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  • 201.
    Kim, Kyounghak
    et al.
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Bang, Heeseon
    Department of Welding and Joining Science Engineering, Chosun University.
    Bang, Hansur
    Department of Welding and Joining Science Engineering, Chosun University.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Joint properties of ultra thin 430M2 ferritic stainless steel sheets by friction stir welding using pinless tool2017Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 243, s. 381-386Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, friction stir butt welding of ultra thin 430M2 ferritic stainless steel sheets with satisfactory joint properties has been achieved using a pinless WC-Co tool. Friction stir welding was carried out at a tool rotational speed of 900 rpm and a travel speed of 96 mm/min. FSW joints were welded completely without any unwelded zone resulting from smooth material flow, despite of being adopted pinless tool. It was revealed that the maximum tensile strength of FSW welds was 468 MPa, equivalent to the tensile strength of base metal. Notably, it was found that sigma phase formation in FSW welds is suppressed compared with that of arc welds, resulting in improving joint strength. These results suggest that the low input process of FSW is an effective substitute for the conventional fusion welding GTAW in ultra thin ferritic stainless steel plate.

  • 202. Koh, Y.S.
    et al.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser cleaning of corroded steel surfaces: A comparison with mechanical cleaning methods2005Inngår i: Lasers in the conservation of artworks: LACONA VI proceedings, Vienna, Austria, Sept. 21 - 25, 2005 / [ed] Johann Nimmrichter ; Wolfgang Kautek, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2005Konferansepaper (Fagfellevurdert)
  • 203.
    Koh, Y.S.
    et al.
    Kiruna Center for Conservation of Cultural Property.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Removal of layers of corrosion from steel surfaces: a qualitative comparison of laser methods and mechanical techniques2007Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 19, nr 2, s. 99-106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of steel substrates with precisely grooved surfaces were produced and subsequently corroded under controlled conditions. The oxidized surfaces were then cleaned by one of eight methods, three of which were mechanical (brushing, micro blasting with Al2O3 or glass) and five of which were laser dependent (TEA CO2 or Nd:YAG laser with or without surface water). Surface profilometry and scanning electron microscopy have been used to compare the cleaned surfaces with the original surface geometries. The relative efficacy of the eight cleaning methods has been qualitatively compared for three different types of grooved surface and three different levels of corrosion

  • 204. Koh, Y.S.
    et al.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The removal of layers of corrosion from steel surfaces: a comparison of laser methods and mechanical techniques2005Inngår i: 10th NOLAMP Conference: the 10th Nordic Laser Materials Processing Conference, 17-19 August 2005, Luleå Sweden / [ed] Alexander Kaplan, Luleå: Luleå tekniska universitet, 2005, s. 315-330Konferansepaper (Fagfellevurdert)
  • 205.
    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

  • 206. Koruk, A.I.
    et al.
    Hrivnak, I.
    Kaplan, Alexander
    Laser weldability of thin sheets1999Inngår i: Proceedings of the laser materials processing conference [: [November 15 - 18, 1999, Catamaran Resort Hotel, San Diego, CA, USA / [ed] Paul Denney, Orlando, Fla: Laser institute of America , 1999Konferansepaper (Fagfellevurdert)
  • 207.
    Lamas, Javier
    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.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Gap bridging for two modes of laser arc hybrid welding2015Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 224, s. 73-79Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 208.
    Lamas, Javier
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Centro Tecnolóxico do Naval Galego, Ferrol.
    Karlsson, Jan Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Norman, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Yañez, Armando
    The effect of fit-up geometry on melt flow and weld quality in laser hybrid welding2013Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 209.
    Lampa, Conny A.
    et al.
    Luleå tekniska universitet.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Resch, M.
    Vienna University of Technology.
    Magnusson, Claes
    Fluid flow and resolidification in deep penetration laser welding1998Inngår i: Lasers in engineering (Print), ISSN 0898-1507, E-ISSN 1029-029X, Vol. 7, nr 3-4, s. 241-253Artikkel i tidsskrift (Fagfellevurdert)
  • 210.
    Lampa, Conny
    et al.
    Luleå tekniska universitet.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Magnusson, Claes
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    The effect of process speed on energy redistribution in deep penetration CO2 laser welding2000Inngår i: High Temperature Material Processes, ISSN 1093-3611, E-ISSN 1940-4360, Vol. 4, nr 2, s. 213-225Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work discusses energy absorption mechanisms in CO2 laser welding and how they are affected by changes in the process speed. Two main energy absorption processes govern the welding interaction: 1. Fresnel absorption at the keyhole walls. 2. Absorption by the partially ionised metal vapour (or plasma) in the keyhole (laser energy absorbed in this way is re-radiated or conducted to the keyhole walls). A theoretical model of these absorption mechanisms has been developed and shown to agree closely with experimental results. Fresnel absorption has been identified as being dominant over plasma absorption and becomes even more influential as welding speeds are increased

