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  • 1. Alam, Md. Minhaj
    et al.
    Karlsson, Jan
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Generalising fatigue stress analysis of different laser weld geometries2011In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, no 4, p. 1814-1823Article in journal (Refereed)
    Abstract [en]

    Two-dimensional elastic-plastic finite element analyses was carried out on a laser welded box beam in order to study the impact of the geometrical aspects of the joint type and weld root on the fatigue stress behaviour. Different experimental and hypothetical weld geometries were studied. Characteristic root shapes, measured by the plastic replica method, and critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the maximum stress. The simulation of hypothetical transition geometries facilitated the identification of trends and the explanation of part of the phenomena. However, quantitative geometry criteria were only partially suitable to describe the relations. The results have shown that the combination of throat depth, local surface radius and its opening angle determines the peak stress value and its location. Beside extended throat depths, particularly larger toe radii and the avoidance of small opening angles and of surface ripples reduces the peak stress. The explanations were developed in a generalising manner, accompanied by illustrative and flow chart description.

  • 2.
    Bunaziv, I.
    et al.
    Norwegian University of Science and Technology, Trondheim, Norway.
    Akselsen, O.M.
    Norwegian University of Science and Technology, Trondheim, Norway; SINTEF Industry, Trondheim, Norway.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Application of laser-arc hybrid welding of steel for low-temperature service2019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 102, no 5-8, p. 2601-2613Article in journal (Refereed)
    Abstract [en]

    Laser-arc hybrid welding (LAHW) is more often used in shipbuilding and oil and gas industries in recent years. Its popularity arises due to many advantages compared to conventional arc welding processes. The laser beam source is used to achieve much higher penetration depths. By adding filler wire to the process area, by means of an arc source, the mechanical properties can be improved, e.g. higher toughness at low temperatures. Therefore, LAHW is a perspective process for low-temperature service. Applicability of LAHW is under concern due to process stability and mechanical properties related to heterogeneous filler wire distribution through the whole weld metal in deep and narrow joints. This can cause reduced mechanical properties in the weld root as well as problems with solidification cracking. The fast cooling rate in the root provides hard and brittle microconstituents lowering toughness at low temperatures. Numerical simulations and experimental observations showed that an increase in heat input from the laser beam is an effective way to reduce the cooling rate, which is also possible by applying preheating.

  • 3.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Trondheim, Norway.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Trondheim, Norway; SINTEF Industry, Trondheim, Norway.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Correction to: Application of laser-arc hybrid welding of steel for low-temperature service2019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 102, no 5-8, p. 2615-2615Article in journal (Other academic)
    Abstract [en]

    The original version of this article contained several mistakes. Due to technical problems at the typesetter, author corrections were not carried out. The original article has been corrected.

  • 4.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Industrial and Mechanical Engineering.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser-arc hybrid welding of thick HSLA steel2018In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 259, p. 75-87Article in journal (Refereed)
    Abstract [en]

    A standard laser-arc hybrid welding (S-LAHW) and LAHW with preplaced cut wire inside the groove before welding were studied and compared. The S-LAHW setup revealed problems with filler wire delivery to the root, resulting in substantial hardness increase due to bainitic-martensitic transformation. The applied finite element modelling confirmed significant cooling rate increase in the root area for deep penetration welds. Preplacement of cut wire prior to welding reduced hardness providing improved welds with higher homogeneity. This method was subsequently applied for multi-pass welding that revealed insufficient nucleation of acicular ferrite on non-metallic inclusions (NMIs). It is implied that a critical cooling rate has been exceeded where the NMIs become inactive, resulting in a microstructure consisting of a martensite and bainite mixture. This kind of microstructure is clearly harmful for the weld metal toughness.

  • 5.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Industrial and Mechanical Engineering.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Deep penetration fiber laser-arc hybrid welding of thick HSLA steel2018In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 256, p. 216-228Article in journal (Refereed)
    Abstract [en]

    The present investigation addresses laser-arc hybrid welding of 45 mm thick steel with variation in a wide range of process parameters. High volume fraction of acicular ferrite formed in the upper part of the weld metal regardless process parameters. Significantly lower fraction of acicular ferrite was found in the root due to substantially increased cooling rates and the inability to deliver filler wire to this region, resulting in bainite-martensite microstructures in the root. The delivery of filler wire to the root can be enhanced by increasing the air gap between the plates. Higher heat inputs reduce cooling rates in the root which create softer and ductile microstructures, at the expense of a much wider and coarser grained HAZ. The results obtained showed high fusion line and weld metal toughness at low temperature (−50 °C).

  • 6.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Hybrid Welding of 45 mm High Strength Steel Sections2017In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, p. 11-22Article in journal (Refereed)
    Abstract [en]

    Thick section welding has significant importance for oil and gas industry in low temperature regions. Arc welding is usually employed providing suitable quality joints with acceptable toughness at low temperatures with very limited productivity compared to modern high power laser systems. Laser-arc hybrid welding (LAHW) can enhance the productivity by several times due to higher penetration depth from laser beam and combined advantages of both heat sources. LAHW was applied to join 45 mm high strength steel with double-sided technique and application of metal cored wire. The process was captured by high speed camera, allowing process observation in order to identify the relation of the process stability on weld imperfections and efficiency. Among the results, it was found that both arc power and presence of a gap increased penetration depth, and that higher welding speeds cause unstable processing and limits penetration depth. Over a wide range of heat inputs, the welds where found to consist of large amounts of fine-grained acicular ferrite in the upper 60-75% part of welds. At the root filler wire mixing was less and cooling faster, and thus found to have bainitic transformation. Toughness of deposited welds provided acceptable toughness at -50 °C with some scattering.

  • 7.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Process stability during fiber laser-arc hybrid welding of thick steel plates2018In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 102, p. 34-44Article in journal (Refereed)
    Abstract [en]

    TThick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources.

  • 8.
    Bunaziv, Ivan
    et al.
    Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Trondheim.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Trondheim.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The penetration efficiency of thick plate laser-arc hybrid welding2018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 97, no 5-8, p. 2907-2919Article in journal (Refereed)
    Abstract [en]

    Double-sided fiber laser-arc hybrid welding was used to join 45 mm thick high strength steel over a wide range of parameters in order to investigate the efficiency of the process. Air gap size, I- and Y-groove type preparation, pulsed and cold metal transfer pulsed arc modes, arc-laser setup, and travel speeds were compared, and in all cases, sufficient filler material was provided to fully fill the gap. The welds were investigated using high speed imaging and cross-sectional analysis to identify penetration depths, morphology, and imperfections. Larger joint air gaps were found to contribute most to weld penetration depth. Surprisingly, increased line energy decreased penetration efficiency in most cases. The laser-arc interdistance was also investigated, revealing an arc size and melt flow dependency for achieving higher penetration depth for a leading arc. It was found that, although penetration can be optimized, solidification cracking can be a limiting factor in the application of deep penetration hybrid welding for thick steel section joining.

