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  • 1.
    Abrahamsson, Lena
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Johansson, Jan
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Rask, Kjell
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Fältholm, Ylva
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Bergquist, Bjarne
    Projekt: LUPO - globala länkar2010Other (Other (popular science, discussion, etc.))
  • 2.
    Akselsen, Odd M.
    et al.
    SINTEF, Trondheim.
    Wiklund, Greger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Østby, Erling
    SINTEF, Trondheim.
    Sörgjärd, Arve
    Kværner Verdal.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    A first assessment of laser hybrid welding of 420 mpa steel for offshore structure application2013In: 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden / [ed] Alexander Kaplan; Hans Engström, Luleå: Luleå tekniska universitet, 2013, p. 171-182Conference paper (Other academic)
    Abstract [en]

    For many years, laser hybrid welding has been used in various industries to increaseproductivity and reduce costs. One example is the adaption of the hybrid process inshipbuilding. The next natural step is to further develop the process for the oil and gasindustry, where the welded joint properties requirements are more severe, and the ability tohandle tolerance deviations is more critical. As a first attempt to develop hybrid laser processfor the use in offshore structures, the present investigation addresses preliminary weldingtrails carried out with 15 kW fibre laser with appropriate gas metal arc welding equipment,using double Y joint geometry and 20 mm thick 420 MPa steel plates. The subsequent weldtesting included both Charpy V notch impact and CTOD fracture mechanical testing at -30°C.The results indicate that the heat affected zone (HAZ) of the examined steel appeared withsatisfactory Charpy and CTOD toughness (> 200 J, > 0.2 mm) while the weld metal hadinsufficient toughness (20-40 J, < 0.2 mm). With a better welding wire, designed for lowtemperature applications, it is reasonable to suggest that laser hybrid arc welding can be usedfor applications even below a temperature of -30°C.

  • 3.
    Akselsen, Odd Magne
    et al.
    SINTEF, Trondheim.
    Wiklund, Greger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Østby, Erling
    SINTEF, Trondheim.
    Sørgjerd, Arve
    Kværner Verdal.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Properties of laser hybrid butt welds of 420 MPa steel2013In: The proceedings of the Twenty-third (2013) International Offshore and Polar Engineering Conference: Anchorage, Alaska, June 30-July 5, 2013 : ISOPE-2013 Anchorage / [ed] Jin S. Chung, Cupertino, Calif.: International Society of Offshore and Polar Engineers , 2013, p. 290-294Conference paper (Refereed)
    Abstract [en]

    Laser hybrid welding has been used in European shipbuilding for many years due to its high productivity. In order to qualify the process for the oil and gas industry, an extensive welding and testing programme is needed, and the properties must satisfy more severe requirements than in shipbuilding. This is particularly the case when these activities are moving to the Arctic regions, where low temperature toughness may be the primary challenge. The present investigation addressed preliminary welding trials carried out with 15 kW fibre laser-gas metal arc (GMA) hybrid welding using double Y joint of 20 mm thick 420 MPa steel plates. Both Charpy V notch impact and CTOD fracture mechanical testing were included with test temperature of -30°C. The results indicate that the heat affected zone (HAZ) of the examined steel appeared with satisfactory toughness (> 200 J, > 0.2 mm) while the employed weld metal had insufficient impact properties. The weld metal CTOD toughness approached 0.2 mm. With a better welding wire, designed for low temperature applications, it is reasonable to suggest that laser hybrid arc welding can be used for applications even below -30 to -40°C

  • 4.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, Stockholm.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint2011In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, no 10, p. 2246-2258Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser hybrid welded eccentric fillet joints has been studied for stainless steel. Two-dimensional linear elastic fracture mechanics analysis was carried out for this joint geometry for four point bending load. The numerical simulations explain for the experimental observations why the crack propagates from the lower weld toe and why the crack gradually bends towards the root. Lack of fusion turned out to be uncritical for the initiation of cracks due to its compressive stress conditions. The linear elastic fracture mechanics analysis has demonstrated in good qualitative agreement with fatigue test results that lack of fusion slightly (<10%) reduces the fatigue life by accelerating the crack propagation. For the geometrical conditions studied here improved understanding of the crack propagation was obtained and in turn illustrated. The elaborated design curves turned out to be above the standard recommendations