  • 211. Lampa, Conny
    et al.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Magnusson, Claes
    An analytical model of laser keyhole welding1997Inngår i: Proceedings of the 6th Nordic Laser Material Processing Conference, Luleå, Sweden, August 27-29, 1997 / [ed] Claes Magnusson; Hans Engström, Luleå: Luleå tekniska universitet, 1997, s. 218-225Konferansepaper (Fagfellevurdert)
  • 212.
    Lampa, Conny
    et al.
    Luleå tekniska universitet.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    An analytical thermodynamic model of laser welding1997Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 30, nr 9, s. 1293-1299Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An earlier model of deep-penetration laser welding has been simplified in order to provide a useful model of process analysis. This work involves the modelling of the various energy-absorption mechanisms which determine the keyhole shape and thus the dimensions of the melt pool. The penetration depth and weld width (top and bottom) predicted by the model are shown to be in close agreement with experimental results. The widening of the top of the weld seam as a result of Marangoni flow is accurately modelled by introducing an artificially enhanced value for the workpiece's thermal conductivity towards the top of the weld. The model allows analysis of the dependence of the weld profile on the process parameters

  • 213.
    Liedl, G.
    et al.
    Forschungsinstitut für Hochleistungsstrahltechnik, University of Technology, Vienna.
    Schröder, K.
    Forschungsinstitut für Hochleistungsstrahltechnik, University of Technology, Vienna.
    Kaplan, Alexander
    Excimer laser processing of ferrite video heads1996Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 106, nr 2, s. 374-378Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The technology of pulsed excimer laser ablation for processing ferrite video heads at 248 nm KrF laser radiation was studied. Using the mask imaging technique two trapezoids were projected onto the surface of the samples producing laser-etched grooves with a depth of approximately 45 μm. A sufficiently sharp contour of the trapezoids was achieved at the workpiece. Since the variations of the critical dimensions with respect to depth were outside the tolerance range the sample was slightly tilted to compensate for the beam divergence and to obtain parallel edges of the trapezoidal grooves with an error of less than 5 μm over the whole depth of the cavities. Micrographs of the samples showed that the surfaces of the laser-etched video heads were covered with ablated material and small droplets of resolidified material. These sediments can be removed easily by a slight polishing of the surface. For the experiments a typical fluence of 5 J/cm2 was used which allowed etch rates of 50 nm per pulse. The work showed that excimer lasers are useful tools for the precise micromachining of ferrite video heads.

  • 214.
    Löthman, J.
    et al.
    Wire Sandviken AB.
    Hedegård, J.
    Swerea KIMAB AB.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Avoiding porosity and spatter in hot-dip galvanized C-Mn steels by laser twin-spot welding2010Inngår i: Istanbul IIW 2010: Proceedings of the International Conference on Advances in Welding Science & Technology for Construction, Energy & Transportation, AWST 2010, Swissôtel "The Bosphorus", Istanbul/Turkey, from July 15 - 16. July, 2010 : is being held in conjunktion with the 63rd Annual Assembly & International Conference of the International Institute of Welding / [ed] Mustafa Kocak, Istanbul: Ridgeview Publishing Company, 2010, s. 325-329Konferansepaper (Fagfellevurdert)
    Abstract [en]

    During welding of zinc-coated materials, zinc trapped in the overlap of a lap joint expands violently because of vaporization, and therefore disturbs the laser keyhole. Laser twin-spot welding is a new approach for welding of thin sheet C-Mn steel. The dual beam principle creates a larger and more stabilized weld pool. Therefore welding of galvanized zero gap lap joints becomes possible. This opens a new joining approach for automotive and other industries to perform high speed laser welding. The possibility to laser weld steels with 20 μm zinc coating thickness with high speed and high quality is a technical breakthrough

  • 215.
    Matti, Ramiz
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Ilar, Torbjörn
    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 laser remote fusion cutting based on a mathematical model2013Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, nr 23, artikkel-id 233107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser remote fusion cutting is analyzed by the aid of a semi-analytical mathematical model of the processing front. By local calculation of the energy balance between the absorbed laser beam and the heat losses, the three-dimensional vaporization front can be calculated. Based on an empirical model for the melt flow field, from a mass balance, the melt film and the melting front can be derived, however only in a simplified manner and for quasi-steady state conditions. Front waviness and multiple reflections are not modelled. The model enables to compare the similarities, differences, and limits between laser remote fusion cutting, laser remote ablation cutting, and even laser keyhole welding. In contrast to the upper part of the vaporization front, the major part only slightly varies with respect to heat flux, laser power density, absorptivity, and angle of front inclination. Statistical analysis shows that for high cutting speed, the domains of high laser power density contribute much more to the formation of the front than for low speed. The semi-analytical modelling approach offers flexibility to simplify part of the process physics while, for example, sophisticated modelling of the complex focused fibre-guided laser beam is taken into account to enable deeper analysis of the beam interaction. Mechanisms like recast layer generation, absorptivity at a wavy processing front, and melt film formation are studied too.

