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Magnesium alloys, renowned for their lightweight yet high-strength characteristics, with exceptional mechanical properties, are highly coveted for numerous applications. The emergence of magnesium alloy additive manufacturing (Mg AM) has further propelled their popularity, offering advantages such as unparalleled precision, swift production rates, enhanced design freedom, and optimized material utilization. This technology holds immense potential in fabricating intricate geometries, complex internal structures, and performance-tailored microstructures, enabling groundbreaking applications. In this paper, we delve into the core processes and pivotal influencing factors of the current techniques employed in Mg AM, including selective laser melting (SLM), electron beam melting (EBM), wire arc additive manufacturing (WAAM), binder jetting (BJ), friction stir additive manufacturing (FSAM), and indirect additive manufacturing (I-AM). Laser powder bed fusion (LPBF) excels in precision but is limited by a low deposition rate and chamber size; WAAM offers cost-effectiveness, high efficiency, and scalability for large components; BJ enables precise material deposition for customized parts with environmental benefits; FSAM achieves fine grain sizes, low defect rates, and potential for precision products; and I-AM boasts a high build rate and industrial adaptability but is less studied recently. This paper attempts to explore the possibilities and challenges for future research in AM. Among them, two issues are how to mix different AM applications and how to use the integration of Internet technologies, machine learning, and process modeling with AM, which are innovative breakthroughs in AM. [ABSTRACT FROM AUTHOR]

In recent years, metal chip powders obtained from solid-state processes have shown great potential as a sustainable raw material for powder technologies. The material and fragmentation process of the chips has a significant role in the final characteristics of the powder particles, such as size and particle size distribution, shape, surface, and structure, which are essential parameters to consider when converting chips to powder for applications. However, tool steel chips as a powder raw material have not yet been significantly studied. In this study, the steel chips were from machining AISI H13 steel and the milling process used a ball mill, and the challenge was to obtain powder particle sizes of around 20 µm with suitable properties from the application of envisaged material extrusion (MEX). A comparison study with the commercial raw material for MEX, such as powder metal filament extrusion, was performed. This study highlights the behaviors of chip powders during all steps of MEX, namely, feedstock and filament production, 3D object shaping, thermal de-binding, and sintering. A comparison of the mixture based on powder from chips and commercial powders for MEX was performed after evaluating the mixing torque of the powder and the system of binders and additives suitable for the rheological characteristics required for an extrusion mixture, and optimizing the binder removal and the sintering conditions. The 3D objects resulting from chip powders had a refined microstructure, showing an increase of 15% in the microhardness when compared with the those resulting from commercial powders.

Lumbar model is an artificial bone that is commonly used in surgical training to simulate working with the human-like bone for the trainer. The common lumbar model is made of rigid polyurethane (PU) foam and is produced using casting. However, the current lumbar model is expensive and has limitations in representing the real human lumbar, especially in geometry, visuals, and haptics. Therefore, an alternative method of fabricating lumbar models made of rigid polyurethane for surgical training using indirect additive manufacturing will be investigated in this paper. The proposed indirect additive manufacturing is a combination of 3D printing and casting methods. The main process of this method is started by fabricating a mold made of polyvinyl alcohol (PVA) using fused deposition modeling (FDM) 3D printing and subsequently casting PU foam material into the 3D printed PVA mold. Accordingly, the aim of this study is to find the optimized casting process parameters, especially for injecting the material into the mold, to achieve a better quality of lumbar model. The study was conducted using a Design of Experiment (DoE) Taguchi Orthogonal Array to optimize the casting process. The geometrical measurements of middle end-plate depth, upper end-plate width, spinal canal width, spinal canal depth, and lower pedicle length show the error ranged from 0.14% to 0.85%. The average porosity, measured from the body, lamina, and spinous, was found to be non-uniform. It is ranged from 19.58% to 21.94% on the middle part and 39.78% to 45.41% on the subsurface of lumbar model. The density was increased by 64.89% compared to the reference open molded PU foam.

