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Process Development for Electron Beam Melting of 316LN Stainless Steel
Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Management and Mechanical Engineering. (Sports Tech Research Centre)ORCID iD: 0000-0002-2543-2809
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Additive manufacturing (AM) is a technology that inverts the procedure of traditional machining. Instead of starting with a billet of material and removing unwanted parts, the AM manufacturing process starts with an empty workspace and proceeds to fill this workspace with material where it is desired, often in a layer-by-layer fashion. Materials available for AM processing include polymers, concrete, metals, ceramics, paper, photopolymers, and resins. This thesis is concerned with electron beam melting (EBM), which is a powder bed fusion technology that uses an electron beam to selectively melt a feedstock of fine powder to form geometries based on a computer-aided design file input. There are significant differences between EBM and conventional machining. Apart from the process differences, the ability to manufacture extremely complex parts almost as easily as a square block of material gives engineers the freedom to disregard complexity as a cost-driving factor. The engineering benefits of AM also include manufacturing geometries which were previously almost impossible, such as curved internal channels and complex lattice structures. Lattices are lightweight structures comprising a network of thin beams built up by multiplication of a three-dimensional template cell, or unit cell. By altering the dimensions and type of the unit cell, one can tailor the properties of the lattice to give it the desired behavior. Lattices can be made stiff or elastic, brittle or ductile, and even anisotropic, with different properties in different directions. This thesis focuses on alleviating one of the problems with EBM and AM, namely the relatively few materials available for processing. The method is to take a closer look at the widely used stainless steel 316LN, and investigate the possibility of processing 316LN powder via the EBM process into both lattices and solid material. The results show that 316LN is suitable for EBM processing, and a processing window is presented. The results also show that some additional work is needed to optimize the process parameters for increased tensile strength if the EBM-processed material is to match the yield strength of additively laser-processed 316L material.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2019. , p. 39
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 164
Keywords [en]
additive manufacturing, beam deflection rate, electron beam melting, energy input, material properties, microstructure, powder bed fusion, process parameters, 316LN stainless steel
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-37840ISBN: 978-91-88947-25-3 (print)OAI: oai:DiVA.org:miun-37840DiVA, id: diva2:1374991
Presentation
2019-12-18, Q221, Akademigatan 1, 831 25 Östersund, 09:00 (Swedish)
Opponent
Supervisors
Funder
Interreg Sweden-Norway, TROJAM3DC
Note

Vid tidpunkten för framläggningen av avhandlingen var följande delarbete opublicerat: delarbete 3 (inskickat).

At the time of the defence the following paper was unpublished: paper 3 (submitted).

Available from: 2019-12-04 Created: 2019-12-03 Last updated: 2019-12-04Bibliographically approved
List of papers
1. Characterization of 316ln lattice structures fabricated via electron beam melting
Open this publication in new window or tab >>Characterization of 316ln lattice structures fabricated via electron beam melting
2017 (English)In: Materials Science and Technology Conference and Exhibition 2017, MS and T 2017, Association for Iron and Steel Technology, AISTECH , 2017, p. 336-343Conference paper, Published paper (Refereed)
Abstract [en]

One of the promising application areas of additive manufacturing (AM) relates to light weight structures, including complex near net shape geometries and lattices. So far one of the limiting factors hampering wider industrial usage of AM technologies is the limited availability of processed materials. The aim of present study was to expand the previous success in electron beam melting (EBM®) manufacturing of 316LN bulk materials into thinner lattice structures thus further widening the application areas available for the method. Present paper reports on the initial results where lattice structures with octagonal basic cells were manufactured using EBM® and characterized using microscopy and compression testing. 

Place, publisher, year, edition, pages
Association for Iron and Steel Technology, AISTECH, 2017
Keywords
316l, Additive manufacturing, Electron beam melting, Lattice, Net structures
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-32865 (URN)10.7449/2017/MST_2017_336_343 (DOI)2-s2.0-85041185273 (Scopus ID)9781510850583 (ISBN)
Conference
Materials Science and Technology Conference and Exhibition 2017, MS and T 2017, Pittsburgh, United States, 8 October 2017 through 12 October 2017
Available from: 2018-02-20 Created: 2018-02-20 Last updated: 2019-12-03Bibliographically approved
2. Macro- and Micromechanical Behavior of 316LN Lattice Structures Manufactured by Electron Beam Melting
Open this publication in new window or tab >>Macro- and Micromechanical Behavior of 316LN Lattice Structures Manufactured by Electron Beam Melting
Show others...
2019 (English)In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 12, no 1, p. 7290-7301Article in journal (Refereed) Published
Abstract [en]

This work focuses on the possibility of processing stainless steel 316LN powder into lightweight structures using electron beam melting and investigates mechanical and microstructural properties in the material of processed components. Lattice structures conforming to ISO13314:2011 were manufactured using varying process parameters. Microstructure was examined using a scanning electron microscope. Compression testing was used to understand the effect of process parameters on the lattice mechanical properties, and nanoindentation was used to determine the material hardness. Lattices manufactured from 316L using EBM show smooth compression characteristics without collapsing layers and shear planes. The material has uniform hardness in strut shear planes, a microstructure resembling that of solid 316LN material but with significantly finer grain size, although slightly coarser sub-grain size. Grains appear to be growing along the lattice struts (e.g., along the heat transfer direction) and not in the build direction. Energy-dispersive x-ray spectroscopy analysis reveals boundary precipitates with increased levels of chromium, molybdenum and silicon. Studies clearly show that the 316LN grains in the material microstructure are elongated along the dominating heat transfer paths, which may or may not coincide with the build direction. Lattices made from a relatively ductile material, like 316LN, are much less susceptible to catastrophic collapse and show an extended range of elastic and plastic deformation. Tests indicate that EBM process for 316LN is stable allowing for both solid and lightweight (lattice) structures.

Keywords
316L additive manufacturing electron beam melting ISO 13314:2011 lattice nanoindentation
National Category
Other Mechanical Engineering Other Mechanical Engineering
Identifiers
urn:nbn:se:miun:diva-37818 (URN)10.1007/s11665-019-04484-3 (DOI)000499641800002 ()2-s2.0-85075894379 (Scopus ID)
Available from: 2019-12-02 Created: 2019-12-02 Last updated: 2020-01-16Bibliographically approved
3. Process window for electron beam melting of 316LN stainless steel
Open this publication in new window or tab >>Process window for electron beam melting of 316LN stainless steel
(English)Manuscript (preprint) (Other academic)
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:miun:diva-37871 (URN)
Available from: 2019-12-04 Created: 2019-12-04 Last updated: 2019-12-04Bibliographically approved

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