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Elongated cavities during keyhole laser welding
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0003-0194-9018
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0003-4265-1541
2021 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 206, p. 109835-, article id 109835Article in journal (Refereed) Published
Abstract [en]

During laser beam deep penetration welding, the characteristic keyhole occurs that enables efficient energy absorption due to multiple reflections. Since this welding mode usually shows high dynamic behaviour, often a high amount of weld imperfections like spattering or porosity occur. Elongated keyholes during buttonhole, a.k.a donut welding, have shown the possibility to create smooth welding tracks when controlled variations of energy input were induced, e.g. beam oscillation. It was observed that the elongated keyholes can maintain themselves due to the balancing effects of the melt pool surface tension, which can form a catenoid shape that does not require any additional forces to be stable. Basic theoretical descriptions of the catenoid shape keyholes were derived. However, the complex system requires a more detailed investigation of the effect of the metal plume and the melt flows in order to explain the opening and maintenance effects of the elongated keyholes.

Therefore, this work examined different modes of elongated keyholes, comparing traditional non-oscillating keyholes to keyholes formed by different beam scanning strategies. Analysis was made mainly by observations with high-speed-imaging and theoretical considerations to explain the phenomena of elongated keyholes. The observations showed that extended keyholes are not necessarily related to a reduced occurrence of imperfections and not either to the formation of perfect catenoid shapes. The keyhole front is deformed where the laser beam impacts and the rear wall is impacted where the vapour plume strikes. The opening of an elongated keyhole is likely related to the keyhole vapour plume that pushes the keyhole rear wall rearwards, while the non-affected rear wall parts do not collapse the keyhole due to the balancing nature of the second curvature of the rear wall.

Place, publisher, year, edition, pages
Elsevier, 2021. Vol. 206, p. 109835-, article id 109835
Keywords [en]
Donut welding, buttonhole welding, metal vapour pressure, beam oscillation, high speed imaging
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-84297DOI: 10.1016/j.matdes.2021.109835ISI: 000661918000003Scopus ID: 2-s2.0-85106340539OAI: oai:DiVA.org:ltu-84297DiVA, id: diva2:1554766
Funder
Swedish Research Council, 2020-04250
Note

Validerad;2021;Nivå 2;2021-06-07 (johcin);

Forskningafinansiärer: Permanova AB; SteelS4EV – STEEL Solutions for Safe and Smart Structures of Electric Vehicles (EC Research Fund for Coal and Steel, RFCS, no. 800726); ACCEL – Adapted Chemical Composition of materials for Enhanced Laser welding (Vinnova SIP Production 2030 project 2019-0078); SAMOA - Sustainable Aluminium additive Manufacturing for high performance Applications (EIT raw materials, no. 18079); SPAcEMAN - Sustainable Powders for AdditivE MANufacturing (EIT raw materials, no. 17070)

Available from: 2021-05-17 Created: 2021-05-17 Last updated: 2021-06-28Bibliographically approved

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Volpp, JoergFrostevarg, Jan

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