Synchronous reluctance (SynR) machines are promising rare-earth material-free alternatives to permanent magnet machines. However, structural challenges limit their operating speed and power density. This paper proposes and investigates multi-material additive manufacturing (MMAM) as a key-enabler to realize power-dense and high-speed SynR machines. It does so by proposing designs that guide magnetic flux through solid rotors realized by selective placement of magnetic and non-magnetic materials. To explore this concept, first, material samples are additively manufactured and experimentally characterized to assess the structural and magnetic properties that can be expected for the proposed rotors. Second, the design space of each rotor type is explored using these measured properties within finite element analysis. The results reveal that MMAM can enable fabrication of SynR motors with power density levels that are at the leading edge of all conventional electric machine topologies. It is shown that tip speeds in excess of 300 m/s can be achieved, resulting in 3-4x improvement in power density over conventional SynR motors. A solid SynR rotor is printed in an experimental MMAM laser powder bed fusion system. The rotor is paired with an existing stator to create a functional SynR motor with a saliency ratio of 2.59 and torque rating of 4.15 Nm. This is the first publication of a SynR rotor prototype constructed via MMAM.

The objective of this work is to study the ability of friction surfacing to deposit metal alloys that are difficult to process with traditional methods. Creep and neutron irradiation-resistant oxide dispersion strengthened (ODS) materials cannot be produced via the conventional casting route due to the insolubility of the oxidic and metallic alloy constituents, causing unintended inhomogeneous oxide dispersion and material behavior. Increasing the silicon content of iron-silicon (Fe-Si) improves electromagnetic properties but embrittles the material significantly, and fusion-based manufacturing methods are unable to process this steel. The solid-state nature of the friction surfacing process offers a potential alternative processing route to enable wider usage of difficult-to-process alloy systems. Both ODS and Fe-Si materials are available in powder forms. While the existing literature in friction surfacing focuses on depositing composites by incorporating small quantities of powders through holes in consumable rods, this is the first study showing that a large charge of powder can be converted to a homogeneous fully consolidated deposit in friction surfacing. A novel methodology is used that incorporates the high portion of powder feedstock into hollow consumable friction surfacing rods (up to 35% volume fraction). It was found that fully consolidated deposits can be produced with powder feedstocks using the proposed methodology. A recrystallized, homogeneous, equiaxed microstructure was observed in Fe-Si 6.8 wt% and a new-generation FeAlOY ODS alloy deposits processed with hollow stainless steel friction surfacing rods. Both powder and rod material plasticize and deposit without bulk intermixing.

Synchronous reluctance (SynR) motor technology is promising to realize rare-earth material-free electric machines. However, structural challenges limit operation speed and subsequently power density compared to machines with rare-earth permanent magnets. This paper proposes and investigates multi-material additive manufacturing (MMAM) as a key-enabler to realize power-dense SynR machines. It does so by guiding magnetic flux through a solid rotor component by selective placement of magnetic and non-magnetic materials to enable high-speed operation. To validate this concept, samples are manufactured using a MMAM process and experimentally characterized to assess the structural and magnetic properties that can be expected for the proposed rotors. The data is then used in a multi-physics modeling framework to explore the design space of new MMAM rotor concepts. The simulated results in this paper reveal that MMAM technology can enable a 4x increase in rotor speed, resulting in 400 % power density improvements. The MMAM rotors achieved tip speeds of approximately 300 m/s and rotational speeds over 55 kRPM at comparable efficiencies to conventional designs, despite the presence of existing MMAM geometry restrictions. This study ultimately demonstrates that MMAM technology has the potential to enhance SynR machine operation speed and power density, making it a valuable option for high-performance applications.

During high-speed X-ray imaging of laser surface polishing experiments of specimens of 316L stainless steel at Argonne National Lab's Advanced Photon Source, it was discovered that the induced keyhole changes shape and dimensions while crossing an engineered surface feature without altering process parameters. It was observed that the post-surface feature keyhole was deeper than that of the pre surface feature keyhole. This work reports on the first in-situ observation of the effect of localized surface geometry on underlying melt pool behavior. This has implications for defect formation mechanisms during laser melting processes that rely on melt pool geometry.

