| 1. |
- Borgue, Olivia, 1989, et al.
(författare)
-
Constraint Replacement-Based Design for Additive Manufacturing of Satellite Components: Ensuring Design Manufacturability through Tailored Test Artefacts
- 2019
-
Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 6:11
-
Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) is becoming increasingly attractive for aerospace companies due to the fact of its increased ability to allow design freedom and reduce weight. Despite these benefits, AM comes with manufacturing constraints that limit design freedom and reduce the possibility of achieving advanced geometries that can be produced in a cost-efficient manner. To exploit the design freedom offered by AM while ensuring product manufacturability, a model-based design for an additive manufacturing (DfAM) method is presented. The method is based on the premise that lessons learned from testing and prototyping activities can be systematically captured and organized to support early design activities. To enable this outcome, the DfAM method extends a representation often used in early design, a function-means model, with the introduction of a new model construct-manufacturing constraints (Cm). The method was applied to the redesign, manufacturing, and testing of a flow connector for satellite applications. The results of this application-as well as the reflections of industrial practitioners-point to the benefits of the DfAM method in establishing a systematic, cost-efficient way of challenging the general AM design guidelines found in the literature and a means to redefine and update manufacturing constraints for specific design problems.
|
|
| 2. |
- Frisk, Karin, et al.
(författare)
-
Characterisation of EBM-built shelled samples of Ti6Al4V compacted by HIP
- 2016
-
Ingår i: World PM 2016 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA). - 9781899072484
-
Konferensbidrag (refereegranskat)abstract
- Compaction of additively manufactured Ti6Al4V components by Hot Isostatic Pressing (HIP) is often applied to eliminate porosity, producing fully dense material. In the present work shelled samples produced by Electron Beam Melting with the Arcam process (EBM) were compacted by HIP to produce fully dense samples. Cylindrical samples were studied. The walls of the cylinders were built with EBM, and the powder from the process was left uncompacted inside the cylinders. Samples with different wall thicknesses were produced. The samples were thereafter subjected to a HIP compaction. The critical wall thicknesses needed for compaction were evaluated, and the microstructures characterized. The results show that fully dense samples, with very fine microstructures, are possible.
|
|
| 3. |
- Leicht, Alexander, 1987, et al.
(författare)
-
As-HIP microstructure of EBM fabricated shell components
- 2016
-
Ingår i: World PM 2016 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA). - 9781899072484
-
Konferensbidrag (refereegranskat)abstract
- Electron Beam Melting (EBM) was used to build Ti-6Al-4V cylindrical shell samples with different wall thickness filled with powder. Built shell samples were HIPed and the difference in microstructure between the EBM-built walls and densified powder inside the shell components was studied as well as the cohesion between these two regions. Components characterization utilizing LOM and SEM+EBSD indicates that columnar grain growth was consistent before and after HIP in the EBM-built part of the components (walls), whereas the densified material in the center of the component had a fine isotropic microstructure, characteristic for HIPed material. The combination of EBM and HIP is shown to be an attractive way of manufacturing complex-shape full density components for high performance applications, involving shortening of built time in the EBM-processing and lead time in capsule fabrication for HIP.
|
|
| 4. |
- Leicht, Alexander, 1987, et al.
(författare)
-
Effect of part thickness on the microstructure and tensile properties of 316L parts produced by laser powder bed fusion
- 2021
-
Ingår i: Advances in Industrial and Manufacturing Engineering. - : Elsevier BV. - 2666-9129. ; 2
-
Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing provides a unique possibility to manufacture parts with advanced design and thin-walled structures. To explore thin-wall capacity, laser powder bed fusion was employed to fabricate 316L samples with different section thicknesses. A detailed microstructure characterization was then carried out, and tensile properties were assessed. It was found that reducing the part thickness did not affect the microstructure but did reduce the tensile properties. Samples with 1 mm thickness exhibited the lowest yield strength of 457 ± 11 MPa and elongation to fracture of 49 ± 20%, while the tensile properties improved when the sample thickness was increased to 3 mm. The 3 mm thick samples generated tensile properties comparable to those of standard dimensions. The results emphasize that part thickness must be considered when assessing mechanical properties and must be adjusted when performing design optimization and simulations of samples produced with laser powder bed fusion.
|
|
| 5. |
- Leicht, Alexander, 1987, et al.