  • 216.
    Matti, Ramiz
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Modelling the cutting geometry for laser remote fusion cutting of metals2013Inngår i: 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, s. 121-132Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The high brilliance fibre and disc lasers that were developed during the last decade providelong range focusing that enables remote laser techniques without assist gas, including remotelaser welding and cutting. In combination with industrial robots these lasers offer industry ahighly flexible production solution, including quick positioning with scanner optics across aworkpiece. The paper presents the state of the art in the field of remote metal cutting with thefocus on analytical models and the physical process analyses. Several remote cuttingtechniques can be distinguished, in particular remote ablation cutting, remote fusion cuttingand remote gravity cutting. The three-dimensional cutting process and kerf geometry isconcluded to an extensive impact on the melted metal flow and the cutting processperformance. A semi-analytical mathematical model has been developed that enables tocalculate and analyse the cutting front with respect to absorption, heat conduction, recoilpressure and melt film flow. Beside analysing the remote laser fusion cutting process, theregimes and their transitions from remote fusion cutting to keyhole laser

    Fulltekst (pdf)
    FULLTEXT01
  • 217.
    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.
    Analysis of moving surface structures at a laser-induced boiling front2014Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 317, s. 560-567Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20-50 μs. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.

  • 218.
    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%.

  • 219.
    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.
    Basic imaging and modelling analysis of the processing front in laser remote fusion cutting2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The nature of the front surface in laser welding and laser remote fusion cutting is of importance. Both processes have in common that their front is governed by the ablation pressure from laser-induced surface boiling. The geometry of the front is calculated by a simplified analytical model, through local calculation of an energy balance between the absorbed laser beam and heat losses, neglected multiple beam scattering. From high speed imaging of the front a pattern can be seen, moving downwards. The pattern is interpreted as mass movement of topology along with temperature variations. In combination with modelling of the front shape, applying simplifying assumptions the greyscale variation of the images were converted to a three-dimensional wavy surface of the front in remote fusion cutting. This modelled geometry including the topology enabled sophisticated analysis regarding the distribution of the angles of beam incidence, absorptivity and absorption in combination with beam projection. The analysis enabled to study sub-trends like roughness sensitivity, shadow regimes, time dependence and separation or combination of peaks and valleys. Statistical analysis by frequency polygons enabled to clearly identify certain trends, despite the very complex front topology and movement.When correlating the angle dependent Fresnel-absorptivity characteristics with the steep main inclination angle of the processing front, conclusions on the sensitivity of the front with respect to a wavy topology can be made. For remote cutting of stainless steel with a fibre laser, in one studied case about 25% of the surface were shadow domains, 15% of the surface had so glancing angles of incidence that the absorptivity became strongly modulated between 0-35%, while most of the surface, namely 60% remained in a narrow absorptivity window of 35-43%. This very robust behaviour is likely to take place for most parameter combinations, demonstrating a very typical and predictable absorption behaviour of lasers with about 1 μm wavelength.Keywords: absorptivity, laser remote fusion cutting, high speed imaging, modelling, front topology.

    Fulltekst (pdf)
    FULLTEXT01
  • 220.
    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.
    Post-modelling of images from a laser-induced wavy boiling front2015Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 357, nr B, s. 2277-2284Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Processes like laser keyhole welding, remote fusion laser cutting or laser drilling are governed by a highly dynamic wavy boiling front that was recently recorded by ultra-high speed imaging. A new approach has now been established by post-modelling of the high speed images. Based on the image greyscale and on a cavity model the three-dimensional front topology is reconstructed. As a second step the Fresnel absorptivity modulation across the wavy front is calculated, combined with the local projection of the laser beam. Frequency polygons enable additional analysis of the statistical variations of the properties across the front. Trends like shadow formation and time dependency can be studied, locally and for the whole front. Despite strong topology modulation in space and time, for lasers with 1 μm wavelength and steel the absorptivity is bounded to a narrow range of 35–43%, owing to its Fresnel characteristics.

  • 221.
    Mishra, Pragya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Energy efficiency contributions and losses during selective laser melting2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikkel-id 032304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Selective Laser Melting technique, SLM, requires remelting of adjacent tracks to avoid cavities and other imperfections. Usually, very conservative process parameters are chosen to avoid imperfections, resulting in a low building rate. The process efficiency relates the energy required for the generation of a new track to the laser beam power. For SLM this efficiency is determined by the process parameters, specifically hatch distance, layer depth and scanning speed, independent of the resulting process mechanisms. For SLM the process efficiency often very low, typically 2‑20%. Apart from beam reflection losses of normally 50-60%, significant energy losses result from the remelting of surrounding layers. Some areas can even experience multiple remelting cycles. Further losses originate inevitably from substrate heating. A simplified mathematical model of the track cross section and the corresponding layer overlap geometry has been developed, to analyze the different loss contributions from remelting with respect to the process parameters. The model explains why increasing the hatch distance or the layer depth proportionally increases the process efficiency. However, these increases are limited by cavity formation. The cross section of the overlapping tracks generated by SLM can be regarded as an experimental fingerprint linked to the process conditions. The track cross section geometries can significantly fluctuate, in terms of area and coordinate position. The fluctuations require additional reduction of the hatch distance or layer depth, to ensure robust, cavity-free processing. Examples are presented for stainless steel where a 180 W laser beam has led to a process efficiency of 5-11%, proportional to a hatch distance that was increased from 50 to 110 µm, for 40 µm powder layer depth, at a speed of 50 m/min.

