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Laser metal fusion and deposition using wire feedstock: Process modelling and CFD simulation
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0002-6102-9021
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laser metal fusion is widely used in production technology to manufacture parts, as in welding, cladding, and additive manufacturing. In this study, conduction mode laser metal fusion is applied without and with metal deposition from a wire feedstock. This manufacturing process encompasses various physical phenomena that are coupled, such as the interaction of anelectro-magnetic wave with the material, phase changes, thermal fluid dynamics, and free surface deformation, which make it complicated to comprehend.

Deeper process knowledge is thus a key to its improvement. Yet, metal is a non-transparent media, which limits experimental observation of this process.

A modelling approach that describes this multi-physics problem paying special attention to convective phenomena was used in this thesis with a two-fold aim:

1) to improve the model reliability,

2) to gain a deeper understandingof the metal fusion and deposition process.

In the first part of this research, metal fusion without wire was addressed. Different beam power density distributions (beam shapes) were investigated. Their effect on the melt pool geometry, which was known from previous experimental studies, could be predicted. Furthermore, as the simulations give access to the melt flow, it could be established that the flow pattern is modified by elongating the beam shape. In addition, a new calculation procedure was introduced to predict the fraction of laser beam energy absorbed by the metal. To validate the model, the predicted melt pool geometry was evaluated through comparison with experimental measurements. The results showed that the proposed absorptivity model that is a function of local surface conditions lead to good agreement with experimental results, with a maximum discrepancy for the melt pool depth of about 10%.

In the second part, the model was applied to study the fusion process with metal transfer from a wire feedstock without and with resistive heating of the filler wire. It was shown that the multipler eflections of beam rays could be ignored at a low laser beam angle whereas with increasing the beam angle the effect became more considerable. It was also found that the laser absorptivity varied up to 50% within the projected laser spot area. The effect of different process parameters such as depositing rate and angle, laser beam angle, position of the wire relative to the beam (offset), and ambient conditions on the metal transfer, thermal flow field, andstability of the process were studied.

The results showed that three different metal transfer modes occurred depending on the offset value. Applying resistive heating on the filler wire decreased the absorptivity. However, this decrease was compensated by the resistive heating, resulting in an increase of the volume of liquid metal. Resistive heating made the melt pool wider due to the augmented role of the thermocapillary force and also the change in flow direction because of the modified position of the melted wire front.

Applying the model at near-vacuum and no gravity conditions, it was obtained that directed energy deposition of metal with laser and wire could be used for manufacturing metal parts in space. However, the process window could need some adjustment as in-space conditions result in some narrowing of the liquid bridge between wire and workpiece compared to on-Earth.

Place, publisher, year, edition, pages
Trollhättan: University West , 2022. , p. 95
Series
PhD Thesis: University West ; 52
Keywords [en]
Directed Energy Deposition with wire, Beam shaping, Absorptivity, Conduction-mode, Free surface deformation, Computational Fluid Dynamics, OpenFOAM.
Keywords [sv]
Riktad energideponering med svetstråd, Stråformning, Absorption, Svetsning, Ytdeformation, Beräkningsströmningsdynamik, OpenFOAM.
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-19232ISBN: 978-91-89325-34-0 (print)ISBN: 978-91-89325-35-7 (electronic)OAI: oai:DiVA.org:hv-19232DiVA, id: diva2:1702434
Public defence
2022-11-02, F131, Gustava Melins gata, 10:00 (English)
Opponent
Supervisors
Note

Paper 3 and 4 is to be submitted and not included in the electronic thesis.

Available from: 2022-10-12 Created: 2022-10-10 Last updated: 2023-01-05Bibliographically approved
List of papers
1. Modelling of beam energy absorbed locally in conduction mode laser metal fusion
Open this publication in new window or tab >>Modelling of beam energy absorbed locally in conduction mode laser metal fusion
2021 (English)In: Journal of physics. D, Applied physics, ISSN 0022-3727, Vol. 55, no 2, article id 025301Article in journal (Refereed) Published
Abstract [en]

Fluid dynamics models for laser material processing with metal fusion in conduction mode generally assume a constant absorptivity. This parameter is known to govern the process. However, it used to be pre-set by extrapolating absorptance measurements made at different conditions or adjusted to reproduce experimental bead shapes. In this study a new approach isd eveloped. It consists in predicting the absorptance as a function of local surface conditions, including the surface temperature. The proposed absorptance model is applied to the metal alloyTi-6Al-4V. It is found that the absorptance of this alloy changes with surface temperature over awide range of beam incidence angles. Thermo-fluid simulations with tracking of the free-surface deformation are performed for conduction mode beam welding test cases with a Yb fibre laser and different travel speeds. It is found that the absorptivity coefficient commonly used for this process clearly underestimates the absorptance and the melt pool geometry predicted for the process conditions of this study. The computational results are also compared against experimental results and good quantitative agreement of the melt pool depth, width, length, free surface contour geometry, and the curvature of the end depression left afterre-solidification at the laser switch-off location is obtained. The results show that the absorptance field predicted depends on the melt pool development stage, on the spatial location within the beam spot, and on the process conditions.

