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  • 251.
    Olsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Nova AB, Östersund, Sweden.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Palmquist, Anders
    Department of Biomaterials, University of Gothenburg, Gothenburg, Sweden.
    Brånemark, Rickard
    Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA.
    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.
    Formation of osseointegrating (bone integrating) surfaces on titanium by laser irradiation2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022508Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pulsed lasers can be used to modify the surface of medical implants in order to accelerate bone growth (osseointegration). A surface covered in attached droplets with diameters between 1 and 20 μm is a beneficial surface for rapid osseointegration. This paper presents the results of an experimental program in which a broad range of laser parameters and different atmospheres were used to create different surface textures on titanium substrates, including the desired "attached droplet" topology. The resulting surfaces were analyzed by scanning electron microscopy and micro-computer tomography. The paper explains how different types of surfaces are created by the laser-material interaction under different conditions and focus characteristics. It is shown that optimization of the laser parameters results in a robust process, which produces a surface that is fundamentally different from those created by nonlaser methods.

  • 252.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Han, Sang-Woo
    Department of Mechanical Engineering, KAIST.
    Cheon, Jason
    Department of Mechanical Engineering, KAIST.
    Na, Suck-Joo
    Department of Mechanical Engineering, KAIST.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Bang, Hee-Seon
    Department of Welding and Joining Science Engineering, Chosun University.
    Numerical simulation of laser ablation driven melt waves2017Inngår i: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 30, s. 303-312Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Numerical simulations on the melt flow down the keyhole front during fibre laser welding are presented here. The calculations confirm the existence of melt waves previously observed by high speed imaging, with velocities ranging between 4-10 m/s. The simulations provide spatial and temporal information on the temperature and flow fields, particularly within the melt film volume, which cannot be observed by high speed imaging. The ablation pressure achieves high values around wave-peaks and at the bottom of the front, just before droplets are sheared off. The simulation results provide explanations on the main liquid transport mechanisms within the keyhole based on information on the temperature, velocity and pressure field and on the geometrical front conditions.

  • 253.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Petring, Dirk
    Fraunhofer-Institute for Laser Technology, Aachen.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Deichsel, Eckard
    Bystronic Laser AG.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Differences in Cutting Efficiency between CO2 and Fiber Lasers when Cutting Mild and Stainless Steels2014Konferansepaper (Annet vitenskapelig)
  • 254.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Petring, Dirk
    Fraunhofer ILT, Steinbachstr. 15, Aachen.
    Powell, John
    Deichsel, Eckard
    Bystronic Laser AG, Industriestr. 21, Niederönz.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Measuring the Melt Flow on the Laser Cut Front2015Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, s. 99-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 255.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Petring, Dirk
    Fraunhofer-Institute for Laser Technology, Aachen.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Deichsel, Eckard
    Bystronic Laser AG.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The Effect of Laser Type and Power on the Efficiency of Industrial Cutting of Mild and Stainless Steels2016Inngår i: Journal of manufacturing science and engineering, ISSN 1087-1357, E-ISSN 1528-8935, Vol. 138, nr 3, artikkel-id 31012Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the effect of material type, material thickness, laser wavelength and laser power on the efficiency of the cutting process for industrial state-of-the-art cutting machines. The cutting efficiency is defined in its most basic terms: as the area of cut edge created per Joule of laser energy. This fundamental measure is useful in producing a direct comparison between the efficiency of fiber and CO2 lasers when cutting any material. It is well known that the efficiency of the laser cutting process generally reduces as the material thickness increases, because conductive losses from the cut zone are higher at the lower speeds associated with thicker section material. However, there is an efficiency dip at the thinnest sections. This paper explains this dip in terms of a change in laser-material interaction at high cutting speeds. Fiber lasers have a higher cutting efficiency at thin sections than their CO2 counterparts, but the efficiency of fiber laser cutting falls faster than that of CO2 lasers as material thickness is increased. This is the result of a number of factors including changes in cut zone absorptivity and kerf width. This paper presents phenomenological explanations for the relative cutting efficiencies of fiber lasers and CO2 lasers, and the mechanisms affecting these efficiencies for stainless steels (cut with nitrogen) and mild steel (cut with oxygen or nitrogen) over a range of thicknesses. The paper involves a discussion of both theoretical and practical engineering issues. Key Words; Laser Cutting, Fiber Laser, CO2 Laser, Efficiency.

