Additive manufacturing letters最新文献

A wide range of additive manufacturing (AM) processing conditions can be rapidly realized within a single specimen via high-speed direct energy deposition laser based (DED-LB), due to a variety of cooling conditions and in-situ powder mixing. Since existing approaches are inefficient in exploring the vast material and process design space in AM, high-speed DED-LB can be employed as a novel technology for high-throughput alloy design tool. However, an evaluation of the process transferability of the high-speed DED-LB process with respect to the currently dominating metal AM technologies, namely laser powder bed fusion (PBF LB/M) and conventional DED-LB, is required. In this study, high-speed DED-LB is applied for the high-throughput sample production, using the nickel alloy IN718 as reference material as well as the AM processes PBF LB/M and DED-LB as reference processes. The resulting microstructures are characterized and compared using optical microscopy and large-area scanning electron microscopy (SEM) analysis combined with energy-dispersive X-ray spectroscopy (EDS). Furthermore, a model for calculation of the volumetric energy density is developed to compare the applied AM processes. The significant influence of the processing conditions on the solidification behavior of the investigated material allows for efficient exploration of the microstructure and phase composition. Specific high-speed DED-LB-process conditions achieved the average solidification cell size and laves phase content as observed in the PBF LB/M- and DED-LB -produced counterparts. The applicability of the high-speed DED-LB process for rapid alloy and process development, i.e., process transferability, is critically evaluated. The results show that high-speed DED-LB can be used to emulate cooling conditions of PBF-LB/M and DED-LB and, therefore, be used as tool for rapid alloy development.

Material extrusion additive manufacturing of thermoplastics is so advanced due to the tunable rheological properties and hence a suitable printability, which is deficient for metals. Even though semi-solid modification and binder indirect modification are used to realize metal extrusion printing, the uncontrollable flow behavior and the metallurgical defects make it challenging to bridge this gap. In this study, mixed powder remelting and printability assessment were first proposed for producing metallic slurry with pre-designed microstructure and suitable printability without adding fillers or polymer carriers. Specifically, the hypoeutectic Sn-Bi metallic slurry was obtained by remelting the mixed powder composed of SnBi58 powder and pure Sn powder. The microstructural characteristics at different temperatures were investigated, demonstrating the ability of microstructure predesign. Furthermore, the printability, including stability, extrudability, and buildability, was evaluated by an advanced rheometer. The combined slurry preparation and printability assessment provides a reliable method for parameters improvement to obtain the structural fidelity.

In this work, a novel Metal Additive Manufacturing using Powder sheets (MAPS) method for printing multi-material composites in one process is proposed. MAPS employs powder sheets (i.e. metal powder-polymer matrix flexible films) as the feedstock material. Its key advantages include a relatively rapid change from one material to another and a minimum wastage of materials due to the elimination of the powder bed. The powder sheets were fabricated using a ‘solvent casting’ method. They were then employed in a commercialised metal printer for printing metal multi-material composites. To prove the disruptive concept of MAPS, a 60-layer trimetallic multi-material composite (304 L stainless steel, In718 and CoCrFeMnNi high entropy alloy) was additively manufactured using three different types of powder sheet material in the same manufacturing system for the first time. Experimental results indicate a high density (99.80 %) multi-material composites was printed by MAPS. EDX and SEM observations of the multi-material composites revealed variations of chemical composition and microstructure along the build direction. The newly proposed MAPS manufacturing method and results of this study provide insights into a new avenue for multi-material metallic parts.

Transition to circular economy requires the production of sustainable and eco-designed materials that help to reduce environmental impacts of metallic components. The development of sensing layers providing luminescent tracking functionalities is a potential method for extending the service life of metallic parts. In this study, incorporation of luminescent Ce³⁺ doped yttrium aluminum garnet (YAG:Ce) within a stainless steel 316L (SS316L) matrix has been achieved for the first time by laser powder bed fusion (L-PBF). Embedding of phosphor particles was successfully carried out on a selected area of the 3D printed sample. Despite harsh processing conditions of L-PBF, luminescent emission was detected by optical spectroscopy. Microstructure and chemical composition of the incorporation zone were investigated in order to better understand optical properties. The precipitated particles exhibit new optical features, arising from the modification of the luminescent host lattice and the intricate interactions with the metal matrix.

Drop-on-Demand additive manufacturing could offer a facile solution for scalable on-site manufacturing. With an increasing number of functional materials available for this technology, there are growing opportunities for applications, such as electronics. Here we report on a novel printing strategy, Off-the-Grid (OtG), which enables refined positioning of individual droplets and enhanced resolution compared to the traditional printing strategy. We demonstrate successful printing of structures with feature position control smaller than a single droplet size, and hence enhanced shape fidelity for intricate designs. This strategy is extended to filled patterns, enabling improved layer coverage and customisable inter-layer droplet positioning to control surface morphology. The OtG strategy is applied to produce functional designs, such as conformable circuitry and miniaturized antennae, and is transferable to different materials, from metal nanoparticle and polymeric inks on inkjet platforms, to molten metals on a MetalJet printer. These results could advance exploitation of AM in electronics, wearable electronics, medical devices, and metamaterials.