(författare)
-
Effect of process parameters on the microstructure, tensile strength and productivity of 316L parts produced by laser powder bed fusion
- 2020
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 159:110016
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of process parameters during laser-powder bed fusion on the microstructure, tensile strength and build time of 316L parts is studied. By increasing both, scan speed and hatch distance, an improved productivity while maintaining acceptable properties were achieved. The samples were evaluated using volumetric energy density. The microstructure characterization showed that all produced samples had elongated grains aligned with the building direction independent on energy density that was used, whereas the grain size was strongly affected by the different energy densities. A high energy density resulted in larger grains with a very strong 〈101〉 crystallographic orientation while the lower energy generated small grains with a random crystallographic orientation. This indicates how both, crystallographic orientation and grain size, can be tailored by altering the energy density. Even if a large variance in microstructure was observed, the tensile test results only showed about 5% difference in yield strength between standard process parameters and the samples produced with the lowest energy density but with a 20% faster build time. Due to the decreased energy density, the amount of defects was increased which had a negative effect on the elongation. The samples produced with the lowest energy density had 32% elongation compared to 45% for the samples produced with standard process parameters. This study clearly indicates that the build time can be improved while maintaining good mechanical properties by adjusting the process parameters.
|
|
| 6. |
- Hryha, Eduard, 1980, et al.
(författare)
-
Surface Oxide State on Metal Powder and its Changes during Additive Manufacturing: an Overview
- 2018
-
Ingår i: Metallurgia Italiana. - 0026-0843. ; 110:3, s. 34-39
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Quality and usefulness of the powder for additive manufacturing (AM) are strongly determined by the surface composition of the powder. In addition, taking into account harsh conditions during AM process, significant changes in the powder surface chemical composition are taking place, limiting powder recyclability. Hence, knowledge concerning amount of oxides, their composition and spatial distribution on the powder surface determines further powder recycling. This communication summarizes possibilities of qualitative and quantitative analysis of powder surface chemistry by surface-sensitive chemical analyses using XPS and HR SEM coupled with EDX. The effect of alloy composition, AM process applied and powder handling on the surface composition of the powder are addressed. Results indicate significant enrichment in the thermodynamically stable surface oxides in case of high-alloyed powder for both, EBM and LS processes. A generic model for the oxide distribution, depending on the alloy composition and powder surface degradation during AM manufacturing, is proposed.
|
|
| 7. |
- Leicht, Alexander, 1987
(författare)
-
Aspects of building geometry and powder characteristics in powder bed fusion
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive manufacturing (AM) produces near-net-shaped parts directly from a 3D-CAD model in a layer-by-layer manner. One of the most common AM technique for fabricating metallic components is powder bed fusion (PBF). The PBF process has shown great potential in fabricating metallic parts with properties better or comparable to conventional methods. However, there are some challenges in reproducibility, process stability, robustness, etc. This thesis elaborates on several of these challenges and addresses the influences of feedstock material, build orientation and part design on the final outcome. The PBF process uses fine metal powder as feedstock material and in order to have an economically feasible process, powder recycling is a necessity. However, to ensure a robust process and consistent material properties, the feedstock material need to be handled with caution as powder properties will affect the part quality. The obtained results for 316L stainless steel from this study indicate that powder degradation in terms of surface product changes occurs when the powder is recycled. It was revealed that both recycled and virgin powder were covered by a heterogeneous oxide layer, composed by a homogeneous iron oxide layer with the presence of Cr-Mn-rich oxide particulates that were growing during PBF processing. The results showed that the powder degradation was more pronounced when used in the electron beam system compared to a laser based system due to the long exposure at high temperatures. The manufacturing capabilities of the PBF process has enabled the production of lattice structures without extensive tooling. The properties of such lattice will be influenced by the microstructure. Hence, it is of importance to understand how the part geometry would affect the microstructure. This study presents the effect of build geometry, as e.g. wall thickness and build angle on the 316L microstructure. The obtained results indicated that in the center of ribs over 0.6 mm in thickness, large elongated grains with preferential orientation were created. Reducing the part thickness to below 0.6 mm reduced the predominant texture. The increased cooling rate close to the part surface inhibited grain growth and changed the preferential grain orientation. For the process parameters used, the critical part thickness to avoid large elongated grains was found to be about 0.4 mm. The obtained results could be used for further development of design rules and prediction of mechanical properties of AM parts with small wall thicknesses.
|
|
| 8. |
- Leicht, Alexander, 1987, et al.