  • 5.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z.
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 265, no 6, p. 1936-1945Article in journal (Refereed)
    Abstract [en]

    Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by four point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

  • 6.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part I2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Welded joints are a major component that is often responsible for causing a structure failure or for being the point at which fatigue cracking initiates and propagates. Despite tremendous research efforts, the understanding of fatigue behaviour is still limited, particularly for new techniques like laser hybrid welding. Beside a comprehensive state-of-the-art study, the paper presents a fatigue study of laser hybrid welded eccentric fillet joint of stainless steel of 10 mm thickness, with 5 mm displacement. Motivation is to study the influence of the surface geometry shape on fatigue performance under a four point bending test. 13 samples were produced, measuring the toe radii and testing under constant amplitude loading with stress ratio R=0. Different techniques have been used to measure local weld geometry, like plastic replica, a 3D optical profiler and a 3D-digitizer. The influence of the local weld geometry, like the toe radii, on the stress concentration was studied by FE-analysis. Occasionally lack of fusion was observed, which was taken into account in the FE-analysis. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. Macro hardness tests were carried out and the crack surfaces were observed in order to detect crack initiation and propagation. Correlations between the toe radii, the corresponding stress maxima and crack initiation locations were studied between the different samples and even along the welds.

  • 7.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of postulated cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the regions most likely to contain original fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often blamed for causing a structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models/techniques for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments. This literature survey compiled useful information on fracture and fatigue analysis of various welded joints. The present review is divided into two major sections- fracture mechanics and fatigue analysis with widely used models. A survey table is also introduced to get the outlook of research trend on fatigue and fracture over last 3 decades. Although tremendous research effort has been implemented on fatigue and fracture analysis of conventional welding, research on relatively new welding technology (laser welding, hybrid laser welding) is still limited and unsatisfactory. In order to give guarantee or make welding standard for new welding technology, further research is required in the field of fatigue and fracture mechanics including FEM and multi-scale modeling.

  • 8.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Geometrical aspects of the fatigue behaviour of laser hybrid fillet welds2009In: Proceedings of the Fatigue Design Conference, Cetim , 2009Conference paper (Refereed)
  • 9.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The effects of surface topography and lack of fusion on the fatigue strength of laser hybrid welds2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics : November 2 - 5, 2009 - Orlando, FL : Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference, poster presentation, gallery, Orlando, Fla: Laser institute of America , 2009, p. 38-46Conference paper (Refereed)
    Abstract [en]

    The geometrical aspects of laser hybrid welding before, during and after the process differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the microgeometry, i.e. the surface ripples can be more critical than the macrogeometry of the weld surface and even than lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface the tendency to LOF can be explained. Stress analysis was carried out by FEA for the complex joint geometry and bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

  • 10.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Analysis of the rapid central melt pool flow in hybrid laser-arc welding2012In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 39, p. 853-862Article in journal (Refereed)
    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.

  • 11.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Tuominen, J.
    Tampere University of Technology, Department of Materials Science.
    Vuoristo, P.
    Tampere University of Technology, Department of Materials Science.
    Miettinen, J.
    Tampere University of Technology, Department of Mechanics and Design.
    Poutala, J.
    Tampere University of Technology, Department of Mechanics and Design.
    Närkki, J.
    Tampere University of Technology, Department of Materials Science.
    Jankala, J.
    Technology Centre KETEK Ltd..
    Peltola, T.
    Technology Centre KETEK Ltd..
    Barsoum, Z.
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, Stockholm.
    Analysis of the stress raising action of flaws in laser clad deposits2013In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 46, p. 328-337Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations.

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

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

  • 13.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Tuominen, Jari
    Tampere University of Technology.
    Vuoristo, Petri MJ J
    Tampere University of Technology.
    Miettinen, Juha S.
    Tampere University of Technology.
    Poutala, J.
    Department of Mechanics and Design, Tampere University of Technology.
    Näkki, Jonne
    Tampere University of Technology.
    Junkala, J.
    Tampere University of Technology.
    Peltola, Tero
    Tampere University of Technology.
    Surface pore initiated fatigue failure in laser clad components2013In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, no 3Article in journal (Refereed)
    Abstract [en]

    A laser clad and machined cylindrical structural steel rod was fatigue tested under four-point bending load. The resulting fracture could be tracked back to a spherical surface pore in the Co-based coating. Due to an oxide inclusion, the pore was not identified by dye penetrant inspection. Two circular buckling strain patterns that were detected beside the pore at the surfaces after fracture confirm local plastic deformation prior to crack initiation. In order to calculate the stress field around the surface pore, linear elastic finite element analysis was carried out. For four-point bending load, a surface pore generally exceeds the maximum stress of a smooth rod as long as the pore is located within an azimuthal angle of ±55°, which was the case for the presented as well as for another pore initiated sample.