Solid-state additive manufacturing (AM) via friction stir based processes is gaining increased attention as these techniques are feasible for several similar and dissimilar material combinations and induce significantly lower energy input to the subjacent structure than fusion-based approaches as material melting is avoided. Available research concentrates on linear depositions; however, further development of these techniques towards application necessitates more complex deposition paths, e.g. curves and the crossing of edges of previously deposited layers. In this study, the solid-state layer deposition process of friction surfacing (FS) is investigated in terms of process behavior and appearance of the resulting deposit when curved deposition paths are applied. With advancing side on the curve's inner edge, material build-up occurs predominantly on this side of the layer, which results in a deposit of inhomogeneous thickness. This phenomenon is related to the FS process characteristic due to the superposition of rotational and travel movement on a curvature, and is more pronounced for curves with small radii. A further challenge exists for closed structures, where the deposition has to cross previously deposited layers. This can be successfully achieved by reducing the travel speed prior to passing the edge to provide sufficient plasticized material thickness below the stud tip. Overall, the study provides an understanding of the FS process behavior and process parameters for curved paths. Furthermore, recommendations for process control and path planning, e.g. for building closed cylindrical shell structures, are deduced.

Conventional robotic wire arc additive manufacturing technologies enable the rapid production of moderate-sized components using low-cost wire feedstocks and robotic welding systems. Efforts to date have primarily focused on single robot solutions. However, new configurations are possible with coordination of multiple robots and multi-degree of freedom positioners. This paper describes a new multi-agent control paradigm that enables multiple robots to work collaboratively on manufacturing a single component on a rotating platform. The advantages of this approach are increased deposition rate and productivity. This paper demonstrates this control strategy on a 19 degrees-of-freedom platform based on three wire arc additive systems surrounding a single rotating platform.

This study investigates the fabrication of conductive structures for electronics applications using embedded 3-D printing coupled with Volumetric Additive Manufacturing (VAM). Electrically conductive carbon grease was suspended within a resin matrix, and the samples underwent VAM printing and post-processing. The resulting three dimensional conductive structure was measured to have a resistance of 4.5 kΩ, corresponding well with the material specifications. The results showed the importance of complete encapsulation of the conductive material within the resin to preserve the conductive structure. The resistivity of the conductive grease remained unaffected, indicating no interaction with the resin. Potential enhancements to improve the structure's fidelity and broaden its range of applications is discussed. This research highlights the potential of embedded 3-D printing for fabricating conductive structures in VAM. The fabrication method allows for unprecedented avenues in developing electronic applications, such as smart sensing, smart drug delivery and cyborganics.

A single-phase Ni-superalloy (Hastelloy X) was fabricated by laser powder bed fusion (L-PBF) using different layer-thicknesses (i.e., 40, 60, 80, and 120 µm), by implementing different optimized volumetric laser energy densities (i.e., VED of 67, 44, 31, and 35 J/mm³). As-built (AB) microstructure, grain morphology, and the recrystallization kinetics were systematically dependent on VED which generally decreases by increasing layer thickness. An increased VED led to a columnar grain morphology, strong texture, large lattice micro-strain, high fraction of low angle boundaries, and increased yield strength. Electron back scattered diffraction (EBSD) analysis revealed that also the recrystallization kinetics was significantly dependent on VED. By decreasing the VED, recrystallization was largely suppressed because of the lower dislocation density in the AB state. A processing map to study the recrystallization as a function of VED, and solution annealing temperature is proposed.

Freeze-dry pulsated orifice ejection method (FD-POEM) shows great potential in producing spherical refractory or multi-component alloy powders. However, addressing the dispersibility issue of high-concentration slurries is required to broaden the application scope of FD-POEM in additive manufacturing. To this end, this study proposes the use of ultrafine bubble (UFB) water as an economical additive to improve slurry dispersibility without introducing impurities. A refractory MoSiBTiC alloy with complex compositions was chosen as an example to demonstrate the effect of UFBs on the dispersibility of the slurry mixture and the morphology of the FD-POEM powders. The underlying mechanism of the improved slurry dispersibility was elucidated through calculations of repulsive forces. Consequently, the operational range for the FD-POEM process was significantly expanded from 10 to 20 % when using UFB water. In addition, the MoSiBTiC alloy build was fabricated via laser powder bed fusion (L-PBF) using FD-POEM-produced powders with UFB additives, exhibiting uniform dendrites and fine TiC nanoparticles distributed in the matrix. This study not only expands the potential applications of UFB water in powder fabrication but also paves the way for the processability of Mo-based parts with advanced microstructures by combining FD-POEM with L-PBF.