Additive manufacturing letters最新文献

This study explores cellular structures in TiC/B₄CCoCrFeMnNi high-entropy composites (HECs) fabricated by direct energy deposition (DED) additive manufacturing process, investigating the role of TiC and B₄C nano-paticles in enhancing mechanical properties. Despite larger dislocation cell structures and thinner boundaries in TiC/B₄CCoCrFeMnNi HECs compared to CoCrFeMnNi high-entropy alloy (HEA), they exhibit significantly higher hardness and strength, challenging traditional strength-size relationships. Additionally, we examine the behavior of ceramic nano-particles (TiC and B₄C) with high melting points relative to matrix CoCrFeMnNi HEA. Rapid scanning prevents full nano-particle melting, leading to distinct element distribution of cell structure. These findings provide insights for selecting suitable nanoceramic particles in HEC development via metal additive manufacturing.

Wire-arc direct energy deposition (wire-arc DED) has been developed to manufacture large-scale metal products with high deposition rates, low material cost, and high material efficiency. However, dynamically varying printing conditions and complex geometries frequently lead to unfavorable part distortions during and after printing which are magnified as part sizes increase. In this study, an effective computational simulation method was developed for large-scale 316 L stainless steel parts using finite element method. The model was validated with the measured distortion using a 3D laser scanner. The distribution of deviation is within 16 % (=1.6 mm) against a measured value for a 483.6 mm tall part with 248 layers, with excellent agreement with the spatial pattern of distortion. The dynamic part deformation during printing and cooling was tracked using vision camera to investigate the thermo-mechanical deformation mechanism. The result showed that long pauses during machine maintenance pauses have strong influence on part distortion.

Hydropower with a small elevation change from inlet to outlet, known as “low-head” hydropower, is a relatively untapped resource for reliable green power generation. One major barrier to entry is the cost of the components needed to generate the power. Each installation site is unique, with various head levels, flow rates, and other unique site characteristics that drive up the cost of development and installation. As a result, custom-made components are necessary because the sites are intrinsically inefficient. However, customized parts are generally more expensive to manufacture than ready-made parts. Often times, the cost of custom-made components is so high that the low-head hydropower installation becomes non-viable. Additive manufacturing offers the ability to make custom components, ideal for one-off applications, at low costs that are well suited for the needs of low-head hydropower. Indirect additive manufacturing, such as making tools or dies rather than end use components, can also be used to make low-cost composite tooling as needed for these custom applications. This paper explores the use of additive manufacturing, both directly and indirectly, to produce the components of a turbine system for a low-head hydropower site. The parts were designed to form a unique modular system, which saves time for future designs and iterations. The system has operated for more than three years without failure at a test site in Wisconsin, USA. This work serves as a basis for future application of AM to low-head systems, in which the modular components can be customized for each unique hydropower installation.

The reliability of additively manufactured flexible electronics or so-called printed electronics is defined as mean time to failure under service conditions, which often involve mechanical loads. It is thus important to understand the mechanical behavior of the printed materials under such conditions to ensure their applicational reliability in, for example, sensors, biomedical devices, battery and storage, and flexible hybrid electronics. In this article, a testing protocol to examine the print quality of additively nanomanufactured electronics is presented. The print quality is assessed by both tensile and electrical resistivity responses during in-situ tension tests. A laser based additive nanomanufacturing method is used to print conductive silver lines on polyimide substrates, which is then tested in-situ under tension inside a scanning electron microscope (SEM). The surface morphology of the printed lines is continuously monitored via the SEM until failure. In addition, the real-time electrical resistance variations of the printed silver lines are measured in-situ with a multimeter during tensile tests conducted outside of the SEM. The protocol is shown to be effective in assessing print quality and aiding process tuning. Finally, it is revealed that samples appearing identical under the SEM can have significant different tendencies to delaminate.

Considering the high correlation of melt-pool size and build quality of a part fabricated by a laser power bed fusion (L-PBF) process, it is important to understand what are the major thermal factors that affect melt-pool size during the build process. This paper conducts an experimental investigation on how interlayer temperature affects the melt-pool morphology through a case study of a square-canonical part of Inconel 718 built with the EOS M280 system. Interlayer temperature is the layer temperature after powder spreading but before scanning a new layer. This paper examines variations in melt-pool morphology across representative layers with a large difference in interlayer temperature. It also investigates how the melt-pool size variation is affected by local temperature change caused by switching the laser scanning direction from hatch-to-hatch within a single layer. It is observed that the melt-pool half-width has increased by 40% - 100% when the interlayer temperature has increased from 100 °C to 300 °C. On the other hand, the variation of melt-pool dimensions due to local temperature change is less significant under a low interlayer temperature at 100 °C. The difference in melt-pool dimensions due to laser turnaround gets amplified when the interlayer temperature reaches high at 300 °C. Moreover, a trend of melt-pool morphology transitioning from a conduction to a convective heat transfer mode is observed at the interlayer temperature of 300 °C. Results of this paper demonstrate that interlayer temperature plays a critical role in thermal effects on melt-pool morphology, indicating a need of controlling interlayer temperature to improve build quality.

