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  • 1.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Analysis of the rapid central melt pool flow in hybrid laser-arc welding2012Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 39, s. 853-862Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hybrid laser arc welding creates a long weld pool tail. By high speed imaging the melt velocity behind the keyhole was measured to be very high, of the order of meters per second. Fluid dynamics simulation was carried out locally in the central axial plane of the pool tail. The high speed melt layer redistributes its momentum to slow movement of the deeper bulk. The consequences of initially high melt speed and its mass flow redistribution on the formation of the central reinforcement peak are discussed.

  • 2.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Hybrid Welding of 45 mm High Strength Steel Sections2017Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, s. 11-22Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    Carlson, Johan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Stener, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Sand, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Pålsson, Bertil
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Monitoring local solids fraction variations in multiphase flow using pulse-echo ultrasound2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 70, s. 376-379Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an ultrasonic pulse-echo technique for on-line monitoring of variations in solids concentrations in particlesuspensions. The method is based on time-frequency analysis of the backscatter signals, exploring variations in spectral content ofthe backscatter as function of depth in the suspension. Experiments on a settling of magnetite particles in water, at varying solidsconcentrations, show that the settling process can be followed by studying the energy of backscattered ultrasound.

  • 4.
    Delaney, Paul
    et al.
    Queen's University Belfast.
    Larsson, Andreas
    Small cluster model of the NV centre in diamond2010Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 3, nr 4, s. 1533-1537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The singlet 1E and 1A 1 energy levels of the Nitrogen-Vacancy centre's ground state configuration each need two Slater determinants in theoretical models, posing difficulties for Density-Functional Theory (DFT) and Hartree-Fock approaches. Configuration Interaction (CI) can handle such states, but not the C 284H 144N - and C 163H 100N - clusters of our recent DFT study as CI computer time and memory scale worse than DFT with system size. Using smaller clusters to model bulk diamond introduces size errors. We examine the smaller diamond cluster C 42H 42N - using DFT to quantify the size error: if not too large it opens the way to CI calculations of these states.

  • 5.
    Eriksson, Ingemar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Guidelines in the choice of parameters for hybrid laser arc welding with fiber lasers2013Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 41, s. 119-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser arc hybrid welding has been a promising technology for three decades and laser welding in combination with gas metal arc welding (GMAW) has shown that it is an extremely promising technique. On the other hand the process is often considered complicated and difficult to set up correctly. An important factor in setting up the hybrid welding process is an understanding of the GMAW process. It is especially important to understand how the wire feed rate and the arc voltage (the two main parameters) affect the process. In this paper the authors show that laser hybrid welding with a 1 μm laser is similar to ordinary GMAW, and several guidelines are therefore inherited by the laser hybrid process.

  • 6.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Undercuts in Laser Arc Hybrid Welding2014Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 56, s. 663-672Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 7.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Robertson, Stephanie
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Embedding Carbon Fibre Structures in Metal Matrixes for Additive Manufacturing2017Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, s. 39-48Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 8.
    Hashemzadeh, M.
    et al.
    Faculty of Engineering, University of Nottingham.
    Suder, W.
    Welding Engineering Research Centre, Cranfield University.
    Williams, S.
    Welding Engineering Research Centre, Cranfield University.
    Powell, John
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    Faculty of Engineering, University of Nottingham.
    The Application of Specific Point Energy Analysis to Laser Cutting with 1 μm Laser Radiation2014Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 56, s. 909-918Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Specific point energy (SPE) is a concept that has been successfully used in laser welding where SPE and power density determine penetration depth. This type of analysis allows the welding characteristics of different laser systems to be directly compared. This paper investigates if the SPE concept can usefully be applied to laser cutting. In order to provide data for the analysis laser cutting of various thicknesses of mild steel with a 2 kW fibre laser was carried out over a wide range of parameter combinations. It was found that the SPE concept is applicable to laser cutting within the range of parameters investigated here

  • 9.
    Ilar, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Eriksson, Ingemar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Root humping in laser welding: an investigation based on high speed imaging2012Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 39, s. 27-32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Regular drop formation (humping) along the weld root during laser welding was studied by high speed imaging of the melt pool underneath the workpiece. The formation of droplets towards the rear of this weld pool was seen to be primarily caused by the pumping of melt from the bottom of the keyhole and the influence of gravity drawing melt into a sagging hump. This is a different process from the one which creates humps on the top surface of welds.

