. Further FNDs offer the possibility of their real-time degradation tracking. Compared to pure PCL scaffolds, the functionalized ones containing 0.001 wt% of 70 nm-diameter nanodiamonds (PCL-FNDs) showed increased tensile moduli (1.25 fold) and improved cell proliferation during 7-day cell cultures (2.00 fold increase). Furthermore, the addition of FNDs slowed down the hydrolytic degradation process of the scaffolds, accelerated for the purpose of the study by addition of the enzyme lipase to deionized water. Pure PCL scaffolds showed obvious signs of degradation after 3 h, not observed for PCL-FNDs scaffolds during this time. Additionally, due to the nitrogen-vacancy (NV) centers present on the FNDs, we were able to track their amount and location in real-time in printed fibres using confocal microscopy. This research shows the possibility for high-resolution life-tracking of MEW PCL scaffolds’ degradation.

Crack Inhibition and Performance Modification of NiCoCr-Based Superalloy with Y2O3 Nanoparticles by Laser Metal Deposition.

A new precipitation strengthening NiCoCr-based superalloy with favorable mechanical performance and corrosion resistance was designed for ultra-supercritical power generation equipment. The degradation of mechanical properties and steam corrosion at high temperatures put forward higher requirements for alternative alloy materials; however, when the superalloy is processed to form complex shaped components through advanced additive manufacturing techniques such as laser metal deposition (LMD), hot cracks are prone to appear. This study proposed that microcracks in LMD alloys could be alleviated with powder decorated by Y2O3 nanoparticles. The results show that adding 0.5 wt.% Y2O3 can refine grains significantly. The increase in grain boundaries makes the residual thermal stress more uniform to reduces the risk of hot cracking. In addition, the addition of Y2O3 nanoparticles enhanced the ultimate tensile strength of the superalloy at room temperature by 18.3% compared to original superalloy. The corrosion resistance was also improved with 0.5 wt.% Y2O3, which was attributed to the reduction of defects and the addition of inert nanoparticles.

In-situ synthesis of Ti5Si3-reinforced titanium matrix nanocomposite by selective laser melting: Quasi-continuous reinforcement network and enhanced mechanical performance

Titanium matrix nanocomposites (TMNCs) with quasi-continuously distributed Ti5Si3 reinforcements exhibit high material strength, good thermal stability, great tribological properties, and high fracture toughness. However, fabrication of such TMNCs via advanced additive manufacturing (AM) techniques has rarely been realized due to the presence of AM-induced large columnar grains and the cracking issue associated with the reinforcement coarsening. Here, we report a nanoparticle-mediated approach to in-situ fabricate nano-Ti5Si3 reinforced TMNC coatings by selective laser melting (SLM) of Ti powders and minor amount of SiC nanoparticles. Results showed that with the optimized SiC amount and SLM processing parameters, a crack-free and ultrahigh-strength TMNC consisted of near-equiaxed grain structure and nano-scale Ti5Si3 network at the grain boundaries was successfully produced. The optimized TMNC showed an ultrahigh surface microhardness of 706 VHN, 51.5% higher than that of SLM-fabricated SiC-free sample (466 VHN). Spherical nanoindentation results showed that the effective indentation modulus and indentation yield strength were improved by 62.6% and 57.2%, respectively. A more pronounced strain hardening phenomenon was also observed in the optimized TMNC. The dry sliding tests revealed that the wear rate was reduced by 70%, and the wear mechanism transferred from abrasion to adhesion.

Mechanical properties and microstructure of laser-cladding additively manufactured 316L stainless steel sheets

Laser cladding (LC) technique, as one of advanced additive manufacturing techniques, has been proved to own great potential to be applied for building and civil engineering. By using the LC technique, the laser cladding sheet (LC sheet) can be realised by overlapping track-by-track in a layer and layer-by-layer through the depth of the sheet. However, the lack of knowledge on the structural performance of this LC sheet impedes the application of the LC technique in building and civil infrastructure. Accordingly, this paper presents the first results of a wide experimental campaign aimed at evaluating the material behaviour of LC sheets. In this investigation, the mechanical properties, degree of anisotropy and microstructure of the LC sheets produced by using commercial 316 L stainless steel powder were studied. Through tensile tests, the influences of the scanning pattern, specimen orientation and thickness on the mechanical properties of the LC sheets were investigated. The test results revealed the elastic isotropy for the elastic modulus and Poisson's ratio, and the plastic anisotropy for the proof stresses, ultimate stress and elongation, but the degree of anisotropy for most of the plastic mechanical properties was less than 20%. The microindentation hardness of the LC sheets was measured, and the linear correlation between the ultimate strength and hardness of the LC sheets was established. Microstructure analyses using metallographic and SEM tests demonstrated that the observations on the mechanical properties could be explained and rationalised by the specific microstructural features.

Design and printing of proprioceptive three-dimensional architected robotic metamaterials.

Advances in additive manufacturing techniques have enabled the creation of stimuli-responsive materials with designed three-dimensional (3D) architectures. Unlike biological systems in which functions such as sensing, actuation, and control are closely integrated, few architected materials have comparable system complexity. We report a design and manufacturing route to create a class of robotic metamaterials capable of motion with multiple degrees of freedom, amplification of strain in a prescribed direction in response to an electric field (and vice versa), and thus, programmed motions with self-sensing and feedback control. These robotic metamaterials consist of networks of piezoelectric, conductive, and structural elements interwoven into a designed 3D lattice. The resulting architected materials function as proprioceptive microrobots that actively sense and move.

