Redesigning a flexural joint for metal-based additive manufacturing

Recently, Additive Manufacturing (AM) technology has been attracting interest because of its process to fabricate directly from CAD data. A laser powder bed fusion (L-PBF), one of the AM technologies, is able to form the metal three dimensional (3D) objects from metal powder by building it layer-by-layer. Generally, intensity distribution of the laser beam employed by L-PBF is Gaussian. Therefore, these beam shape has energy gradient. It is difficult to fabricate with high precision due to metal powder is aggregated at the lower energy area of beam spot. In this study, fabricated with L-PBF for the purpose to clarify the effects of energy gradient of beam spot on surface roughness Ra of 3D objects. As the evaluation method of 3D objects fabricated with L-PBF, it is employed to measuring surface roughness Ra and Vickers hardness.Recently, Additive Manufacturing (AM) technology has been attracting interest because of its process to fabricate directly from CAD data. A laser powder bed fusion (L-PBF), one of the AM technologies, is able to form the metal three dimensional (3D) objects from metal powder by building it layer-by-layer. Generally, intensity distribution of the laser beam employed by L-PBF is Gaussian. Therefore, these beam shape has energy gradient. It is difficult to fabricate with high precision due to metal powder is aggregated at the lower energy area of beam spot. In this study, fabricated with L-PBF for the purpose to clarify the effects of energy gradient of beam spot on surface roughness Ra of 3D objects. As the evaluation method of 3D objects fabricated with L-PBF, it is employed to measuring surface roughness Ra and Vickers hardness.

Advancements in understanding the microstructure and properties of additive manufacturing Ti-6Al-4V alloy: A comprehensive review

Additively manufactured high permeability Fe-Ni alloys and novel bi-metallic magnetic shields

This paper reviews advanced heat transfer devices utilizing advanced manufacturing technologies, including well-established thermal management applications. Several factors have recently contributed to developing novel heat transfer devices. One of the potential technologies revolutionizing the field of energy conversion is additive manufacturing (AM), colloquially known as three-dimensional (3D) printing. This technology permits engineers to develop a product with a high level of freeform features both internally and externally within a complex 3D geometry. Among different AM approaches, selective laser melting (SLM) is a well-used technique for developing products with a lower cost-to-complexity ratio and quicker time production compared to other manufacturing processes. The integration of SLM technology into heat exchangers (HXs) and heat sinks (HSs) has a strong potential, especially to fabricate customized and complex freeform shapes. The aim of this research is to review the advancement in design complexities of different industrial heat transfer devices incorporating metal SLM fabrication. The review is not meant to put a ceiling on the AM process, but to enable engineers to have an overview of the capabilities of SLM technology in the field of thermal management applications. This review presents the opportunities and challenges related to the application of SLM technology in connection to novel HXs and HSs, as well as heat pipes (HPs). The latter are passive heat transfer devices utilized in many thermal control applications, especially related to electronics cooling and energy applications.

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.

Molded interconnect device (MID) technology is a key enabling technology with growing markets in automotive, communications, consumer electronics through integration with lighting and sensor technologies. Additive manufacturing (AM) is also a key technology as energy, material and resource efficient alternative to conventional subtractive and formative production technologies. In this contribution, powder-based additive layered manufacturing mainly selective laser melting (SLM) is focused to check the potential for substrate manufacturing, system integration and packaging concepts in electronic systems particularly for high-temperature MID applications. The challenge for an optimal mechatronic integrated device design is to simultaneously consider both the application-specific requirements and to integrate advantages of MID technology. This work focuses on the process development for the generation of conductive patterns on ceramic substrates by SLM technique. The process influencing parameters such as laser power, velocity and scan concepts were tested to check the bonding characteristics. The obtained layer thicknesses and the corresponding process-generated failure mechanisms and the mechanical stability are presented. The potential of SLM for high temperature applicability is further discussed. The influences of the printed powder height, laser parameters in combination with laser scan strategies and pattern height are discussed. The hurdles and prospects of SLM as alternative for functionalization are highlighted and discussed.