  • 14.
    Al-Mashikhi, S.O.
    et al.
    University of Notttingham.
    Powell, John
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Voisey, K.T.
    University of Notttingham.
    An explanation of ‘striation free' cutting of mild steel by fibre laser2009In: 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 , 2009Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of an experimental and theoretical investigation into the phenomenon of ‘striation free cutting', which is a feature of fibre laser cutting of thin section mild steel. The paper concludes that the creation of very low roughness edges is related to an optimisation of the cut front geometry when the cut front is inclined at angles close to the Brewster angle for the laser - material combination. For purely geometric reasons this particular type of cut front optimisation is not possible for CO2 laser cutting of mild steel.

  • 15.
    Al-Mashikhi, S.O
    et al.
    Salalah College of Technology, Engineering Department, Salalah, Oman and Faculty of Engineering, University of Nottingham.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Voisey, K.T.
    Faculty of Engineering, University of Nottingham.
    Heat affected zones and oxidation marks in fiber laser–oxygen cutting of mild steel2011In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, no 4Article in journal (Refereed)
    Abstract [en]

    The effect of cutting speed and sheet thickness on surface oxidation and heat affected zones (HAZs) has been investigated for laser–oxygen cutting of mild steel sheet with a fiber laser. Optical and scanning electron micrographs were used to determine the extent of surface oxidation and HAZ from plan and cross-sectional views, respectively. The HAZ is consistently wider at the bottom of the cut compared to the HAZ at the top of the cut. With increasing speed, the width of the HAZ at the top of the cut decreases whereas the HAZ width at the bottom of the cut generally increases. No simple, direct relationship between HAZ width and surface oxidation was seen. However, it is possible to state that in each case considered here, the HAZ would be completely removed if they are machined back by a depth equal to the extent of the surface oxidation.

  • 16.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling2009In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, no 21, p. 8917-8925Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to study the effect of the laser spot diameter on the shock wave generated in the ablation process of an Nd:YAG laser pulse on a Zn target under atmospheric pressure. For different laser spot diameters and time delays, the propagation of the expanding vapour and of the shock wave were recorded by intensity maps calculated using the recorded digital holograms. From the latter phase maps, the refractive index and the density field can be derived. A model was developed that approaches the density distribution, in particular the ellipsoidal expansion characteristics. The induced shock wave has an ellipsoid shape that approaches a sphere for decreasing spot diameter. The ellipsoidal shock waves have almost the same centre offset towards the laser beam and the same aspect ratio for different time steps. The model facilitates the derivation of the particle velocity field. The method provides valuable quantitative results that are discussed, in particular in comparison with the simpler point source explosion theory.

  • 17.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shaer, M. El
    Department of Engineering Physics and Mathematics, Faculty of Engineering, Zagazig University.
    Comparison of the laser ablation process on Zn and Ti using pulsed digital holographic interferometry2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 14, p. 4633-4641Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to compare the laser ablation process of a Q-switched Nd-YAG laser pulse (wavelength 1064 nm, pulse duration 12 ns) on two different metals (Zn and Ti) under atmospheric air pressure. Digital holograms were recorded for different time delays using collimated laser light (532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. Intensity maps were calculated from the recorded digital holograms and are used to calculate the attenuation of the probing laser beam by the ablated plume. The different structures of the plume, namely streaks normal to the surface for Zn in contrast to absorbing regions for Ti, indicates that different mechanisms of laser ablation could happen for different metals for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism.