  • 256.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Expertise Ltd., Acorn Park Industrial Estate.
    Deichsel, Eckard
    Bystronic Laser AG, Industriestrasse 21, CH-3362 Niederönz.
    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.
    Fibre laser cutting stainless steel: Fluid dynamics and cut front morphology2017Inngår i: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 87, s. 87-93Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper the morphology of the laser cut front generated by fibre lasers was investigated by observation of the ‘frozen’ cut front, additionally high speed imaging (HSI) was employed to study the fluid dynamics on the cut front while cutting. During laser cutting the morphology and flow properties of the melt film on the cut front affect cut quality parameters such as cut edge roughness and dross (residual melt attached to the bottom of the cut edge). HSI observation of melt flow down a laser cutting front using standard cutting parameters is experimentally problematic because the cut front is narrow and surrounded by the kerf walls. To compensate for this, artificial parameters are usually chosen to obtain wide cut fronts which are unrepresentative of the actual industrial process. This paper presents a new experimental cutting geometry which permits HSI of the laser cut front using standard, commercial parameters. These results suggest that the cut front produced when cutting medium section (10 mm thick) stainless steel with a fibre laser and a nitrogen assist gas is covered in humps which themselves are covered by a thin layer of liquid. HSI observation and theoretical analysis reveal that under these conditions the humps move down the cut front at an average speed of approximately 0.4 m/s while the covering liquid flows at an average speed of approximately 1.1 m/s, with an average melt depth at the bottom of the cut zone of approximately 0.17 mm.

  • 257.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Expertise Ltd., Acorn Park Industrial Estate.
    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.
    Investigation of the Piercing Process in Laser Cutting of Stainless Steel2017Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 29, nr 2, artikkel-id 022201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the laser piercing process which precedes nearly every laser cutting operation. The two most important aspects of the piercing process are: a) How long does it take to pierce the material? And b) How wide is the pierced hole? If the hole is no wider than the cut line, the material can be pierced on the line to be cut. In this paper 10 mm thick stainless steel was pierced by a multikilowatt fibre laser to compare efficiency and quality when piercing with a continuous wave (cw) output and a selected range of power modulation parameters. The different processes were observed by high speed imaging and subsequently examined by visual observation. High speed imaging is used to time the penetration event and to study the laser-material interactions involved in drilling the pierced holes. The results show that appropriate laser power modulation settings can considerably reduce both the piercing time and the required energy to generate any piercing hole required for the subsequent cutting process. This pulse-pierce technique and the differences between piercing with a continuous and a power modulated laser beam are further explained and discussed. Also the effect on the size of the entrance to the pierced hole depending on power modulation regimes was investigated in this paper.

  • 258.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    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 F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Dynamic laser piercing of thick section metals2018Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 100, s. 82-89Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Before a contour can be laser cut the laser first needs to pierce the material. The time taken to achieve piercing should be minimised to optimise productivity. One important aspect of laser piercing is the reliability of the process because industrial laser cutting machines are programmed for the minimum reliable pierce time. In this work piercing experiments were carried out in 15 mm thick stainless steel sheets comparing a stationary laser and a laser which moves along a circular trajectory with varying processing speeds. Results show that circular piercing can decrease the pierce duration by almost half compared to stationary piercing. High speed imaging (HSI) was employed during the piercing process to understand melt behaviour inside the pierce hole. HSI videos show that circular rotation of the laser beam forces melt to eject in opposite direction of the beam movement, while in stationary piercing the melt ejects less efficiently in random directions out of the hole.

