Structural Electronics through Additive Manufacturing and Micro-Dispensing

Two types of additive manufacturing (AM) techniques, fused filament fabrication (FFF) and selective laser sintering (SLS), were employed to fabricate specimens from three widely used AM polymers: polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyamide (PA): the first two using FFF and PA using SLS. The single‐edge notch bending (SENB) test was employed to measure the mode‐I fracture toughnesses of bulk and AM specimens in three directions relative to the printing direction. Unlike their bulk counterparts, AM polymers exhibited anisotropic fracture toughness. The degree of anisotropy in FFF‐PLA was much larger than FFF‐ABS and SLS‐PA. The smallest fracture toughness value for each AM polymer was achieved along the transverse printing direction. Different AM techniques affect fracture toughness differently. For instance, FFF is shown to increase PLA's plastic deformation, while SLS reduces PA's ductility. The decrease in fracture toughness is consistently observed when transitioning from bulk polymers to AM ones, reaching as much as 75%. This study provides insights into the fracture toughness of AM parts made via popular plastics, which are crucial for designing structural parts using FFF and SLS processes.

This thesis reports investigations on Additive Manufacturing (AM) techniques, namely valvejet technology and fused deposition modelling for the production of personalised dosage forms of low dose and low-melting drugs. Inkjet printing has been examined by several research groups for its potential to dispense pharmacological agents into final products, ranging from solid oral dosage forms to functionalized medical devices. However, the thermal and piezoelectric print heads reported in these investigations are best suited to printing solution and nano-suspension inks with particle sizes, solvents and rheological parameters in a narrow range specified by their manufacturers. In the work presented here, we examined a more robust valvejet (â electromagneticâ ) technology which allows coarse and viscous micro-suspensions to be dispensed with high accuracy and precision. More than 40% of newly discovered drugs and an estimated 90% of pipeline drugs are poorly soluble, so there is a clear need for robust printing methods, suitable for printing coarse suspensions. Paracetamol and indomethacin were selected to demonstrate the feasibility of printing soluble and poorly soluble APIs in the form of solution and suspension inks respectively. Valvejet technology has been investigated as a means of depositing solutions with a broader range of viscosity and suspensions with average particle sizes exceeding 2 μm. Printed samples were characterised for their morphology, chemical and solid-sate properties of the active ingredient and content uniformity and mechanical robustness of the coatings. Results from this investigation were used to develop a fixed dose combination of pharmacologically relevant fixed dose combination of ramipril and glimepiride. Also, valvejet technology (being devoid of temperature and stress elements often associated with most additive manufacturing techniques) has been demonstrated to be a promising alternative for producing personalised drug products of drugs that are susceptible to processing conditions. Fused deposition modeling (FDM) is the most commonly investigated of the additive manufacturing techniques to produce drug products and is well suited for the production of high-dose dosage forms. Higher temperatures associated with FDM is the major limiting factor in application of this technique for lower-melting drugs. Kollidon VA64 and Kollidon 12PF, immediate release polymers and PEG 1500 as the primary plasticizer have been investigated to lower the FDM temperature to <100 °C. Ramipril a thermolabile drug with a low melting point 109 °C has been chosen as model drug, the filaments of which were produced using Kollidon VA64 and Kollidon 12PF and was printed at 90 °C- the lowest temperature reported until this work was published and is the lowest melting point drug investigated to date by FDM printing. Developing a library of polymer and excipient combinations that are suited for FDM printing at lower temperatures deserves further investigation.

Chapter 7 - Additive manufacturing techniques used for preparation of scaffolds in bone repair and regeneration

4 - Biofabrication via integrated additive manufacturing and electrofluidodynamics

Metal Additive Manufacturing (AM) is increasingly being used to make functional components. One of the barriers for AM components to become mainstream is the difficulty to certify them. AM components can have widely different properties based on process parameters. Improving an AM processes requires an understanding of process-structure-property correlations, which can be gathered in-situ and post-process through nondestructive and destructive methods. In this study, two metal AM processes were studied, the first is Ultrasonic Additive Manufacturing (UAM) and the second is Laser Powder Bed Fusion (L-PBF). The typical problems with UAM components are inter-layer and inter-track defects. To improve the UAM process, an in-situ quality evaluation technique was desired. Several NDE techniques were tested in a lab environment before ultrasonic NDE was chosen as a practical, robust, and cost-effective NDE tool. An in-situ monitoring setup was designed and built on an UAM system. NDE results showed interesting features that were simulated through analytic and finite element wave-propagation models. AM layers with defects were characterized as an intact layer and a finite interfacial stiffness spring. The spring stiffness coefficient is a quality parameter that was used to characterize AM layers through a model-based inversion method. In-situ and post-process NDE provided an understanding of defect generation and propagation in UAM. A novel solid-state repair mechanism based on Friction Stir Processing (FSP) was proposed and demonstrated. The quality of L-PBF components depends on several factors including laser power, scan speed, hatch spacing, layer thickness, particle shape/size distribution and other build conditions. Developing process parameters for a new material is an expensive and complex optimization problem. Post-process ultrasonic NDE tests revealed that the model-based in-situ quality monitoring developed for UAM is also applicable to L-PBF Additive Manufacturing. A similar NDE set-up was designed and installed on an open-architecture L-PBF system. A layer-by-layer bond quality evaluation demonstrates the ability to detect good-quality bonds hidden behind poor-quality regions for Inconel 625 alloy. A cost-effective, process parameter development methodology has been proposed and demonstrated.

