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Phenomena in wire based multi-layer laser welding and hybrid deposition
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0003-2596-5303
2019 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Fenomen i trådbaserad, flerskiktad lasersvetsning och hybriddeposition (Swedish)
Abstract [en]

Several laser materials processing technologies using metal wire addition have been researched during the last decades. Especially in the field of joining, as well as in the field of Additive Manufacturing (AM), multiple major benefits have been reached, e.g. higher welding speeds and lower heat input. With laser and arc hybrid welding techniques, additional prospects become accessible. These can combine and improve both deep penetration of autogenous laser welding and gap bridging capabilities of traditional arc welding. In the field of AM, wire feed has been a much-appreciated way of supplying additional material. Reasons include clean and easy handling, high utilisation and availability. A high intensity heat source, e.g. a laser beam or an electrical arc, continuously melts a metal wire; the melt being deposited onto a substrate in one or multiple layers to generate a new surface or three dimensional structure. An alternative joining process is Narrow Gap Multi-Layer Welding (NGMLW). This technique utilises the former mentioned AM processes to fill a gap to join sheets together, instead of depositing on an open surface. NGMLW is a capable competitor to the above-mentioned joining processes due to its prospects of being able to join essentially any thickness of sheets, as long as the beam and wire can accurately reach the gap floor and a sufficient number of layers are used.

In this thesis, multiple types of NGMLW, Papers A – D, and hybrid material deposition, Papers E and F, using laser and hybrid heat sources with metal wire addition have been studied. Techniques such as High-Speed Imaging (HSI), 3D and Computed Tomography (CT) scanning have been used to gain greater insight into the workings of these modern manufacturing processes. The multi-layered way of material deposition within a gap to form a welded joint and onto a surface for AM have many similarities, e.g. wire melting behaviour and melt flow.

Paper A introduces the workings of NGMLW, highlighting possible welding imperfections and welded joint morphology. HSI of the process is analysed both qualitatively and quantitatively: qualitative analysis identifying possible causes for said imperfections; quantitative analysis highlighting the potential for using similar and lower frame rate camera footage for closed loop control to suppress the formation of such imperfections.

In Paper B, an alternative near-vertical building strategy for NGMLW is presented and compared to its more common horizontal counterpart. This upright strategy is found to be fully capable of producing sound welded joints, sporting less than 0.3% cavities. The near-vertical welded joints also have potential for unique material properties due to their much different thermal history.

Papers C and D return to the topic of horizontal NGMLW, but with resistance heating of the metal wire for easier processing, also referred to as Laser Hot-Wire Welding (LHWW). Process behaviour and the resulting morphology of welded joints are the main topics of Paper C. Theoretical reasoning for the formation of occasional centre-line cracks, relating to the shape of the melt pool during solidification, are presented. Arcing is observed in some of the experiments, although prior theory indicates that the applied wire voltage was too low for arcing to occur. This arcing phenomenon is further covered in Paper D, where HSI observations are used to correlate process parameters to arcing probability and a theoretical explanation of why arcing can occur is suggested.

Papers E and F take the step out of the gap, studying the impact of laser beam augmentation in different orientations on Wire-Arc Additive Manufacturing (WAAM). Paper E focuses on a method of quantifying melt pool movement. Fluctuations of the melt pool surface decreased by more than 35% with the introduction of a laser beam to the process. Paper F analyses the generated structures, evaluating the usable portion of the “as deposited” shapes and material composition. Surface irregularities decreased by more than 50% on application of a trailing laser beam. Additional aspects relating to the resulting morphology are also presented, including observations and reasoning for surface irregularities and sloping.

The knowledge gained and methods used in the presented work intertwine to form a strong insight into both laser and laser-hybrid materials processing with wire addition. They also introduce approaches for processing and quantifying HSI footage for process evaluation and improvement.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-74543ISBN: 978-91-7790-407-6 (print)ISBN: 978-91-7790-408-3 (electronic)OAI: oai:DiVA.org:ltu-74543DiVA, id: diva2:1324904
Public defence
2019-10-23, E632, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-06-19 Created: 2019-06-14 Last updated: 2019-10-01Bibliographically approved
List of papers
1. Arc formation in narrow gap hot wire laser welding
Open this publication in new window or tab >>Arc formation in narrow gap hot wire laser welding
2018 (English)In: Welding Journal, ISSN 0043-2296, Vol. 97, no 6, p. 171S-178SArticle in journal (Refereed) Published
Abstract [en]

