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Measuring the effects of a laser beam on melt pool fluctuation in arc additive manufacturing
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0003-2596-5303
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-3569-6795
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. Vol. 25, no 3, p. 488-495
Keywords [en]
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: urn:nbn:se:ltu:diva-71688DOI: 10.1108/RPJ-01-2018-0033ISI: 000464998000006OAI: oai:DiVA.org:ltu-71688DiVA, id: diva2:1264717
Note

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

Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2019-06-14Bibliographically approved
In thesis
1. Phenomena in wire based multi-layer laser welding and hybrid deposition
Open this publication in new window or tab >>Phenomena in wire based multi-layer laser welding and hybrid deposition
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Fenomen i trådbaserad, flerskiktad lasersvetsning och hybriddeposition
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:nbn:se:ltu:diva-74543 (URN)978-91-7790-407-6 (ISBN)978-91-7790-408-3 (ISBN)
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

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Näsström, JonasBrueckner, FrankKaplan, Alexander

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