  • 222.
    Moradi, Mahmoud
    et al.
    Department of Mechanical Engineering, Faculty of Engineering, Malayer University, Malayer, Iran. Laser Materials Processing Research CentreMalayer University, Malayer, Iran.
    Arabi, Hossein
    Department of Mechanical Engineering, Faculty of Engineering, Malayer University, Malayer, Iran. Laser Materials Processing Research CentreMalayer University, Malayer, Iran.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    An experimental investigation of the effects of diode laser surface hardening of AISI 410 stainless steel and comparison with furnace hardening heat treatment2019Inngår i: Journal of the Brazilian Society of Mechanical Sciences and Engineering, ISSN 1678-5878, E-ISSN 1806-3691, Vol. 41, nr 10, artikkel-id 434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study investigated the ability of the continuous wave diode laser surface hardening of AISI 410 martensitic stainless steel with a maximum power of 1600 W. Variable process parameters scanning speed (4–7 mm/s), laser power (1200–1600 W) and stand-off distance (65–75 mm) were considered in this study. Microhardness, the geometry of hardened layer (depth and width), microhardness deviation from the base metal microhardness (MHD), microstructure analysis of the laser-hardened zone through optical microscopy and field emission scanning electron microscopy and percentage of the ferrite phase in AISI 410 microstructure by using Clemex software were considered as process output responses. Results confirmed that by increasing the laser power and reducing the scanning speed, the surface hardness and the depth of hardness increase. It is also revealed the width of the hardened area increases by enhancing stand-off distance and reducing the laser power. Maximum hardness of 630 HV0.3 with 2.2 mm depth is obtained. Also, the furnace hardening heat treatment is compared with the laser hardening process. Microstructure, microhardness, and impact tests of the two processes are compared. Results showed that the hardness of the diode laser is 1.4 times the hardness of the furnace hardening heat treatment.

  • 223.
    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 tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    An investigation on stability of laser hybrid arc welding2013Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 51, nr 4, s. 481-487Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 224.
    Moradi, Mahmoud
    et al.
    Department of Mechanical Engineering, Faculty of Engineering, Malayer University, Malayer, Iran.
    Meiabadi, Saleh
    Department of Mechanical Engineering, École de Technologie Supérieure, Montreal, Canada.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    3D Printed Parts with Honeycomb Internal Pattern by Fused Deposition Modelling: Experimental Characterization and Production Optimization2019Inngår i: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 25, nr 5, s. 1312-1325Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study additive manufacturing of Polylactic acid by fused deposition modeling were investigated based on statistical analysis. The honeycomb internal pattern was employed to build inside of specimens due to its remarkable capability to resist mechanical loads. Simplify 3D was utilized to slice the 3D model and to adjust fixed parameters. Layer thickness, infill percentage, and extruder temperature were considered as controlled variables, while maximum failure load (N), elongation at break (mm), part weight (g), and build time (min) were selected as output responses and analysed by response surface method. Analysis of variance results identified layer thickness as the major controlled variable for all responses. Interaction of infill percentage and extruder temperature had a significant influence on elongation at break and therefore, tough fracture of printed parts. The input parameters were optimized to materialize tow criteria; the first one was to rise maximum failure load and the second was to attain tough fracture and lessen build time and part weight at a time. Optimal solutions were examined by experimental fabrication to evaluate the efficiency of the optimization method. There was a good agreement between empirical results and response surface method predictions which confirmed the reliability of predictive models. The optimal setting to fulfill the first criterion could bring on a specimen with more than 1500 (N) maximum failure load and less than 9 (g) weight.