  • 9.
    Bunaziv, Ivan
    et al.
    SINTEF Industry, Trondheim, Norway.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ren, Xiaobo
    SINTEF Industry, Trondheim, Norway.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    SINTEF Industry, Trondheim, Norway.
    Porosity and solidification cracking in welded 45 mm thick steel by fiber laser-MAG process2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 101-111Article in journal (Refereed)
    Abstract [en]

    Porosity and solidification cracking in joining of thick sections are very common issues in deep penetration keyhole laser-arc hybrid welding (LAHW). In the present work, 45 mm thick high strength steel was joined by a double-sided technique. With combined use of fast welding speeds and larger air gap between plates, higher amount of porosity was found because of the dynamic behavior of the keyhole walls. Solidification cracking formed at the centerline in the bottom of the weld due to high-depth-to-width geometrical ratio. Numerical simulations have been performed and showed very high cooling rate and stresses occurred in the root of the deep welds, which corresponds with higher cracking tendency.

  • 10.
    Bunaziv, Ivan
    et al.
    SINTEF Industry, Norway.
    Wenner, Sigurd
    SINTEF Industry, Norway.
    Ren, Xiaobo
    SINTEF Industry, Norway.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    SINTEF Industry, Norway.
    Filler metal distribution and processing stability in laser-arc hybrid welding of thick HSLA steel2020In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 54, p. 228-239Article in journal (Refereed)
    Abstract [en]

    Welds made by high power laser beam have deep and narrow geometry. Addition of filler wire by the arc source, forming the laser-arc hybrid welding (LAHW) process, is very important to obtain required mechanical properties. Distribution of molten wire throughout the entire weld depth is of concern since it tends to have low transportation ability to the root. Accurate identification of filler metal distribution is very challenging. Metal-cored wires can provide high density of non-metallic inclusions (NMIs) which are important for acicular ferrite nucleation. Accurate filler distribution can be recognized based on statistical characterization of NMIs in the weld. In the present study, it was found that the amount of filler metal decreased linearly towards the root. The filler metal tends to accumulate in the upper part of the weld and has a steep decrease at 45–55 % depth which also has wavy pattern based on longitudinal cuts. Substantial hardness variation in longitudinal direction was observed, where in the root values can reach > 300 HV. Excessive porosity was generated at 75 % depth due to unstable and turbulent melt flow based on morphology of prior austenite grains. The delicate balance of process parameters is important factor for both process stability and filler metal distribution.

  • 11.
    Engström, Hans
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Karlsson, Jan
    Hybridsvetsning av lastbilskomponenter med 15 kW fiberlaser och MAG2010Report (Other academic)
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  • 12.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Comparison of three different arc modes for laser-arc hybrid welding steel2016In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 28, no 2, article id 22407Article in journal (Refereed)
    Abstract [en]

    Traditionally, Laser Arc-Hybrid Welding (LAHW) is made using a gas metal arc heat source in pulsed mode. In this study, welds made with three different arc modes under various conditions are compared. The arc modes compared for LAHW are: Standard, Pulsed, and Cold Metal Transfer (CMT). The pulsed mode, using power modulation, is more controlled than the "natural" Standard mode and offers globular drop transfer with reduced heat input to the work piece, enabling thinner materials to be welded. The CMT arc mode also uses power modulation as well as controlled wire feeding. This enables surface tension drop transfer, involving even less heat input and is also considered to generate less undercuts and spatter than the other two arc modes. The welds compared were made in 7 mm thick S420 laser cut steel sheets with two different welding speeds and gap sizes. They were made using close-to-production setup within the limitations of the CMT capabilities, i.e., low and medium wire feed rates. The weld caps and roots were studied optically and the structures were analyzed by making cross-sectional macrographs longitudinally and transversally. These cross sections were analyzed geometrically, structurally, and also hardness tested. The welds were also studied and analyzed by means of pre- and postweld scanning as well as high speed imaging. The study shows that the laser keyhole reduces the effect of the arc modes, enabling higher welding speeds than without the laser. The gouge formed in front of the keyhole determines occurrence of undercuts and bead uniformity. The material mixing of filler and base material, and laser penetration spiking is also influenced by the depth of the arc gouge. The material structure is also affected to some degrees for expected performances. Even though the short-arc technique CMT show promising results, the pros and cons for each arc technique are discussed

  • 13.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Comparison of Three Different Arc Modes When Laser-arc Hybrid Welding in Steel2015In: ILSC 2015 Conference Program and Proceeding, Laser Institute of America , 2015Conference paper (Refereed)
    Abstract [en]

    Traditionally, Laser Arc-Hybrid Welding (LAHW) is made using a Gas Metal Arc (GMA) heat source in pulsed mode. In this study, welds made with three different arc modes under various conditions are compared. The arc modes compared for LAHW are; Standard, Pulsed and Cold Metal Transfer (CMT). The pulsed mode, using power modulation, is more controlled than the “natural” Standard mode and offers globular drop transfer with reduced heat input to the work piece, enabling thinner materials to be welded. The CMT arc mode also uses power modulation as well as controlled wire feeding. This enables surface tension drop transfer, involving even less heat input and is also considered to generate less undercuts and spatter than the other two arc modes.The welds compared were made in 7 mm thick S420 laser cut steel sheets with two different welding speeds and gap sizes. They were made using close-to-production setup within the limitations of the CMT capabilities, i.e. low and medium wire feed rates. The weld caps and roots were studied optically and the structures were analyzed by making cross-sectional macrographs longitudinally and transversally. These cross sections were analyzed geometrically, structurally and also hardness tested. The welds were also studied and analyzed by means of pre- and post-weld scanning as well as High Speed Imaging (HSI).The study shows that the laser keyhole reduces the effect of the arc modes, enabling higher welding speeds than without the laser. The gouge formed in front of the keyhole determines occurrence of undercuts and bead uniformity. The material mixing of filler and base material, and laser penetration spiking, is also influenced by the depth of the arc gouge. The material structure is also affected to some degrees for expected performances. Even though the short-arc technique CMT show promising results, the pros and cons for each arc technique are discussed.