One of the main factors keeping additive manufactured metal parts from being used in industry is the relatively low fatigue life of the as-printed parts when compared to their conventionally manufactured counterparts. In addition, certain areas on additively manufactured parts need finishing operations in order to make them functional. While laser polishing has demonstrated the ability to reduce the roughness of various metal surfaces, including additive manufactured ones, it is necessary to study the influence of this process to ensure the surface roughness improvements are not gained at the detriment of fatigue life. The objective of this work is to determine the influence of laser polishing on the fatigue life of both conventionally and additively manufactured metal parts. Fatigue samples were generated from 316L stainless steel using conventional machining and additive manufacturing through laser powder bed fusion. A single set of laser polishing parameters was used to determine the influence of laser polishing on samples manufactured from both methods. This work has shown that surface roughness of both machined and additive manufactured parts can be reduced without sacrificing fatigue life under certain polishing conditions. This demonstrates that laser polishing is a practical method for addressing additively manufactured surface roughness challenges while not negatively impacting fatigue performance.

This study employs high-speed X-ray imaging to capture the process dynamics during FSW in-situ, using a high-intensity X-ray beam to image a 2 mm x 2 mm area at 20,000 frames per second. The friction stir (FS) tool made of H13 tool steel with threads and 3-flats on the probe was used in an aluminum 6061-T6 workpiece. The process parameters employed result in a fully consolidated weldment without any observable sub-surface voids. The density changes captured by the high-intensity X-ray beam show the formation and filling of cavities in the wake of the tool three times per rotation.(c) 2022 Society of Manufacturing Engineers (SME). Published by Elsevier Ltd. All rights reserved.

and in Fig. 2 for the CoCr-LPBF-manufactured surfaces. The mild steel 1.0122 surfaces show significant influence of the overlap rate. A path overlap of 15 % leads to an increased surface roughness Sa, while the surface roughness then decreases with growing path overlap. Hence, the lowest surface roughness for these experiments is achieved with a path overlap of 80 %. The spatial wavelengths show that the microand meso-roughness decrease to similar levels below 0.25 μm depending on the overlap. Regarding the long wavelength surface features, there is a much more significant dependency on the path overlap. For these wavelengths, the waviness was reduced using a path overlap of 80 %, while path overlaps of 15 % and 38 % lead to significant increases of the high spatial wavelengths. The results of the laser polished LPBF surfaces show a reduced surface roughness Sa at both 80.5 % and 90 % path overlaps compared to the as-built surface. The examination of the different spatial wavelength sections has shown that the microand meso-roughness as well as the waviness are reduced compared to the initial surface depending on the overlap. The laser polishing was done with a TruDisk 12002 by Trumpf with a cw-wavelength of 1030 nm. The beam diameter on the material surface was 652 μm and the laser power was set to 1 kW. The influence of the path overlaps on the surface topography of mild steel 1.0122 was analyzed. Subsequently, the obtained results were transferred to cuboids made of CoCr-alloy (Stellite-21), which were produced via LPBF. The process speed was set to 200 mm/s, while the path overlap was varied between 15 % and 80 %. With the results obtained here the LPBF components were processed afterwards. For this purpose, the laser polishing parameters were a process speed of 1000 mm/s, a power of 1.25 kW, and path overlaps of 80.5 % and 90 %. Surface topography measurements were made by confocal microscopy to analyze the results of the laser polishing process. These microscopic images were processed using a fast Fourier transformation (FFT) to determine the amplitude of the spatial wavelengths of the surfaces with a focus on the waviness as well as the microand meso-roughness. The results of the FFT analysis of the surface topography measurements are shown in Fig. 1 for the mild steel surfaces The production of components using laser powder bed fusion (LPBF) offers a wide range of applications. The selective local energy input and layer-by-layer melting of powder particles allows high design flexibility and a wide range of component geometries. It is often necessary to apply post-processing steps in the process chain to meet the design requirements. Besides metallurgical reasons, which may, for example, require a heat treatment, a subsequent treatment may be necessary due to the surface topography. During the LPBF process, partially-melted powder particles often remain on the surfaces. Additionally, the layer-by-layer melting of the powder particles can contribute to the waviness of the surface. Therefore, LPBF components usually have a process chain with post-processes such as machining, grinding, mechanical polishing, shot peening and similar techniques. Laser polishing is an alternative that allows complex surfaces to be polished contact-free and non-abrasively without tool wear. Thus, it is not only possible to smooth the surfaces by remelting, but also to reduce the porosity close to the surface. Typical polishing rates are in the range of a few mm2/s. The melt pool dynamics and the associated waviness limit the melt pool size and processing speed and therefore the achievable polishing rates. Nevertheless, an increase of the polishing rate is desirable. The polishing rate depends on beam diameter, process speed and path overlap. According to the literature different approaches to increase the polishing rate are possible. For example, this problem can be countered by beam shaping or adjusted intensity distribution. Within this study, the approach of using high process speeds in combination with high path overlaps is investigated. It is based on the hypotheses that the high path overlaps can limit the resulting waviness and therefore enable high polishing rates. BIAS ID 200471 Beste 2020 processparameters