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Aspects of material and heat transfer in drop- and powder-based laser additive manufacturing
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0002-0649-0130
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.  

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2023.
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nationell ämneskategori
Produktionsteknik, arbetsvetenskap och ergonomi
Forskningsämne
Produktionsutveckling
Identifikatorer
URN: urn:nbn:se:ltu:diva-95798ISBN: 978-91-8048-280-6 (tryckt)ISBN: 978-91-8048-281-3 (digital)OAI: oai:DiVA.org:ltu-95798DiVA, id: diva2:1741809
Disputation
2023-05-03, E632, Luleå tekniska universitet, Luleå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2023-03-07 Skapad: 2023-03-07 Senast uppdaterad: 2023-09-01Bibliografiskt granskad
Delarbeten
1. Additive Manufacturing by laser-assisted drop deposition from a metal wire
Öppna denna publikation i ny flik eller fönster >>Additive Manufacturing by laser-assisted drop deposition from a metal wire
2021 (Engelska)Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 209, artikel-id 109987Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
Elsevier, 2021
Nyckelord
Laser Metal Wire Deposition, Wire-Laser Additive Manufacturing, Laser Droplet Generation, Laser Droplet Formation Process, Drop-on-Demand
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-83628 (URN)10.1016/j.matdes.2021.109987 (DOI)000701685800004 ()2-s2.0-85110453172 (Scopus ID)
Projekt
LAM-4DLAM-4D stage 2SAMOA
Forskningsfinansiär
Vinnova, 2018-04324; 2019-04872
Anmärkning

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

Ytterligare forskningsfinansiär: EIT Raw Materials (no. 18079)

Tillgänglig från: 2021-04-13 Skapad: 2021-04-13 Senast uppdaterad: 2023-03-07Bibliografiskt granskad
2. Acceleration of metal drops in a laser beam
Öppna denna publikation i ny flik eller fönster >>Acceleration of metal drops in a laser beam
2021 (Engelska)Ingår i: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 127, nr 1, artikel-id 4Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
Springer, 2021
Nyckelord
Laser ablation propulsion, Laser drop generation, Recoil pressure, Ablation pressure, Spatters trajectory
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-82252 (URN)10.1007/s00339-020-04177-y (DOI)000599501100001 ()2-s2.0-85097611880 (Scopus ID)
Projekt
LAM-4DSYMAXSAMOAC3TS
Forskningsfinansiär
Vinnova, 2018-04324Interreg Nord, 20201279
Anmärkning

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

Tillgänglig från: 2021-01-11 Skapad: 2021-01-11 Senast uppdaterad: 2023-09-04Bibliografiskt granskad
3. The effects of laser irradiation on an aluminium powder stream in Directed Energy Deposition
Öppna denna publikation i ny flik eller fönster >>The effects of laser irradiation on an aluminium powder stream in Directed Energy Deposition
2021 (Engelska)Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 41, artikel-id 101968Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
Elsevier, 2021
Nyckelord
Direct Metal Deposition, recoil pressure, powder disintegration, power attenuation, powder deviation
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-83402 (URN)10.1016/j.addma.2021.101968 (DOI)000663107000002 ()2-s2.0-85104986249 (Scopus ID)
Forskningsfinansiär
Vinnova, 2019-04872
Anmärkning

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

Finansiär: EIT Raw Materials (18079)

Tillgänglig från: 2021-03-25 Skapad: 2021-03-25 Senast uppdaterad: 2023-03-07Bibliografiskt granskad
4. Influence of aluminium powder aging on Directed Energy deposition
Öppna denna publikation i ny flik eller fönster >>Influence of aluminium powder aging on Directed Energy deposition
Visa övriga...
2022 (Engelska)Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 218, artikel-id 110677Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The use of aluminium alloys for Additive Manufacturing is of high interest for advanced geometries and lightweight applications. In Directed Energy Deposition, a powder stock is processed with a laser beam, which offers a high process flexibility. However, aging of the powder feedstock during storage or after recycling remains fundamentally challenging for aluminium alloys because of their sensitivity to oxida-tion and porosity. In order to investigate these effects, AlSi10Mg powder batches were aged in different conditions and processed by Directed Energy Deposition. The results showed that powder aging does not significantly change the particle size or morphology, but it introduces more oxygen and hydrogen in the powder. The oxidation of the particles reduces the laser beam absorbance of the powder and increases wetting of the melt pool, which affects the track geometry. A 3.5 to 4.2 times higher porosity was observed in the material deposited from aged powder, which are most likely hydrogen pores causedby the increased hydrogen content in the aged powder. The tensile properties of the parts built with aged powder showed 19.0% lower yield strength, 14.2% lower ultimate strength and 99.2% higher elongation, which are most likely the results of the coarser microstructure and increased porosity.

