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Acceleration of metal drops in a laser beam
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-0649-0130
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
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-3569-6795
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. Vol. 127, no 1, article id 4
Keywords [en]
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: urn:nbn:se:ltu:diva-82252DOI: 10.1007/s00339-020-04177-yISI: 000599501100001Scopus ID: 2-s2.0-85097611880OAI: oai:DiVA.org:ltu-82252DiVA, id: diva2:1516048
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
In thesis
1. Laser-induced recoil pressure on metal drops and powder particles
Open this publication in new window or tab >>Laser-induced recoil pressure on metal drops and powder particles
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:nbn:se:ltu:diva-83629 (URN)978-91-7790-817-3 (ISBN)978-91-7790-818-0 (ISBN)
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
2. Aspects of material and heat transfer in drop- and powder-based laser additive manufacturing
Open this publication in new window or tab >>Aspects of material and heat transfer in drop- and powder-based laser additive manufacturing
2023 (English)Doctoral 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. Novel approaches of material deposition are also developed, such as Laser Droplet Generation, which could potentially be applied to Additive Manufacturing. During the process, the laser beam light is partly absorbed by the material, and is then converted to heat, which can induce melting and even vaporization. Additive Manufacturing presents several processing challenges, such as the recoil pressure acting on the drops and powder particles that affects their trajectory. Storage and recycling of the powders is also an important aspect since the powder properties are changed through aging. Another challenge is the adjustment of process parameters according to varying deposition conditions, where the use of process monitoring techniques is crucial.

Therefore, this thesis aims at better understanding (i) the effects of recoil pressureon metal drops and powder particles, (ii) powder aging and its effects on the process, and (iii) process optimisation and stability via monitoring. In the six adjoined papers, high-speed imaging and thermal imaging were used to observe laser Additive Manufacturing processes involving both metal drops and powders. The videos enabled to observe drop detachments, measure trajectories, plot powder density maps, quantify powder catchment in the melt pool, measure themelt pool geometry, detect oxides, and extract cooling rates. The experimental results were supplemented with material analysis and theoretical calculations of thermodynamics, recoil pressure and surface tension.

These studies allowed to conclude that the recoil pressure induced by laser irradiation on a drop or a powder particle can have some significant effect such as acceleration, change of trajectory, or disintegration. However, these effects seem to be considerably lower than what theoretical models predict. It was also found that the recoil pressure can be used to accurately detach drops from a wire, which was utilised as a new material deposition method for Additive Manufacturing. In Directed Energy deposition, it was showed that aging of the aluminium powder feedstock should be avoided since it induces high porosity, high dilution and decreased mechanical properties. Finally, to guarantee a defect-free deposition during the whole process, it was demonstrated that a thermal camera can be used to monitor the melt pool size, which allows to apply appropriate laser power adjustments to compensate for changing building conditions.  

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-95798 (URN)978-91-8048-280-6 (ISBN)978-91-8048-281-3 (ISBN)
Public defence
2023-05-03, E632, Luleå tekniska universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2023-03-07 Created: 2023-03-07 Last updated: 2023-09-01Bibliographically approved

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Da Silva, AdrienVolpp, JoergFrostevarg, JanKaplan, Alexander F.H

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