This work investigates the applicability of Molten Metal Deposition (MMD) for additive manufacturing of high-strength aluminum alloys (6xxx). Molten Metal Deposition (MMD) is a novel wire-based metal additive manufacturing (AM) technique with an initial focus on aluminium. MMD involves the direct melting and deposition of wire feedstock onto a heated substrate. Process parameter optimization demonstrated the feasibility for manufacturing 6061 samples without detection of solidification cracking. Extensive metallurgic testing revealed opportunities of the technology: hardness values approaching T4–T5 conditions, attributed to intrinsic thermal cycling during deposition. Fusion inconsistencies, primarily driven by oxide-induced microbridging, were identified as the dominant defect mechanism. Experimental analysis demonstrated that layer adhesion improves significantly through tailored energy input, reduced extrusion at geometrical discontinuities, and controlled track geometry. To further mitigate oxidation, suggestions are formulated for future work and applications are briefly elaborated on such as the potential of printing structures in space.

Molten metal deposition (MMD) offers a promising approach to metal additive manufacturing due to its relatively low and controllable cooling rates compared with laser or arc-based processes. However, most investigations related to MMD remain as simulation studies with limited microstructural and defect-based studies. In this work, the microstructural and porosity defects of MMD-fabricated aluminium alloy 4043 are systematically examined across varying process parameters. The results show that high substrate temperatures combined with higher nozzle temperatures result in reduced cooling rate, thereby increasing grain size and defect levels. Conversely, both average grain size and defect levels decrease progressively along the build direction as interlayer height increases, reflecting an enhancement in the effective cooling rate with successive layer deposition. Hardness and nanoindentation testing revealed mechanical properties comparable to those achieved through conventional manufacturing routes, highlighting the promising applicability of MMD technology. When overall optimising is considered, lowering the substrate temperature and energy input tends to increase the cooling rate; this enables fewer defects and finer grain structures in MMD specimens. The present study provides quantitative process-microstructure-defect relationships to enable promising enhancements in MMD of aluminium alloy components.

Molten Metal Deposition (MMD) is an emerging additive manufacturing process for aluminum alloys that operates without forming a localized melt pool, instead depositing a continuous stream of molten metal, thereby reducing porosity and thermal distortion. In this study, a coupled numerical–experimental framework is developed to investigate the influence of process parameters on thermal behavior, porosity, and mechanical properties of AA 4043 structures. A conduction-based finite-element thermal model with element-wise activation was implemented to mimic layer-wise deposition and validated against in-situ thermocouple measurements at multiple build heights using root-mean-square error (RMSE) as a quantitative metric. Within the investigated parameter window, the approach identifies parameter sets yielding measured cross-sectional porosity below 0.1%, ultimate tensile strength up to 132 MPa, and elongation up to 21–23%. SEM–EDS mapping revealed directional eutectic Si-rich film evolution along columnar α-Al grains, closely linked to local cooling rates. Overall, the results demonstrate MMD’s viability for producing Al-4043 wall structures with low porosity and favorable strength–ductility combinations within the studied conditions, while providing a model-driven framework for parameter tuning in melt-pool-free deposition.

Two aluminum alloys (4043 and 6061) were fabricated using the innovative Molten Metal Deposition (MMD) technique. Three types of samples were produced by varying selected deposition parameters. The quality of the resulting components was assessed in terms of defects, density, and microstructure. In the 4043 alloy, the microstructure consists of α-Al dendrites surrounded by an Al–Si eutectic phase. All 4043 samples exhibited this microstructure, regardless of the deposition parameters. The mechanical response was preliminarily evaluated through HV0.5 microhardness measurements. The indentations produced under a 500 g load enabled the assessment of the contribution of both the α-Al matrix and the surrounding Al–Si eutectic. As for the 6061 alloy, its microstructure is composed of an α-Al matrix containing dispersed Al–Si–Fe intermetallics. Some oxide particles were observed at the grain boundaries, indicating the need for processing under a controlled atmosphere. In this study, no inert shielding atmosphere was used for the fabrication of the samples. Thanks to its high processing speed, sustainability, and ease of deployment, MMD can be regarded as a viable alternative to more conventional additive manufacturing technologies.