Fuzzy logic based expert system for prediction of tensile strength in Fused Filament Fabrication (FFF) process

Embossing technique is an essential operation in the print finishing process. It entails permanently changing the shape of the paper surface by applying pressure with the embossing die, so as to create a recessed or raised image. Embossing dies are made using conventional techniques such as chemical etching or milling. These techniques in the production of conventional embossing die imply the use of different machines and devices, plenty workspace, and often insufficient flexibility in quick job changes. By replacing conventional with additive manufacturing techniques, these problems imposed by the market can be overcome to a great extent. Using additive manufacturing techniques in embossing dies production process requires prior understanding of factors influencing mechanical and physical properties of produced samples. Fused Deposition Modelling (FDM) technique is commonly used in additive manufacturing due to its simplicity and availability. The surface roughness of FDM produced embossing dies is an important factor which can alter the quality of the embossed paper material. Excellent mechanical properties of the die are also required due to pressure forces applied in the embossing process. This paper aims to investigate the influencing process factors in FDM additive manufacturing found in current scientific researches and implement these findings for embossing dies production. Influence of these factors on surface roughness, tensile and compression strength, the quantity of used material and production time were investigated. Findings imply that vast variety of process factors influence chosen dependent variables of samples printed with FDM technique. Many researchers have investigated these factors, but mainly in the field of industrial engineering, electronics and bioengineering. Hence, the importance of this paper is in finding a way to implement these findings in the field of graphic engineering and design.

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.

Purpose The development of additive manufacturing (AM) techniques has significantly expanded the design space for engineering structures and facilitated the practical application of novel concepts, such as meta-materials with diverse microstructures. However, in load-bearing applications—particularly in aerospace and aeroengine fields—additively manufactured (AMed) metallic materials and structures still face limitations due to the presence of inherent defects. For meta-materials, the geometric accuracy of microstructural cells is also difficult to ensure using current metal AM technologies. These defects and geometric inaccuracies can markedly affect the mechanical properties of mechanical meta-materials. Consequently, a substantial body of research has focused on investigating the mechanical behavior and performance of AMed mechanical meta-materials. This paper presents a comprehensive review of recent advancements in metal AM technologies, with a particular focus on defect characterization methods and the evaluation of strength and fatigue properties in AMed mechanical meta-materials. Design/methodology/approach This paper provides a state-of-the-art review on the AM techniques for mechanical meta-materials, defects and defect characterization methods in AMed structures, and evaluation methods of strength and fatigue properties of mechanical meta-materials. Findings Metal AM techniques for mechanical meta-materials, like selective laser melting, wire-arc AM, etc, and recently developed technologies like, online inspection during the AM process, are reviewed. The defects in AMed meta-materials, along with the corresponding characterization methods, are systematically summarized. Additionally, this paper presents a comprehensive overview of evaluation approaches for the strength and fatigue properties of mechanical meta-materials, encompassing experimental testing, theoretical modeling, numerical simulation, and machine learning techniques. Future perspectives on manufacturing and the mechanical property study of mechanical meta-materials are also given. Originality/value A systematic summary of metal AM techniques, as well as defect detection and characterization methods in AMed mechanical meta-materials, is provided. Furthermore, the paper presents a comprehensive review of the mechanical properties of mechanical meta-materials, with a particular focus on strength and fatigue performance.

By allowing the production of complicated geometries with less tooling and material waste, Additive Manufacturing (AM) is transforming the fabrication of parts. The objective of this study is to compare the feasibility and performance of two AM techniques, Fused Deposition Modeling (FDM) and Stereolithography (SLA) to produce snap-fit plastic parts. The study specifically investigates how process parameters and prints orientation affect defect formation, dimensional accuracy, and structural suitability. The parts were assessed through qualitative defect analysis and quantitative dimensional measurements. Additionally, the effect of build orientation and support structure design was evaluated. A mathematical model was applied to estimate and validate printing time based on layer height. SLA parts demonstrated superior dimensional accuracy, with average deviations significantly lower than those observed in FDM prints. However, SLA was more prone to support-induced surface damage and brittleness. FDM produced structurally stronger but dimensionally less accurate parts, affected by brim residues and sagging. The validated print time model further confirmed the reliability of predictive manufacturing planning. Although AM, particularly SLA, seems encouraging for creating exact, low-volume snap-fit assemblies, both methods have their own difficulties. While FDM is preferable for fast prototyping of mechanically strong components, SLA is appropriate for applications needing critical details. The results underline AM's present constraints for mass production even if they show promise in generating tailored functional components.