Additive manufacturing (AM) of hot-work tool steels such as H13 offers unique opportunities for producing complex, conformally cooled tools with reduced production time and material waste. In this study, five metal AM technologies—Fused Deposition Modeling and Sintering (FDMS, Desktop Metal Studio System and Zetamix), Binder Jetting (BJ), Laser Powder Bed Fusion (LPBF), and Directed Energy Deposition (DED)—were compared in terms of microstructure, porosity, and post-processing heat treatment response. The as-printed microstructures revealed distinct differences among the technologies: FDMS and BJ exhibited high porosity (6–9%), whereas LPBF and DED achieved near-full densification (<0.1%). Samples with sufficiently low porosity (BJ, LPBF, DED) were subjected to tempering and quenching treatments to evaluate hardness evolution and microstructural transformations. The satisfactory post-treatment hardness was observed in both tempered and quenched and tempered BJ samples, associated with secondary carbide precipitation, while LPBF and DED samples retained stable martensitic structures with hardness around 600 HV0.5. Microstructural analyses confirmed the dependence of phase morphology and carbide distribution on the thermal history intrinsic to each AM process. The study demonstrates that while FDMS and BJ are more accessible and cost-effective for low-density prototypes, LPBF and DED offer superior density and mechanical integrity suitable for functional tooling applications.

Powder recoating is a critical aspect of powder-based Additive Manufacturing (AM) techniques. The creation of a uniform powder layer is a top priority due to the dependence of the mechanical and microstructural properties of the specimen. Several recoaters, including blade and roller, are reported in the literature to distribute and level uniform powder layers to fulfill the layerwise AM approach. However, the literature fails to report a framework for selecting the optimal blade recoater. This study proposes a framework based on four parameters: deep-dipping approach, layer thickness, recoating time, and powder wastage. The authors tailored the deep-dipping approach from the Stereolithography (SLA) AM process and applied it to the powder-based AM processes. The framework is applied to seven-blade recoater combinations based on the blade count (one or two) and directionality (unidirectional or bidirectional). The analytical and experimental study resulted in the selection of the dual-blade bidirectional recoater. The selected recoater fulfilled the deep-dipping approach and achieved the required layer thickness (ta=tr) in minimum recoating time (T = Tmin) and powder wastage (Vw=2 V). Subsequently, the selected recoater is physically realized with a proof-of-concept (POC) followed by full-scale model installation in a self-developed laser-powder bed fusion (L-PBF) apparatus. The experimental study resulted in the production of a uniform sand layer and multiple specimens. The analysis revealed that the deviation in average specimen dimension along the build direction was < 3.23%, i.e., 51.41 mm, against the actual 49.8 mm. Thus, the results demonstrate the capability of the blade recoater selected via the proposed framework.

Flexure-based compliant mechanisms are increasingly promising in precision engineering, robotics, and other applications, thanks to the excellent advantages of no friction, no backlash, no wear, and minimal assembly. However, their design and analysis are still challenging due to the coupling of kinematic-mechanical behaviors with large nonlinear deflections in comparison to their rigid-body counterparts. Optimal design is an important aspect in the field of compliant mechanisms and has attracted much attention during the last decades. Especially, when considering a multiobjective optimization design for compliant mechanisms, the problem is becoming more complicated. Thus, this article presents a new efficient hybrid computational method to resolve multiobjective optimization design of compliant mechanisms. A Scott Russell compliant mechanism is employed as the design example and to show the advantages of the proposed optimizing method. The proposed method is developed by hybridizing the desirability function approach, fuzzy logic system, adaptive neuro-fuzzy inference system (ANFIS), and lightning attachment procedure optimization (LAPO). First of all, a 3D finite element model is created and central composite design is employed to build a numerical matrix. First, design variables are refined by using analysis of variance and Taguchi approach in terms of considerably eliminating space of design variables. Subsequently, desirability values of two objective functions are determined and transferred into the fuzzy logic system. The output of the fuzzy logic system is considered as a single combined objective function. Next, modeling for fuzzy output is established via developing the ANFIS model. At last, the LAPO algorithm is adopted for solving the multiobjective optimization problem for the mechanism. Three numerical examples are investigated to validate the feasibility and the effectiveness of performance efficiency of the proposed methodology. The results find that the proposed methodology is more efficient than traditional Taguchi-based fuzzy logic. Besides, the performance efficiency of the proposed approach outperforms the Jaya algorithm and TLBO algorithm through the Wilcoxon signed rank test and Friedman test. The results of this article give a useful approach for complex optimization problems.