  • 225.
    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 tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Parameter dependencies in laser hybrid arc welding by design of experiments and by a mass balance2014Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 2, artikkel-id 22004Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 226.
    Nilsson, Klas
    et al.
    Luleå tekniska universitet.
    Engström, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Heimbs, Sebastian
    University of Kaiserslautern.
    Kaplan, Alexander
    Parameter Influence in CO2-laser/MIG Hybrid Welding2003Inngår i: 56th Annual assembly of International Institute of Welding, 2003, Vol. IIW Doc. IV-843-03Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Hybrid welding, as the combination of laser beam and arc welding, is an innovative joining technology that has many advantages compared to the single processes. With the hybrid process joint gap can overbridges and hence additional and costly joint preparation can be avoided. Also the weld metal composition can be controlled by the filler wire. The laser/MIG hybrid welding pårocess is up to 50 % faster compare to autogenous laser welding. This paper presents results from an ongoing investigation into laser/MIG hybrid welding of 6 mm thick, high strength steels.The results include welding parameters for a 6 kW CO2-laser combined with conventional pulsed MIG/MAG equipment. The influences of the basic MIG parameters as the voltage, pulsing time and pulsing frequency on the welding result were investigated, where especially the geometry of the weld seams as well as undercut formation is considered. The influence of the welding result by adjusting the lateral position of laser beam and MIG arc was also examined as well as suitable parameter setup for different joint configurations like V- and butt joints. In the case of butt joint, the maximum bridgeable gap width was determined.It was found that the MIG power has a major influence at the weld geometry. A high MIG power leads to increased undercut size and increased porosity. The variation of the lateral displacement of the MIG arc was shown to be tolerant. It can be stated that a variation of the lateral displacement of 1.5 mm gave still acceptable welding results. It was possible to weld butt joints with a gap of up to 2.0 mm and a maximum in welding speed was reached with a gap of 1.0 mm.

    Fulltekst (pdf)
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  • 227.
    Nilsson, Klas
    et al.
    Luleå tekniska universitet.
    Engström, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Influence of butt and T-joint preparation in laser arc hybrid welding2002Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Using a hybrid CO2 laser/MAG welding process, the weldability of butt and T joints (fillet welds) in mild steel (0.056%C, 0.61%Mn) plate of 8 mm thickness, as received from laser or mechanical cutting, was investigated. A 6 or 17 kW laser was used in conjunction with a conventional MIG/MAG welding gun and a mixture of helium and argon with carbon dioxide or oxygen as the shielding gas. Ranges of welding speeds, wire feed rates, stick out, welding current and voltages, arc to laser beam distances, and shielding gas compositions were used. The welds were assessed by appearance and shape, and by measurements of tensile, impact and bending properties

  • 228.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Bäckström, Mikael
    Luleå tekniska universitet.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Svoboda, Ales
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    A sophisticated platform for characterization, monitoring and control of machining2006Inngår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, nr 4, s. 847-854Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The potential for improving the performance of machine tools is considerable. However, for this to be achieved without tool failure or product damage, the process must be sufficiently well understood to enable real-time monitoring and control to be applied. A unique sophisticated measurement platform has been developed and applied to two different machining centres, particularly for high-speed machining up to 24 000 rpm. Characterization and on-line monitoring of the dynamic behaviour of the machining processes has been carried out using both contact-based methods (accelerometer, force sensor) and non-contact methods (laser Doppler vibrometry and magnetic shaker) and numerical simulation (finite element based modal analysis). The platform was applied both pre-process and on-line for studying an aluminium testpiece based on a thin-walled aerospace component. Stability lobe diagrams for this specific machine/component combination were generated allowing selection of optimal process parameters giving stable cutting and metal removal rates some 8-10 times higher than those possible in unstable machining. Based on dynamic characterization and monitoring, a concept for an adaptive control with constraints based machine tool controller has been developed. The developed platform can be applied in manifold machining situations. It offers a reliable way of achieving significant process improvement

  • 229.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Engström, Hans
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Kaplan, Alexander
    Correlation between photodiode monitoring and high speed imaging of the dynamics causing laser welding defects2008Inngår i: Congress proceedings: ICALEO, 27th International Congress on Applications of Lasers and Electro-Optics : October 20 - 23, 2008 Pechanga Resort & Casino, Temecula, CA, USA ; [includes] Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference / [ed] Yongfeng Lu, Orlando, Fla: Laser institute of America , 2008, s. 829-837Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Today merely a few monitoring systems for in-process detection of laser welding defects are commercially available. Despite a trend towards cameras, industrially more robust is still a photodiode, measuring in an optically filtered spectral window either the thermal emissions from the melt and vapour or the laser beam reflections. The monitoring rule for each application is identified empirically through correlations between the signal dynamics and welding defects, as the linking mechanism is non-trivial and therefore hardly understood. Thus the method does not provide a systematic guideline to detect a certain welding defect.The here presented approach studies the context between the photodiode signal, the welding defects and the vapour, melt pool, keyhole and temperature dynamics. Simultaneous laser-illuminated high speed imaging is compared to photodiode monitoring at three spectral windows in order to identify through simultaneous timing any linking dynamics in a qualitative manner. Supportive methods are emission modelling and thermal imaging. Several cases of joints, materials and defects were studied to develop an illustrated theoretical description of the defect-signal correlations.