  • 14.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Factors affecting weld root morphology in laser keyhole welding2018In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 101, p. 89-98Article in journal (Refereed)
    Abstract [en]

    Welding production efficiency is usually optimised if full penetration can be achieved in a single pass. Techniques such as electron and laser beam welding offer deep high speed keyhole welding, especially since multi-kilowatt lasers became available. However, there are limitations for these techniques when considering weld imperfections such as weld cap undercuts, interior porosity or humps at the root. The thickness of sheets during full penetration welding is practically limited by these root humps. The mechanisms behind root morphology formation are not yet satisfactory understood. In this paper root humping is studied by reviewing previous studies and findings and also by sample examination and process observation by high speed imaging. Different process regimes governing root quality are presented, categorized and explained. Even though this study mainly covers laser beam and laser arc hybrid welding, the presented findings can generally be applied full penetration welding in medium to thick sheets, especially the discussion of surface tension effects. As a final result of this analysis, a map of methods to optimise weld root topology is presented.

  • 15.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The Morphology of Laser Arc Hybrid Welds2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is about formation of surface imperfections formed in welding when using the manufacturing methods of laser welding and laser arc hybrid welding. In hybrid welding a traditional arc welding source and a laser share the same melt pool, making the process even more complex. Laser welding is often considered as a non-traditional but highly advanced manufacturing technique in industry. As more is getting known about these advanced welding techniques, coupled with reduced prices of laser sources, the interest in industry gradually increases. In welding, control over the quality is essential, particularly to suppress imperfections and unfavourable surface geometries, like undercuts. The mechanical behaviour of a product in service, in particular fatigue life, can suffer from these small, sometimes hardly visible weld imperfections. The final weld quality results from a very complex process, involving non-linear multi-physics. The documentation of parameters, process conditions and the resulting quality is also complex, difficult and so far unsatisfactory. Therefore, the survey manuscript Paper i address the mechanisms and challenges for the documentation of knowledge in laser welding. In addition to the survey manuscript, six journal publications utilize the study of macrographs, surface scanning and High Speed Imaging as methods for capturing and identifying why weld surface imperfection formation can take place. Paper I studies the surface geometry of welds resulting from fibre laser welding with various parameters, also applying the new documentation method called Matrix Flow Chart, MFC. In Paper II, III, IV and VI the formation and shape of undercuts under various circumstances are compared, mapped, analysed and explained. When causes for undercuts are known, counter measures are suggested. Paper V is about accepting undercut formation and instead “repairing” the welded surface by re-melting it with a defocussed laser, effectively eliminating previous surface imperfections. Finally, Paper VI also provides a survey on undercuts in welding and describes the different parameter causes and physical mechanisms.

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  • 16.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Bunaziv, Ivan
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Axelsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Laser-arc hybrid welding of 45 mm thick steel sections for cold climate applications2017In: 70th IIW International conference proceedings, 2017Conference paper (Refereed)
  • 17.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Bunaziv, Ivan
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Axelsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Kaplan, Alexander F.H
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    45 mm thick steel section joining for cold climate applications by applyinglaser-arc hybrid welding2018In: 71st IIW International Conference, 2018Conference paper (Refereed)
    Abstract [en]

    Production and joining of components for energy industries(wind, oil and gas) for cold climate applications is achallenging task. Joining of thick steels is usually performedby using arc techniques such as submerged arc welding(SAW) or Gas Metal Arc Welding (GMAW). To fill thicksections, wide gap preparation is made and gradually filled inseveral weld passes. To reduce the number of weld passes,high power laser-arc hybrid welding (LAHW) is a promisingalternative, but can also weld at higher travel rates therebyreducing the total heat input and reduced filler material.LAHW is applied using a metal-cored wire, demonstratingwelding in 45 mm thick steel sheets. Setup and selection ofprocess parameters are essential for obtaining high processstability, penetration efficiency and material mixingthroughout the depth of the weld. Each weld where repeatedand performed on 500x200x45 mm (x,y,z) steel sheets withmilled joint edges. Using LAHW and selected materials, largeamounts of acicular ferrite was formed in the upper half of thejoint, gradually having increasingly more bainitic structurescloser to the weld root. 

    From these results, it is concluded thatLAHW has high potential for increased production efficiencyand lowered costs, potentially replacing arc welding for thesetypes of applications.

  • 18.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Heussermann, Thilo
    University of Stuttgart.
    Dropout formation in thick steel plates during laser welding2015Conference paper (Refereed)
    Abstract [en]

    Laser welding is a promising technique for welding thick metal sheets, which is usually used for achieving full penetration in a single weld pass. However, among the imperfections that can occur, dropout formation becomes an increasingly larger problem when the sheets to be welded get thicker. When the sheets are 15 mm or thicker it is a challenge to suppress and countermeasures to suppress dropouts get less impact. If full penetration is not achieved, the dropout formation cannot be formed and the melt flows to form better weld caps. Therefore a typical method when welding 15 mm and thicker is to use partial penetration from both sides of the joint and thereby achieving full penetration, at a cost of increasing plate handling complexities and time losses.If the mechanisms behind the dropout formation can be understood, countermeasures may be developed and applied in order to be able to laser weld thicker plates with full penetration single pass welding. In order to understand the mechanics of the formation of dropout during full penetration welding in 15 mm thick plates, experiments have been conducted using laser hybrid arc welding (LAHW) using the laser in CW mode and also applying power modulation. During the experiments, the root has been observed with High Speed Imaging (HSI) to observe the mechanisms behind the formation. It is determined that the downward flow from the keyhole along with the surface tensional forces of the molten steel and its cooling rate play the most significant roles.

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  • 19.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Differences between arc models in laser hybrid arc welding upon weld bead stability and undercut formation2013In: 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden / [ed] Alexander Kaplan; Hans Engström, Luleå: Luleå tekniska universitet, 2013, p. 205-216Conference paper (Other academic)
    Abstract [en]

    In this study, three different arc modes are studied in laser hybrid arc welding with a gasmetal arc, i.e. Standard, Pulsed and Cold Metal Transfer mode. Originally developed forbeing able to weld thin materials, the pulsed mode is the favoured arc mode in both ordinaryarc welding and hybrid welding. The pulsed mode is a more controlled gas metal arc weldingprocess that uses less heat and is able to weld thinner materials than the spray mode processwith globular drop transfer. The cold metal transfer mode utilizes surface tension droptransfer, compared to the free flying drops governing the other modes and is thus even morecontrolled than the pulsed mode. The cold metal transfer mode is much colder than the otherarc modes and is considered to generate less undercuts and spatter than the other modes, byboth developers and users alike.This study compares welds made by the three arc modes for both low and highdeposition rates. The welds are studied by macrographs, scanning and high speed imaging.This study shows that the differences between drop transfer modes are partially eliminateddue to the presence of a laser keyhole. The main arguments to use either arc mode arediscussed.

