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Laser-induced recoil pressure on metal drops and powder particles
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-0649-0130
2021 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Additive Manufacturing became a major research topic and part of industrial production in the past years. Numerous techniques now allow to build 3D structures with a wide choice of materials. When it comes to processing of metals, a laser beam is often used as a heat source to melt either a wire or powder, where the trajectory of spatters and powder particles can be affected by the laser beam radiation. Laser beam irradiation is partly absorbed by the material, and is then converted to heat, which can cause melting and even vaporization. The vaporization of material induces a recoil pressure on the melt pool, which affects its geometry and dynamics. However, the effects of the recoil pressure on airborne objects such as drops and powder particles are still relatively unknown. Their different sizes and boundary conditions compared to a melt pool might affect their behaviour under high laser beam radiation. 

Therefore, this thesis aims at better understanding the effects of the recoil pressure on metal drops and powder particles, as well as their impacts on Additive Manufacturing processes, especially Directed Energy Deposition and Laser Metal Wire Deposition. In the three adjoined papers, high-speed imaging was used to observe (i) powder blown through a laser beam, (ii) drops falling in a laser beam, and (iii) drops detaching from a wire in a laser beam. The videos enabled to calculate the acceleration of powder particles and drops of different sizes, the density map of the powder stream, and the detachment direction of the drops. The experimental results were completed with theoretical calculations of thermodynamics, recoil pressure and surface tension. 

These studies allowed to conclude that the acceleration induced by the recoil pressure on a drop or a powder particle increases with decreased size. Moreover, the recoil pressure causes a slight deviation of the powder stream in Directed Energy Deposition that can induce a better powder focusing. The recoil pressure can also cause the disintegration of powder particles in the laser beam. Finally, it was shown that the recoil pressure can be used to detach drops on demand from a wire and accelerate them towards the substrate where they can be strategically deposited for building additive structures.

Place, publisher, year, edition, pages
Luleå University of Technology, 2021.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-83629ISBN: 978-91-7790-817-3 (print)ISBN: 978-91-7790-818-0 (electronic)OAI: oai:DiVA.org:ltu-83629DiVA, id: diva2:1543981
Presentation
2021-06-08, A109, Luleå tekniska Universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2021-04-14 Created: 2021-04-13 Last updated: 2021-11-02Bibliographically approved
List of papers
1. Acceleration of metal drops in a laser beam
Open this publication in new window or tab >>Acceleration of metal drops in a laser beam
2021 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 127, no 1, article id 4Article in journal (Refereed) Published
Abstract [en]

Different processes require the detachment of metal drops from a solid material using a laser beam as the heat source, for instance laser drop generation or cyclam. These techniques imply that the drops enter the laser beam, which might affect their trajectory. Also, many laser processes such as laser welding or additive manufacturing generate spatters that can be accelerated by the laser beam during flight and create defects on the material. This fundamental study aims at investigating the effects of a continuous power laser beam on the acceleration of intentionally detached drops and unintentionally detached spatters. Two materials were studied: 316L steel and AlSi5 aluminium alloy. High-speed imaging was used to measure the position of the drops and calculate their acceleration to compare it to theoretical models. Accelerations up to 11.2 g could be measured. The contributions of the vapor pressure, the recoil pressure, and the radiation pressure were investigated. The recoil pressure was found to be the main driving effect but other phenomena counteract this acceleration and reduce it by an order of magnitude of one to two. In addition, two different vaporization regimes were observed, resulting respectively in a vapor plume and in a vapor halo around the drop.