    Fulltekst (pdf)
    FULLTEXT01
  • 230.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Engström, Hans
    Kaplan, Alexander
    State-of-the-art of monitoring and imaging of laser welding defects2007Inngår i: 11th NOLAMP Conference :: 11th NOLAMP Conference in Laser Processing of Materials ; Lappeenranta, August 20 - 22, 2007 / [ed] Veli Kujanpää, Lappeenranta: Lappeenranta University of Technology Press, 2007Konferansepaper (Fagfellevurdert)
  • 231. Norman, Peter
    et al.
    Engström, Hans
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Theoretical analysis of photodiode monitoring of laser welding defects by imaging combined with modelling2008Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, nr 19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On-line process monitoring of laser welding defects by detecting characteristic changes of the process emissions via photodiodes has high potential but, due to the complex process, lack of directly interpretable and thus controllable correlations. Deep analysis of the process by high speed imaging in combination with modelling enables one to discuss the correlations between the signal and the process, as was demonstrated for quasi-steady state conditions and for transient phenomena. Despite improved knowledge through the study, several uncertainties like the emissivity, the keyhole radiation characteristics and the temperature field need to be identified more accurately for a complete theoretical description of the signal causes.

  • 232. Norman, Peter
    et al.
    Eriksson, Ingemar
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Monitoring laser beam welding of zinc coated sheet metal to analyze the defects occurring2009Inngår i: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    During laser welding of overlapping zinc-coated steel sheets typically blowouts as a defect can occur. They can be crucial to the mechanical performance and to the optical appearance of the product. In the present research approved regions are compared to regions where the blowouts are in majority. Time-dependent radiation is captured with a commercial photodiode monitoring system in three different wavelengths ranges, 400-600 nm, 1100-1800 nm and 1064 nm, corresponding to metal vapour emissions, surface temperature emissions and reflected laser light, respectively. Accompanying high speed imaging as well as mathematical modelling of the process emissions was carried out, enabling combined analysis. Different gap widths and laser beam positions were studied. From imaging, surface elevations of the melt indicate a Zn-bubble formation that travels to the rear part of the melt pool before it breaks through, often completely separated from the keyhole. The escaping vapour ejects melt and causes a significant crater, if not flooded with melt again. Although this violent surface event is clearly visible, it was hardly found in the temperature sensor signal. The separate mechanisms that can be responsible for the lack of contribution of the dynamic blow-out formation to the emissions generating the photodiode signal are discussed, e.g. melt surface geometry changes, drops, temperature and emissivity changes, the role of the Znvapour and the detection area of the sensor. This study demonstrates that obvious defects can sometimes be hard to detect on-line.

    Fulltekst (pdf)
    FULLTEXT01
  • 233.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Engström, Hans
    Modelling of the impact of melt surface dyanmics on a photodiode monitoring signal in laser welding2007Inngår i: Congress proceedings: 2007 ICALEO, 26th International Congress on Applications of Lasers & Electro-Optics : October 29 - November 1, 2007, Hilton in the Walt Disney World Resort, Orlando, FL, USA ; [including] Laser Materials Processing Conference, Laser Microprocessing Conference [and] Nanomanufacturing Conference / [ed] Yongfeng Lu, Laser institute of America , 2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Today merely a few monitoring systems for inprocess detection of laser welding defects are commercially available. Despite a trend towards cameras, the industrially most powerful concept is still a photodiode with optical filter, measuring thermal emissions from the melt surface and from the plasma or laser beam reflections. The monitoring rule for each application is identified empirically through temporal correlations between dynamic signal changes and obtained welding defects. The mechanisms behind are widely not understood. Thus the method does not provide a systematic estimation of success for identifying a certain welding defect. The here presented research approach studies the context between welding defects, the physical mechanisms behind, particularly the dynamics of melt pool, plasma and temperature field, and the photodiode signal. Numerical simulation results of the thermal emissions from the weld pool and keyhole dynamics and their non-linear conversion into a voltage signal are presented. An essential outcome is the sensitivity of the sensor signal to certain sub-mechanisms of the motion for judging under which conditions they can be monitored. Various results are discussed for simplified hypothetic cases as well as for observed weld pool dynamics of practical relevance.

  • 234.
    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)
    Fulltekst (pdf)
    FULLTEXT01
  • 235.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Svenningsson, Inge
    AB Sandvik Coromant, Sandviken.
    Study of a sensor platform for monitoring machining of aluminium and steel2007Inngår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 18, nr 5, s. 1155-1166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Being able to measure and monitor the forces applied and the resulting vibrations is important to be able to understand and control the process of milling, which is a highly interrupted process based on many variables. The present work concerns analysis of signals gathered during shoulder milling of toughened steel 2541-3 and aluminium alloy 7010. The signals acquired are force in three dimensions and accelerometer in the two horizontal dimensions. Moreover, a laser Doppler vibrometer is applied. The correlations of the analysed signals of the different sensors with the surface roughness were studied. While the signal stability and correlation were unsatisfactory for several sensors, the three sensors measuring along the feed direction were most suitable to monitor the increase of the machined surface roughness with increasing feed rate

