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Zekavat, A. R. (2019). Application of X-ray Computed Tomography for Assessment of Additively Manufactured Products. (Doctoral dissertation). Örebro: Örebro University
Open this publication in new window or tab >>Application of X-ray Computed Tomography for Assessment of Additively Manufactured Products
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
Additive manufacturing, X-ray computed tomography, Surface roughness
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-75190 (URN)978-91-7529-296-0 (ISBN)
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: 2019-09-20Bibliographically approved
Zekavat, A. R., Jansson, A., Larsson, J. & Pejryd, L. (2019). Investigating the effect of fabrication temperature on mechanical properties of fused deposition modelling parts using X-ray computed tomography. The International Journal of Advanced Manufacturing Technology, 100(1-4), 287-296
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
Zekavat, A. R., Pejryd, L. & Gundlach, C. (2018). Effect of X-Ray Computed Tomography Magnification on Porosity Analysis of Additively Manufactured Parts. In: World PM2018 Congress Proceedings: . Paper presented at 2018 World Congress on Powder Metallurgy (WORLDPM2018), Beijing, China, September 16-20, 2018.
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
Zekavat, A. R., Jansson, A., Gundlach, C. & Pejryd, L. (2018). Effect of X-ray Computed Tomography Magnification on Surface Morphology Investigation of Additive Manufacturing Surfaces. In: 8th Conference on Industrial Computed Tomography: . Paper presented at iCT conference 2018, Wels, Austria, 7 February, 2018.
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
Jansson, A., Ekengren, J., Zekavat, A. R. & Pejryd, L. (2016). Effects of X-ray Penetration Depth on Multi Material Computed Tomography Measurements. In: iCT 2016: . Paper presented at 6th Conference on Industrial Computed Tomography (iCT 2016), Wels, Austria, February 9-12, 2016 (pp. 143-150). NDT.net
Open this publication in new window or tab >>Effects of X-ray Penetration Depth on Multi Material Computed Tomography Measurements
2016 (English)In: iCT 2016, NDT.net , 2016, p. 143-150Conference paper, Published paper (Refereed)
Abstract [en]

The complexity of today’s products and materials is ever increasing. There is a demand on the industry to produce lighter, stronger, and more precise products. A common practice to achieve such products is to combine different materials to enhance strengths and reduce weaknesses; multi material products. Fabricating complex parts using multi materials does, however, lead to an increased difficulty in metrological verification and material characterisation. The use of computed tomography is today widespread within the industry, providing new possibilities for internal measurements, but there are still many uncertainties associated with the method. It is well known that large variations in density of multi materials greatly affects the contrast obtained by computed tomography, resulting in difficulties to scan and acquire reliable data from certain material setups.In this work the effects on internal measurements as a consequence of differences in X-ray penetration depth have been studied with regards to multi material setups. The main interest was the ability to acquire measurements from internal features of material compositions that are commonly used in the industry. In the result, difficulties and uncertainties associated with computed tomography of multi materials are highlighted and suggestions on how to reduce problems and obtain a more reliable test method are discussed.

Place, publisher, year, edition, pages
NDT.net, 2016
Keywords
Multi-materials, computed tomography, X-ray penetration depth, dual-energy computed tomography
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-47802 (URN)
Conference
6th Conference on Industrial Computed Tomography (iCT 2016), Wels, Austria, February 9-12, 2016
Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2019-06-13Bibliographically approved
Zekavat, A. R. & Pejryd, L. (2016). Surface characterization of additively manufactured Al10SiMg thin-walled structures. In: 7th Swedish Production Symposium: . Paper presented at 7th Swedish Production Symposium, Lund, Sweden, October 25-27, 2016.
Open this publication in new window or tab >>Surface characterization of additively manufactured Al10SiMg thin-walled structures
2016 (English)In: 7th Swedish Production Symposium, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Additive manufacturing (AM) is a newly developed technique for fabrication of parts with complexgeometries. Despite the fact that this technique has made it possible to fabricate near net shape and complexgeometries, there can be a mismatch between as-designed and as-fabricated geometries. These geometricalimperfections can hinder the structural response of fabricated structures by not fulfilling the strength theyare designed for. These mismatches, specifically surface morphology become even more important factorin case of manufacturing of thin-walled structures by AM. This is due to the fact that the surface regionwhich is mainly consist of partially melted powders does not necessarily contribute in strength. Thus, theeffect of surface morphology on mechanical properties in such structure should be investigated and takeninto account in the design stage. In this study high resolution X-ray computed tomography (micro-CT) hasbeen used for qualitative investigation of surface morphology of specimens made of AlSi10Mg. Flatspecimens with different thicknesses has been fabricated by selective laser melting (SLM). Using micro-CT it was possible to non-destructively measure the surface region in thin-walled builds. The measurementfrom micro-CT as well as result from optical profilometry showed the usefulness of micro-CT for thoroughinvestigation of AM parts. The study showed that micro-CT is a robust method for qualitative measurementof surface morphology of parts made of AlSi10Mg using SLM technique. It also gave an insight on wherethe geometrical mismatch specifically at micro scale become an important factor in design of such structuresfabricated using SLM technique. The result from this study lead to development in design stage of AMprocesses.

Keywords
X-ray computed tomography, additive manufacturing, thin-walled structure
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-53785 (URN)
Conference
7th Swedish Production Symposium, Lund, Sweden, October 25-27, 2016
Note

Note: LUMSA, means "Libera Università Maria SS. Assunta" private Roman Catholic university founded in 1939

Available from: 2016-12-05 Created: 2016-12-05 Last updated: 2018-07-17Bibliographically approved
Jansson, A., Zekavat, A. R. & Pejryd, L. (2015). Measurement of internal features in additive manufactured components by the use of computed tomography. In: : . Paper presented at Digital Industrial Radiology and Computed Tomography (DIR 2015), Ghent, Belgium, June 22-25, 2015. German Society for Non-Destructive Testing
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
Zekavat, A. R., Adibi, P. T., Johannesson, P., Karlsson, P., Pejryd, L. & Sjögren, T.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
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(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
Zekavat, A. R.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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1286-3420

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