Mechanical Properties of Continuous Kevlar Fiber Reinforced Composites Fabricated by Fused Deposition Modeling Process

Recently, high-performance lightweight materials with outstanding mechanical properties have opened up their way to some sophisticated industrial applications. As one of these systems, aluminum matrix composites/nanocomposites (AMCs) offer an outstanding combination of relative density, hardness, wear resistance, and mechanical strength. Until now, several additive manufacturing methods have been developed for fabrication of 3D metallic components among them, selective laser melting (SLM), electron beam melting (EBM), laser metal deposition (LMD), Wire+Arc additive manufacturing (WAAM), and ultrasonic additive manufacturing (UAM) are of prime significance. Unlike other methods, in ultrasonic additive manufacturing, the ultrasonic waves are used instead of applying the sintering process. This technique is well-known for its ability to produce 3D components by repeating the alternative welding and machining procedures at low temperatures. This is why it can overcome the technological issues arisen from the high-temperature sintering. The present review strives to provide an inclusive introduction to the principles of ultrasonic additive manufacturing method and recent advances in ultrasonic additive manufacturing of aluminum matrix composites/nanocomposites. Also, the challenges of this new emerging technique, i.e. its dependence to the applied weld power, is addressed in the paper. The authors attempt to give some perspectives to the researchers for further investigations in this new-emerging field.

Auxetic structures are a special class of structural components that exhibit a negative Poisson’s ratio (NPR) because of their constituent materials, internal microstructure, or structural geometry. To realize such structures, specialized manufacturing processes are required to achieve a dimensional accuracy, reduction of material wastage, and a quicker fabrication. Hence, additive manufacturing (AM) techniques play a pivotal role in this context. AM is a layer-wise manufacturing process and builds the structure as per the designed geometry with appreciable precision and accuracy. Hence, it is extremely beneficial to fabricate auxetic structures using AM, which is otherwise a tedious and expensive task. In this study, a detailed discussion of the various AM techniques used in the fabrication of auxetic structures is presented. The advancements and advantages put forward by the AM domain have offered a plethora of opportunities for the fabrication and development of unconventional structures. Therefore, the authors have attempted to provide a meaningful encapsulation and a detailed discussion of the most recent of such advancements pertaining to auxetic structures. The article opens with a brief history of the growth of auxetic materials and later auxetic structures. Subsequently, discussions centering on the different AM techniques employed for the realization of auxetic structures are conducted. The basic principle, advantages, and disadvantages of these processes are discussed to provide an in-depth understanding of the current level of research. Furthermore, the performance of some of the prominent auxetic structures realized through these methods is discussed to compare their benefits and shortcomings. In addition, the influences of geometric and process parameters on such structures are evaluated through a comprehensive review to assess their feasibility for the later-mentioned applications. Finally, valuable insights into the applications, limitations, and prospects of AM for auxetic structures are provided to enable the readers to gauge the vitality of such manufacturing as a production method.

This work evaluates the applicability of machine learning (ML) tools in additive manufacturing (AM) processes. One of the most employed AM techniques is fused deposition modeling (FDM), where a part is created from a computer-aided design (CAD) model using layer-by-layer deposition of a feedstock plastic filament material extruded through a nozzle. Owing to the large number of parameters involved in the manufacturing process, it is necessary to identify printing parameters ranges to improve mechanical properties as yield and ultimate strength. In that sense, ML has proven to be a reliable tool in engineering and materials processing, where hybrid ML algorithms are the best alternative since one-part acts as a forecaster, and the other part acts as an optimizer. To evaluate the performance of wood composite filament fabricated by FDM a uniaxial tensile test was performed at room temperature. The experimental procedure was carried out with a design of experiments of four factors at three levels, where the statistical significance of layer thickness, fill density, printing speed and raster angle was obtained as well as their interactions. Furthermore, ML’s algorithm accuracy was explored, where a neuro-fuzzy system (ANFIS) was trained and tested with the experimental data. Through the development of the present work, it is concluded that layer thickness and raster angle play a significant role in FDM of a wood composite filament where fibers presence increases the layer thickness accelerating the FDM process.

Additive manufacturing methods are briefly reviewed. Proposals are outlined for the use of ultrasound in fused deposition modeling (FDM) and selective laser melting (SLM). Approaches to ultrasonic additive manufacturing (UAM) are discussed.