Metal Extrusion Additive Manufacturing (MEAM) is an emerging class of additive manufacturing (AM) processes that deposit continuous filaments of semi-solid or liquid metal. MEAM may offer complementary advantages to established methods such as powder bed fusion, directed energy deposition, and binder-based techniques, including lower costs, reduced energy consumption, and potential for enhanced microstructural control. The ability to operate at lower and precisely tunable processing temperatures enables the fabrication of reactive or low-boiling-point metals—such as aluminum and magnesium alloys—that are challenging to process using high-temperature or powder-based AM. However, varied terminology and overlapping definitions across related approaches have complicated communication and slowed broader coordination. This review adopts MEAM as a unifying term encompassing these methods within a clearly defined framework. It synthesizes current research on MEAM’s historical development, process physics, system architectures, and explored material systems; evaluates its benefits and limitations within the wider metal AM landscape; and identifies key research opportunities to advance MEAM toward industrial viability as a complementary and potentially transformative technology.

Aluminium chips resulting from subtractive manufacturing form an unattractive material flow for recycling. Their high surface to volume ratio leads to a higher concentration of oxides compared to other types of scrap, thus exacerbating inefficiencies in recycling and resulting in significant material losses. The field of solid state recycling has seen various technological developments trying to mitigate this problem, but struggles with its industrial adoption due to the rigorous quality demands of finished high-strength aluminium products. In this study, Friction Stir Extrusion (FSE) was used as an intermediary process to directly recycle aluminium chips into a wire suitable as feedstock for the Molten Metal Deposition (MMD) process, a recent development within the category of additive manufacturing. Despite the use of low-quality feedstock and the inclusion of dispersed oxide particles, it was found that the use of FSE wire as feedstock for the MMD process was possible without process modifications, and generated parts with increased hardness (+ 15 %). A life cycle assessment study indicated that the environmental impact was significantly lowered (− 52 %) for the feedstock production for MMD, generating an overall reduction of 6 kg equivalent CO2 emissions per kg of aluminium chips exchanged between the subtractive manufacturing source and the MMD sink. Obtained results demonstrate that selectively combining generated waste and processing options according to the principles of industrial symbiosis opens up opportunities to reduce the environmental impact of aluminium part production processes. This approach practically eliminates waste to achieve full use of the sourced materials.

This study delves into the dynamics of molten metal deposition (MMD)-based drop-on-demand (DoD) printing, focusing on the interaction between aluminum droplets and substrates. Nozzle-to-substrate distances below 20 mm prevent droplet pinch-off, while distances exceeding 40 mm result in no droplet-substrate adhesion. Operating within the substrate temperature range of 350–550 °C is crucial, avoiding delamination and shrinkage pits at lower temperatures, and substrate deformation and heightened oxidation at higher temperatures. Droplet adhesion is impeded at nozzle temperatures below 700 °C. Impact-driven and inviscid, DoD-MMD exhibits spreading outpacing overall solidification, particularly at higher temperatures. Surface tension forces dominate, influencing droplet spreading and leading to underdamped interfacial oscillations. Weak droplet-substrate adherence, facilitated by Van der Waals forces, allows easy droplet detachment, beneficial for successive drop-on-drop deposition. Unique to DoD-MMD, ridges along the droplet periphery act as solidification paths, influenced by thermal contraction and surface tension. The spherical pancake shape of the droplet, characterized by a solidification angle greater than 90°, is elucidated through Weber and Freezing numbers. The final deposited droplet width to initial diameter ratio increases with the droplet temperature and deposition height. In contrast to other metal DoD studies, the spreading factor decreases with a rise in substrate temperature, attributed to intensified oxidation at higher substrate temperatures.

Aluminum (Al) alloys have significant applications in many sectors, including but not limited to the automotive, aerospace, and aircraft industries. Although additive manufacturing (AM) of Al alloys has gained significant interest in industry and academia, its full-scale implementation is currently restricted due to issues such as porosity, low mechanical properties and large solidification shrinkage. This study highlights a new molten metal deposition-based AM technique developed by ValCUN that not only alleviates the aforementioned issues but also provides a pathway for fast and affordable Al 3D printing. The technique reduces capital investment and operating costs by foregoing the use of lasers and improves safety and sustainability by employing safe-to-handle wire feedstock, including recycled feedstock, instead of powders. The process employs continuous extrusion of molten metal at an adaptive resolution, providing high build rates for medium-sized and complex 3D-printed aluminium components. A parametric study investigates how the initial conditions of a molten aluminium droplet influence post-impingement behaviour and final shape, providing input for fine-tuning process parameters.