Many heavy industrial applications, e.g. shipbuilding and offshore, rely on thick-section, high-quality welds. Unfortunately, traditional arc-based techniques are often found wanting due to a limited penetration depth and excessive heat-affected zone. The former is typically solved by having a wide groove filled by multiple weld passes, which is both costly and time consuming. Other processes such as autonomous laser or electron beams can join thick materials, but have disadvantages such as increased hardness and solidification cracks inside the welds. A promising in-between technique to join thick sheets is narrow gap multi layer laser welding (NGMLW), using less filler material while also offering more control of weld properties. This technique is often used with laser scanning optics and cold wire, or a defocused laser and electrically heated wire. This paper investigates the limitations of the latter during NGMLW, mainly using high-speed imaging to directly observe and explain process behavior. Increased deposition rates are wanted, but heating also consequently needs to be increased for proper bead fusion. Arc occurrences are found to be the cause of instabilities. They are observed occasionally even at low voltages, but more frequently at higher outputs, and then are also more disruptive to the process.

Place, publisher, year, edition, pages
American Welding Society, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-70165 (URN)10.29391/2018.97.015 (DOI)000435429400018 ()2-s2.0-8504937533 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-07-26 (inah)

Available from: 2018-07-26 Created: 2018-07-26 Last updated: 2019-06-14Bibliographically approved
2. Multipass laser hot-wire welding: Morphology and process robustness
Open this publication in new window or tab >>Multipass laser hot-wire welding: Morphology and process robustness
2017 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 29, no 2, article id 022014lArticle in journal (Refereed) Published
Abstract [en]

There are great prospects for utilizing multipass laser hot-wire welding to join thick steel sheets, especially for techniques commonly performed in single passes, e.g., laser arc hybrid welding, fall short, presenting great opportunities for vehicle industries and offshore applications. Many modern approaches for applying these techniques rely on customized wire feeding nozzles or special scanner optics to ensure proper laser–wire interactions and, in turn, robust process behavior, making them less accessible to many industries. Here, we present a modified adaption of laser hot-wire welding, utilizing more readily available equipment, including an unmodified welding source and a nozzle, presented and evaluated through means of, e.g., high speed imaging and macroscopy. This technique was found to have high process robustness, especially for sealing passes, if wire resistance heating is kept within suitable levels. It is able to both maintain proper laser–wire interaction and produce close to net-shape weld caps. Also, recommended process parameters are presented, together with a description of a potential method for suppressing solidification cracking.

Place, publisher, year, edition, pages
Laser Institute of America, 2017
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-63886 (URN)10.2351/1.4983758 (DOI)000405475100003 ()2-s2.0-85020710900 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-06-12 (andbra)

Available from: 2017-06-12 Created: 2017-06-12 Last updated: 2019-06-14Bibliographically approved
3. Imperfections in Narrow Gap Multi-Layer Welding - potential causes and countermeasures
Open this publication in new window or tab >>Imperfections in Narrow Gap Multi-Layer Welding - potential causes and countermeasures
(English)In: Article in journal (Refereed) Submitted
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-74542 (URN)
Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-14
4. A near-vertical approach to Laser Narrow Gap Multi-Layer Welding
Open this publication in new window or tab >>A near-vertical approach to Laser Narrow Gap Multi-Layer Welding
2020 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 121, article id 105798Article in journal (Refereed) Published
Abstract [en]

A novel, near-vertical approach to the usually horizontal laser Narrow Gap Multi-Layer Welding process is introduced. The process is applied to join X100 pipeline steel and studied through High Speed Imaging. The produced welded joints are compared to their horizontally welded counterparts using 3D scanning, longitudinal & perpendicular cross sections and Computed Tomography analysis. The near-vertical approach is found to be robust and produce welded joints with a uniform appearance. The top surface exhibits certain reoccurring morphological features, and variations in internal track melting boundaries are observed. Any observed cavities appear similar to those produced using the horizontal process, with the difference of their orientation. A combination of the horizontal and the near-vertical process could be beneficial; the near-vertical approach offers potential for shorter inter-layer time and the horizontal method for better surface finish than that of its counterpart. Potential benefits of, and improvements to, the near-vertical process are discussed.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Laser welding, Narrow Gap, Vertical Welding, Multi-Layer, Filler wire
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-74541 (URN)10.1016/j.optlastec.2019.105798 (DOI)000491217800032 ()2-s2.0-85072045298 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-09-20 (johcin)

