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Powder incorporation and spatter formation in high deposition rate blown powder directed energy deposition
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0002-7213-0002
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0002-3569-6795
2020 (Engelska)Ingår i: Additive Manufacturing, E-ISSN 2214-8604, Vol. 35, artikel-id 101413Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A high deposition rate blown powder directed energy deposition process is presented. Clad tracks are deposited and the process is observed by high-speed imaging. An island of unmelted powder forms inside the melt pool, in the centre of the laser spot, which can be attributed to the highly focussed powder flow and the laser beam configuration used. On contact with the melt pool, the powder grains melt to join the melt pool, or they overcome surface tension and are engulfed by the melt. Powder grains can also incorporate into a mushy zone that may be present on the powder island. The powder island appears to rotate in the melt pool and incorporates relatively slowly. The speed of rotation is connected to the size of the island, which also depends on the energy density used. Spatter can form from the edges of the melt pool or from areas around the island when molten metal droplets burst. Frames from high-speed videos are presented and reasons for the various phenomena observed are discussed.

Ort, förlag, år, upplaga, sidor
Elsevier, 2020. Vol. 35, artikel-id 101413
Nyckelord [en]
Laser cladding, Island formation, Laser Metal Deposition, Powder catchment, Spatter, High-speed imaging
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
URN: urn:nbn:se:ltu:diva-80090DOI: 10.1016/j.addma.2020.101413ISI: 000576651400005Scopus ID: 2-s2.0-85086827120OAI: oai:DiVA.org:ltu-80090DiVA, id: diva2:1449067
Anmärkning

Validerad;2020;Nivå 2;2020-06-29 (alebob)

Tillgänglig från: 2020-06-29 Skapad: 2020-06-29 Senast uppdaterad: 2021-04-13Bibliografiskt granskad
Ingår i avhandling
1. Phenomena in laser based material deposition
Öppna denna publikation i ny flik eller fönster >>Phenomena in laser based material deposition
2021 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Fenomen i laserbaserad materialdeponering
Abstract [en]

This thesis is regarding the use of a laser beam to deposit material. Phenomena in two processes, laser beam welding with filler wire and blown powder directed energy deposition (DED) also known as laser metal deposition (LMD)1, are discussed. High-speed imaging is used as a central tool, supported by cross-sectional macrographs, surface images, X-ray images, computed tomography scans and quantitative analysis of the acquired results to observe many phenomena. Several results generated could be used in the manufacturing industry.

A novel concept of feeding the filler wire off-axis to the joint in laser beam welding is presented. The formation of defects called undercuts depended mainly on the stability of the wire feed and irregular melting of its tip. Process parameters played a key role in the robustness of the process, with higher welding speeds and laser powers increasing the chance for formation of defects.

Powder catchment in DED, and the various influencing factors are discussed. The position of initial interaction between powder grains and the melt pool plays an important role in defining incorporation behaviour. Powder grains can float on the surface of melt pool and travel along the direction of surface tension driven melt flows before fully incorporating. In high-deposition rate DED, an island of unmelted powder can form in the melt pool, depending on the laser beam shape and powder feeding configuration used. This island could lead to formation of spatter from the melt pool and porosity in resulting clads. Solid oxide skins present on the melt pool in low temperature areas can act like a barrier preventing complete incorporation of powder grains or possibly causing localised boiling, forming spatter.

For the first time, near-unprocessed material was used as feedstock in the DED process. A single large melt pool is formed in the relatively calm process, and phenomena like cloud formation while feeding of material and spatter were observed. Single and multi-layered deposition resulted in porous tracks and delamination from the substrate. While the process is not industrially useable in its current state, it is a step towards processing cheap unprocessed material with a laser beam to manufacture low cost parts or for in-situ reduction. 

The roles of material composition and surface conditions of the substrate in DED are also presented. Both, the composition and surface condition affect the absorption of the laser radiation. Material composition influences the time taken for incorporation of powder grains. The size of the melt pool and dilution depends on the thermal conductivity of the substrate material. Surfaces that are rough or coated with (several sorts of) paint produce wider tracks, with better wetting angles as compared to milled or ground surfaces. Coatings like paints or cold-galvanising primers do not negatively affect the process. Deposition directly on rough or painted surfaces could significantly reduce processing time and the resources needed for cleaning before cladding or repair processes. 

Ort, förlag, år, upplaga, sidor
Luleå University of Technology, 2021
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-83613 (URN)978-91-7790-819-7 (ISBN)978-91-7790-820-3 (ISBN)
Disputation
2021-06-10, A109, Luleå tekniska universitet, Luleå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2021-04-14 Skapad: 2021-04-13 Senast uppdaterad: 2021-11-12Bibliografiskt granskad

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Prasad, Himani SivaBrueckner, FrankKaplan, Alexander F.H.

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