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Absorbance study of powder conditions for laser additive manufacturing
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. JENOPTIK Optical Systems GmbH, System Development Advanced Manufacturing, Göschwitzerstraße 25, 07745 Jena, Germany.ORCID iD: 0000-0001-8601-2923
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-0649-0130
Fraunhofer, Institute for Material and Beam Technology IWS, Winterbergstraße 28, 01277 Dresden, Germany.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Fraunhofer, Institute for Material and Beam Technology IWS, Winterbergstraße 28, 01277 Dresden, Germany.
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2022 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 216, article id 110591Article in journal (Refereed) Published
Abstract [en]

Absorbance is often used for simulations or validation of process parameters for powder-based laser materials processing. In this work, the absorbance of 39 metal powders for additive manufacturing is determined at 20 laser wavelengths. Different grain sizes and aging states for: steels, aluminum alloys, titanium alloys, Nitinol, high entropy alloy, chromium, copper, brass and iron ore were analyzed. For this purpose, the absorbance spectrum of the powders was determined via a dual-beam spectrometer in the range of λ = 330 - 1560 nm. At the laser wavelengths of λ = 450 nm, 633 nm and 650 nm, the absorbance averaged over all materials was found to increase by a factor of 2.4 up to 3.3 compared to the usual wavelength of λ = 1070 nm, with minimal variations in absorbance between materials. In the investigation of the aged or used powders, a loss of absorbance was detectable. Almost no changes from the point of view of processing aged and new AlSi10Mg powders, is expected for laser sources with λ = 450 nm. The resulting measurements provide a good basis for process parameters for a variety of laser wavelengths and materials, as well as a data set for improved absorbance simulations.

Place, publisher, year, edition, pages
Elsevier, 2022. Vol. 216, article id 110591
Keywords [en]
Spectroscopic measurement, Absorption spectra, Laser powder bed fusion, Metal powder, Multiple reflections, Laser absorption
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-90043DOI: 10.1016/j.matdes.2022.110591ISI: 000793277800004Scopus ID: 2-s2.0-85128304808OAI: oai:DiVA.org:ltu-90043DiVA, id: diva2:1648830
Note

Validerad;2022;Nivå 2;2022-04-01 (joosat);

 Funder: EIT Raw Materials, European SAMOA project (18079)

Available from: 2022-04-01 Created: 2022-04-01 Last updated: 2023-09-04Bibliographically approved
In thesis
1. Spectral analysis in laser powder bed fusion
Open this publication in new window or tab >>Spectral analysis in laser powder bed fusion
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Alternative title[sv]
Spektralanalys vid laser powder bed fusion
Abstract [en]

This thesis is about the investigation of the spectral interaction of electromagnetic radiation with metal powders. For this purpose, spectral data of powders for laser powder bed fusion processes are investigated in three papers using different techniques. In paper A the spectral radiation behavior of the laser interaction zone is considered, in paper B and C the absorbance behavior of different metal powders depending on their state and measurement method.  

Paper A investigates the spectral signal of the process light generated by laser material interaction in laser powder bed fusion. The detection is performed by a coaxially guided measuring beam and a quasi-coaxial measuring beam simultaneously guided by another scanning optics. The signal characteristics depend on the angle of incidence of the measuring beam to the laser material interaction zone. Using high-speed recordings and optical simulations, a model for describing the signal behavior could be determined. The measured spectral intensity distribution representing the degree for energy coupling can be corrected with a correction factor over the whole field for solid materials. This correction includes a function describing the numerical aperture of the measuring channel and the laser intensity on the working field. For the investigated powder, the measurement signal fluctuated strongly and no transferable model could be formed. The reason for this was the different absorbance behavior of the powders investigated. Paper B therefore deals in detail with the spectral absorbance behavior of metal powders for additive manufacturing. Using a high-precision spectrometer, 39 powders were measured reflectively over a wide spectral range and the absorbance determined. By varying the degree of use, aging, grain size and impurities, various influence parameters are determined experimentally and discussed theoretically. Based on 20 derived laser wavelengths, technically usable wavelengths with better process efficiency and stability are proposed. From the obtained absorbance, the efficiency of energy coupling can be estimated and form a broad data base for the optimization of laser parameters. In order to perform the absorbance determinations also in situ in a laser powder bed fusion system paper C describes a possibility of an inline absorbance determination by high resolution coaxial imaging. A method is discussed for geometrically correct and gapless imaging of the processing plane, recorded through the laser optics. By imaging at six different wavelengths, metal powders can be distinguished by their absorbance spectrum and impurities can be detected. In an experimental implementation the functionality of the method is proven. The results are validated by optical simulations, ray tracing and comparative measurements with a high-precision spectrometer.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2022. p. 200
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Spectral monitoring, Laser powder bed fusion, Laser optics, Absorbance
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-90525 (URN)978-91-8048-098-7 (ISBN)978-91-8048-099-4 (ISBN)
Presentation
2022-06-16, A109, Luleå university of technology, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2022-05-10 Created: 2022-05-09 Last updated: 2022-05-26Bibliographically approved

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Brandau, BenediktDa Silva, AdrienBrueckner, FrankKaplan, Alexander F.H.

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