  • 18. Arwidson, Claes
    et al.
    Bernspång, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Verification of numerical forming simulation in high strength steels2004In: Proceedings of the Conference Innovations in metal forming, 2004Conference paper (Refereed)
  • 19.
    Bang, Han-Sur
    et al.
    Chosun University, Department of Welding & Joining Science Engineering.
    Bang, HeeSeon
    Department of Welding and Joining Science Engineering, Chosun University.
    Hong, J.H.
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Jeon, Geunhong
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Kim, G.S.
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Effect of Tungsten-Inert-Gas Preheating on Mechanical and Microstructural Properties of Friction Stir Welded Dissimilar Al Alloy and Mild Steel2016In: Strength of Materials, ISSN 0039-2316, E-ISSN 1573-9325, Vol. 48, no 1, p. 152-159Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to clarify the effect of tungsten-inert-gas (TIG) welding preheating on the mechanical properties of Al6061-T6 and SS400 welded joints by friction stir welding (FSW). FSW joints with and without TIG welding preheating are characterized and compared in terms of their mechanical and microstructural properties. The results show that the TIG assisted hybrid FSW welded joints (TIG-HFSW) provide an enhanced joint strength. The transversal tensile strength of the TIG-HFSW joints exhibited approximately 104% of the Al6061-T6 base metal tensile strength and was higher than that of the FSW joints. Microstructural investigations also reveal that in the HAZ and TMAZ of TIG-HFSW joints, the grains of Al6061-T6 are smaller than those of the FSW welds

  • 20. Bergström, David
    et al.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Mathematical modelling of laser absorption mechanisms in metals: a literature survey2003In: Proceedings of the 16th Meeting on Modelling, Simulation, Virtuality in High Power Laser Technology, M4PL 16: Igls/Innsbruck, 22.01.2003-24.01.2003 / Vienna University of Technology, Department of Nonconventional Processing, Forming and Laser Technology ... Ed.: D. Schuöcker ..., 2003Conference paper (Refereed)
  • 21.
    Bergström, David
    et al.
    Mid Sweden University, Östersund.
    Powell, John
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    A ray-tracing analysis of the absorption of light by smooth and rough metal surfaces2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 11, p. 113504-1Article in journal (Refereed)
    Abstract [en]

    Ray tracing has been employed to investigate the absorption of light by smooth and random rough metal surfaces. For normally incident light the absorptance of the surface increases with surface roughness. However, for light incident at a tangent to the surface the absorptance-surface roughness relationship is more complex. For example, in certain cases the absorptance can rise, fall, and rise again as the surface roughness increases. In this paper this complex absorptance-roughness relationship is defined and explained. The wavelengths of the light chosen for this study correspond to the primary and secondary output wavelengths of Nd:YAG lasers.

  • 22.
    Bergström, David
    et al.
    Mid Sweden University.
    Powell, John
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Absorptance of nonferrous alloys to Nd:YLF and Nd:YAG laser light at room temperature2007In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, no 8, p. 1290-1301Article in journal (Refereed)
    Abstract [en]

    The measurement of absorptance is important for the analysis and modeling of laser-material interactions. Unfortunately, most of the absorptance data currently available consider only polished pure metals rather than the commercially available (unpolished, oxidized) alloys that are actually being processed in manufacturing. We present the results of absorptance measurements carried out at room temperature on as-received engineering grade nonferrous metals (Al, Cu, and Zn alloys). The measurements were made using an integrating sphere with a Nd:YLF laser at two wavelengths (1053 and 527 nm, which means that the results are also valid for Nd:YAG radiation at 1064 and 532 nm). The absorptance results obtained differ considerably from the existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified. For all 22 cases studied the absorptance was higher than for ideal pure, polished metals. For all Al and Cu samples the absorptance was higher for the green than it was for the infrared wavelength, while for all Zn coatings this trend was reversed. No clear correlation between absorptance and surface roughness was found at low roughness values (Sa 0.15-0.60), but one rougher set of samples (Sa 2.34) indicated a roughness-absorptance correlation at higher roughness levels.

  • 23.
    Bergström, David
    et al.
    Mittuniversitetet.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fresnel absorption of rough metal surfaces using ray-traycing analysis2007In: 2007 European conference on lasers and electro-optics, IEEE Communications Society, 2007Conference paper (Refereed)
  • 24. Bergström, David
    et al.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser absorption measurements in opaque solids2005In: 10th NOLAMP Conference: the 10th Nordic Laser Materials Processing Conference, 17-19 August 2005, Luleå Sweden / [ed] Alexander Kaplan, Luleå: Luleå tekniska universitet, 2005, p. 91-115Conference paper (Refereed)
  • 25. Bergström, David
    et al.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Light scattering and absorption in Gaussian random rough metal surfaces using the geometric optics approximation2007In: Proceedings / M4PL 20: Igls/Innsbruck (A), 17. - 19.01.2007, 2007Conference paper (Refereed)
  • 26.
    Bergström, David
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nd:YAG laser absorptance of rough metal surfaces2007In: 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, Orlando, Fla: Laser institute of America , 2007Conference paper (Refereed)
    Abstract [en]