As a new type of lightweight structure, metallic lattice structure has higher stiffness and strength to weight ratio. To freely obtain 316L lattice structures with designed cell structure and adjustable porosity, additive manufacturing combined with investment casting was conducted to fabricate the 316L lattice structures with Kelvin cell. The compression simulation of 316L lattice structures with different porosities was carried out by using the finite element method. The numerical simulation results were verified by compression experiment, and the simulated results were consistent with the compression tests. The compressive mechanical properties of 316L lattice structures are directly related to porosity and independent of strut diameters. The 316L lattice structures with Kelvin cell have a smooth stress-strain curve and obvious plastic platform, and the hump stress-strain curves are avoided. [ABSTRACT FROM AUTHOR]

This work studied the influence of hydrogel's physical properties (geometry and hierarchical roughness) on the in vitro sorption/release profiles of molecules. To achieve this goal, chitosan (CS) solutions were cast in 3D-printed (3DP) molds presenting intricate shapes (cubic and half-spherical with/without macro surface roughness) and further immersed in alkaline solutions of NaOH and NaCl. The resulting physically crosslinked hydrogels were mechanically stable in aqueous environments and successfully presented the shapes and geometries imparted by the 3DP molds. Sorption and release profiles were evaluated using methyl orange (MO) and paracetamol (PMOL) as model molecules, respectively. Results revealed that distinct MO sorption/PMOL release profiles were obtained according to the sample's shape and presence/absence of hierarchical roughness. MO sorption capacity of CS samples presented both dependencies of hierarchical surface and geometry parameters. Hence, cubic samples without a hierarchical surface presented the highest (up to 1.2 × greater) dye removal capacity. Moreover, PMOL release measurements were more dependent on the surface area of hydrogels, where semi-spherical samples with hierarchical roughness presented the fastest (~1.13 × faster) drug delivery profiles. This work demonstrates that indirect 3DP (via fused filament fabrication (FFF) technology) could be a simple strategy to obtain hydrogels with distinct sorption/release profiles. [ABSTRACT FROM AUTHOR]

Electroforming on additively manufactured templates has the potential to become a manufacturing process for making complex metal parts in a flexible and economical way. However, the main challenge of electroforming is the high surface roughness when deposition thickness increases (thickness ​> ​100 ​μm), due to the high current density on edges and co-deposition of impurities while electroforming. In this work, a hybrid electrochemical manufacturing process to fabricate high-precision metal parts is proposed combining electroplating and surface levelling to achieve thick deposits (up to 1 ​mm) with a low surface roughness. The presented work includes a comparative study of electroforming technologies to fabricate precision metal parts on additively manufactured templates. The potential of this methodology was demonstrated by forming a copper layer on additively manufactured ABS (acrylonitrile butadiene styrene) models. The proposed hybrid electroforming method results in a simple process design, as no specific chemistry (e.g. lack of additives) is needed. Another benefit of this indirect additive manufacturing process is the reduction of the carbon footprint compared to direct printing by usage of metal salts instead of refined metals.

Metal foams are a material, featuring interesting characteristics for the aeronautical and automotive fields because of their low specific weight, high thermal properties, and mechanical performances. In particular, this paper deals with thermal and fluid dynamic study of 24 open-cell aluminum EN43500 (AlSi10MnMg) metal foams produced by indirect additive manufacturing (I-AM), combining 3D printing and metal casting to obtain a controllable morphology. A study of foam behavior function of the morphological features (pores per inch (PPI), branch thickness (r), and edges morphology (smooth-regular)) was performed. The samples produced were heated by radiation and tested in an open wind circuit gallery to measure the fluid dynamic properties such as pressure drop (Δp), inertial coefficient (f), and permeability (k), in an air forced convection flow. The thermal characterization was performed evaluating both the theoretical (kth) and effective (keff) thermal conductivity of the foams. Also, the global heat transfer coefficient (HTCglobal) was evaluated with different airflow rates. Analysis of variance (ANoVA) was performed to figure out which geometrical parameters are significant during both thermal and fluid dynamic processes. The results obtained show how the controllable foam morphology can affect the involved parameters, leading to an ad hoc design for industrial applications that require high thermo-fluid-dynamical performances. [ABSTRACT FROM AUTHOR]

Using additive manufacturing (AM) as aid to manufacture parts with traditional manufacturing methods is one of the many applications of AM, yet one of the less investigated. In this article, for the first time, a way to produce soluble AM customizable sacrificial moulds for resin casting is explained. The moulds are produced through fused filament fabrication using polyvinyl alcohol (PVA) as raw material. After curing, the moulds are dissolved in water leaving the solid resin parts away. The results of indirect additively manufactured resin components in PVA moulds are examined, supported by surface and dimension analysis on prism-like sample parts for different sets of process parameters. Possible applications and limitations of the technique are exposed, as well as recommendations for future works. [ABSTRACT FROM AUTHOR]