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  • 20.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Undercut suppression in laser-arc hybrid welding by melt pool tailoring2014In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, no 3, p. 4-, article id 31501Article in journal (Refereed)
    Abstract [en]

    In welding, high welding speeds are usually limited by an increase in undercut. This study shows that the geometrical conditions of the melt flow can be tailored to suppress undercut when using the arc leading setup. By applying high speed imaging, it can be seen that the keyhole and its position affects the melt flow, making the distance between the laser and the arc an important parameter. Undercut formation usually occurs due to a narrowing or necking of the melt flow behind the gouge that can be prevented if the melt flow is changed by optimizing the laser/arc positioning

  • 21.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Undercuts in Laser Arc Hybrid Welding2014In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 56, p. 663-672Article in journal (Refereed)
    Abstract [en]

    Undercuts are usually an imperfection in welding that either continuously or sporadically form, especially when welding at high speed. Efforts, usually lowering the welding speed or overfilling, are applied to avoid undercuts as they can significantly lower the fatigue properties of the welded workpiece. Undercut formation is complex and occurs by various means, mainly based on temperature and melt flow mechanisms. When having two power sources as in laser arc hybrid welding, the melt flow can be tailored to suppress undercut formation. This can be done e.g. by narrowing the width of the gouge or by optimum positioning of the power sources relative to each other. The present paper shows and explains the main reasons of various types of undercut formation. By following the herein generated guidelines, the critical welding speed during laser arc hybrid welding can be further increased, free of undercuts

  • 22.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Lamas, Javier
    Comparison of CMT with other arc modes for laser arc hybrid welding of 7 mm steel2013Conference paper (Refereed)
    Abstract [en]

    In this study, three different arc modes in laser arc hybrid welding with a Gas Metal Arc (GMA) are studied, i.e. Standard, Pulsed and Cold Metal Transfer (CMT) mode. Originally developed for being able to weld thin materials, the pulsed mode is the favoured arc mode in both ordinary arc welding and laser hybrid welding. The pulsed mode is a more controlled GMA welding process that uses less heat and is able to weld thinner materials than the Standard mode process while utilizing globular drop flight transfer. The CMT mode utilizes surface tension drop transfer with controlled wire feeding and can thereby be used for much less heated welds compared to the other arc modes. It is also considered to generate less undercuts and spatter compared to the other modes, by both developers and users alike. This study compares hybrid welds made by the three arc modes for low and medium wire deposition rates, within the limits of the CMT process. The welds are studied by macrographs, scanning and high speed imaging. The study shows that the differences between the drop transfer modes are partially eliminated due to the presence of a laser keyhole. The dominating impact on the solidification and melt flow is the arc and especially the gouge created ahead of the keyhole. The main pros and cons to use either arc mode are discussed.

  • 23.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Lamas, Javier
    Luleå University of Technology, Centro Tecnolóxico do Naval Galego, Ferrol.
    Comparison of CMT with other arc modes for laser-arc hybrid welding of steel2014In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 58, no 5, p. 649-660Article in journal (Refereed)
    Abstract [en]

    In this study, three different arc modes in laser-arc hybrid welding with a gas metal arc were studied, i.e. the standard, pulsed and cold metal transfer (CMT) modes. The pulsed mode is more controlled than the standard mode and offers reduced heat input to the workpiece, which enables welding of thinner materials. The CMT mode utilizes surface tension drop transfer with controlled wire feeding, and therefore, involves less heat input than the other arc modes, and it is also considered to generate less undercut and spatter than the other modes. This study compares hybrid welds made by the three arc modes with a close-to-production setup for low and medium wire deposition rates, within the limits of the CMT process. The welds were studied by scanning and high speed imaging. The study shows that the differences between the drop transfer modes are reduced due to the presence of a laser keyhole. The dominating influence on the solidification and melt flow is the arc and especially the gouge created ahead of the keyhole. The main pros and cons of the different arc modes are discussed.

  • 24.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Olsson, Rickard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Laser Nova AB, Östersund, Sweden.
    Powell, John
    Laser Nova AB, Östersund, Sweden.
    Palmquist, Anders
    Department of Biomaterials, University of Gothenburg, Gothenburg, Sweden.
    Brånemark, Rickard
    Department of Orthopaedic Surgery, University of California, San Francisco, USA.
    Formation mechanisms of surfaces for osseointegration on titanium using pulsed laser spattering2019In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 458, p. 158-169Article in journal (Refereed)
    Abstract [en]

    Accelerated bone grow (osseointegration) can be achieved by modifying the surface of medical implants. For this purpose, pulsed lasers can be used to successfully texture such beneficial surfaces on titanium, e.g. a BioHelix™ structure. This surface typically includes ridges and droplets with a size range between 1 and 20 μm. This paper presents the results of an experimental program where a range of laser parameters was used to create different surface textures on titanium substrates, using pulsed laser spattering. The resultant surfaces are analysed by scanning electron microscope and X-ray Micro Computer Tomography. It is shown that optimisation of the laser parameters results in a robust process which produces a surface that has proven to be beneficial for osseointegration. The results are also deeper analysed, explaining how different types of surface are created by the laser-material interaction under different conditions. Further, droplet flight distances and the formation of the spongeous nano-scale surface that characterizes the surface structure depends on very fast cooling and is also evaluated.