(författare)
-
Characterization of virgin and recycled 316L powder used in additive manufacturing
- 2016
-
Ingår i: SPS16, Lund, Sweden 2016.
-
Konferensbidrag (refereegranskat)abstract
- Gas atomized 316L powder used in electron beam melting was investigated in virgin and recycled stateto indicate the influence of recycling on the powder properties. A cross sectional investigation of thepowder microstructure was performed by means of light optical microscopy and the phase compositionwas determined by means of X-ray diffraction analysis. The powder surface characterization was doneby using X-ray photoelectron spectroscopy and high resolution scanning electron microscopy equippedwith an energy dispersive X-ray analyser. Results showed that evenly distributed oxide particles in thesubmicron range can be observed on the surface of both virgin and recycled powder. The size of theseoxide features on the surface of recycled powder is on average around 200 nm which is four times largerin comparison to virgin powder which is around 50 nm. The EDX analysis indicated enrichment of Si,Cr and Mn in the oxides. According to XPS, both powders are covered by homogenous Fe-oxide layerwith particulate oxide features rich in Cr and Mn. Significantly higher amount of Cr oxide was detectedon the surface of recycled powder compared to the surface of the virgin powder. The recycled powderalso had lower Mn content on the surface. The reason for this is proposed to be the sublimation of Mn,which drives the decomposition of Mn-oxide. The powder cross-section showed that the microstructureof the recycled powder had a tendency to change towards cellular structure, while the microstructure ofvirgin powder is fully dendritic.
|
|
| 9. |
- Leicht, Alexander, 1987, et al.
(författare)
-
Effect of build geometry on the microstructural development of 316L parts produced by additive manufacturing
- 2018
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 143, s. 137-143
-
Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) technology has shown great potential in manufacturing complex products, such as lattice structures without extensive tooling. The focus of this study was to understand the effect of the part geometry on the resulting microstructure. Direct metal laser sintering was used for fabrication of ribs with thicknesses varying between 0.2 and 3.0 mm as well as inclined ribs the with build angles of 30° and 45°. The investigation showed that grains were growing in an epitaxial manner parallel to the building direction. The large elongated grains had a preferential <101> orientation, resulting from the temperature gradient. Additionally, it was found that small grains had formed close to the part surface which were inclined towards the center of the rib. In contrast to the elongated grains, they had a random orientations. The results also indicated that at build angles below 45° the formed microstructure consisted of the large grains elongated in the building direction. For the used process parameters, the critical part thickness to avoid large elongated grains was found to be about 0.4 mm. These findings allowed us to establish the basics for design rules when it comes to thin wall structures.
|
|
| 10. |
- Leicht, Alexander, 1987, et al.
(författare)
-
Effect of scan rotation on the microstructure development and mechanical properties of 316L parts produced by laser powder bed fusion
- 2020
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 163
-
Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing possesses appealing features for producing high-performance components, for a wide range of materials. One of these features is the ability to locally tailor the microstructure and in turn, the mechanical properties. This study investigates how the microstructure of stainless steel 316L parts produced by laser powder bed fusion are affected by alternating the laser scan orientation. The microstructure consists of large elongated grains with a fine cell substructure. This study established the correlation between the orientation of this substructure and the crystallographic orientation. The results show that by producing parts without any rotation a quite unique crystallographic orientation can be achieved. The grain structure primarily consisted of large 〈101〉 oriented grains, that were separated by thin bands of small 〈100〉 oriented grains with respect to the building direction. As rotation was added these bands were eliminated. Samples that were produced without any rotation generated the highest tensile strength (527 ± 5.4 MPa), yield strength (449 ± 2.4 MPa) and ductility (58 ± 1.3%). The lowest mechanical properties were obtained for samples that were produced using a scan rotation of 67° with the tensile strength of 485 ± 4.8 MPa, yield strength of 427 ± 5.4 MPa and ductility of 50 ± 1.3%. This indicates that cell orientation and crystallographic orientation plays an essential role in the tensile properties of 316L parts produced by laser powder bed fusion (L-PBF).
|
|
