The decreasing cost of space travel has intensified interest in space-based manufacturing to support long-term exploration and habitation. High launch costs necessitate utilizing extraterrestrial resources like lunar regolith and recycled space debris for in-space additive manufacturing (ISAM). Metal debris in Earth’s orbit presents a valuable feedstock, while lunar regolith, composed of fine particles, aligns well with powder-based manufacturing techniques. Powder-based additive manufacturing (AM) processes offer design flexibility, reduced material waste, and on-demand production of tools and infrastructure in space. However, powder behavior in microgravity, vacuum conditions, and extreme temperature variations presents significant challenges. Unlike typical AM powders, lunar regolith has a wide size distribution and irregular particle shapes, affecting flowability and printability. Further, certain powder production and characterization methods show greater adaptability to low-pressure environments, while others require modifications to function effectively in microgravity conditions. Reduced gravity amplifies interparticle forces, impacting powder handling and necessitating alternative containment strategies. Various powder characterization techniques are analyzed to determine their viability for space applications, emphasizing the need for modifications to account for non-Earth environments. Furthermore, the study reviews real-time monitoring technologies essential for ensuring print quality in ISAM and highlights recent advancements in computational modeling for predicting powder behavior in space. By refining powder production, characterization, and AM process adaptation, ISAM can minimize reliance on Earth-based supply chains, enabling the construction of tools, habitats, and infrastructure directly in space. Addressing the complexities of powder behavior in non-terrestrial environments will be critical to achieving sustainable, autonomous manufacturing beyond Earth.

Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing (AM) process where a laser is used to sinter and fuse powder particles together on a baseplate which acts as a heatsink. This heat transfer results in undesirable residual stresses and potential part failure. A proposed method to study the process of sintering powder without a baseplate is acoustic levitation. A type of acoustic levitation uses a standing pressure wave generated between a set of transducers and a reflector to trap particles at the nodes of the wave. The purpose of this work is to leverage and optimize current standing wave levitation techniques to enable the levitation of metal powder for sintering, i.e., to achieve “bed-less” LPBF through acoustic levitation. Common acoustic levitators are limited to very small or low-density particles. Thus, the first step of this work was to create a simulation tool for the pressure field of an acoustic levitator. The program architecture prioritized input flexibility, including phase, voltage, frequency, number, and position of transducers. The program also outputs the lift capacity to facilitate the following stage of this project which will involve finding optimization solutions for the transducer inputs and acoustic levitator setup suitable for bed-less LPBF.

Additive manufacturing (AM) is a disruptive technology that enables the fabrication of intricate geometries layer-by-layer by discretizing the given geometry into multiple slices. Overhangs are regions of these slices where the surface projection exceeds the underlying horizontal support. AM techniques, like material extrusion (MEX), require explicit support structures, which are added to ensure proper printability and dimensional stability. Although supports provide part balancing to avoid material sagging, they should be minimised as they increase the overall material usage, print time and associated costs. Limited studies have been done on the self-supporting capacity of thin-walled AM structures. This research presents a novel analytical model based on the beam bending principle to determine the material’s limit to self-sustain overhangs. The model determines this limit in terms of an overhang angle (from the vertical) using part geometry, process parameters and material properties. It is found that the overhang angle has an inverse square root relation with an apparent number of layers, which can be linearly approximated as a function of the number of layers. The model is further extended to incorporate buckling effects in the extruder fibres. Analytical results showed that overhangs as high as 75o are possible without any external supports, as against the conventional 45° limit. The presented model can alleviate the AM process by increasing the printing efficiency and reducing material wastage.

Additive manufacturing creates parts by depositing a preform, typically layer by layer. Subtractive manufacturing involves removing material from a preform to create parts. Hybrid machine tools combine both additive and subtractive processes in the same workspace. They can be used to create parts that meet functional tolerance and surface finish requirements, or to create features that are difficult to produce using additive or subtractive processes alone. This paper describes hybrid metal additive/subtractive machine tools. It covers design considerations, sensors and controls, process management, programming and software, and the impact on the design space. It also identifies future research challenges. (c) 2024 CIRP. Published by Elsevier Ltd. All rights reserved.