  • 25.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Olsson, Rickard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Lasernova.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Laser Expertise Ltd.
    Palmquist, Anders
    Department of Biomaterials, University of Gothenburg, Gothenburg, Sweden.
    Brånemark, Rickard
    Department of Orthopaedic Surgery, University of California, San Francisco, USA.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The formation of osseointegrating surfaceson titanium by laser irradiation2018In: 71st IIW General Assembly, C-IV, 2018Conference paper (Refereed)
    Abstract [en]

    Pulsed lasers can be used to modify the surface of medical implants in order to accelerate bone growth(osseointegration). Here, it is used to create a surface that is beneficial for rapid osseointegration, also calledBioHelix™, having ridges and covered in attached droplets of diameters between 1 and 20 μm. This paper presentsthe results of an experimental program in which a range of laser parameters were used to create different surfacetextures on titanium substrates. The resulting surfaces were analyzed by scanning electron microscope and MicroComputer Tomography. The paper explains how different types of surface are created by the laser-materialinteraction under different conditions. It is shown that optimization of the laser parameters results in a robustprocess which produces a surface that is fundamentally different from those created by other methods

  • 26.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Pocorni, Jetro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Laser Expertise Ltd.
    Differences between continuous, pulsing and dynamic piercing processes for laser cutting2017In: Proceedings of IIW General Assembly, C-IV, Shanghai, 2017Conference paper (Refereed)
    Abstract [en]

    This paper investigates the laser piercing process preceding nearly all laser cutting operations. An important aspect of laser piercing is the pierce time and reliability of the process since industrial laser cutting machines are programmed for the minimum reliable pierce time. Another important aspect is the width of the pierced hole. If the hole width is less than the cut line, piercing can be made directly on the cut path, possibly saving time and material. In this paper, stainless steel is pierced using CW stationary mode in 10 mm and 15 mm thick sheets, compared with pulse modulation and circular trepanning movement of the laser beam for a selected wide range of parameters. High speed imaging was applied to observe spatter formation and measure pierce times. The results show that appropriate settings can halve piercing times for either laser power modulation or trepanning motion, compared to stationary continuous laser piercing.

  • 27.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Qinglong, Pan
    Joining and Welding Research Institute, Osaka University.
    Mizutani, Masami
    Joining and Welding Research Institute, Osaka University.
    Kawahito, Yousuke
    Joining and Welding Research Institute, Osaka University.
    Katayama, Seiji
    Joining and Welding Research Institute, Osaka University.
    Effects of edge oxides from laser cutting in laser-arc hybrid welding2018In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, no 1, article id 012014Article in journal (Refereed)
    Abstract [en]

    Laser-arc hybrid welding (LAHW) is a promising technique for joining sheets due to fast processing speeds and small gap bridgeability. Prior to welding, the edges are often prepared using laser cutting. However, this often leaves small striations with a thin oxide layer that may affect the weld quality. Compared to milled edges, these striations produces a quasigap in a butt joint configuration. The effects of these cutting oxides upon welding are yet unknown. Here, the effects of these oxides in combination with CO2 in the shielding gas are investigated for the LAHW process, using a cold metal transfer arc process.

  • 28.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Qinglong, Pan
    Osaka University.
    Mizutani, Masami
    Osaka University.
    Kawahito, Yousuke
    Osaka University.
    Katayama, Seiji
    Osaka University.
    Investigation of laser-arc hybrid welding utilizing CMT, effects upon oxygen and nitrogen contents as well as the weld stability due to oxygen contents of the shielding gas and gap oxides2015Conference paper (Other academic)
    Abstract [en]

    In this study, the effects upon weld arc stability and contents of oxygen and nitrogen inside the weld is investigated for laser-arc hybrid welding (LAHW) using the CMT arc mode. CMT is a controlled short arc technique that is here expected to be less sensitive to oxygen levels in the shielding gas. Having oxides or nitrogen inside the weld region is also known to alter the fluid mechanics such as surface tension, but also a cause for porosity. The gap preparation prior to welding is typically carried out by thermal cutting, water jet cutting or grinding. These edges are then placed to form the joint to be welded. In the case of thermal cutting, oxides are usually formed on the cut edge, adding oxygen into the melt pool when welding is conducted. The effects are studied by macroscopy, HSI and chemical analysis. The arc stability and oxygen and nitrogen levels in the welds are more affected by the oxides remaining from the laser cut edges than the oxygen in the shielding gas when the cutting oxides are removed.

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  • 29.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Robertson, Stephanie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Embedding Carbon Fibre Structures in Metal Matrixes for Additive Manufacturing2017In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, p. 39-48Article in journal (Refereed)
    Abstract [en]

    It is possible to reinforce structures and components using carbon fibres for applications in electronics and medicine, but most commonly used in reinforcing resin fibre composites for personal protection equipment and light weight constructions. Carbon fibres act as stress redistributors while having increased electrical and thermal conductivities. These properties could also be utilized in metal matrixes, if the fibres are properly fused to the metal and the structure remains intact. Another recently developed high potential carbon structure, carbon nanotube- (CNT) yarns, has similar but even greater mechanical properties than common carbon fibres. Via laser cladding, these reinforcing materials could be used in a plethora of applications, either locally (or globally) as surface treatments or as structural reinforcements using multi-layer laser cladding (additive manufacturing). The challenges of embedding carbon fibres or CNT-yarns in a CuAl mixture and SnPb solder wire using lasers are here investigated using high speed imaging and SEM. It is revealed that the carbon fibres have very high buoyancy in the molten metal and quickly degrades when irradiated by the laser. Wetting of the fibres is shown to be improved by a Tungsten coating and embedding of the structures after processing are evaluated using SEM and Raman spectroscopy.

  • 30.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Torkamany, Mohammad
    Department of Materials Engineering, Tarbiat Modares University.
    Laser re-melting to remove weld cap undercuts2016Conference paper (Refereed)
    Abstract [en]

    Undercuts in welded components are known as a stress raiser that reduces fatigue life, a well-known origin for construction failures. If fatigue life is increased, many components will have longer service time, preventing wasting of resources for repairing or re-building. Undercuts form when conditions for welding are bad, generally due to dilutes in the weld zone, bad shielding gas, arc properties or too high welding speeds leading to premature cooling of weld gouge edges. These conditions may result in poor wetting at the melt pool rim, preventing the melt from reaching the base plate surface. Sometimes undercuts are not at all tolerated by industrial requirements, such as for flat steel extension welding where the surface needs to be flat. In these cases post weld treatment is required. The here proposed solution is a technique of laser re-melting laser hybrid arc weld caps in order to remove occurring undercuts and even out weld caps and roots. In this case, the same laser used for welding can also be used in a second run but defocussed. This technique is advantageous to techniques such as TIG dressing since the equipment is already present. After the focused laser has been in conjunction with an arc to produce an approved weld, except for including irregular weld bead or undercutting, the laser is used again in a defocussed position to re-melt the weld cap. The wider but shallower weld surface created has redistributed the melt cap in order to fill the occasional undercuts and surface irregularities.

  • 31.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Torkamany, Mohammad
    Department of Materials Engineering, Tarbiat Modares University.
    Powell, John
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Improving weld quality by laser re-melting2014In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, no 4, article id 41502Article in journal (Refereed)
    Abstract [en]

    Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and varying penetration. In some cases, it is technically and commercially viable to reduce undercut at the weld cap and smooth out the weld root profile by defocussing the welding laser and using it to remelt the welded surfaces.