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-11-06Bibliographically approved
5. Laser enhancement of wire arc additive manufacturing
Open this publication in new window or tab >>Laser enhancement of wire arc additive manufacturing
2019 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, no 2, article id 022307Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing (AM) can be used for the fabrication of large metal parts, e.g., aerospace/space applications. Wire arc additivemanufacturing (WAAM) can be a suitable process for this due to its high deposition rates and relatively low equipment and operationcosts. In WAAM, an electrical arc is used as a heat source and the material is supplied in the form of a metal wire. A known disadvantageof the process is the comparably low dimensional accuracy. This is usually compensated by generating larger structures than desired andmachining away excess materials. So far, using combinations of arc in atmospheric conditions with high precision laser heat sources forAM has not yet been widely researched. Properties of the comparable cheap arc-based process, such as melt pool stability and dimensionalaccuracy, can be improved with the addition of a laser source. Within this paper, impacts of adding a laser beam to the WAAMprocess are presented. Differences between having the beam in a leading or a trailing position, relative to the wire and arc, are alsorevealed. Structures generated using the arc-laser-hybrid processes are compared to ones made using only an arc as the heat source. Bothgeometrical and material aspects are studied to determine the influences of laser hybridization, applied techniques including x ray,energy-dispersive X-ray spectroscopy, and high precision 3D scanning. A trailing laser beam is found to best improve topological capabilitiesof WAAM. Having a leading laser beam, on the other hand, is shown to affect cold metal transfer synergy behavior, promotinghigher deposition rates but decreasing topological accuracy.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
Keywords
additive manufacturing, laser augmentation, gas metal arc, hybrid processing, wire arc additive manufacturing/WAAM
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-74233 (URN)10.2351/1.5096111 (DOI)000484435200037 ()
Conference
Proceedings of the International Congress of Applications of Lasers & Electro-Optics (ICALEO® 2018)
Funder
Interreg Nord, 20200060
Note

Konferensartikel i tidskrift

Available from: 2019-06-07 Created: 2019-06-07 Last updated: 2019-10-01Bibliographically approved
6. Measuring the effects of a laser beam on melt pool fluctuation in arc additive manufacturing
Open this publication in new window or tab >>Measuring the effects of a laser beam on melt pool fluctuation in arc additive manufacturing
2019 (English)In: Rapid prototyping journal, ISSN 1355-2546, E-ISSN 1758-7670, Vol. 25, no 3, p. 488-495Article in journal (Refereed) Published
Abstract [en]

Purpose

The steadily growing popularity of additive manufacturing (AM) increases the demand for understanding fundamental behaviors of these processes. High-speed imaging (HSI) can be a useful tool to observe these behaviors, but many studies only present qualitative analysis. The purpose of this paper is to propose an algorithm-assisted method as an intermediate to rapidly quantify data from HSI. Here, the method is used to study melt pool surface profile movement in a cold metal transfer-based (CMT-based) AM process, and how it changes when the process is augmented with a laser beam.

Design/methodology/approach

Single-track wide walls are generated in multiple layers using only CMT, CMT with leading and with trailing laser beam while observing the processes using HSI. The studied features are manually traced in multiple HSI frames. Algorithms are then used for sorting measurement points and generating feature curves for easier comparison.

Findings

Using this method, it is found that the fluctuation of the melt surface in the chosen CMT AM process can be reduced by more than 35 per cent with the addition of a laser beam trailing behind the arc. This indicates that arc and laser can be a viable combination for AM.

Originality/value

The suggested quantification method was used successfully for the laser-arc hybrid process and can also be applied for studies of many other AM processes where HSI is implemented. This can help fortify and expand the understanding of many phenomena in AM that were previously too difficult to measure.

Place, publisher, year, edition, pages
Emerald Group Publishing Limited, 2019
Keywords
Melt flow, Cold metal transfer, High speed imaging, Material deposition, Quantifying results
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-71688 (URN)10.1108/RPJ-01-2018-0033 (DOI)000464998000006 ()
Note

Validerad;2019;Nivå 2;2019-04-23 (oliekm)

Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2019-06-14Bibliographically approved

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