  • 236.
    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

  • 237.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Karlsson, Jan
    Kaplan, Alexander
    Monitoring undercut, blowouts and root sagging during laser beam welding2009Inngår i: Lasers in Manufacturing 2009: proceedings of the Fifth International WLT-Conference Lasers in Manufacturing, LIM 2009 : Munich, Germany, June 15th - 18th, 2009 / [ed] Andreas Ostendorf, Stuttgart: Gabler Verlag/GWV Fachverlage GmbH, 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Using a 14 kW CO2-laser, 12mm thick cold-formed steel S420MC has been welded to a machined shaft pivot made of 25CrMo4 steel as part of a truck rear axel. A photodiode-based, on-line process monitoring system has been applied for detecting defects. However, the occurrence of certain defects, namely undercut, blowouts and root sagging is often not detectable from the sensor signal. The time dependent signal is collected from emissions from the melt pool surface as well as from the plasma plume. Based on the evaluation of high speed images, an explanation of the potential and limitations of detection of these defects has been generated. Although preliminary conclusions have been drawn, uncertainties regarding emissivity and the keyhole and plasma radiation characteristics require further studies.

    Fulltekst (pdf)
    FULLTEXT01
  • 238.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Svenningsson, Inge
    Kaplan, Alexander
    Monitoring of the machining process for aluminium and steel2006Inngår i: Proceedings, 10th International Research/Expert Conference, Trends in the Development of Machinery and Associated Technology: TMT 2006, 2006Konferansepaper (Fagfellevurdert)
  • 239.
    Norman, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Wiklund, Greger
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Janiak, P.
    Swerea KIMAB AB.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Comparison of 22MnB5-steel with and without AlSi-coating during laser hybrid arc welding2011Inngår i: 13th NOLAMP Conference: 13th Conference on Laser Materials Processing in the Nordic Countries 27 - 29 June 2011 / [ed] Einar Halmøy, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    22MnB5/Usibor1500 is a hot-dip aluminized manganese-boron steel grade that is used withinthe car manufacturing industry and as lasers are increasingly used for welding of the car bodythe amount of research concerning laser welding of this material follows. For thicker materialthe laser hybrid arc welding process has grown to a well-known tool to increase productivity,but for thinner materials the advantages are less obvious. In the present research the melt pooland wire drop transfer was observed with a high speed camera. Differences between welding,with and without the coating were clearly visible and are described and discussed in the paper.The resulting welds were examined microscopically and chemically to unveil the compositionof the material. It is aimed to avoid possible brittle inter-metallic phases directly during theprocess, hence by skipping the usual additional manufacturing step of removing the AlSicoatingin advance.

    Fulltekst (pdf)
    FULLTEXT01
  • 240.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    A near-vertical approach to Laser Narrow Gap Multi-Layer Welding2020Inngår i: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 121, artikkel-id 105798Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 241.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser enhancement of wire arc additive manufacturing2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022307Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 242.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, IWS, Dresden, Germany.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Measuring the effects of a laser beam on melt pool fluctuation in arc additive manufacturing2019Inngår i: Rapid prototyping journal, ISSN 1355-2546, E-ISSN 1758-7670, Vol. 25, nr 3, s. 488-495Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose

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

    Design/methodology/approach

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

    Findings

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

    Originality/value

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

  • 243.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, IWS, Germany.
    Kaplan, Alexander F.H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Imperfections in narrow gap multi-layer welding: Potential causes and countermeasures2020Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 129, artikkel-id 106011Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Narrow Gap Multi-Layer Welding (NGMLW) using a laser as the main heat source and metal wire for material addition has been a growing topic of interest in the last decade. This is in part due to its potential for joining much thicker sheets of steel than what is usually considered possible when using autogenous laser welding. The process has shown great potential but improvements can still be made, e.g. through increased process control to decrease welding imperfections. Using closed-loop control, where the process is continuously monitored and regulated automatically, can help to account for variations during manufacturing. However, achieving functional closed loop control can be challenging due to limitations in data gathering and processing speeds. Important initial steps include identifying what data can be useful and how frequently this data has to be recorded. Too much data takes too long to process while too little causes risks of missing important details. In this study, 20 mm thick X80 pipeline steel sheets are joined together using this multi-layer approach; the samples are examined using 3D scanning and Computed Tomography (CT) analysis and the process is observed using High-Speed Imaging (HSI). The quality of the welded joint and welding imperfections are discussed and potential points of formation are identified. Suggestions on how to mitigate imperfections to improve the quality of the welded joint are presented, including the potential to use camera imaging for closed-loop process control and additional industrial uses of the HSI footage.