Place, publisher, year, edition, pages
Bristol: IOP Publishing, 2021
Keywords
Surfaces, Coatings and Films, Acoustics and Ultrasonics, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-17583 (URN)10.1088/1361-6463/ac296a (DOI)2-s2.0-85117731214 (Scopus ID)
Funder
Knowledge Foundation
Available from: 2021-10-19 Created: 2021-10-19 Last updated: 2022-10-10
2. CFD-Based Feasibility Study of Laser-Directed Energy Deposition With a Metal Wire for On-Orbit Manufacturing
Open this publication in new window or tab >>CFD-Based Feasibility Study of Laser-Directed Energy Deposition With a Metal Wire for On-Orbit Manufacturing
2022 (English)In: Frontiers in Space Technologies, E-ISSN 2673-5075, Vol. 3, p. 1-13, article id 880012Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing of parts on-site in space requires investigating the feasibility ofadapting to zero-gravity and near-vacuum conditions, a technology applied today on Earthat standard conditions. While a few studies have been conducted for powder bed fusion, afeasibility study remains to be explored for direct energy deposition using a laser beam anda metal wire. This is the purpose of this study, which is conducted using a modelingapproach based on computational fluid dynamics. The simulation model developedincludes melting, re-solidification, vaporization, prediction of beam energy absorptionas a function of the local surface temperature and curvature, ray tracing, tracking of freesurface deformation and metal transfer, and wire-resistive heating. The study is carried outby starting from process parameters suited for stable on-Earth metal deposition. Theseconditions were also studied experimentally to validate the simulation model, leading tosatisfactorily results. A total of three other test cases with ambient pressure lowered downto near-vacuum and/or gravitation down to zero are investigated. It is found that,compared to on-Earth conditions, in-space conditions can induce vaporization of themetal alloy that is large enough to result in a curvature of the melt pool free surface but toosmall to lead to the formation of a keyhole. The in-space conditions can also modify theforce balance at the liquid melt bridge between the wire and the melt pool, leading to smallchanges in the curvature and temperature field at the free surface of the wire tip. Among theobserved consequences are a small increase of the melt pool length and a small elevationof the bead height. More importantly, for process control, changing to in-space conditionsmight also affect the stability of the process, which could be assessed through the width ofthe liquid metal bridge. However, by using appropriate process control to maintain acontinuous liquid metal bridge, it is concluded that direct energy deposition of metal usinga laser and a wire could be used for manufacturing metal parts in-space in a temperedatmosphere.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2022
Keywords
LDEDw, ambient pressure, gravity, metal deposition, melt pool simulation, OpenFOAM
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-19031 (URN)10.3389/frspt.2022.880012 (DOI)001188287500001 ()
Note

This research work is supported by grants from the SwedishKnowledge Foundation projects AdOpt (20170315) and SAMw(20170060), which is gratefully acknowledged.

Available from: 2022-08-10 Created: 2022-08-10 Last updated: 2024-04-12Bibliographically approved
3. Effect of shaped laser beam profiles on melt flow dynamics in conduction mode welding
Open this publication in new window or tab >>Effect of shaped laser beam profiles on melt flow dynamics in conduction mode welding
Show others...
2021 (English)In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 166, p. 1-15, article id 106957Article in journal (Refereed) Published
Abstract [en]

A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusion welding on melt thermal flow. Three beam shapes are studied at several welding travel speeds: a reference Gaussian profile and its elliptic elongations along and transverse to the welding travel direction. It is found that these beam shapes change not only the intensity and direction of the melt thermocapillary flow but also the flow pattern. For instance, and contrary to the other profiles, the beam shape elongated along the welding travel direction generates melt front vortices that assist metal pre-heating. It can result in deeper penetration, larger melt volume, and lower amount of thermal energy diffused into the heat affected zone. The simple elongation of a beam profile has thus a non-linear effect on the melt flow and in turn on the seam geometry as well as the temperature gradients in the heat affected zone.

Keywords
Laser beam welding, Beam shaping, Phase change, Melt flow, Free surface deformation
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-17409 (URN)10.1016/j.ijthermalsci.2021.106957 (DOI)000645187000002 ()2-s2.0-85103695215 (Scopus ID)
Available from: 2021-09-01 Created: 2021-09-01 Last updated: 2023-01-05Bibliographically approved

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Noori Rahim Abadi, Seyyed Mohammad Ali

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