    The Nd:YLF/Nd:YAG laser absorptance of rough metal surfaces has been investigated using 3D ray tracing simulations on computer-generated Gaussian random rough metal surfaces. The impact of multiple scattering, shadowing and Fresnel-equation based angle dependence on the overall absorption is discussed

  • 27. Bergström, David
    et al.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ray-tracing analysis of Nd:YAG laser absorption by random rough metal surfaces2007In: 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, 2007Conference paper (Refereed)
  • 28.
    Bergström, David
    et al.
    Luleå tekniska universitet.
    Powell, John
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The absorptance of metal surfaces to Nd:YAG/Nd:YLF laser light2008In: Conference proceedings: / 3rd Pacific International Conference on Applications of Lasers and Optics, PICALO : April 16 - 18, 2008, Capital Hotel, Beijing, China / [ed] Minlin Zhong, Orlando, Fla.: Laser institute of America , 2008, p. 375-380Conference paper (Refereed)
    Abstract [en]

    The absorptance of real metallic engineering surfaces used in Laser Material Processing depends strongly upon the particular surface conditions, including the degree of roughness and oxidation. In this paper the influence of surface topography on Nd:YAG/Nd:YLF laser absorptance has been studied, both experimentally and theoretically, on a set of randomly selected as-received metallic engineering surfaces. The surfaces were sputter-coated with a thin layer of gold to eliminate differences in surface chemistry and oxidation. The absorptance was measured using integrating sphere reflectometry and compared to calculations from 3D ray-tracing simulations of AFM-scanned images of the surfaces. The results have increased the understanding of how surface roughness influences the laser-workpiece coupling efficiency.

  • 29.
    Bergström, David
    et al.
    Mid Sweden University.
    Powell, John
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The absorptance of steels to Nd:YLF and Nd:YAG laser light at room temperature2007In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 253, no 11, p. 5017-5028Article in journal (Refereed)
    Abstract [en]

    The measurement of absorptance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the absorptance data presently available considers only polished pure metals rather than the commercially available (unpolished, oxidised) alloys, which are actually being processed in manufacturing. This paper presents the results of absorptance measurements carried out at room temperature on as-received engineering grade steels including hot and cold rolled mild steel and stainless steels of various types. The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053 and 527 nm, which means that the results are also valid for Nd:YAG radiation at 1064 and 532 nm). The absorptance results obtained differ considerably from existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified; for all materials studied, the absorptance was considerably higher than the previously published values for the relevant pure metals with polished surfaces. For all 15 samples the absorptance was higher for the green than for the infrared wavelength. No clear trend correlating the absorptance with the roughness was found for mild steel in the roughness range Sa 0.4-5.6 μm. A correlation between absorptance and roughness was noted for stainless steel for Sa values above 1.5 μm.

  • 30.
    Bergström, David
    et al.
    Mid Sweden University, Department of Engineering, Physics and Mathematics.
    Powell, John
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The absorption of light by rough metal surfaces: a three-dimensional ray-tracing analysis2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 10Article in journal (Refereed)
    Abstract [en]

    The laser absorptance of rough surfaces has been investigated by using Monte Carlo simulations based on three-dimensional (3D) ray tracing. The influence of multiple scattering, shadowing, and the Fresnel-equation based angle dependence is discussed. The 3D results are compared to previously published results from a two-dimensional ray-tracing analysis and the different applications of the two models are explained

  • 31.
    Bergström, David
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The absortion of light by rough metal surfaces: a three-dimensional ray-tracving analysis2007In: 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, Orlanndo, Fla: Laser institute of America , 2007Conference paper (Refereed)
  • 32.
    Bergström, David
    et al.
    Mittuniversitetet, Östersund.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The reflectance of steels and non-ferrous alloys to Nd:YAG and Nd:YLF laser light2006In: Peer reviewed conference proceedings: / PICALO 2006, 2nd Pacific International Conference on Applications of Lasers and Optics : April 3 - 5, 2006, Grand Hyatt Melbourne, Melbourne, Australia / [ed] Milan Brandt, Orlando, Fla.: Laser institute of America , 2006, p. 140-145Conference paper (Refereed)
    Abstract [en]