  • 244.
    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.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Arc formation in narrow gap hot wire laser welding2018Inngår i: Welding Journal, ISSN 0043-2296, Vol. 97, nr 6, s. 171S-178SArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 245.
    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.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Multipass laser hot-wire welding: Morphology and process robustness2017Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 29, nr 2, artikkel-id 022014lArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 246.
    Olsson, Rickard
    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.
    Advances in pulsed laser weld monitoring by the statistical analysis of reflected light2011Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 49, nr 11, s. 1352-1359Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes two new techniques for monitoring the quality of laser welds by statistical analysis of the reflected light signal from the weld surface. The first technique involves an algorithm that analyses the variance of the peak values of the reflected signal as a measure of the stability of the surface during pulsed Nd:YAG laser welding in the heat conduction mode. Kalman filtering is used to separate a useful signal from the background noise. A good correlation between weld disruption and signal fluctuation has been identified. This technique could be used in tandem with the present practice of simply using the peak values of reflected (or emitted) light as an indicator of weld quality. The second technique investigated involves an assessment of the temporal shape of the power distribution of individual reflected pulses in comparison with an average of the results from a high quality weld. Once again a high correlation between a poor signal match and inferior quality welding was discovered, which may pave the way towards a new generation of optical weld monitoring devices.

  • 247. Olsson, Rickard
    et al.
    Eriksson, Ingemar
    Powell, John
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Pulsed laser weld quality monitoring by the statistical analysis of reflected light2009Inngår i: Lasers in manufacturing 2009: proceedings of the Fifth International WLT-Conference Lasers in Manufacturing, LIM 2009 : Munich, Germany, June 15th - 18th, 2009 / [ed] Andreas Ostendorf, Stuttgart: AT-Fachverlag , 2009, s. 369-374Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper describes a technique for monitoring the quality of laser welds by statistical analysis of the reflected light signal from the weld surface. An algorithm is used which analyses the variance of the peak values of the reflected signal as a measure of surface weld dynamics during pulsed Nd:YAG laser welding in the heat conduction mode. Kalman filtering is used to separate a useful signal from the background noise. A good correlation between weld disruption and signal fluctuation has been identified. This technique could be used in tandem with the present practice of simply using the peak values of the reflected (or emitted) light as an indicator of weld quality.

    Fulltekst (pdf)
    FULLTEXT01
  • 248.
    Olsson, Rickard
    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
    Langtry, A.V.
    GE Healthcare, Oxford.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Challenges to the interpretation of the electromagnetic feedback from laser welding2011Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 49, nr 2, s. 188-194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper considers the point that it is not possible to interpret individual weld perturbations from the raw electromagnetic feedback collected from laser weld zones. The presentation of electromagnetic data as a 3D cloud is presented as a new, useful tool in the analysis of this feedback. It is shown that there is a very low correlation between the plasma or thermal signals and the reflected light signal from the weld zone, and that a strong correlation exists between the plasma and thermal signals. It is also demonstrated that data points from a weld perturbation form a different 3D cluster to those from the stable welding process. A strategy for future real time data analysis is presented utilising a suitably shaped data cloud envelope. The rates of data fit to the various segments of such an envelope could be correlated with specific weld anomalies.

  • 249.
    Olsson, Rickard
    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
    Langtry, A.V.
    GE Healthcare, Oxford.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Studies in the interpretation of the reflected feedback from laser welding2010Inngår i: Congress proceedings ICALEO: 29th International Congress on Applications of Lasers & Electro-Optics : September 26 - 30, 2010, Anaheim, CA, USA, [including] Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference / [ed] Xinbing Liu, Anaheim, CA: Laser institute of America , 2010, s. 191-199Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates two methods of monitoring the laser welding process by statistical analysis of the reflected laser light signal. It has been discovered that statistical data analysis reveals more about perturbations in the welding process than the simple upper and lower threshold limits which are in common use today. This work indicates the way forward for the development of the next generation of laser processing monitoring equipment

  • 250.
    Olsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Nova AB.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Palmquist, A.
    Department of Biomaterials, University of Gothenburg.
    Brånemark, R.
    Department of Orthopaedic Surgery, University of California, San Francisco.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The production of osseointegrating (bone bonding) surfaces on titanium screws by laser melt disruption.2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 4, artikkel-id 042009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several techniques can be used to modify implant surfaces in order to accelerate bone growth around titanium implants. One method is to generate a surface structure which stimulates bone growth and remodelling. This paper describes and explains a non-ablative method for producing osseointegrating (structural and functional bone bonding) surfaces on titanium implants using laser processing. The focus is especially on surface texturing of dental implant screws, where the ability of a Nd:YAG laser to generate ‘splashy’ surfaces covered in resolidified micro scale droplets coated with nano-scale surface oxides is assessed. The surfaces produced were analysed by scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS). It is concluded that laser processing using Q-pulsed Nd:YAG lasers can generate surfaces which match the demands set by clinical experience. One important characteristic of the surfaces discussed here is that they involve overhanging features which are suitable for trapping red blood cells and which cannot be created by mechanical or chemical roughening techniques.

234567 201 - 250 of 325
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