High-strength martensitic stainless steels such as 17-4 PH (SS 17-4 PH) generally exhibit poor ductility and strain-hardening rates. In this study, an Ultrasonic Impact Treatment (UIT) is combined with a powder bed fusion (PBF) manufacturing process with the objective of enhancing the mechanical properties of SS 17-4 PH. UIT is introduced as a surface peening step at regular intervals during the PBF process after depositing a set of predetermined number of layers. The coupon specimens extracted from the build are then subjected to a post-build heat treatment. Then the microstructural and the mechanical properties of these specimens are characterized. The characterizations reveal that the heavy plastic deformation induced by UIT drives microstructural relaxation and recrystallization under heat treatment, reducing defects extensively. The heavy plastic deformation also drives diffusional reversion of the austenite phase during deposition and an inhibition of the martensitic phase transformation during the post-build heat treatment. As a result, the UIT specimens subjected to post-build heat treatment exhibit remarkable enhancement in ductility along with high strength and strain-hardening rate compared to the non-UIT PBF specimens under as-built condition.

The objective of this research was to quantify the change in magnitude and depth of compressive residual stress (CRS) retained in the subsurface by interlayer coldworking when subjected to localized annealing that superimposed tensile stress. The approach was to hybridize additive manufacturing of AlSi10Mg alloy by coupling powder bed fusion (PBF) with laser shock peening (LSP) and characterize the resultant residual stress state by the hole-drilling method. The research found localized annealing from layer deposition formed two distinct regions in the subsurface, which was driven by localized and bulk stress redistribution. The experiments also showed that residual stress redistribution from LSP reached 550 µm into the subsurface, whereas local annealing from the deposition of layers extended only to a depth of 160 µm. Hence, compressive stress imparted by LSP was not entirely canceled by local annealing from PBF. This work provides the first quantification of the stress state response of hybrid additively manufactured parts to thermal loads and is fundamental to improving part performance through increased functional reliability, fatigue life, and corrosion resistance.

Powder bed fusion is an innovative additive manufacturing (AM) technique to achieve metallic wick structures for efficient two-phase thermal management systems. However, a technical challenge lies in the lack of standard process maps as it currently relies on an expensive trial and error approach. In this study, five types of surrogate models for classification analysis (i.e., naïve Bayes, logistic regression, random forest, support vector machine, and Gaussian process classification) were constructed and compared to efficiently unlock the relations between five process parameters (i.e., laser power, scan speed, hatch spacing, spot diameter, and effective laser energy) and wick manufacturability. The models were trained using data from a total of 187 AM wick manufacturability experiments. Using four process parameter (PP) model (five PP model without effective laser energy), the Gaussian process classification (GPC) showed the maximum median prediction accuracy (PA) of 93

This study explored the relationship between process parameters and fracture behavior in 316L stainless steel printed by laser powder bed fusion. Fracture testing was conducted according to ASTM E1820 for single edge notch bending, and elastic mechanical properties were determined using ultrasonic surface wave analysis. Five test sets were considered in a vertical building configuration using five different volumetric energies belonging to conduction mode. The critical fracture toughness was calculated and discussed along with the plastic deformations at the crack tip. The study found that local plastic deformation for single edge notch bending was influenced by powder bed fusion process parameters. A correlation was observed between energy density, fracture toughness, and the dimensions of the fracture process zone. The R-curves showed different fracture behaviors depending on the energy density. The energy required to grow a crack was associated with larger plastic zones, resulting in fracture toughness values ranging from 43 (43 J.mm-3) to 427 kJ/m2 (68 J.mm-3). Results are discussed in terms of porosity and strain hardening capacity depending on the manufacturing conditions.

Additive manufacturing is proposed as a novel tool to produce complex scaffold constructs for use in cell cultured meat. The presence of scaffolds in the final cell cultured products raises the need to understand the thermal behavior of biopolymers through culturing and cooking as it relates to the final organoleptic properties. Therefore, the objective of this study was to understand how aqueous and high temperature environments influence plasticization and contraction of biopolymer scaffolds through the physio–chemical mechanisms of hydrolysis and negative thermal expansion. To achieve this objective, scaffolds were printed using a negative thermal expansion stretch–dominated design in both PLA and PLA-TPU material configurations. The samples were evaluated after a simulated cooking experiment (90 °C for 10 mins). The formation of crystals in the single material PLA during cooking led to bend–dominated contraction while the dual-material PLA-TPU experienced stretch–dominated contraction. Furthermore, exceeding the glass transition temperature of PLA during simulated cooking in an aqueous environment caused irreversible deformation to the scaffold structure that has the potential to influence organoleptic properties.