  • 32.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Volpp, Jöerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Thompson, Cassidy
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Prasad, Himani Siva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fedina, Tatiana
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Brückner, Frank
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Influence of the vapour channel on processing in laser powder bed fusion2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 80-87Article in journal (Refereed)
    Abstract [en]

    Additive Manufacturing provides many opportunities to design and manufacture parts that are difficult or not possible to produce with conventional methods. In Selective Laser Melting (SLM) in powder bed fusion (PBF), melt pool dynamics and stability is dependent on a large number of factors, e.g. laser power output, power density, travel speed, reflectivity of powder bed, rapid heating and vaporization. Since travel speeds are often very fast and the laser interaction zone is small, the physical events become difficult to predict but also to observe. This work aims to describe the formation and geometrical characteristics of the vaporization zone during processing. Using a combination of theoretical descriptions, resulting material structures and a comprehensive analysis of high-speed images of the processing zone for different heat inputs and travel speeds, explanations for the dynamic melt pool behaviour are derived. The melting and pressures from processing involved moves powder particles next to it, changing the conditions for neighbouring tracks due to lack of material. These findings can provide a basis for creating more efficient and stable SLM processing, with fewer imperfections.

  • 33.
    Haglund, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Westinghouse Electric Sweden AB, Västerås.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Eriksson, Igemar
    Dalco Elteknik AB, Östersund.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses2018In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 100, p. 1-6Article in journal (Refereed)
    Abstract [en]

    Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.

  • 34.
    Johansson, Christian
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Karlsson, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Bertoni, Marco
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Chirumalla, Koteshwar
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Enhancing intra-cognitive communication between engineering designers and operators: a case study in the laser welding industry2012In: Proceedings of the 3rd IEEE International Conference on Cognitive Communications: CogInfoCom 2012, Piscataway, NJ: IEEE Communications Society, 2012, p. 493-497Conference paper (Refereed)
    Abstract [en]

    In manufacturing, metal parts can be joined using a laser as a welding tool, i.e. laser welding. Despite huge amount of research over the years, the process is neither sufficiently understood nor mathematically predictable. This study aims to holistically analyze the knowledge management issues occurring in laser welding. Emerging from observations and semi-structured interviews from industry and academy, the complexity and the criticalities of the process as well as the current knowledge transfers is explained and analyzed, using a knowledge lifecycle framework as a reference. Besides enhanced awareness of the limiting issues, information and knowledge visualization, e.g. knowledge maps, is identified as a key for progress in the community. The Matrix Flow Chart is suggested as an alternative descaled map of process changes.

  • 35.
    Kaplan, Alexander F.H
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Robertson, Stephanie M.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ramasamy, Anandkumar
    Lincoln Electric Europe, Nijmegen, Netherlands.
    Kalfsbeek, Bert
    Lincoln Electric Europe, Nijmegen, Netherlands.
    Microstructure morphology characterization of welding consumables studied by pulse-shaped laser heating2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 184-191Article in journal (Refereed)
    Abstract [en]

    During welding, wire consumables can essentially contribute to the resulting microstructures and mechanical properties. In order to maintain high toughness even for high strength steel, certain microstructures are desirable, particularly acicular ferrite. An efficient, controllable test method was developed during which the wire is molten and experiences a thermal cycle by a shaped laser pulse, or a sequence of pulses, which shall resemble continuous laser-arc hybrid welding or narrow gap multi-layer laser welding. Different thermal cycles and wire chemistries have led to manifold microstructures. The morphology of the microstructures can become complex. Therefore, more detailed characterization of essential morphology aspects was carried out, to distinguish different results. The thermal cycles from quenching have led to shorter, thicker laths with more random orientation. The latter can be favourable for high toughness. Short reheating cycles by about 200 K/s caused finer, longer and more parallel laths, as for bainite, in varying size of blocks. Other aspects considered were grain boundary ferrite and non-metallic inclusions. Systematic variation of the thermal cycle by the testing method along with systematic description of microstructure morphology in more detail is a promising method to identify and optimize favoured routes for wire chemistry and welding techniques.

  • 36.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ilar, Torbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Bang, Hee-Seon
    Chosun University, Department of Welding & Joining Science Engineering.
    Bang, Han-Sur
    Chosun University, Department of Welding & Joining Science Engineering.
    Evolution of a Laser Hybrid Welding Map2015In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, p. 2-13Article in journal (Refereed)
    Abstract [en]

    Laser arc hybrid welding combines the advantages but also the complex physical mechanisms of gas metal arc welding and laser keyhole welding. From manifold mainly experimental but also theoretical research results a map with versatile functions was initiated for the first time. The purpose is to survey the overall context and to facilitate navigation to the various phenomena that are shown through case studies accompanied by theoretical explanations and guidelines for optimization. Though not complete, the map enables systematic and graphical navigation to relevant publications. Based on a fundamental structure of the map, which was decided early, it is inherently extendable in the future by adding existing and new knowledge, also from other research groups, enabling evolution. The fundament of the map structure comprises gouge thickness, joint type and metal grade, in coherence with product and weld designers’ starting points. The next hierarchy level of the map offers options in the joint type as well as in hybrid welding techniques. The latter contains techniques like double-sided welding, pulse shaping management of the arc or laser, CMT arcs, tandem arcs, or remelting of undercuts. In addition to laser-arc hybrid welding, other hybrid laser techniques like multilayer hot-wire laser welding of narrow gaps or hybrid laser friction stir welding can be taken into account. At the other end of the hierarchy, the map offers via a database-like archive electronic navigation to research results like weld macrographs, high speed imaging or numerical simulation results of the welding process.