    The measurement of reflectance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the reflectance data presently available consider only polished pure metals rather than the commercially available (unpolished, oxidised) alloys which are actually being processed. This paper presents the results of reflectance measurements carried out on asreceived engineering grade metals including: hot and cold rolled mild steel, zinc coated mild steel, stainless steel, aluminium alloys, copper and brass. The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053 nm and 527 nm). The results obtained differ considerably from existing data for polished, pure metals and should help to improve the accuracy of laser-material interaction models.

  • 33.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Industrial and Mechanical Engineering.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser-arc hybrid welding of thick HSLA steel2018In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 259, p. 75-87Article in journal (Refereed)
    Abstract [en]

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

  • 34.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Industrial and Mechanical Engineering.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Deep penetration fiber laser-arc hybrid welding of thick HSLA steel2018In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 256, p. 216-228Article in journal (Refereed)
    Abstract [en]

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

  • 35.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Hybrid Welding of 45 mm High Strength Steel Sections2017In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, p. 11-22Article in journal (Refereed)
    Abstract [en]

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

  • 36.
    Bunaziv, Ivan
    et al.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    Norwegian University of Science and Technology, Department of Engineering Design and Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Process stability during fiber laser-arc hybrid welding of thick steel plates2018In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 102, p. 34-44Article in journal (Refereed)
    Abstract [en]

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

  • 37.
    Bunaziv, Ivan
    et al.
    Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Trondheim.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Akselsen, Odd M.
    Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Trondheim.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The penetration efficiency of thick plate laser-arc hybrid welding2018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 97, no 5-8, p. 2907-2919Article in journal (Refereed)
    Abstract [en]

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

  • 38.
    Chen, Y
    et al.
    Chinese Academy of Sciences, Beijing.
    Gan, C.H.
    Chinese Academy of Sciences, Beijing.
    Wang, L.X.
    Chinese Academy of Sciences, Beijing.
    Yu, G.
    Chinese Academy of Sciences, Beijing.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser surface modified ductile iron by pulsed Nd:YAG laser beam with two-dimensional array distribution2005In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 245, no 1-4, p. 316-321Article in journal (Refereed)
    Abstract [en]

    A novel modification layer on the surface of pearlite-ferrite matrix ductile iron was fabricated under irradiation of Nd:YAG laser beam equipped with self-designed diffractive optical element (DOE) which produces a 5×5 two-dimensional array distribution at the focal plane. The microstructure of the layer along the surface and the direction of the layer depth had obvious gradient distribution, and therefore the two-dimensional microhardness map of the layer alternated higher hardness with lower hardness. The results showed that the novel modification layer is expected to have excellent combination of strength and toughness

  • 39.
    Chen, Yao
    et al.
    Chinese Academy of Sciences, Beijing.
    Gan, Cuihua
    Chinese Academy of Sciences, Beijing.
    Zhang, Tainua
    Chinese Academy of Sciences, Beijing.
    Yu, Gang
    Chinese Academy of Sciences, Beijing.
    Bai, Pucun
    Chinese Academy of Sciences, Beijing.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser-surface-alloyed carbon nanotubes reinforced hydroxyapatite composite coatings2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 25, p. 251905-251907Article in journal (Refereed)
    Abstract [en]

    Carbon-nanotube (CNT)-reinforced hydroxyapatite composite coatings have been fabricated by laser surface alloying. Microstructural observation using high-resolution transmission electron microscopy showed that a large amount of CNTs remained with their original tubular morphology, even though some CNTs reacted with titanium element in the substrate during laser irradiation. Additionally, measurements on the elastic modulus and hardness of the composite coatings indicated that the mechanical properties were affected by the amount of CNTs in the starting precursor materials. Therefore, CNT-reinforced hydroxyapatite composite is a promising coating material for high-load-bearing metal implants