  • 259.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Expertise Ltd., Acorn Park Industrial Estate.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F.H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The geometry of the cutting front created by Fibre and CO2 lasers when profiling stainless steel under standard commercial conditions2018Inngår i: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 103, s. 318-326Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cutting fronts created by CO2 and fibre lasers in stainless steel at thicknesses between 2 mm and 10 mm have been ‘frozen’ and their geometry has been measured. Standard commercial cutting parameters were used to generate the cuts for both types of laser. The resulting three-dimensional cutting front shapes have been curve fitted as polynomials and semicircles. Various features of the cutting front geometry are discussed including the lack of correlation of the cut front inclination with either the relevant Brewster angle or the inclination of the striations on the cut edge.

  • 260.
    Pocorni, Jetro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Schwarz, A.
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Measuring the State-of-the-Art in Laser Cut Quality2013Inngår 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. 101-108Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper discusses the strategy appropriate to investigating the state of the art of laser cutting from an industrial point of view. The importance of creating the samples in a high quality industrial environment is emphasised and preliminary results are presented.

    Fulltekst (pdf)
    FULLTEXT01
  • 261. Powell, John
    et al.
    Al-Mashikhi, S.O.
    Faculty of Engineering, University of Nottingham.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    Faculty of Engineering, University of Nottingham.
    Fibre laser cutting of thin section mild steel: An explanation of the ‘striation free’ effect2011Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 49, nr 8, s. 1069-1075Artikkel i tidsskrift (Fagfellevurdert)
    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/oxygen 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 lasermaterial combination

  • 262.
    Powell, John
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Gedda, Hans
    Luleå tekniska universitet.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser casting and laser clad-casting: new processes for rapid prototyping2002Inngår i: Congress proceedings: Laser Materials Processing Conference [and] Laser Microfabrication Conference [presented at] ICALEO 2002, 21st International Congress on Applications of Lasers & Electro-Optics, October 14 - 17, 2002, Double Tree Paradise Valley Resort, Scottsdale, Arizona, USA / [ed] Eckhard Beyer, Orlando, Fla: Laser institute of America , 2002Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents preliminary experimental results from two new processes: Laser casting involves a process similar to blown powder laser cladding but the final product is not joined to the substrate. The substrate surface therefore acts as a mould in a laser casting process and the eventual casting retains the topological features of the substrate. Laser clad-casting involves the production of clad tracks which are welded as usual to a substrate but which are laid down between machined copper blocks. The eventual clad track therefore has its cross sectional profile determined by the blocks which are removed after completion of the cladding process. In this way clad tracks with large depth to width ratios can be achieved with pre determinated cross sections

  • 263. Powell, John
    et al.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Torkamany, Mohammad
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Na, Suck-Joo
    Department of Mechanical Engineering, KAIST, Daejeon.
    Petring, Dirk
    Fraunhofer-Institute for Laser Technology, Aachen.
    Zhang, Linjie
    Department of Physics, Xi'an Jiaotong University.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Weld root instabilities in fiber laser welding2015Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, nr Suppl. 2, artikkel-id S29008Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fiber laser welding and fiber laser-arc hybrid welding have been developed into very useful industrial processes over the past few years. However, the use of fiber lasers can be associated with quality problems at the weld root such as intermittent penetration, melt ejection, and humping. This paper explains the mechanisms which create these instabilities and suggests a repair technique which would alleviate the problems in some cases. The main difference between fiber and CO2 laser welding is that during fiber laser welding there is a strong downward thrust on the melt in the keyhole.(This is not the case during CO2 laser welding.) The downward thrust on the melt is generated as a result of the fiber laser evaporating the top faces of bumps on the melt surface. The downward flow has two main effects;(a) the melt can achieve velocities which result in melt ejection from the root of the weld-which can result in intermittent penetration,(b) the supply of hot metal to the bottom of the weld makes the process much more thermally uniform at the top and bottom of the weld. This uniformity means that the melt is extended backward several millimeters on the top and bottom surfaces-which can result in melt humping in the weld root as well as on the top surface. This paper examines these weld root instabilities and also describes a technique of weld root remelting which has been shown to be effective in smoothing out the root of the weld to improve its tensile and fatigue properties

  • 264.
    Powell, John
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser cutting: from first principle to the state of art2004Inngår i: Peer reviewed conference proceedings: PICALO 2004, 1st Pacific International Conference on Applications of Lasers and Optics : April 19 - 21, 2004, Grand Hyatt Melbourne, Melbourne, Australia, Orlando, Fla: Laser institute of America , 2004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents an overview of the subject of laser cutting. Subjects covered include; Laser-materials interactions, different laser types, the technical and commercial growth of laser cutting and the state of the art.