Additive manufacturing of aluminum (Al) alloys has attracted significant attention in the aerospace industry. However, achieving ultrahigh-strength (&gt;500 MPa) Al alloys remains challenging due to their intrinsic poor printability. Here, we report a novel hybrid additive manufacturing (HAM) approach to process ultrahigh-strength AlMgSc alloy, which combines laser powder bed fusion (LPBF) with interlayer ultrasonic shot peening (USP). The results show that the interlayer ultrasonic shot peening depth reached ∼700 µm, leading to almost full density and residual stress convection from tension to compression. The HAM method promotes equiaxed grain formation and refines grain due to grain recrystallizations. Interestingly, the HAM followed by aging treatment tailors the hierarchically multi-gradient structures, inhibits Mg element intragranular segregation, and promotes the multi-nanoprecipitates (e.g. Al3(Sc, Zr) and Al6Mn) precipitation. Remarkably, the HAM followed by aging treatment achieves yield strength of 609 MPa and breaks elongation of 7.5%, demonstrating ultrahigh strength and good ductility compared with other Al alloys manufactured by AM and forging as reported in the literature. The strength enhancement mechanisms in this AlMgSc alloy are discussed. The high-density Al3(Sc, Zr) precipitates are the main strengthening contributor, and unique hetero-deformation induced (HDI) strengthening (originates from the heterogeneous microstructures) further enhances the strength of the material. This work highlights a novel approach for processing complex-structured ultrahigh strength Al alloy components by hybrid additive manufacturing.

In the field of metal additive manufacturing (AM), one of the most used methods is selective laser melting (SLM)—building components layer by layer in a powder bed via laser. The process of SLM is defined by several parameters like laser power, laser scanning speed, hatch spacing, or layer thickness. The manufacturing of small components via AM is very difficult as it sets high demands on the powder to be used and on the SLM process in general. Hence, SLM with subsequent micromilling is a suitable method for the production of microstructured, additively manufactured components. One application for this kind of components is microstructured implants which are typically unique and therefore well suited for additive manufacturing. In order to enable the micromachining of additively manufactured materials, the influence of the special properties of the additive manufactured material on micromilling processes needs to be investigated. In this research, a detailed characterization of additive manufactured workpieces made of AISI 316L is shown. Further, the impact of the process parameters and the build-up direction defined during SLM on the workpiece properties is investigated. The resulting impact of the workpiece properties on micromilling is analyzed and rated on the basis of process forces, burr formation, surface roughness, and tool wear. Significant differences in the results of micromilling were found depending on the geometry of the melt paths generated during SLM.

Advances in computational modeling for laser powder bed fusion additive manufacturing: A comprehensive review of finite element techniques and strategies