  • 37.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    A procedure to fully control and trace the weld quality for laser-arc hybrid welding under production conditions2014In: International Journal of Manufacturing Research, ISSN 1750-0591, Vol. 9, no 1, p. 92-111Article in journal (Refereed)
    Abstract [en]

    Hybrid welding combining a laser beam with a MIG/MAG-arc has high potential to fill joint gaps and to shape the weld surface. The geometrical variations and the oxidation of the joint edges can have significant influence on the resulting weld surface shape and on fatigue life. In the presented study, edge tolerances such as edge mismatch were measured. By consequent scanning of the tolerances, high speed imaging of the melt pool flow dynamics and scanning of the resulting weld surface profile, a systematic identification and explanation of the weld quality on the joint edge conditions can be achieved, even for complex products in rough industrial environment. A corresponding general procedure is presented. From a case study, the limits of quality aspects such as undercuts were quantitatively identified and qualitatively explained.Copyright

  • 38.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kim, K. H.
    Bang, Hee-Seon
    Bang, Han-Sur
    Näsström, Jonas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Narrow gap laser welding by multilayer hot wire addition2015In: ILSC 2015 Conference Program and Proceeding, Laser institute of America , 2015Conference paper (Refereed)
  • 39.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kim, Kyounghak
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Bang, Hee-Seon
    Chosun University, Department of Welding & Joining Science Engineering.
    Bang, Han-Sur
    Chosun University, Department of Welding & Joining Science Engineering.
    Näsström, Jonas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Narrow gap laser welding by multilayer hot wire addition2016In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 28, no 2, article id 22410Article in journal (Refereed)
    Abstract [en]

    Welding of thick section butt joints experiences limitations for different techniques. One option is to fill a narrow gap layer by layer with laser melted wire, a laser metal deposition technique where the complexity of a keyhole is avoided. The presented results show that wire addition can enable relatively thick layers. In particular, when electrically preheating the wire the process becomes more energy-efficient and favorable wetting conditions might be achieved. Since the wire was preheated by an electric current conducted through the wire to the workpiece, high speed imaging has shown that the wire tip can occasionally ignite small electric arcs. The wire deposited in the narrow gap also shows a fluctuating but self-stabilizing movement of the tip. Imperfections that have to be avoided are hot cracks, cavities, lack of fusion, and an irregular final weld surface topology. The technique shows high potential.

  • 40.
    Kaplan, Alexander
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Lamas, Javier
    Centro Tecnolóxico do Naval Galego, Ferrol.
    Karlsson, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Yañez, Armando
    Centro de Investigacións Tecnolóxicas, Universidade da Coruña, Ferrol.
    Scanner analysis of the topology of laser hybrid welds depending on the joint edge tolerances2011In: 13th NOLAMP Conference: 13th Conference on Laser Materials Proce Nordic Countries 27 - 29 June 2011 / [ed] Einar Halmøy, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2011Conference paper (Refereed)
    Abstract [en]

    The surface geometry after laser hybrid arc welding is an important quality criterion. What isoften called welding in a rough industrial environment can in many cases systematically bereduced to a few local conditions of the joint edge during welding, particularly depending onthe edge preparation technique. In the present study, beside the influence of surface oxidesstudied in separate publications, the conditions are reduced to the local gap width, verticalsurface position and edge mismatch. Gas cut edge conditions are compared to milling andlaser cutting. By scanning the steel edges of a 10 mm butt joint before and during hybridwelding and relating the systematic variation of the above three properties to the scannedtopology of the resulting weld, quantitative correlations are identified. By the aid of highspeed imaging, explanations for the trends can be found. Operating windows with controllabletrends can be quantitatively mapped and distinguished from instable regimes. Beside higherroughness, gas cut edges show a superimposed edge oscillation of longer periodicity, beingless visible but important. During welding, concave surface bending and gap widening alterthe initial conditions. Awareness and quantitative identification of the edge conditions isrecommended to control the welding process in a rough industrial environment.

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  • 41.
    Karlsson, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Knowledge platform approach for fiberlaser welding of high strength steel2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
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  • 42.
    Karlsson, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Two laser welding cases and suitable documentation methods2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis is about laser welding, in particular about geometrical defects, but it also addresses how to improve the documentation of the findings. Laser welding is an important and highly advanced manufacturing technique in industry. An emerging option is laser hybrid arc welding. In welding, control over the quality is essential, particularly to suppress defects and unfavourable surface geometries. The mechanical behaviour of a product in service can even suffer from small, hardly visible welding defects like undercuts. The process causing the quality involves complex multi-physics and is nonlinear. The documentation of parameters, process conditions and of the resulting quality is difficult and unsatisfactory so far. Therefore Paper 1 addresses the mechanisms and challenges for the documentation of laser welding knowledge. According to the knowledge lifecycle theory, these difficulties not only address how welding knowledge is generated, identified, captured and stored, but also how it is accessed, shared and eventually used. In Paper 2 the geometry resulting from fibre laser welding of a corner joint, including defects like undercuts, is studied for varying parameters. The results are categorized and mapped. Then they are documented by a new method, the Matrix Flow Chart, MFC, as an attempt to improve knowledge formalizing, storing and access, which is also discussed in Paper 1. In Paper 3 and 4 two different kinds of undercuts, caused by different metal surface conditions during the laser hybrid arc welding process, are investigated by visual analysis, SEM, chemical analysis and high speed imaging. In Paper 3 the observed findings are documented in common letter journal format as an extremely brief type of documentation. In Paper 4 the physical mechanisms of the welding process causing the two types of undercuts are explained in regular manuscript format. Here a sequential flow chart turned out to be suitable for documentation of the findings.

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  • 43.
    Karlsson, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Analysis of a fibre laser welding case study, utilising a matrix flow chart2011In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 257, no 9, p. 4113-4122Article in journal (Refereed)
    Abstract [en]

    For fibre laser welding of an eccentric corner joint, the quality of the resulting weld cross section was studied with respect to the dependence on process parameters like lateral laser beam alignment, beam inclination, focal plane position or welding speed. The complex load situation of the support beamer was simplified to bending of one corner. Due to fatigue load, the weld properties causing the peak stress are essential, in particular the top and root shape of the weld cross section. For the parameters varied, the resulting shapes were categorized into different top and root classes, determined by certain key dimensions, considering also welding defects like undercuts. The shapes are boundary conditions for Finite Element Analysis of the joint under load for quantitative comparative analysis of the maximum stress. As two high strength steel grades were joined, the hardness transition across the weld was of interest, too. High speed imaging of the weld pool surface shape provided additional information on the relation between the parameter input and quality output. The different trends identified were discussed and guidelines were derived. As the systematic documentation of results is unsatisfactory in welding, a new method was developed and applied for the first time, called the Matrix Flow Chart. It enables an illustrative view on the resulting welding trends in a combined manner and is extendable by other researchers

  • 44. Karlsson, Jan
    et al.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fibre laser welding for lightweight design2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics : November 2 - 5, 2009 - Orlando, FL : Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference, poster presentation, gallery, Orlando, Fla.: Laser institute of America , 2009, Vol. 102, p. 1548-1557Conference paper (Refereed)
    Abstract [en]

    Two different high strength steel grades have been welded by a fibre laser as a fillet corner joint. The purpose of the experiments is to use thinner materials of higher strength as a weight reduction strategy. The sensitivity of the welding process to the beam inclination angle, the beam positioning and the focal plane position were studied. High-speed imaging, process emission monitoring, measurement of the weld surface topography, mechanical testing and FE-analysis have been used to analyze the process and the resulting weld. The combined study by these methods gives a more comprehensive picture for studying the weld quality. The Bifurcation Flow Chart (BFC) as a new method has been applied to standardize and generalize the findings.

