Additive manufacturing letters最新文献

Additive manufacturing with local composition control is uniquely suited for the development and exploration of advanced materials with compositionally graded structures. A fused filament fabrication printer was designed with in situ composition control facilitated by using an active-mixing hotend. Stepper motors drive three filament extruders and a mixing rod in proportions instructed by a print file to control composition and material distribution within extrusions. Composition tailoring was demonstrated by printing specimens with twelve distinct regions each consisting of unique filament mixtures. Local control of composition was demonstrated by printing a variety of specimens with composition gradients having horizontal, vertical, radial, and circumferential orientations. The tensile properties of printed materials were modified by printing with mix ratios of polylactic acid and thermoplastic polyurethane. Eight blend ratios were tested in tension and have tensile moduli ranging from 17.3 to 3480 MPa. These methods demonstrate advanced capabilities that are well suited for manufacturing functionally graded structures.

Processing of soft magnetic materials with additive manufacturing has shown capability to deliver good magnetic properties and increased silicon content of Fe-6.5 wt%Si, however methods must be used to reduce the eddy currents in large bulk cross-sections in components created by additive manufacturing. Geometrical design has been shown to do this effectively, however stochastically cracked parts show similar magnetic performance with a large increase in stacking factor. To enable their use in electrical machines the mechanical properties of this material must be understood. Therefore, this study uses uniaxial tensile testing to understand the mechanical performance. The ultimate tensile strength of the material in the as-built condition was 17.9 MPa (σ = 4.5 MPa), which was improved by 40% to 25.5 MPa (σ = 5.7 MPa) by infiltrating the cracks with a low viscosity resin. This brings the material strength to more than three standard deviations from the required strength of 7 MPa to be used in a specific axial flux machine. The material exhibited an elongation to failure of 8-10%, showing that the suppression of ordered phases by high cooling rates has improved the ductility of the material. Hence, the stochastically cracked parts have sufficient properties to be used in the 3D magnetic circuits of electrical machines.

A report on twinning-induced plasticity in 316L stainless steel manufactured by metal additive manufacturing (AM) is presented. A tapered tensile test geometry was used which enabled the investigation of twin formation over a range of strain levels in a single specimen. Hardness and twinning concentration were observed to increase with strain up to peak values of 380 ± 10 HV and 28 ± 4%, respectively. Furthermore, twin formation was found to be regulated by grain size and crystal texture. This methodology can be applied to new AM materials development and will inform the design of energy-absorbing structures that maximise the benefits of AM design and strain-hardenable materials.

Fe-Co alloys are an important class of soft magnetic materials that often pose challenges in their fabrication because of the brittle B2-ordered phase. We show that laser beam powder bed fusion (PBF-LB), owing to its rapid cooling rates, offers an avenue for the fabrication of these alloys by suppressing the disorder →order phase transformation at room temperature. We use neutron diffraction to understand the phase transformations in a Fe-50 %Co alloy fabricated via PBF-LB. We report that the disorder→order phase transformation in this alloy occurs concurrently via homogeneous ordering and classical nucleation and growth.

In the current study, the effects of different post-processing methods, including heat treatment (HT) and electro-chemical polishing (ECP) as well as their combination on the surface texture, porosity, microstructure, mechanical properties, and rotating bending fatigue behavior of U-notched laser powder bed fused AlSi10Mg specimens were comprehensively investigated. In addition, to better understand the effects of the applied post-processing methods on the sensitivity of the notched specimen to surface and near-surface defects, finite element analysis was performed. Chemical treatment was found to be very influential on surface texture modification of the very narrow notched parts, for which the application of other treatments can be quite challenging. It was also found that the fatigue behavior of the notched specimens was more sensitive to the surface texture rather than to the near-surface defects. The hybrid treatment involving HT+ECP was the most effective for fatigue behavior improvement due to simultaneous homogenization of the microstructure, released tensile residual stresses, enhanced ductility and high surface texture modification.

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.