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Thermal monitoring for directed energy deposition of stainless steel, bronze, and cobalt-based alloy
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: 0000-0003-4265-1541
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-3569-6795
2022 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 451, article id 129078Article in journal (Refereed) Published
Abstract [en]

Laser cladding and Directed Energy Deposition are two related processes that allow the deposition of specific surface coatings and the production of additively manufactured parts. In both processes, the selection of optimised parameters results in the deposition of high-density material with low dilution. However, the thermal and geometrical conditions constantly change during the process and the parameters need to be continually adapted in order to avoid defects or poor properties. In this context, the development of closed-loop monitoring systems is crucial in order to widen the field of possible applications towards more complexity, with a more stable process and higher materials properties. In this research, the possibility of thermal monitoring with middle-wave and long-wave infra-red cameras is investigated for Directed Energy Deposition of 316L, Stellite 21 and CuSn10. The melt pool length and the cooling rate are extracted from thermal imaging while the laser power was varied, and these results are compared to the materials properties of the deposited tracks. The main results show that an increase of melt pool length results in a decrease of porosity and an increase of dilution, which induces a change of hardness. The melt pool length can be regulated by adjusting the laser power in order to keep both the porosity and the dilution within acceptable values.

Place, publisher, year, edition, pages
Elsevier, 2022. Vol. 451, article id 129078
Keywords [en]
Copper, Dilution, Laser cladding, Laser metal deposition, Porosity
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-94289DOI: 10.1016/j.surfcoat.2022.129078ISI: 000891100700002Scopus ID: 2-s2.0-85142195979OAI: oai:DiVA.org:ltu-94289DiVA, id: diva2:1713810
Projects
MONACO
Funder
Vinnova, 2021-02154 MONACO
Note

Validerad;2022;Nivå 2;2022-11-28 (hanlid)

Available from: 2022-11-28 Created: 2022-11-28 Last updated: 2023-05-08Bibliographically approved
In thesis
1. 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, AdrienFrostevarg, JanKaplan, Alexander F.H.

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