  • 10.
    Jiang, Biao
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Castaño, Miguel
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Lindblad, Philip
    Öhman, Johan
    Ultrasonic Imaging Through Thin Reverberating Materials2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 70, s. 380-383Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Imaging through anisotropic or highly heterogeneous materials is challenging for the existence of strong boundary and volume reverberations. To image small cracks or flaws in a reverberating thin layers, high resolution techniques are needed in both temporal and spatial domain, so that the reverberation can be suppressed to some level. In this paper, the reverberation suppression performance of the total focusing beamforming method (TFM) was evaluated by simulation and real data processing. The results showed that the more the focusing point moves away from the array central line, the more multi-reflections can be suppressed. Furthermore, TFM combined with adaptive processing greatly improves the small flaw detection performance. Test results on real samples confirmed the robustness and reverberation suppression capability of the TFM imaging method.

  • 11.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Modelling the Primary Impact of an Yb:Fibre Laser Beam Profile on the Keyhole Front2011Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 12, nr 1, s. 627-637Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During laser materials processing the direct interaction between the laser beam and the processing zone essentially determines the process. A self-regulating processing front develops. A simplified mathematical model was applied to describe this first order mechanism. In particular, a high power Yb:fibre laser beam was characterized and modelled. The dependence of the keyhole shape on different beam models was studied. While a top-hat beam would cause a very different interaction, the impact from the more accurate beam model hardly differed from a Gaussian beam, as can be explained by interaction solely with selected peripheral domains of the beam.

  • 12.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    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 Map2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, s. 2-13Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 13.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Samarjy, Ramiz S.M.
    University of Mosul, College of Engineering, Department of Mechanical Engineering.
    CYCLAM: Recycling by a Laser-driven Drop Jet from Waste that Feeds AM2017Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, s. 187-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing of metal parts is supplied by powder or wire. Manufacturing of this raw material causes additional costs and environmental impact. A new technique is proposed where the feeding directly originates from a metal sheet, which can even be waste. When cutting is done by laser-induced boiling, melt is continuously ejected downwards underneath the sheet. The ejected melt is deposited as a track on a substrate, enabling additive manufacturing by substrate movement along a desired path. The melt first flows downwards as a column and after a few millimeters separates into drops, here about 500 micrometer in diameter, as observed by high speed imaging. The drops incorporate sequentially and calmly into a long melt pool on the substrate. While steel drops formed regular tracks on steel and aluminium substrates, on copper substrate periodic drops solidified instead. For this new technique, called CYCLAM, the laser beam acts indirectly while the drop jet becomes the main tool. From imaging, properties like the width or fluctuations of the drop jet can be statistically evaluated. Despite oscillation of the liquid column, the divergence of the drop jet remained small, improving the precision and robustness. The melt leaves the cut sheet as a liquid column, 1 to 4 mm in length, which periodically separates drops that are transferred as a liquid jet to the substrate. For very short distance of 2 to 3 mm between the two sheets this liquid column can transfer the melt continuously as a liquid bridge. This phenomenon was observed, as a variant of the technique, but the duration of the bridge was limited by fluid mechanic instabilities.

  • 14.
    Karlsson, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Markmann, Christoph
    Luleå tekniska universitet.
    Alam, Md. Minhaj
    Kaplan, Alexander
    Parameter influence on the laser weld geometry documented by the matrix flow chart2010Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, nr 2, s. 183-192Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 15.
    Keskitalo, M.
    et al.
    University of Oulu, University of Oulu, Oulu Southern Institute.
    Sundqvist, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Mäntyjärvi, Kari
    University of Oulu.
    Powell, John
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The Influence of Shielding Gas and Heat Input on the Mechanical Properties of Laser Welds in Ferritic Stainless Steel2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, s. 222-229Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser welding of ferritic steel in normal atmosphere gives rise to weld embrittlement and poor formability. This paper demonstrates that the addition of an argon gas shield to the welding process results in tough, formable welds. Post weld heat treatment and microscopic analysis has suggested that the poor ductility of welds produced without a gas shield is, to some extent, the result of the presence of oxides in the weld metal.