  • 265.
    Powell, John
    et al.
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser cutting technology - a commercial perspective: Fiber or CO2 laser – which one to buy next?2012Inngår i: Laser Technik Journal, ISSN 1613-7728, Vol. 9, nr 2, s. 39-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Since the advent of commercial fibre and disk laser cutting machines there has been a lot of controversy about the performance of these devices – particularly in comparison to their more established CO2 counterparts. In the early days the sales staff promoting fibre technology would often declare that the new lasers would completely take over from CO2 technology very quickly – but this has not happened. Even taking into account the entrenched position of the older technology, fibre and disk lasers have not been as widely accepted as was predicted, although they have been proven to outperform CO2 lasers in certain important areas.This article presents a discussion of the advantages and disadvantages of both types of cutting technology from a commercial point of view – written from the perspective of a laser cutting jobshop owner trying to decide between buying a fibre or CO2 laser cutting machine

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

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

  • 267.
    Powell, John
    et al.
    Nottingham University, School of Mechanical, Materials and Manufacturing.
    Petring, D
    Fraunhofer-Institute for Laser Technology, Aachen.
    Kumar, R.V.
    Cambridge University, Department of Materials Science.
    Al-Mashikhi, S.O.
    Nottingham University, School of Mechanical, Materials and Manufacturing.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    Nottingham University, School of Mechanical, Materials and Manufacturing.
    The energy generated by the oxidation reaction during laser-oxygen cutting of mild steel2008Inngår i: Congress proceedings: I ICALEO, 27th International Congress on Applications of Lasers and Electro-Optics : October 20 - 23, 2008 Pechanga Resort & Casino, Temecula, CA, USA / [ed] Yongfeng Lu, Orlando, Fla: Laser institute of America , 2008, s. 628-636Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents an in-depth analysis of the Iron to FeO oxidation reaction in the context of laser-oxygen cutting of mild steel. The paper concludes by presenting a number of guidelines for future theoretical models of laser-oxygen cutting.

  • 268. Powell, John
    et al.
    Petring, D.
    Fraunhofer-Institute for Laser Technology, Aachen.
    Kumar, R.V.
    University of Cambridge.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    University of Notttingham.
    Laser-oxygen cutting of mild steel: the thermodynamics of the oxidation reaction2009Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 42, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In a considerable proportion of the published work on the subject of laser-oxygen cutting of mild steel, the details of the oxidation reaction are overlooked or confused. For example, it is not uncommon for the oxidized material to be attributed with the physical characteristics of iron rather than iron oxide. Also, the fact that the oxidation reaction cannot take place above a certain temperature limit is usually overlooked. This paper presents, for the first time, an in-depth analysis of the Iron to FeO oxidation reaction in the context of laser-oxygen cutting of mild steel. The paper concludes by presenting a number of guidelines for future theoretical models.

  • 269.
    Prasad, Himani Siva
    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 IWS, Winterbergstrasse 28, 01277, Dresden, Germany.
    Volpp, Joerg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser metal deposition of copper on diverse metals using green laser sources2020Inngår i: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 107, nr 3-4, s. 1559-1568Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Green laser sources are advantageous in the processing of copper due to the increase of absorptivity compared with more commonly available infrared lasers. Laser metal deposition of copper with a green laser onto various substrate metals namely copper, aluminium, steel and titanium alloy was carried out and observed through high-speed imaging. The effects of process parameters such as laser power, cladding speed and powder feed rate, and material attributes such as absorptivity, surface conditions and thermal conductivity are tied together to explain the size and geometry of the melt pool as well as the fraction of the power used for melting material. The copper substrate has the smallest melt pool with a high angle, followed by aluminium, steel and titanium alloy. The incorporation times for powder grains in the melt pools vary based on the substrate materials. Its dependency on material properties, including surface tension forces, melting temperatures and material density, is discussed. Oxide skins present on melt pools can affect powder incorporation, most significantly on the aluminium substrate. The lower limits of the fraction of power irradiated on the surface used purely for melting were calculated to be 0.73%, 2.94%, 5.95% and 9.78% for the copper, aluminium, steel and titanium alloy substrates, respectively, showing a strong dependence on thermal conductivity of the substrate material. For a copper wall built, the fraction was 2.66%, much higher than a single clad on a copper substrate, due to reduced workpiece heating. The results of this paper can be transferred to other metals with low absorptivity such as gold.