Additive manufacturing (AM) is a modern manufacturing technique that facilitates the production of components layer by layer from CAD files, with more recent developments in the field leading to the ability to create these components from metal. Laser powder bed fusion (LPBF) is one of the many techniques used to manufacture metallic components and has drawn significant attention for its ability to create parts with high degrees of complexity, exceptional strength-to-weight ratios and internal structures. However, parts produced by AM are documented to suffer from build defects such as porosity, which can negatively affect not only its mechanical properties but its corrosion resistance, particularly its resistance to pitting corrosion. Whilst the mechanical properties of components produced through metal AM have been well documented since the technology’s inception, there are significant knowledge gaps in understanding the corrosion behaviour of metals produced in this way. This thesis aims to expand upon the current understanding of this manufacturing method with a particular focus on its corrosion resistance. High Entropy Alloys (HEAs) are a class of advanced materials that differ from conventional alloys in composition. Traditional alloys usually consist of one or two principal elements with smaller amounts of additional elements to impart specific properties. In contrast, HEAs are characterised by the presence of multiple principal elements in roughly equal proportions. HEAs' complex and disordered structure can result in unique mechanical, thermal, and magnetic properties. HEAs have shown promise in exhibiting high strength, hardness, and corrosion resistance, making them attractive for various engineering applications. Studies of HEAs have been increasing over recent years; however, significant knowledge gaps are still associated with this classification of materials, especially concerning their corrosion resistance. This lack of knowledge is intensified when discussing the properties of these alloys when manufactured by AM methods. LPBF was used to produce parts in 316L with process induced porosity by manipulating the process parameters to investigate the effect density has on the corrosion resistance of AM parts. The corrosion resistance of these parts were compared to their wrought counterpart using potentiodynamic polarisation. It was observed that increasing the porosity in the AM parts resulted in poorer corrosion resistance, both by weaker performance across key metrics and a greater degree of unreliability. It was also found that the AM parts proved to have a greater corrosion resistance than the wrought material. However, the decreased consistency in this resistance is often cited as a barrier these components must overcome to supplace conventionally manufactured components.316L was also produced through induction casting as well as a schedule more representative of industry that consisted of a solution anneal at 1080 °C followed by water quenching followed by a cold rolling reduction by 70 %, and a final anneal at 900 °C. The microstructures and corrosion resistance of these were investigated using SEM-EDS, XRD and potentiodynamic polarisation, and whilst the corrosion resistance of the cold rolled sample had increased, it was less than expected due to the formation of detrimental chromium carbides. A Swansea University developed AlCrFeMnNi HEA was put through the same 3 manufacturing processes to investigate their effect on the microstructure and corrosion resistance. It was found that, unlike 316L, the HEA suffered less from pitting corrosion and more from a generalised corrosion attack. Very similar corrosion results were seen across the manufacturing methods; however, the cast sample was observed to have the most consistent display of corrosion resistance. Based on the pitting resistance equivalent number, which relates the amount of Cr and Mo by wt.% in a stainless steel to its corrosion resistance, it was theorised that the addition of Mo to this HEA could also increase its corrosion resistance. The results were inconclusive; however, better corrosion resistance was seen in the AM sample of the HEA with the addition than in the AM sample without.

Chapter 25 - State-of-the-art in additive manufacturing of Ti–6Al–4V: recent progress and insights into future developments

Additive manufacturing (AM) technology can potentially disrupt offshore and marine industry by effectively reducing manufacturing processes and leadtime, and enabling new product designs. A review of existing literature has revealed limited knowledge in using AM to process shipbuilding materials, which can otherwise enhance existing shipbuilding manufacturing workflow. This has led to the research motivation to establish the technical feasibility of using selective laser melting (SLM) to process ASTM A131 EH36 shipbuilding steel. SLM process is a widely understood AM technology that has been used extensively to process other type of steels, for example stainless steel 316L. EH36 belongs to a class of high tensile low alloy steel which has traditionally been processed through casting. However, knowledge on using lasers to process EH36 is largely unknown, especially in AM applications. Using SLM to process EH36 is novel and will solve the problem of lack of knowledge in this field. The study thus aims to further the understanding of the mechanical properties and microstructure of SLM processed EH36. A preliminary investigation was first carried out to establish the technical feasibility of using SLM to process EH36. The process parameters obtained were then used to further the investigations. Heat treatment process was applied as a possible post processing technique. Mechanical testing was carried out to characterise its mechanical properties. The fracture surfaces and microstructures were then studied to characterise the material. The results showed that EH36 can be processed using SLM without any visible cracks. The mechanical properties of as built SLM processed EH36 exhibit very high tensile strength, but low ductility. The ductility can be improved through tempering heat treatment process, but at the partial sacrifice of tensile strength. Fractography analysis also affirmed the lack of ductility in the SLM processed EH36 samples. Finally, the microstructure showed that fine grain size and martensitic microstructure were the primary drivers behind its high tensile strength. Tempered samples experience grain coarsening and phase transformation to a mainly ferritic structure, which led to recovery in its ductility but a decrease in the tensile strength. A scaled model was fabricated to validate the results from the microstructure studies, and the findings indicate similar microstructures formed. This demonstrates the repeatability of the developed process parameters on fabrication of complex joints. The study contributes to the scientific knowledge with regard to material and mechanical property characterisation of SLM processed EH36. The findings from the fractography and microstructural analysis will contribute towards building the knowledge and facilitate future work on AM of EH36.