The use of metal additive manufacturing has seen significant growth in recent years, making it a key manufacturing process for producing lightweight, complex components. However, common technologies such as laser powder bed fusion and directed energy deposition are less efficient for aluminium alloys because of high reflectivity, powder management, superheating and intensive cooling rates. Molten Metal Deposition is a novel 3D-printing approach that enables intricate geometries using reactive materials including aluminium. This study investigates the influence of process parameters on defect formation and the microstructure of single-walled rectangular samples in the as-built condition. Aluminium alloy 4043 was used as feedstock. Digital microscopy assessed surface waviness and deposition-related defects; optical and scanning electron microscopy characterised the microstructure, and microhardness testing evaluated the influence of process parameters on overall performance.

Additive manufacturing technologies offer significant advantages in producing lightweight alloys with complex geometries. Aluminium alloys are widely used in automotive, aerospace and defence applications, but defects including porosity, lack of fusion and flaws in border and interlayer regions can impair mechanical performance. In this study, Molten Metal Deposition technology implemented in the ValCUN Minerva system was used to manufacture Al4043 alloy parts and evaluate their production quality. Scaled photographs were used for dimensional assessment, and cross-sectional analyses examined border regions and interlayer bonding. The infill and outer-wall layers were consistently aligned with the designed geometry, while only a limited number of voids and defects were identified. The findings demonstrate that MMD enables reliable production of Al4043 alloy parts and highlight the importance of border regions in quality assessment.

This work investigates the applicability of Molten Metal Deposition (MMD) for additive manufacturing of high-strength aluminum alloys (6xxx). Molten Metal Deposition (MMD) is a novel wire-based metal additive manufacturing (AM) technique with an initial focus on aluminium. MMD involves the direct melting and deposition of wire feedstock onto a heated substrate. Process parameter optimization demonstrated the feasibility for manufacturing 6061 samples without detection of solidification cracking. Extensive metallurgic testing revealed opportunities of the technology: hardness values approaching T4–T5 conditions, attributed to intrinsic thermal cycling during deposition. Fusion inconsistencies, primarily driven by oxide-induced microbridging, were identified as the dominant defect mechanism. Experimental analysis demonstrated that layer adhesion improves significantly through tailored energy input, reduced extrusion at geometrical discontinuities, and controlled track geometry. To further mitigate oxidation, suggestions are formulated for future work and applications are briefly elaborated on such as the potential of printing structures in space.

Molten Metal Deposition (MMD) is a novel wire-based metal additive manufacturing (AM) technique with an initial focus on aluminium. MMD involves the direct liquefaction and deposition of wire feedstock onto a heated substrate. This method eliminates the need for auxiliary energy sources like lasers, binders, or support structures, thereby reducing thermal stress and enhancing process efficiency. MMD is particularly suited for the production of high-strength aluminium alloys in the 6xxx and 7xxx series. To optimize the parameters of this process, a detailed finite element analysis (FEA) is performed using an element-birth technique to accurately simulate the dynamic conditions during deposition. Following this, experimental validation of the thermal profiles of the components is carried out to ensure consistency with the simulated results. An extensive design of experiments is performed to obtain the optimum process parameters. The study demonstrates the potential of MMD to fabricate components with diverse geometrical configurations effectively.

Metal additive manufacturing (AM) is lagging behind in terms of industrial implementation. Despite the well-recognized benefits, feedstock handling, post-processing and slow print process and integration efforts are significant barriers, especially for aluminium alloys. Molten Metal Deposition (MMD) is a new innovative metal AM technology that tackles these barriers. The use of wire as feedstock material, the avoidance of lasers as heat sources, in combination with a reduced need for support structures and significantly lower thermal stress development during part fabrication by MMD, allow easy integration and automation of MMD technology and quick industrial adoption. MMD also enables successful fabrication of crack-sensitive high strength aluminium alloys (6xxx & 7xxx series). This study evaluates the quality of supportless overhangs up to 75°, manufactured by MMD. Microstructural analysis provides information about the adhesion quality, grain structure and porosities. The results allow for strategies to extend supportless overhangs exceeding 75° and address further opportunities and limitations.