  • 16.
    Kong, Choon Yen
    et al.
    TWI Ltd., Granta Park, Great Abington, Cambridge .
    Bolut, M.
    TWI Ltd., Granta Park, Great Abington, Cambridge .
    Sundqvist, Jesper
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Assunção, E.
    EWF, Porto Salvo .
    Blackburn, J.
    TWI Ltd., Granta Park, Great Abington, Cambridge .
    Single-pulse Conduction Limited Laser Welding Using A Diffractive Optical Element2016Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 83, s. 1217-1222Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Conduction limited laser welding is commonly used in electronic and battery applications, where a high width-to-depth ratio weld is desirable. A laser beam with Gaussian or top-hat distributions is often used to produce conduction limited spot welds. Both these energy distributions result in a higher proportion of the laser beam energy being introduced towards the centre of the welded spot and consequently, a reduced penetration weld towards the circumference of the beam spot. The use of diffractive optical elements to tailor the energy distribution of the laser beam has been evaluated. An incident laser beam with an energy distribution in the shape of a ring or C-shape was projected onto the material, which results in heat propagating towards the centre, producing a shallow weld with a consistent depth of penetration across the entire overlapped joint. The results confirmed a corresponding thermal model which predicted an even distribution of heat at the joint interface

  • 17.
    Matti, Ramiz
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Analyzing and Post-modelling the High Speed Images of a Wavy Laser Induced Boiling Front2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, s. 192-201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The boiling front in laser materials processing like remote fusion cutting, keyhole welding or drilling can nowadays be recorded by high speed imaging. It was recently observed that bright waves flow down the front. Several complex physical mechanisms are associated with a stable laser-induced boiling front, like beam absorption, shadowing, heating, ablation pressure, fluid flow, etc. The evidence of dynamic phenomena from high speed imaging is closely linked to these phenomena. As a first step, the directly visible phenomena were classified and analyzed. This has led to the insight that the appearance of steady flow of the bright front peaks is a composition of many short flashing events of 20-50 μs duration, though composing a rather constant melt film flow downwards. Five geometrical front shapes of bright and dark domains were categorized, for example long inclined dark valleys. In addition, the special top and bottom regions of the front are distinguished. As a second step, a new method of post-modelling based on the greyscale variation of the images was applied, to approximately reconstruct the topology of the wavy front and subsequently to calculate the absorption across the front. Despite certain simplifications this kind of analysis provides a variety of additional information, including statistical analysis. In particular, the model could show the sensitivity of front waves to the formation of shadow domains and the robustness of fiber lasers to keep most of an irradiated steel surface in an absorptivity window between 35 to 43%.

  • 18.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Karlsson, Jan
    Classification and generalization of data from a fibre-laser hybrid welding case2010Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 5, nr 2, s. 69-76Artikkel i tidsskrift (Fagfellevurdert)
  • 19.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Karlsson, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Mechanisms forming undercuts during laser hybrid arc welding2011Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 12, nr 1, s. 201-207Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    That the final quality of a welded joint, using a laser hybrid arc process, is sensitive not only to the geometrical joint conditions, but also to the content of elements in the surface itself, is already known. However the description of the mechanisms forming undercut defects is still vague. In the following study two kinds of undercuts were identified. It is shown how the mill scales affects the melt motion and what mechanisms actuate the creation of the defects. The conclusion that surface oxides affect the severity of weld undercuts is straight forward but here also the mechanism is explained. Keywords: laser; hybrid; welding; mill scale; oxides; defects; undercut