  • 40. Duftschmid, K.
    et al.
    Kaplan, Alexander
    Schröder, K.
    Schuöcker, D.
    Strahlenbelastung durch UV Emission beim Laserschweissen1991In: Strahlen - Felder - Ströme : Schlußbericht = Radiation - fields - currents = Rayonnements - champs - courants électriques = Radiaciones - campos - corrientes, Köln: IVSS Sektion Elektrizität , 1991Conference paper (Refereed)
  • 41. Dyberg, Pål
    et al.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    New possibilities in laser hybrid welding with metal cored wires2007In: 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, 2007Conference paper (Refereed)
  • 42. Dyberg, Pål
    et al.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Zachrisson, J.
    ESAB AB.
    On the influence of metal cored wire deposition on the hybrid welding process2007In: Congress proceedings: 2007 ICALEO, 26th International Congress on Applications of Lasers & Electro-Optics : October 29 - November 1, 2007 / [ed] Yongfeng Lu, Orlando, Fla: Laser institute of America , 2007Conference paper (Refereed)
    Abstract [en]

    Metal cored wires are often used in gas metal arc welding to increase productivity. Cored wires can, however, also easily be designed to affect weld metal composition or arc characteristics. Specially formulated metal cored wires, designed for laser hybrid welding, could therefore potentially be used to improve the arc and weld pool characteristics and enhance the process flexibility, robustness and productivity. The range of process parameters available in hybrid welding could thereby be extended and the process stability improved further for standard parameters. Small additions of certain elements in the wire can influence the arc plasma state and the surface tension, resulting in an altered arc and weld pool behaviour. A number of metal cored wires have therefore been produced containing additions of several different arc stabilising elements, varied from 0-10% of the powder filling. High speed filming of the welding process with synchronised arc current and voltage measurements was conducted enabling e.g. to detect short short-circuiting. Preliminary results indicate differences in process stability, arc length, surface appearance and penetration profiles between the wires in pulsed mode transfer. The experimental results are accompanied by a theoretical discussion of the phenomena observed, including the use of the Saha equation to calculate electron number density as a function of temperature for relevant chemical elements.

  • 43. Engström, Hans
    et al.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Adaptive process control in laser robotic welding2003In: 9th NOLAMP Conference: 9th Conference on Laser Materials Processing in the Nordic Countries ; 4 - 6 August 2003, [Trondheim] / [ed] Einar Halmøy, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2003, p. 251-258Conference paper (Refereed)
    Abstract [en]

    An adaptive process control and seam tracking system for robotic laser welding with filler was developed and then evaluated for the butt welding of SS-1147 mild steel sheets of thickness 2 mm. The system comprises a 3 kW Nd:YAG laser, an industrial robot and a laser camera for seam tracking and measurement of gap width. The gap width data are used to control welding speed and wire feed rate. Experiments were carried out to weld butt joints of SS-1147 mild steel with gap widths varying between 0-0.8 mm. The resultant weld geometry was evaluated to determine the operating range of the laser camera (measured gap width) for monitoring to result in acceptable welds.

  • 44.
    Engström, Hans
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Education of Industrial Users of Laser Materials Processing Technology2005In: 10th NOLAMP Conference: the 10th Nordic Laser Materials Processing Conference, 17-19 August 2005, Luleå Sweden / [ed] Alexander Kaplan, Luleå: Luleå tekniska universitet, 2005, p. 33-40Conference paper (Refereed)
    Abstract [en]

    The extensive use of high power laser for materials processing in industry has brought a new era in manufacturing technology. High speed processing with low heat input and high precision offers up-to-date manufacturing. New processes like laser hybrid welding are developed and introduced in industry. But the potential of laser technology is not by far fully utilised due to lack of knowledge of laser processes in the industrial environment.The national Swedish programme, "proDesign - Expert competence in industrial product development and materials processing", offers new opportunities of providing education for industrial managers, designers and manufacturing people. Within the scope of proDesign, Luleå University of Technology has developed several new courses in laser material processing for people in industry. These courses have now uccessfully been introduced to the Swedish market and this paper presents experiences from this work.