Current methods for modeling hybrid additive manufacturing are computationally inefficient for use in optimization algorithms. An analytical tool is needed to understand how cycling thermal and mechanical loads via 3D printing and cold working reshapes cumulative residual stress within a build volume. A novel analytical model was developed that couples beam theory and superposition to rapidly predict cumulative residual stress. Modeling results were experimentally validated on AlSi10Mg after laser shock peening prescribed layers during powder bed fusion. Results demonstrated a vertically translating heat-affected zone, and the use of beam-based superposition accurately accounted for residual stress redistribution from cyclic printing and peening. (c) 2024 CIRP. Published by Elsevier Ltd. All rights reserved.

This research evaluates the cellular response from Ti6Al4V scaffolds fabricated by hybrid additive manufacturing (AM) with the goal of improving bone tissue growth and biocompatibility of titanium implants. Since cellular adhesion and viability are subject to microstructure, hybrid AM was sought to dictate biological response by creating a dispersed and gradient microstructure within implants. The objective was to evaluate the effect of gradient microstructures within Ti6Al4V scaffolds on cellular metabolic activity. Gradient microstructure was incorporated within scaffolds by hybrid AM coupling directed energy deposition (DED) with interlayer milling. The cellular response from the scaffolds was evaluated using cell viability assays in two stages: the Ti6Al4V powder used for DED was first evaluated, followed by the fabricated scaffolds. Cell viability on hybrid AM scaffolds was compared with as-printed, i. e., DED-fabricated and annealed Ti6Al4V scaffolds. The cell viability assays demonstrated that Ti6Al4V powder was non-toxic as cells cultured with powder exhibited metabolic activity similar to cells in growth media without powder. The cell viability study on scaffolds indicated, on average, cell adhesion on hybrid AM scaffolds outperformed as- printed and annealed scaffolds. This study provides preliminary data demonstrating the use of hybrid AM to dictate cell activity. A larger sample set would be required in future work to understand the effects of grain refinement through coldworking on biological response.

The production of animal-derived food using cultured whole-muscle meats requires scaffolding, but current scaffold manufacturing technologies are not suitable for achieving scalable and cost-effective production required to compete with traditional animal agriculture. To address this, vat polymerization using a renewable soy-based resin is proposed as an emerging material-process combination capable of economies of scale. However, the thermo-mechanical behavior of edible photocured materials under physiologically relevant conditions needs to be understood, particularly enzymatic degradation and aging under long-term exposure in bioreactors. Results demonstrated that enzymatic hydrolysis shifted the glass transition temperature below standard bioreactor operating temperatures and stabilized after seven days.

Metal components with functionally organized microstructures for specific applications are emerging thanks to hybrid additive manufacturing (AM). The customization of these high value components accentuates the need for nondestructive methods to characterize their microstructural functional patterns. Nondestructive evaluation (NDE) methods that are economical, fast, energy efficient, and easy to integrate into routine component inspections are preferred. Most importantly, NDE methods must be sensitive to changes in the microstructure such that regions that do not satisfy the design requirements (i.e. out-of-spec regions) can be detected. In this work, ultrasonic NDE methods grounded in diffuse backscatter modeling were used to detect and quantify spatial property variations resulting from a hybrid AM process. The manufacturing process coupled directed energy deposition (DED) with milling in a cyclical manner. These methods were successfully implemented to evaluate the microstructural uniformity of Ti6Al4V samples as well as to make comparisons across an ensemble of samples manufactured with identical parameters. Out-of-spec regions were mapped with respect to the sample geometry on a layer-by-layer basis. The results of this work are expected to inform future NDE strategies for both research and practitioner contexts, and limitations are discussed.

Additive manufacturing (AM) often results in high strength but poor ductility in titanium alloys. Hybrid AM is a solution capable of improving both ductility and strength. In this study, hybrid AM of Ti-6Al-4 V was achieved by coupling directed energy deposition with interlayer machining. The microstructure, residual stress, and microhardness were examined to explain how interlayer machining caused a 63% improvement in ductility while retaining an equivalent strength to as-printed samples. Interlayer machining introduced recurrent interruptions in printing that allowed for slow cooling-induced coarsening of acicular alpha laths at the machined interfaces. The coarse alpha laths on the selectively machined layers increased dislocation motion under tensile loads and improved bulk ductility. The results highlighted in this publication demonstrate the feasibility of hybrid AM to enhance the toughness of titanium alloys.