Place, publisher, year, edition, pages
Springer, 2021
Keywords
Laser ablation propulsion, Laser drop generation, Recoil pressure, Ablation pressure, Spatters trajectory
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-82252 (URN)10.1007/s00339-020-04177-y (DOI)000599501100001 ()2-s2.0-85097611880 (Scopus ID)
Projects
LAM-4DSYMAXSAMOAC3TS
Funder
Vinnova, 2018-04324Interreg Nord, 20201279
Note

Validerad;2021;Nivå 2;2021-01-11 (johcin);

Finansiär: SYMAX (2019-02458) EIT Raw Materials, project SAMOA (18079);

For correction, see: Da Silva, A., Volpp, J., Frostevarg, J. et al. Correction: Acceleration of metal drops in a laser beam. Appl. Phys. A 129, 637 (2023). https://doi.org/10.1007/s00339-023-06853-1

Available from: 2021-01-11 Created: 2021-01-11 Last updated: 2023-09-04Bibliographically approved
2. The effects of laser irradiation on an aluminium powder stream in Directed Energy Deposition
Open this publication in new window or tab >>The effects of laser irradiation on an aluminium powder stream in Directed Energy Deposition
2021 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 41, article id 101968Article in journal (Refereed) Published
Abstract [en]

Additive Manufacturing with aluminium alloys is a subject of increasing industrial interest. Directed Energy Deposition using high power lasers and a powder feed is a useful option but the interactions between the powder stream and the laser beam are not completely understood. It is well known that the powder particles heat up in the laser beam and some theoretical models predict that they can reach their vaporisation temperature and have their flight path altered by the associated recoil pressure. In order to learn more about these phenomena, powder streams were observed with a high-speed camera at different laser powers (up to 6 kW) and with three batches of powder (AlSi10Mg) of different particle sizes. The results showed an increase of powder focussing with increased laser power. In addition, some particles were found to disintegrate in the laser beam. It is demonstrated that particle disintegration is most likely to be caused by the momentum induced by the recoil pressure.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Direct Metal Deposition, recoil pressure, powder disintegration, power attenuation, powder deviation
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-83402 (URN)10.1016/j.addma.2021.101968 (DOI)000663107000002 ()2-s2.0-85104986249 (Scopus ID)
Funder
Vinnova, 2019-04872
Note

Validerad;2021;Nivå 2;2021-04-20 (alebob);

Finansiär: EIT Raw Materials (18079)

Available from: 2021-03-25 Created: 2021-03-25 Last updated: 2023-03-07Bibliographically approved
3. Additive Manufacturing by laser-assisted drop deposition from a metal wire
Open this publication in new window or tab >>Additive Manufacturing by laser-assisted drop deposition from a metal wire
2021 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 209, article id 109987Article in journal (Refereed) Published
Abstract [en]

The subject of Additive Manufacturing includes numerous techniques, some of which have reached very high levels of development and are now used industrially. Other techniques such as Micro Droplet Deposition Manufacture are under development and present different manufacturing possibilities, but are employed only for low melting temperature metals. In this paper, the possibility of using a laser-based drop deposition technique for stainless-steel wire is investigated. This technique is expected to be a more flexible alternative to Laser Metal Wire Deposition. Laser Droplet Generation experiments were carried out in an attempt to accurately detach steel drops towards a desired position. High-speed imaging was used to observe drop generation and measure the direction of detachment of the drops. Two drop detachment techniques were investigated and the physical phenomena leading to the drop detachment are explained, wherein the drop weight, the surface tension and the recoil pressure play a major role. Optimised parameters for accurate single drop detachment were identified and then used to build multi-drop tracks. Tracks with an even geometry were produced, where the microstructure was influenced by the numerous drop depositions. The tracks showed a considerably higher hardness than the base wire, exhibiting a relatively homogeneous macro-hardness with a localised softening effect at the interfaces between drops.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Laser Metal Wire Deposition, Wire-Laser Additive Manufacturing, Laser Droplet Generation, Laser Droplet Formation Process, Drop-on-Demand
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-83628 (URN)10.1016/j.matdes.2021.109987 (DOI)000701685800004 ()2-s2.0-85110453172 (Scopus ID)
Projects
LAM-4DLAM-4D stage 2SAMOA
Funder
Vinnova, 2018-04324; 2019-04872
Note

Validerad;2021;Nivå 2;2021-07-26 (beamah);

Ytterligare forskningsfinansiär: EIT Raw Materials (no. 18079)

Available from: 2021-04-13 Created: 2021-04-13 Last updated: 2023-03-07Bibliographically approved

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