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Multi-keyhole separation during multi-spot laser welding of duplex steel
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-8298-292x
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-3569-6795
2021 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 143, article id 107382Article in journal (Refereed) Published
Abstract [en]

Separated keyholes generated during a multi-beam laser welding process were observed, analyzed, and quantified. Two high-speed cameras were utilized to capture process phenomena of bead on plate experiments, with a near vertical and a horizontal view. The films were analyzed for: the ability to form a unique keyhole for each beam, the time and location of observed fully penetrated keyhole, and other associated trends. The number of beams was correlated to fully penetrated, separate keyholes. Keyhole separations were observed to be stable while full penetration was less regular. The location of a fully penetrating keyhole correlated with the position of the stronger beam. The dynamic melt wall width separating the keyholes was measured with beam orientation and power ratios between beams having a significant impact. Beam orientation showed that the lagging inter-keyhole wall of a quad-beam process was impacted by the presence of a fully molten front in the in-line beam arrangement. For the cross-beam orientation, the lagging wall did not seem impacted by the melt front. Large power differences between leading beams for the quad-beam, in-line orientation formed a melt column in the location of the weaker beam and spattering from the column.

Place, publisher, year, edition, pages
Elsevier, 2021. Vol. 143, article id 107382
Keywords [en]
Multi-focal, Multi-spot, Multi-beam, Beam shaping, Keyhole dynamics, Laser welding
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-86334DOI: 10.1016/j.optlastec.2021.107382ISI: 000687055900007Scopus ID: 2-s2.0-85110145313OAI: oai:DiVA.org:ltu-86334DiVA, id: diva2:1579841
Funder
Vinnova, 2019-00781
Note

Validerad;2021;Nivå 2;2021-07-12 (beamah);

Forskningsfinansiär: EC Research Fund for Coal and Steel (800726)

Available from: 2021-07-12 Created: 2021-07-12 Last updated: 2021-09-06Bibliographically approved
In thesis
1. Laser welding and laser heat treatment of high strength steels
Open this publication in new window or tab >>Laser welding and laser heat treatment of high strength steels
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Laser-svetsning och värmebehandling av höghållfast stål
Abstract [en]

Laser materials processing, including thermal treatment and laser welding has been undergoing continuous growth in the manufacturing industry for decades. A laser beam offers high precision and energy transfer, capable of various processing. For many cases a Gaussian beam is applied, but lately development of more complex beam shapes has been developed, where e.g. multiple beams (beam splitting) can be used for increased tolerances during welding.

This thesis presents six papers (Papers A-F) on welding of high strength steels, laser pulse shaping, thermal treatments, and microstructural investigations. Different methods for obtaining a desirable weld were investigated through tailoring of the laser beam process. This affected the resulting temperature fields and thermal histories of the specimens. Experimental analysis was supported through various in-situ observation techniques and metallurgical studies.

Papers A-C present thermal processing and chemical manipulation to obtain the desired microstructure, by introducing and applying the here introduced Snapshot method. Paper A explores tailoring a laser pulse to mimic a hybrid welding process, Paper B elaborates the simulation to a multi-cycle process, and Paper C explores dilution. The manuscripts utilize a specialized experimental setup, optical analysis methods, and standard thermal measuring techniques. Metallographic analysis showed that thermal process optimization and/or dilution rate control during welding improved weld zone characteristics.

Improvements also include joint macrostructure characteristics, which are impacted by process stability, the theme of Papers D-F. Melt pool phenomena are studied in depth in Papers D and E. Paper D explores material ejections in a single beam welding scenario. Paper E investigates six beam shapes, from a single beam to a quad-beam arrangement. Paper F studies hybrid welding, a process that was simulated in Papers A-C but focused on the stability of the process instead of thermally guiding the microstructure. 

The studies complement each other in knowledge and methods. Welding of high strength steel is joining method-dependent, which imposes a unique thermal profile that affects the microstructures. The microstructure is also influenced by the chemical composition, an important point when multiple materials are used. The studies contribute an analysis of certain aspects of thermal and chemical effects of different laser-based processes to further optimize processing of specifically high strength steels, though the aspects can be generalized to other metals

Place, publisher, year, edition, pages
Luleå University of Technology, 2021
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Laser welding, heat treatment, high strength steel, Snapshot method, microstructure
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-84181 (URN)978-91-7790-848-7 (ISBN)978-91-7790-849-4 (ISBN)
Public defence
2021-09-09, E632, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2021-05-11 Created: 2021-05-07 Last updated: 2022-01-17Bibliographically approved

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Robertson, Stephanie M.Kaplan, Alexander F.H.

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