Eliminating porosity remains a major challenge in metal additive manufacturing (AM). The current approach is thermal management, which involves optimizing process parameters to minimize porosity formation from repeated stacking of layers. However, auxiliary mechanisms other than laser power, scan speed, and hatch spacing simultaneously affect the repeatability of the process. For example, the flow of shielding gas over a powder bed causes convective heat transfer that results in keyhole porosity. Although conduction is widely attributed as the main mode of heat transfer during printing, in this study, the importance of convection was highlighted when keyhole porosity was observed to be spatially aligned in a pattern and uniformly distributed based on the recoater position. The pore pattern aligned with the layout of print cells when the recoater position was on the left (odd layers). Local disturbances caused by the printing process on 316 stainless steel were investigated by x-ray computed tomography. Results indicated that porosity formation emanated from an irregular nitrogen flow across the build-plate. The nitrogen flow was periodically disrupted throughout the print as the position of the recoater during odd layers obscured gas movements close to the build-plate. These observations were validated with a simulation of the gas flow on a 2D cross-section of the build-chamber using ANSYS Fluent. The disrupted flow created regions with low gas velocity, which led to a heat retention at the boundary of the print cells. The heat retained generated a concentrated occurrence of keyhole defects since the melt pools were deeper. The effect of the shielding gas, which is usually neglected, was highlighted as an important factor to ensure part quality.

Porosity is a major challenge in laser powder bed fusion systems (PBF) and a crucial contributor to fatigue life. The current approach to remedy this challenge is thermal management, which involves optimizing process parameters to minimize porosity formation from repeated stacking of layers to produce a fully dense part. However, auxiliary mechanisms other than laser power, scan speed, and hatch spacing simultaneously affect the repeatability of the process. For example, the irregular flow of shielding gas over a powder bed disrupts the melt's pool convective heat transfer resulting in keyhole porosity. This study aims to explain the defect formation associated with the print process caused by local disturbances of the shielding gas flow pattern and the interaction of adjacent rasters. Additively manufactured 316 stainless steel cuboids were investigated by x-ray computed tomography. Results indicated that pores were spatially aligned in a pattern and uniformly distributed. A comparison of the CT scans and the print file showed that the pore pattern aligned with the layout of print cells during the melting of odd layers. During odd layers, the position of the recoater disrupted the shielding gas flow. The disrupted flow created regions with low gas velocity, which led to heat retention at the boundary of the print cells. The heat retained generated a concentrated occurrence of keyhole defects since the melt pools were deeper. (c) 2023 The Authors. Published by ELSEVIER Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)

Emerging cell-cultured meat uses advances in stem cell biology and tissue engineering to manufacture animal-derived food from culturing. To achieve complex textures in cell-cultured meat, bioprinted soy-based polymers are proposed as a photosensitive edible scaffold material. Understanding the properties of these scaffolds across critical product development stages (i.e., cooking and consumption) is important in design for manufacturing. The results demonstrated that the thermomechanical and -chemical properties were not affected by high-temperature exposure associated with cooking. This research provides a foundation for high-temperature edible mechanics in photolithographic manufacturing of cell-cultured meat and establishes a new design space for tunable food properties.

Cultivated meat is being explored as one of the sustainable solutions, complementing traditional meat manufacturing to meet global demand. This paper presents the novel results of a 3D food printing process for scaffolds produced from edible hydrolyzed collagen intended for biomanufacturing cultivated meat. The hydrolyzed collagen ink is designed with combinatorial chemistries and post-printing freeze-dried to create scaffold constructs. Rheological properties of the ink for 3D food printing are studied. Variation in average pore size and pore morphology of the scaffold caused by changing collagen ink composition and freeze-drying conditions is analyzed. This novel study focuses on using commercially available food-grade ingredients for cultivated meat scaffolds. Results of this study are applied to explore the viability of edible hydrolyzed collagen scaffold biomanufacturing with appropriate pore morphology using 3D food printing and freeze-drying technique.