  • 270.
    Ren, X.B.
    et al.
    SINTEF Materials and Chemistry, Trondheim.
    Akselsen, Odd M.
    SINTEF Materials and Chemistry, Trondheim.
    Ås, S.K.
    SINTEF Materials and Chemistry, Trondheim.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Residual stresses of hybrid larser-arc welding for arctic application2013Inngår 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. 183-191Konferansepaper (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 271. Resch, M.
    et al.
    Furst, M.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Schuöcker, D.
    The blown powder process: a promising method of laser-assisted rapid prototyping2001Inngår i: ICIT 2001: Conference proceedings / [ed] Karl. Kuzman, Celje: TECOS , 2001Konferansepaper (Fagfellevurdert)
  • 272.
    Resch, M.
    et al.
    Vienna University of Technology.
    Kaplan, Alexander
    Heat conduction modelling of laser welding1998Inngår i: Lasers in engineering (Print), ISSN 0898-1507, E-ISSN 1029-029X, Vol. 7, nr 3-4, s. 229-240Artikkel i tidsskrift (Fagfellevurdert)
  • 273. Resch, M.
    et al.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Schuöcker, D.
    Laser-assisted generating of three-dimensional parts by the blown powder process2001Inngår i: Proceedings: XIII International Symposium on Gas Flow and Chemical Lasers and High-Power Laser Conference, 18 - 22 September 2000, Florence, Italy / [ed] Antonio Lapucci, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2001, s. 555-558Konferansepaper (Fagfellevurdert)
  • 274.
    Robertson, Stephanie
    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.
    Hong, Seong Min
    Department of Welding and Joining Science Engineering, Chosun University, Gwangju, Republic of Korea.
    Kim, Jong-Hee
    Department of Welding and Joining Science Engineering, Chosun University, Gwangju, Republic of Korea.
    Bang, Hee-Song
    Department of Welding and Joining Science Engineering, Chosun University, Gwangju, Republic of Korea.
    Tailored laser pulse method to manipulate filler wire melt metallurgy from thermal cycles2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022605Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A robust method is introduced to simulate and study the filler wire metallurgy for controlled cooling conditions after melting, enabling efficient mapping with prompt analysis of trends. Proposed is a reduced, though representative, process with more controllable conditions. Short lengths of filler wires are preplaced in a cavity, drilled into a base metal sheet. Irradiation by a pulsed laser beam melts the wire to generate a sample nugget. Pulse shaping influences the cooling rate, granting the ability to tailor weldament microstructures. The method is demonstrated for S1100QL steel and undermatched filler wire, to obtain high toughness for processes like laser-arc hybrid welding, where a representative thermal cycle is needed. For high toughness, a controlled amount of acicular ferrite and, in turn, nonmetallic inclusions is desirable. This “snapshot” method has revealed a characteristic histogram of inclusion sizes, for different pulse shapes. Additional information on the thermal cycle can be acquired by employing thermocouples, a pyrometer, or advanced methods like high speed imaging or modeling. The method offers a wide spectrum of variants and applications.