Additive manufacturing of bioactive and biodegradable porous iron-akermanite composites for bone regeneration

Advanced additive manufacturing techniques have been recently used to tackle the two fundamental challenges of biodegradable Fe-based bone-substituting materials, namely low rate of biodegradation and insufficient bioactivity. While additively manufactured porous iron has been somewhat successful in addressing the first challenge, the limited bioactivity of these biomaterials hinder their progress towards clinical application. Herein, we used extrusion-based 3D printing for additive manufacturing of iron-matrix composites containing silicate-based bioceramic particles (akermanite), thereby addressing both of the abovementioned challenges. We developed inks that carried iron and 5, 10, 15, or 20 vol% of akermanite powder mixtures for the 3D printing process and optimized the debinding and sintering steps to produce geometrically-ordered iron-akermanite composites with an open porosity of 69–71%. The composite scaffolds preserved the designed geometry and the original α-Fe and akermanite phases. The in vitro biodegradation rates of the composites were improved as much as 2.6 times the biodegradation rate of geometrically identical pure iron. The yield strengths and elastic moduli of the scaffolds remained within the range of the mechanical properties of the cancellous bone, even after 28 days of biodegradation. The composite scaffolds (10–20 vol% akermanite) demonstrated improved MC3T3-E1 cell adhesion and higher levels of cell proliferation. The cellular secretion of collagen type-1 and the alkaline phosphatase activity on the composite scaffolds (10–20 vol% akermanite) were, respectively higher than and comparable to Ti6Al4V in osteogenic medium. Taken together, these results clearly show the potential of 3D printed porous iron-akermanite composites for further development as promising bone substitutes. Statement of significancePorous iron matrix composites containing akermanite particles were produced by means of multi-material additive manufacturing to address the two fundamental challenges associated with biodegradable iron-based biomaterials, namely very low rate of biodegradation and insufficient bioactivity. Our porous iron-akermanite composites exhibited enhanced biodegradability and superior bioactivity compared to porous monolithic iron scaffolds. The murine bone cells proliferated on the composite scaffolds, and secreted the collagen type-1 matrix that stimulated bony-like mineralization. The results show the exceptional potential of the developed porous iron-based composite scaffolds for application as bone substitutes.

3D-Printed Tubular Scaffolds Decorated with Air-Jet-Spun Fibers for Bone Tissue Applications.

The fabrication of instructive materials to engineer bone substitute scaffolds is still a relevant challenge. Current advances in additive manufacturing techniques make possible the fabrication of 3D scaffolds with even more controlled architecture at micro- and submicrometric levels, satisfying the relevant biological and mechanical requirements for tissue engineering. In this view, integrated use of additive manufacturing techniques is proposed, by combining 3D printing and air-jet spinning techniques, to optimize the fabrication of PLA tubes with nanostructured fibrous coatings for long bone defects. The physicochemical characterization of the 3D tubular scaffolds was performed by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, profilometry, and mechanical properties. In vitro biocompatibility was evaluated in terms of cell adhesion, proliferation, and cell–material interactions, by using human fetal osteoblasts to validate their use as a bone growth guide. The results showed that 3D-printed scaffolds provide a 3D architecture with highly reproducible properties in terms of mechanical and thermal properties. Moreover, nanofibers are collected onto the surface, which allows forming an intricate and interconnected network that provides microretentive cues able to improve adhesion and cell growth response. Therefore, the proposed approach could be suggested to design innovative scaffolds with improved interface properties to support regeneration mechanisms in long bone treatment.

Advances in Additive Manufacturing Techniques for Bioprinting

The advancements in the field of additive manufacturing have led to the significant developments in the field of biomedical sciences. This combinational progression has led to implementation of 3D printed biological components, such as cartilage, bone parts, skin layers, and other implants. Moreover, the inception of this technology in tissue engineering through integration of living cells for specific functions is another achievement bringing about a revolution in biomedical sciences. This research article aims at providing an in-depth review of the development in the additive manufacturing technologies that have been utilized for bioprinting of various tissue types, including dermal layers, bone implants, cardio-vascular parts, etc. The authors will also discuss the challenges and limitations in the technology considering the biocompatibility, mechanical properties, and incorporation of functional materials to make these artificially 3D printed components mimic properties to human biology.

Additive Manufacturing of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Poly(D,L-lactide-co-glycolide) Biphasic Scaffolds for Bone Tissue Regeneration.

Polyhydroxyalkanoates are biopolyesters whose biocompatibility, biodegradability, environmental sustainability, processing versatility, and mechanical properties make them unique scaffolding polymer candidates for tissue engineering. The development of innovative biomaterials suitable for advanced Additive Manufacturing (AM) offers new opportunities for the fabrication of customizable tissue engineering scaffolds. In particular, the blending of polymers represents a useful strategy to develop AM scaffolding materials tailored to bone tissue engineering. In this study, scaffolds from polymeric blends consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(D,L-lactide-co-glycolide) (PLGA) were fabricated employing a solution-extrusion AM technique, referred to as Computer-Aided Wet-Spinning (CAWS). The scaffold fibers were constituted by a biphasic system composed of a continuous PHBV matrix and a dispersed PLGA phase which established a microfibrillar morphology. The influence of the blend composition on the scaffold morphological, physicochemical, and biological properties was demonstrated by means of different characterization techniques. In particular, increasing the content of PLGA in the starting solution resulted in an increase in the pore size, the wettability, and the thermal stability of the scaffolds. Overall, in vitro biological experiments indicated the suitability of the scaffolds to support murine preosteoblast cell colonization and differentiation towards an osteoblastic phenotype, highlighting higher proliferation for scaffolds richer in PLGA.