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Application of X-ray Computed Tomography for Assessment of Additively Manufactured Products
Örebro University, School of Science and Technology.ORCID iD: 0000-0003-1286-3420
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Additive Manufacturing (AM) is a novel method for fabricating parts from three-dimensional model data, usually by joining materials in layer upon layer fashion. The freedom of design in this method has resulted in new possibilities for fabrication of parts with complex geometries. Manufacturing nearnet- shape parts as well as geometrically complex components such as periodic cellular structures that are used in lightweight structural components, has made AM a promising manufacturing method in industry.

Despite the numerous advantages of the AM methods, the imperfections associated with the manufacturing processes has limited the application of additively manufactured parts. Porosity and surface texture of AM parts especially those fabricated using Laser Powder Bed Fusion (LPBF) methods, have been studied in this thesis. It was observed that the mentioned imperfections have a considerable impact on the mechanical performance of thin-wall structures that are the constituting units of surface-based periodic cellular structures. The quality of internal structure in components fabricated using Fused Deposition Modelling (FDM) and its effect on the strength of those components were the other issues investigated in this thesis.

In order to investigate the mechanical strength of AM parts, as the result of mentioned mesoscale imperfections, appropriate evaluation methods that are capable of quantitatively assessing these imperfections are required. X-ray Computed Tomography (CT), a non-destructive evaluation method, has shown high capabilities for providing useful and reliable geometrical information of both internal and external features of AM components. The challenges involved with the application of CT for assessment of AM component are also studied in this thesis.

Apart from the contributions of this thesis on how CT may be used in AM field, the results of this thesis has provided insight into the design process of cellular structures. This thesis has provided essential information about the strength dependency of thin-walls as the result of mesoscale fabrication defects and how these defects are dependent on the selected material and design of the structure.

Place, publisher, year, edition, pages
Örebro: Örebro University , 2019. , p. 61
Series
Örebro Studies in Technology, ISSN 1650-8580 ; 85
Keywords [en]
Additive manufacturing, X-ray computed tomography, Surface roughness
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:oru:diva-75190ISBN: 978-91-7529-296-0 (print)OAI: oai:DiVA.org:oru-75190DiVA, id: diva2:1338292
Public defence
2019-09-17, Örebro universitet, Långhuset, Hörsal L1, Fakultetsgatan 1, Örebro, 09:15 (English)
Opponent
Supervisors
Available from: 2019-07-22 Created: 2019-07-22 Last updated: 2019-08-30Bibliographically approved
List of papers
1. Measurement of internal features in additive manufactured components by the use of computed tomography
Open this publication in new window or tab >>Measurement of internal features in additive manufactured components by the use of computed tomography
2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Additive manufacturing (AM) is a set of manufacturing processes currently in rapid development providing designersnew freedoms in their designs. One distinct difference from other manufacturing methods is the ability to makecomplex internal features which can be of great benefit for applications in many industries. These features can bechannels, cavities, filled or not filled with powder, parts in parts etc. In order for these advantages to be industriallyapplicable there is a need for robust verification methods for these internal features. X-ray computed tomography (CT)holds the promise of being one of the few powerful tools for non-destructive imaging of internal features. In this work,selective laser sintering (SLS) has been used to manufacture parts of a complex geometry containing internal cavities.The test specimens were manufactured in two different materials; Polyamide12 and Titanium (Ti6Al4V). In order toinvestigate the limitations and controllability of the process, the dimensions of the internal cavities were determinedby a correlation of tactile measurements on external features and CT-data. The results were also compared to computeraided design (CAD) data. This work provides some insight concerning part accuracy of today’s frontier of AM systemsand the ability to measure and characterize internal features using CT.

Place, publisher, year, edition, pages
German Society for Non-Destructive Testing, 2015
Keywords
Computed tomography, additive manufacturing, internal features, selective laser melting
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-47801 (URN)
Conference
Digital Industrial Radiology and Computed Tomography (DIR 2015), Ghent, Belgium, June 22-25, 2015
Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2019-08-27Bibliographically approved
2. Investigating the effect of fabrication temperature on mechanical properties of fused deposition modelling parts using X-ray computed tomography
Open this publication in new window or tab >>Investigating the effect of fabrication temperature on mechanical properties of fused deposition modelling parts using X-ray computed tomography
2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 100, no 1-4, p. 287-296Article in journal (Refereed) Published
Abstract [en]

Fused deposition modeling (FDM) is one of the most common additive manufacturing (AM) techniques for fabricating prototypes as well as functional parts. In this technique, several parameters may influence the part quality and consequently mechanical properties of fabricated components. In this paper, an experimental investigation on effects of fabrication temperature as one of the influential parameters on mechanical properties of manufactured parts is presented. A series of specimens fabricated at temperatures ranging from 180 to 260 C were used for this investigation. X-ray computed tomography (CT) was used in order to non-destructively analyze the internal geometry of the specimens especially the bond between extruded filaments. Finally, the specimens were subjected to a uniaxial tensile load for evaluation of mechanical properties. The results showed that the specimens fabricated at lower temperatures have relatively lower tensile strength despite their considerably higher strain at break. In addition, the specimens fabricated at higher temperature range had significantly higher tensile strength because of the better bond between extruded filaments. The different mechanical responses were highly related to the internal geometry of the specimens and not necessarily the porosity. CT showed great potential as a non-destructive tool for investigation and development of FDM process.