  • 20.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Silver, Tore
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Hot-wire Laser Welding of Deep and Wide Gaps2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, s. 247-254Artikkel i tidsskrift (Fagfellevurdert)
  • 21.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Petring, Dirk
    Fraunhofer ILT, Steinbachstr. 15, Aachen.
    Powell, John
    Deichsel, Eckard
    Bystronic Laser AG, Industriestr. 21, Niederönz.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Measuring the Melt Flow on the Laser Cut Front2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, s. 99-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The flow characteristics on the laser cut front for 10 mm stainless steel AISI 304 (EN 1.4301) are studied in this paper using High Speed Imaging (HSI). The laser cut samples were produced with a 6 kW fiber laser with nitrogen gas assist. Previous work in this field has used unusual cutting parameters to make the experimentation easier. This work presents, for the first time, HSI results from standard commercially viable cutting parameters. This was made possible by the development of a new experimental technique. The results presented here suggest that the cut front produced when cutting stainless steel with a fiber laser and a nitrogen assist gas is covered in bumps which themselves are covered in a thin layer of liquid. Under the conditions shown here the bumps move down the cut front at an average speed of approximately 0.4m/s. The liquid flows at an average speed of approximately 1.1m/s. The average melt depth at the bottom of the cut zone under these conditions is approximately 0.17 mm.

  • 22. Powell, John
    et al.
    Lamas, J.
    Centro Tecnolóxico do Naval Galego, Ferrol.
    Karlsson, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Norman, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Yañez, A.
    Centro de Investigacións Tecnolóxicas, Universidade da Coruña, Ferrol.
    The sensitivity of hybrid laser welding to variations in workpiece position2011Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 12, nr 1, s. 188-193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High speed imaging has been used to analyze the sensitivity of the Hybrid laser welding process to variations in the laser-arcworkpiece geometry along the axis of the laser beam. The welding process was found to be stable within a certain range of workpiece positions. Outside of this range the process became unstable. If the workpiece was too close to the laser/arc combination, the two energy sources did not supplement each other sufficiently. If the workpiece was too far away the droplets from the arc interfered with the laser-keyhole interaction.

  • 23.
    Samarjy, Ramiz Saeed Matti
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Imaging of the Dynamic Melt Movement Induced by a Pulsed Laser2016Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 83, s. 1308-1318Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A special case of an interrupted superheated process was developed, governed by the ablation pressure of a boiling melt, induced by a pulsed Nd:YAG-laser. A kind of cutting process was carried out, but at very low speed to generate a large melt pool that can be well studied. The interaction zone was observed by high speed imaging, with and without illumination. When switching the laser pulse on or off, different dynamic phenomena can be clearly observed, like drilling into a bulk of melt, breaking of a melt bridge, controlled pushing of the melt pool, waves running down, all driven by boiling. After the pulse, the melt smoothens and oscillates and is dragged back upwards by the surface tension forces from the melt shape curvature, ending in a torus-like equilibrium shape. The fundamental understanding that was generated could be applied to improve processes like keyhole laser welding, laser remote fusion cutting or laser drilling

  • 24.
    Svennungsson, Josefine
    et al.
    University West, Department of Engineering Science, 461 32 Trollhättan.
    Choquet, Isabelle
    University West, Department of Engineering Science, 461 32 Trollhättan.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser Welding Process: A Review of Keyhole Welding Modelling2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, s. 182-191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser welding is used in several industrial applications. It can be distinguished between conduction mode and keyhole mode welding, between pulsed wave and cw laser welding and between CO2-lasers with a wavelength of 10 μm and various laser types of about 1 μm wavelength. A deeper understanding of laser welding allows improving weld quality, process control and process efficiency. It requires a complementary combination of precise modelling and experimental investigations. The here presented review focuses on modelling of laser keyhole welding, for both wavelength regimes. First, the fundamentals of the laser welding process and its physics such as beam propagation, keyhole formation and melt pool dynamics are addressed. The main approaches for modeling energy transfer from laser beam to keyhole surface as well as fluid flow in the material are then discussed. The most relevant publications are systematically structured, particularly categorized with regard to the respective physical phenomena addressed. Finally some open questions are underlined.

1 - 24 of 24
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