  • 45.
    Engström, Hans
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    New laser projects to strengthen the manufacturing industry in northern Scandinavia2011In: 13th NOLAMP Conference: 13th Conference on Laser Materials Processing in the Nordic Countries 27 - 29 June 2011 / [ed] Einar Halmøy, Department of Geography, Norwegian University of Science and Technology, 2011Conference paper (Refereed)
    Abstract [en]

    The industrial development in northern part of Scandinavia has for the last years steadily beengrowing, primarily driven by strong expansion in mining, hydro power and wind powerindustries, which influences the growth and also demand on the mechanical industry in thearea. In order to further develop the competitiveness of manufacturing companies and thepromotion of laser technology in the north of Sweden and Finland, three new laser projectswere approved. These projects will be presented in this paper.. One project at LuleåUniversity of Technology (LTU) will support industry to develop and implement lasers inmanufacturing, combined with further development of an interesting laser process useful forthe regional industry. One project is a cooperation project between LTU and University ofOulu that will focus on developing optimal laser welds in high strength steels using highpower fibre- and disc lasers and evaluation of fatigue properties of the welds. The thirdproject deals with fatigue properties of laser clad surfaces and is a cooperation projectbetween LTU and Centria Research unit of Central Osterbothnia of Applies Sciences,involving also Tampere University of Technology.

  • 46. Engström, Hans
    et al.
    Norman, Peter
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    DATLAS: a new approach for monitoring the laser welding process2007In: 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, 2007Conference paper (Refereed)
  • 47.
    Eriksson, Ingemar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    New high-speed photography technique for observation of fluid flow in laser welding2010In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 49, no 10Article in journal (Refereed)
    Abstract [en]

    Recent developments in digital high-speed photography allow us to directly observe the surface topology and flow conditions of the melt surface inside a laser evaporated capillary. Such capillaries (known as keyholes) are a central feature of deep penetration laser welding. For the first time, it can be confirmed that the liquid capillary surface has a rippled, complex topology, indicative of subsurface turbulent flow. Manipulation of the raw data also provides quantitative measurements of the vertical fluid flow from the top to the bottom of the keyhole.

  • 48.
    Eriksson, Ingemar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Haglund, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Holographic measurement of thermal distortion during laser spot welding2012In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 51, no 3Article in journal (Refereed)
    Abstract [en]

    Welding distortion is an important engineering topic for simulation and modeling, and there is a need for experimental verification of such models by experimental studies. High-speed pulsed digital holography is proposed as a measurement technique for out-of-plane welding distortion. To demonstrate the capability of this technique, measurements from a laser spot weld are presented. A complete twodimensional deformation map with submicrometer accuracy was acquired at a rate of 1000 measurements per second. From this map, particular points of interest can be extracted for analysis of the temporal development of the final distortion geometry.

  • 49. Eriksson, Ingemar
    et al.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Evaluation of laser weld monitoring: a case study2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics : November 2 - 5, 2009 - Orlando, FL : Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference, poster presentation, gallery, Orlando, Fla: Laser institute of America , 2009, Vol. 102, p. 1419-1425Conference paper (Refereed)
    Abstract [en]

    On-line monitoring of the quality of laser welding is of interest for many industrial applications. For photodiodes the monitoring strategy usually aims at observing whether the signal exceeds a threshold. This well known technique is mainly based on empirical values, thus the monitoring has to be trained for each application. For improved understanding of the context between the physics of a welding defect generated and the resulting voltage signal, the experiments were observed by high speed imaging, followed by evaluation and modelling. A commercial system with three detector wavelength windows was studied for nine different industrial welding applications with distinct defects. We here present selected cases for which we try to generalise the findings and to draw conclusions for the applicability of commercial monitoring systems. For example humping was clearly detected by the signal, spatter and crater formation for overlapping Zn-coated steel surprisingly not. An interesting cause for welding defects is contamination of the joint prior to welding by oil, grease or detergents. The corresponding experiments showed unexpected signal responses, which can be partially explained by the analysis. We summarise that improved understanding of the signal causes facilitates to apply monitoring systems in a reliable manner.

  • 50.
    Eriksson, Ingemar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Melt behavior on the keyhole front during high speed laser welding2013In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 51, no 6, p. 735-740Article in journal (Refereed)
    Abstract [en]

    The flow of molten metal on the front wall of a laser generated welding keyhole has been observed by high speed photography, optically measured by mapping the flow of ripples on the liquid surface and theoretically calculated. A clear downward flow can be observed and measured by a Particle Image Velocimetry algorithm. A theoretical calculation of the melt thickness on the keyhole front is also presented. Results indicate that the thickness of the liquid on the keyhole front is similar to that of the resolidified layer found in micrographs of the front if the laser is suddenly turned off. The measured surface ripple flow speeds are between two and four times as high as the theoretical average fluid flow rate.

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