Laser beam powder bed fusion (PBF-LB) of AlSi10Mg has attained technology maturity in various industries. Nevertheless, the manufactured components often require thermal treatments to tailor their microstructures and mechanical properties. Experimental development of suitable thermal cycles for the printed parts is time and energy intensive. However, the characteristic microstructure of parts produced by PBF-LB resembles that of gas-atomised powder. Therefore, this study presents an in-depth investigation on the correlation between the properties of the powder and PBF-LB samples. In-situ heat treatment methodology was deployed to consistently heat-treat the powder and PBF-LB samples using elevated build-plate temperatures (220 - 500 ºC). Scanning electron microscopy revealed Si atoms’ diffusion, followed by eutectic network's disruption and Si particles’ coarsening, with increased build plate temperatures, in both parts and powder. X-ray diffraction and differential scanning calorimetry showed a strong correlation between the powder and parts treated at the same build-plate temperatures. A 500 ºC in-situ heat-treatment temperature reduced the hardness by ∼43% (powder) and ∼52% (printed samples). Nano- and micro-hardness values on the powder and printed samples also exhibited high correlation. Similarities between the powder and part's microstructural changes with temperature were attributed to the similar scale of cooling rates in gas-atomisation and PBF-LB, respectively. The findings in this study pave a clear pathway that experimentation on small batches of powder via ex-situ heat treatments could be efficiently used as a high-throughput method to predict the effect of thermal treatments on printed parts and to design new heat treatment protocols, specifically for PBF-LB materials.

Defects are a major issue in 3D printed electronics because even a tiny inaccuracy will lead to a faulty electronic circuit. This article presents a novel approach to correct printing defects with a neural network based automatic error correction. The errors are detected during printing by recording images of each wire with a high-resolution camera and segmenting the wires using convolutional neural networks. The neural network is trained with a dataset of printed wires with marked wire positions. A novel error detection algorithm then identifies connection breaks and generates repair paths for every connection break in the circuit, which are then executed by the printer. Multiple objects with deliberately inserted defects were printed and automatically repaired on different substrates using a Neotech AMT PJ15X printer to evaluate the performance. The algorithm detected all connection breaks, generated repair paths, and successfully repaired the faulty wires. This article also shows this approach's limitations and areas for future research, like complex circuits printed on 5-axis machines. The automatic error correction is highly reliable and is an important step towards a first-time-right production.

Additive manufacturing using Powder Bed Fusion by Laser Beam (PBF-LB) enables products with high design freedom. In addition, the ability to process more than one material in all three spatial directions makes it possible to produce highly functional components in one single process. This article investigates whether multi-material manufacturing using PBF-LB is suitable for producing coils for electric motors, which are designed with integrated cooling channels to increase the power density. For this purpose, the copper alloy CuCr1Zr for the coils and the stainless steel 1.4404 (316L) for the core are processed simultaneously. The component designs were verified using 2D and 3D finite element analysis and then manufactured in a multi-material PBF-LB process. While good electrical conductivity of the copper alloy was achieved by heat treatment, it was found that thermal distortion caused deviations from the nominal geometry. The measurement of the electrical properties showed that this distortion leads to short-circuit currents within the coils and the teeth. On this basis, ideas for solutions were developed, with the help of which the functionality of the coils can be ensured or the power density can also be increased. In addition to adapting the design of the component, this includes processing additional or other materials, such as soft magnetic composites.

A hydrogen reduction-based method for additive manufacturing of carbon steels from low cost and stable oxide powders is presented. This method uses materials extrusion processes to extrude inks composed of oxide powders, plastic binders, and solvents. Oxide powders are synthesized into viscous inks and extruded under ambient conditions into three-dimensional architectures. The three-dimensional printed green bodies are reduced at elevated temperatures in hydrogen-rich environments to burn off the polymer binder and reduce the oxide powders, yielding metal alloys with controlled compositions. While this approach has been demonstrated in previous publications for various alloys, the addition of carbon, an important element in most industrial steels, has been a persistent challenge. This paper demonstrates an approach to introduce carbon during the reduction process, resulting in through-thickness carburization of the final parts.

The structural instability in the β-type titanium alloys could affect the stability of vacancies. The stability of vacancies in a β-type Ti-15Mo-5Zr-3Al alloy, fabricated via laser powder bed fusion (LPBF), was investigated using positron annihilation spectroscopy and first-principles calculations. The observed positron lifetimes were close to the experimental and calculated bulk lifetime of Ti-15Mo-5Zr-3Al, which indicates that vacancies were not detected in Ti-15Mo-5Zr-3Al by positron lifetime measurements. Therefore, for the first time, it has been confirmed that quenched-in vacancies are not introduced in the LPBF-manufactured β-type Ti-15Mo-5Zr-3Al despite the fast cooling rate in LPBF process. This feature is preferable for the structural stability in biomedical and industrial applications. The calculated atomic displacement from the ideal bcc lattice positions decreased in β-type Ti-Mo alloys with increasing Mo concentration, indicating that the bcc structure was stabilized by the added Mo. The calculated vacancy formation energies of Ti atoms in β-type Ti-14.5Mo and Ti-27.0Mo alloys exhibited an increasing trend with an increasing number of neighboring Mo atoms. Mo atoms also increased the migration energies of the neighboring paths of vacancies. The calculated results for Ti-15Mo-5Zr-3Al suggest that, while the bcc structure was stabilized by the Mo atoms in Ti-15Mo-5Zr-3Al, the migration and formation energies were still low enough for the diffusion of vacancies.