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Transient interaction of a boiling melt with a pulsed Nd:YAG-laser
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. University of Mosul, College of Engineering, Department of Mechanical Engineering.ORCID iD: 0000-0002-4569-8970
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-3569-6795
Number of Authors: 22017 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 88, p. 28-36Article in journal (Refereed) Published
Abstract [en]

The boiling front induced by a pulsed Nd:YAG-laser at very slow translation speed was studied. The purpose is to understand fundamental melt movement mechanisms. The melt was observed by high speed imaging, with and without illumination. When switching on the laser beam a hole is drilled through a bulk of melt. The hole expands and the boiling pressure gradually opens the melt bridge, instead developing an interaction front similar to cutting. These conditions remain in quasi-steady state during the pulse. The ablation pressure from boiling shears waves down the front and keeps the melt downwards in a stable position. When switching off, the waves smoothen and in absence of boiling the surface tension drags the melt back upwards, to semi-torus-like Catenoid shape. Evidence on the large melt pool and its shape was achieved by three-dimensional reconstruction from cross section macrographs. The basic findings how melt can move with and without ablation pressure can enable controlled melt dynamics for various laser processing techniques, like remote cutting, ablation, keyhole welding or drilling.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 88, p. 28-36
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-2565DOI: 10.1016/j.optlaseng.2016.07.008ISI: 000385319500005Scopus ID: 2-s2.0-84979583922Local ID: 02fc10a6-5cd3-4344-b21e-01891485dc6eOAI: oai:DiVA.org:ltu-2565DiVA, id: diva2:975418
Note

Validerad; 2016; Nivå 2; 20160816 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-09-13Bibliographically approved
In thesis
1. Interaction mechanisms for a laser-induced metallic boiling front
Open this publication in new window or tab >>Interaction mechanisms for a laser-induced metallic boiling front
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is about fundamental interaction mechanisms of laser remote fusion cutting, RFC, which is based on the formation of a quasi-stationary laser-induced boiling front that causes drop ejection, preferably downwards. Laser cutting of metals, invented in 1967, has developed from a niche to a well established high quality cutting technique in the manufacturing industry. Usually a gas jet is employed concentric to the laser beam, to eject the molten metal. One technique option, interesting though hardly applied yet because of usually low quality and speed, is remote laser cutting. Two techniques are distinguished, remote ablation cutting, grooving down through a sheet, layer-by-layer, and the here addressed remote fusion cutting, by a single pass through the sheet. For the latter, the ablation pressure from laser-induced boiling at the cutting front continuously accelerates and ejects the melt downwards. Advantages of remote laser cutting, facilitated by high brilliance lasers during the last decade, are the possibility of a larger working distance along with the avoidance of cutting gas and of a gas jet nozzle.

 

The review paper of the thesis surveys different laser remote cutting techniques, including their modelling, as well as the transition to keyhole welding, owing to similarities particularly from the boiling front and from root spatter ejection. The six Papers I-VI that compose the thesis address fundamental mechanisms of laser remote fusion cutting, theoretically and experimentally. In Paper I a simplified mathematical model of the RFC cutting front enables to estimate the geometrical and energetic conditions of the process. By evidence and post-modelling from high speed imaging, HSI, the simplified smooth cutting front model is developed further to a wavy topology in Paper III, for more sophisticated absorption analysis. As a systematic support, Paper II categorizes and analyses for the first time the different wavy topologies observed at the front, from HSI. The melt dynamics induced by a pulsed laser beam was studied in Paper IV, again from HSI. Apart from other interesting transient melt phenomena it was demonstrated that the ablation pressure can push the melt to a certain pending position during the laser pulse while the melt retreats by surface tension during the pulse break. To engage remote fusion cutting with additive manufacturing, Paper V introduces a novel technique where the drops ejected from RFC are transferred to a substrate, about a centimetre underneath, on which a continuous track forms. This technique can even be applied as an efficient recycling approach. In Paper VI a variant of the technique is presented, to develop a boiling front along the edge of a metal sheet from which the drop transfer takes place, in a different manner. This enables to systematically machine-off the entire sheet, which can be converted to a new shape and product.

 

Summarizing, the thesis provides a variety of analysis of fundamental mechanisms of a laser-induced boiling front that bear a certain simplicity and in turn controllability, of interest for established as well as for new applications, in manufacturing and in other sectors, including remote fusion cutting.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Laser remote fusion cutting, Boiling front, High speed imaging, Additive manufacturing, Ejection, Absorption, Wavy surface, Deposition
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-65281 (URN)978-91-7583-945-5 (ISBN)978-91-7583-946-2 (ISBN)
Public defence
2017-11-09, E632, Luleå University of Technology,S-97187, Luleå, 08:30 (English)
Opponent
Supervisors
Available from: 2017-08-28 Created: 2017-08-28 Last updated: 2017-11-24Bibliographically approved

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Samarjy, R.S.M.Kaplan, Alexander

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