    Fulltekst (pdf)
    fulltext
  • 275.
    Samarjy, Ramiz S. M.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Department of Mechanical Engineering, College of Engineering, University of Mosul, Mosul, 41002, Iraq.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Additive manufacturing and recycling by a laser-induced drop jet from a sheet edge2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 4, artikkel-id 042010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new technique for additive manufacturing was recently presented by depositing droplets as a continuous track on a substrate, where the droplets were ejected from laser remote fusion cutting of a metal sheet. For the here presented approach, the droplets are instead ejected from the sheet edge, termed the machining mode, which is compared to cutting. Here, the transmitted part of the laser beam does not hit and interact with the deposited track because of lateral dislocation. High speed imaging has shown that laser-induced boiling, which drives the melt downwards, causes asymmetric conditions in the machining mode by lateral pushing of the generated drop jet under the sheet, where the melt can even attach. Compared to machining, the cutting mode keeps less deviation of the drop trajectories, higher precision, and a smoother surface finish. It was demonstrated that the edge conditions after machining are sufficient to repeat the process. This enables additional technique opportunities, including recycling of a whole sheet of waste metal. By the aid of high speed imaging from two different perspectives, the melt flow behavior, the drop jet precision, and process trends with respect to parameters, drop ejection, and deposition were studied.

  • 276.
    Samarjy, Ramiz Saeed Matti
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Imaging of the Dynamic Melt Movement Induced by a Pulsed Laser2016Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 83, s. 1308-1318Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 277.
    Samarjy, Ramiz Saeed Matti
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. University of Mosul, College of Engineering, Department of Mechanical Engineering.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Using laser cutting as a source of molten droplets for additive manufacturing: A new recycling technique2017Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 125, s. 76-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new variant of additive manufacturing is proposed which involves transferring molten droplets via a laser beam to a substrate. The droplets are generated by laser remote fusion cutting of a supply sheet that could be a waste material, for recycling purposes. The laser-induced ablation pressure at the cutting front continuously drives melt downwards below the supply sheet in the form of a liquid column. Droplets separate from the column and solidify as a track on a substrate below. The droplets, surrounded by vapour, had in this case an average diameter of 500 μm and a speed of 2 m/s, with deviations up to 50%. Sound clad tracks were generated on steel and aluminium substrates. In the case of a copper substrate discontinuous clad tracks were produced as a result of poor wetting. The droplet jet had a small divergence of about 5°, which is suitable for controlled deposition. The transmitted part of the laser beam interacted with the clad track but did not affect the process result. High speed imaging was found to be a suitable tool for qualitative and quantitative analysis of the technique.

  • 278.
    Samarjy, Ramiz Saeed Matti
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F.H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser-induced boiling and melt transfer from a metal edge2017Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new technique for additive manufacturing was recently presented, by depositing droplets as a continuous track on a substrate, where the droplets were ejected from laser remote fusion cutting of a metal sheet. For the here presented approach, the droplets are instead ejected from the sheet edge, termed the machining mode, which is compared to cutting. Here the transmitted part of the laser beam does not hit and interact with the deposited track because of lateral dislocation. High speed imaging has shown that laser-induced boiling, which drives the melt downwards, causes asymmetric conditions in the machining mode by lateral pushing of the generated drop jet under the sheet, where the melt even can attach. Compared to machining, the cutting mode keeps less deviation of the drop trajectories, higher precision and a smoother surface finish. It was demonstrated that the edge conditions after machining are sufficient to repeat the process. This enables additional technique opportunities, including recycling of a whole sheet of waste metal. By the aid of high speed imaging from two different perspectives, the melt flow behaviour, the drop jet precision as well as process trends with respect to parameters, drop ejection and deposition were studied.

  • 279.
    Samarjy, R.S.M.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. University of Mosul, College of Engineering, Department of Mechanical Engineering.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Transient interaction of a boiling melt with a pulsed Nd:YAG-laser2017Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 88, s. 28-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The boiling front induced by a pulsed Nd:YAG-laser at very slow translation speed was studied. The purpose is to understand fundamental melt movement mechanisms. The melt was observed by high speed imaging, with and without illumination. When switching on the laser beam a hole is drilled through a bulk of melt. The hole expands and the boiling pressure gradually opens the melt bridge, instead developing an interaction front similar to cutting. These conditions remain in quasi-steady state during the pulse. The ablation pressure from boiling shears waves down the front and keeps the melt downwards in a stable position. When switching off, the waves smoothen and in absence of boiling the surface tension drags the melt back upwards, to semi-torus-like Catenoid shape. Evidence on the large melt pool and its shape was achieved by three-dimensional reconstruction from cross section macrographs. The basic findings how melt can move with and without ablation pressure can enable controlled melt dynamics for various laser processing techniques, like remote cutting, ablation, keyhole welding or drilling.