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  • 45.
    Karlsson, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Markmann, Christoph
    Luleå tekniska universitet.
    Alam, Md. Minhaj
    Kaplan, Alexander
    Parameter influence on the laser weld geometry documented by the matrix flow chart2010In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, no 2, p. 183-192Article in journal (Refereed)
    Abstract [en]

    Three variants of fibre laser welding of corner joints where studied. In service a welded piece experiences fatigue load in a complex manner. The peak stress responsible for the fatigue life of the product is mainly determined by positioning and the geometry of the resulting weld. Some top and root shapes where identified for the joints studied. While parameter documentation is straightforward, generalization and combination of knowledge is a challenge. A new documentation method, the Matrix Flow Chart, MFC, turned out to be a powerful solution for large scale documentation, combination and generalization. Three variants of fibre laser welding of corner joints where studied. The peak stress responsible for the fatigue life of the product is mainly determined by the geometry of the resulting weld. Different top and root shape classes were identified for the joints studied. The shapes mainly depend on geometrical laser beam parameters and govern the peak stress. While parameter documentation used to be straightforward, generalization and combination of knowledge is a challenge. A new documentation method, the Matrix Flow Chart, MFC, turned out to be a promising solution for large scale documentation.

  • 46.
    Karlsson, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Rubin, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lamas, Javier
    Centro Tecnolóxico do Naval Galego, Ferrol.
    Yañez, Armando
    Universidade da Coruña, Ctr Invest Tecnol.
    Observation of the mechanisms causing two kinds of undercut during laser hybrid arc welding2011In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 257, no 17, p. 7501-7506Article in journal (Refereed)
    Abstract [en]

    Two different kinds of undercut were identified when laser hybrid welding hot rolled HSLA-steel in either the as-rolled condition or with the top surface mill scale removed. The presence of mill scale on the steel surface was found to give a sharp angled undercut combined with a sharp oxide inclusion at the edge of the weld which would have the same mechanical effect as a crack in this position. Removal of the surface oxides before welding resulted in the elimination of the oxide inclusions and a more rounded undercut geometry indicative of superior mechanical properties, particularly fatigue life. The mechanisms of the formation of both types of undercut have been analysed by high speed photography and SEM.

  • 47.
    Lamas, Javier
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gap bridging for two modes of laser arc hybrid welding2015In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 224, p. 73-79Article in journal (Refereed)
    Abstract [en]

    The topology of welds is an important quality criterion for which the mechanisms behind are only partially understood. The impact of gap width on the resulting weld shape produced by laser-arc hybrid welding was studied for two arc modes: pulsed arc and cold metal transfer. The weld bead and root topology were scanned and analysed. For widening gaps below a limiting width, top reinforcement turns into underfill. Above a certain gap width (0.8 mm in this case), a bridge of melt is created across the weld zone. Although high speed imaging shows very different drop transfer and weld pool formation for the two arc modes, the bridging behaviour shows the same trend for both modes. This bridging effect is important from an industrial point of view because, when viewed from the top, it gives the misleading impression that a good weld has been produced. For even wider gaps the melt collapses into the gap. These different regimes are analysed and discussed for both modes.

  • 48.
    Lamas, Javier
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Centro Tecnolóxico do Naval Galego, Ferrol.
    Karlsson, Jan Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Yañez, Armando
    The effect of fit-up geometry on melt flow and weld quality in laser hybrid welding2013In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, no 3Article in journal (Refereed)
    Abstract [en]

    Hybrid laser-arc welding has a good tolerance to poor fit up as compared to simple laser welding. For a butt joint, the joint fit-up variations can be reduced to two local properties: the gap width and the vertical edge mismatch. The impact of these two properties on the resulting weld quality has been studied systematically in this paper. The original edges as well as the resulting weld surface topography have been scanned in three dimensions in order to study trends. During hybrid welding, the melt flow and the electric arc were observed at the top surface by high speed imaging to analyze the complex fluid flow phenomena.

  • 49.
    Moradi, Mahmoud
    et al.
    Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Tehran.
    Ghoreishi, Majid
    Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Tehran.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    An investigation on stability of laser hybrid arc welding2013In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 51, no 4, p. 481-487Article in journal (Refereed)
    Abstract [en]

    The stability of the weld surface quality resulting from laser–arc hybrid welding of 4 mm thick steel was studied. The trends of stability in terms of top weld width variation were estimated by using design of experiments, where different types of unstable welds were distinguished. High speed imaging of the process supported the interpretation of the trends. High arc voltage and short distance laser–arc has destabilized the process. For a stable process the applied spray mode has caused a short arc and symmetric central drop transfer while for high voltage the arc became long and wide and the drops traveled sideward. The potential and limits of the design of experiments method for such kinds of applications were discussed.

  • 50.
    Moradi, Mahmoud
    et al.
    Department of Mechanical Engineering, Faculty of Engineering, Malayer University.
    Salimi, Nahid
    Department of Computer Engineering, Malayer Branch, Islamic Azad University.
    Ghoreishi, M.
    Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Tehran.
    Abdollahi, Hadi
    Department of Mechanical Engineering, Urmia University of Technology.
    Shamsborhan, Mahmoud
    Department of Engineering, Mahabad Branch, Islamic Azad University.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ilar, Torbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Parameter dependencies in laser hybrid arc welding by design of experiments and by a mass balance2014In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, no 2, article id 22004Article in journal (Refereed)
    Abstract [en]

    Reinforcement, undercut, and root drop-through during laser hybrid arc welding of steel were studied in dependence of gap width, welding speed, and wire feeding rate. Generalized trends were obtained through design of experiments. Most of the trends could be explained by a mass balance while some parameter impacts relied on more complex mechanisms. In particular, different levels of complexity of parameter dependencies were distinguished, ranging from monotonous behaviour to maxima and to changing signs of the trends. The findings are of high practical relevance to optimize the process with respect to the weld quality. Moreover, the potential and limits of the design of experiments method, of a mass balance, and of the matrix flow chart method are discussed.

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