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Tailored laser pulse method to manipulate filler wire melt metallurgy from thermal cycles
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: 0000-0003-4265-1541
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-3569-6795
Department of Welding and Joining Science Engineering, Chosun University, Gwangju, Republic of Korea.
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2019 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, no 2, article id 022605Article in journal (Refereed) Published
Abstract [en]

A robust method is introduced to simulate and study the filler wire metallurgy for controlled cooling conditions after melting, enabling efficient mapping with prompt analysis of trends. Proposed is a reduced, though representative, process with more controllable conditions. Short lengths of filler wires are preplaced in a cavity, drilled into a base metal sheet. Irradiation by a pulsed laser beam melts the wire to generate a sample nugget. Pulse shaping influences the cooling rate, granting the ability to tailor weldament microstructures. The method is demonstrated for S1100QL steel and undermatched filler wire, to obtain high toughness for processes like laser-arc hybrid welding, where a representative thermal cycle is needed. For high toughness, a controlled amount of acicular ferrite and, in turn, nonmetallic inclusions is desirable. This “snapshot” method has revealed a characteristic histogram of inclusion sizes, for different pulse shapes. Additional information on the thermal cycle can be acquired by employing thermocouples, a pyrometer, or advanced methods like high speed imaging or modeling. The method offers a wide spectrum of variants and applications.

Place, publisher, year, edition, pages
USA: Laser Institute of America , 2019. Vol. 31, no 2, article id 022605
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-75401DOI: 10.2351/1.5096145ISI: 000484435200093Scopus ID: 2-s2.0-85065039863OAI: oai:DiVA.org:ltu-75401DiVA, id: diva2:1340778
Conference
37th International Congress of Applications of Lasers & Electro-Optics (ICALEO 2018), Orlando, FL, USA, October 14-18, 2018
Projects
OptoSteel
Note

Konferensartikel i tidskrift

Available from: 2019-08-06 Created: 2019-08-06 Last updated: 2021-05-07Bibliographically 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.Frostevarg, JanKaplan, Alexander

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