Place, publisher, year, edition, pages
Springer London, 2019
Keywords
Fused deposition modeling, Computed tomography, Polylactic acid, Additive manufacturing
National Category
Other Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-69110 (URN)10.1007/s00170-018-2664-8 (DOI)000455946000025 ()2-s2.0-85053832455 (Scopus ID)
Available from: 2018-09-28 Created: 2018-09-28 Last updated: 2019-08-27Bibliographically approved
3. Effect of X-ray Computed Tomography Magnification on Surface Morphology Investigation of Additive Manufacturing Surfaces
Open this publication in new window or tab >>Effect of X-ray Computed Tomography Magnification on Surface Morphology Investigation of Additive Manufacturing Surfaces
2018 (English)In: 8th Conference on Industrial Computed Tomography, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Additive manufacturing (AM) in the last decade has become a widespread manufacturing process. The possibilities that such technologies have provided for manufacturing of complex geometries compared to conventional manufacturing processes has made them popular in many branches of industry. Despite the advantages of these methods, there are limiting issues which needs to be thoroughly investigated. A limiting factor, especially for powder bed AM parts is their undesired surface finish. AM surfaces can be investigated using various methods such as optical or tactile methods, however for complex AM surfaces they are incapable of capturing all details such as deep valleys at surface level. X-ray computed tomography (CT), can provide 3D information of complex AM surfaces and does not have limitations that line of sight and tactile methods have. There are several parameters in CT investigation, which can potentially alter the obtained results. Depending on the CT magnification at which the data is acquired the result specifically surface level detail might be affected. The aim of this study is to investigate the effect of different CT magnifications on surface texture measurement of additively manufactured surfaces. Surface features, including highest peaks and deepest valleys contributing to maximum and minimum thickness of specimen from different magnifications were compared with each other. The result shows that, the lower magnification scans underestimate both peak and valley measurements in comparison to the highest magnification scan. Measurement of valleys and re-entrant features were underestimated at more considerable level. The results from this study provide some understanding regarding surface morphology assessment of AM parts and the level of detail which can be expected depending on the CT magnification.

Keywords
Computed tomography, Additive manufacturing, Surface texture
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-65426 (URN)
Conference
iCT conference 2018, Wels, Austria, 7 February, 2018
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2019-08-27Bibliographically approved
4. Effect of X-Ray Computed Tomography Magnification on Porosity Analysis of Additively Manufactured Parts
Open this publication in new window or tab >>Effect of X-Ray Computed Tomography Magnification on Porosity Analysis of Additively Manufactured Parts
2018 (English)In: World PM2018 Congress Proceedings, 2018Conference paper, Published paper (Refereed)
Abstract [en]

X-ray computed tomography has been widely used for inspection of parts manufactured using additive manufacturing (AM) and powder metallurgy (PM). The ability of this method to non-destructively evaluate the porosity content of parts fabricated using AM and PM has made it a reliable method for such inspection. The results obtained from this method are highly dependent on CT acquisition parameters such as the magnification (resolution) at which the part has been scanned. Depending on the size of the parts the scan might need to be performed at lower magnifications which results in loss of information for porosity analysis. Therefore the effect of changing CT magnification on the obtained porosity of an additively manufactured specimen made of AlSi10Mg is investigated in this study. The specimen was scanned at various magnifications resulting in data sets with different resolutions. The porosity content was measured for each data set and the results showed that the porosity measurement using CT is highly dependent on the magnification (resolution) at which the data sets are acquired. The results from this study provided essential information about the porosity content which should be expected depending on the CT magnification.

Keywords
Porosity, X-ray computed tomography (CT), Additive manufacturing (AM)
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-69047 (URN)
Conference
2018 World Congress on Powder Metallurgy (WORLDPM2018), Beijing, China, September 16-20, 2018
Available from: 2018-09-25 Created: 2018-09-25 Last updated: 2019-08-28Bibliographically approved
5. An experimental approach to investigatethe influential parameters on mechanical strength of AlSi10Mgthin-wall structures manufactured by selective laser melting
Open this publication in new window or tab >>An experimental approach to investigatethe influential parameters on mechanical strength of AlSi10Mgthin-wall structures manufactured by selective laser melting
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-75923 (URN)
Available from: 2019-08-27 Created: 2019-08-27 Last updated: 2019-08-27Bibliographically approved
6. Surface Characterization of Additively Manufactured AlSi10Mg andTi6Al4V thin-wall Structures using X-Ray Computed Tomography
Open this publication in new window or tab >>Surface Characterization of Additively Manufactured AlSi10Mg andTi6Al4V thin-wall Structures using X-Ray Computed Tomography
(English)Manuscript (preprint) (Other academic)
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-75922 (URN)
Available from: 2019-08-27 Created: 2019-08-27 Last updated: 2019-08-27Bibliographically approved

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Zekavat, Amir Reza

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