Ort, förlag, år, upplaga, sidor
Elsevier, 2022
Nyckelord
Direct Metal Deposition, Laser Metal Deposition, Laser Powder Bed Fusion, Oxidation, Porosity
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-90849 (URN)10.1016/j.matdes.2022.110677 (DOI)000800225800004 ()2-s2.0-85129120353 (Scopus ID)
Projekt
SAMOA (no. 18079)
Anmärkning

Validerad;2022;Nivå 2;2022-06-02 (sofila);

Funder: EIT Raw Materials.

Tillgänglig från: 2022-06-01 Skapad: 2022-06-01 Senast uppdaterad: 2023-09-04Bibliografiskt granskad
5. Thermal monitoring for directed energy deposition of stainless steel, bronze, and cobalt-based alloy
Öppna denna publikation i ny flik eller fönster >>Thermal monitoring for directed energy deposition of stainless steel, bronze, and cobalt-based alloy
2022 (Engelska)Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 451, artikel-id 129078Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
Elsevier, 2022
Nyckelord
Copper, Dilution, Laser cladding, Laser metal deposition, Porosity
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-94289 (URN)10.1016/j.surfcoat.2022.129078 (DOI)000891100700002 ()2-s2.0-85142195979 (Scopus ID)
Projekt
MONACO
Forskningsfinansiär
Vinnova, 2021-02154 MONACO
Anmärkning

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

Tillgänglig från: 2022-11-28 Skapad: 2022-11-28 Senast uppdaterad: 2023-05-08Bibliografiskt granskad
6. Melt pool monitoring and process optimisation of directed energy deposition via coaxial thermal imaging
Öppna denna publikation i ny flik eller fönster >>Melt pool monitoring and process optimisation of directed energy deposition via coaxial thermal imaging
2023 (Engelska)Ingår i: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 107, s. 126-133Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In Laser-based Directed Energy Deposition of metal powder, the use of optimised parameters allows the deposition of defect-free material, while diverging from these optimised parameters can typically result in high porosity, high dilution or different track geometry. One of the main challenges when building complex geometries is that the geometrical and thermal conditions of the deposition are constantly changing, which requires to adjust the process parameters during the production. In order to facilitate this process, sensors such as thermal cameras can be used to extract data from the process and adapt the parameters to keep the process stable despite external disturbances. In this research, different signals extracted from a coaxial thermal camera are investigated and compared for process optimisation. To investigate such possibilities, five overlapped tracks are deposited at constant laser powers in order to extract average pixel values as well as the melt pool area, length, width and orientation. The behaviour of each track deposition is modelled as a function of the laser power, and these models are used to calculate and test laser power reduction strategies based on different signals. The results show that the melt pool area is the most relevant signal to use for an efficient process control, resulting in a stable process with only ±1.6 % of signal variation from track to track.

Ort, förlag, år, upplaga, sidor
Elsevier, 2023
Nyckelord
Laser cladding, Laser metal deposition, Direct metal deposition, Thermal camera, Process control
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-95797 (URN)10.1016/j.jmapro.2023.10.021 (DOI)001105292800001 ()2-s2.0-85174179072 (Scopus ID)
Projekt
MONACOIDiDI2P
Forskningsfinansiär
Vinnova, 2021-02154Region Norrbotten, 20358021, KO4012
Anmärkning

Validerad;2023;Nivå 2;2023-10-30 (hanlid);

Funder: EU-Interreg Aurora (20358021); EU-Kolarctic CBC (KO4012);

Licens full text: CC BY

Tillgänglig från: 2023-03-06 Skapad: 2023-03-06 Senast uppdaterad: 2024-03-07Bibliografiskt granskad

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