  • 280. Sarady, Istvan
    et al.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Investigation of interaction mechanisms in laser processing using digital speckle photography2003Inngår i: Congress proceedings: Laser Materials Processing Conference [and] Laser Microfabrication Conference [at] ICALEO 2003, 22nd International Congress on Applications of Lasers & Electro-Optics, October 13 - 16, 2003, Adam's Mark Hotel, Jacksonville, Florida, USA / [ed] Xiangli Chen, Orlando, Fla: Laser institute of America , 2003, s. 314-321Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Digital, defocused speckle photography was used for the in-situ, real-time determination of the strain field round the focus spot of a pulsed Nd:YAG laser. These surface strains can cause cracking during laser cutting and drilling of advanced engineering ceramic materials. A CW HeNe laser was used for illumination, images being captured by CCD camera with a 633 nm band pass filter, synchronised to operate between the individual laser pulses. Targets included alumina and stainless steel.

  • 281. Sarady, Istvan
    et al.
    Miroshnikova, N.
    Yalukova, O.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Drilling of different materials with pulsed lasers at short wavelengths2005Inngår 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. 245-256Konferansepaper (Fagfellevurdert)
  • 282. Sarady, Istvan
    et al.
    Yalukova, O.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Drilling of polymeric materials with pulsed lasers at short wavelengths2005Inngår 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. 245-255Konferansepaper (Fagfellevurdert)
  • 283.
    Schuöcker, D.
    et al.
    Vienna University of Technology.
    Kaplan, Alexander
    Modellbildung zum Laserschweissen1997Inngår i: Laser von der Wissenschaft zur Anwendung, Bremen: BIAS Verlag , 1997, s. 57-66Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 284. Schuöcker, D.
    et al.
    Kaplan, Alexander
    Overview over modelling for laser applications1994Inngår i: Ikke angivet, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 1994, s. 236-247Konferansepaper (Fagfellevurdert)
  • 285. Schuöcker, D.
    et al.
    Kaplan, Alexander
    Recent developments in laser-assisted forming1999Inngår i: Ikke angivet, IVF , 1999Konferansepaper (Annet vitenskapelig)
  • 286. Schuöcker, D.
    et al.
    Kaplan, Alexander
    Simplified model of deep penetration laser welding1990Konferansepaper (Fagfellevurdert)
  • 287. Schuöcker, D.
    et al.
    Kaplan, Alexander
    Liedl, G.
    Zimmermann, J.
    Experimental and theoretical studies of laser welding1999Inngår i: International Symposium on Automotive Technology and Automation: 32nd ISATA,advances in automotive and transportation technology and practice for the 21st Century, Croydon: ISATA , 1999, s. 399-408Konferansepaper (Fagfellevurdert)
  • 288. Schuöcker, D.
    et al.
    Vees, G.
    Kaplan, Alexander
    Penz, A.
    Weingartner, W.
    Recent results in laser applications at the Institute for high power beam technology (IST, Vienna)1996Inngår i: Proceedings of the 13th Conference BIAM / [ed] B. Vanjes, 1996, s. L10-L13Konferansepaper (Fagfellevurdert)
  • 289. Schuöcker, D.
    et al.
    Weingartner, W.
    Schröder, K.
    Kaplan, Alexander
    Basic concepts of high power lasers1999Inngår i: Ikke angivet, IVF , 1999Konferansepaper (Fagfellevurdert)
  • 290.
    Siva Prasad, Himani
    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 IWS, Winterbergstrasse 28, Dresden, Germany.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powder catchment in laser metal deposition2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser metal deposition (LMD) of Inconel 718 using a coaxial nozzle is investigated by high-speed imaging. The interaction of individualpowder grains with the laser induced melt pool surface and, finally, their catchment in the LMD track is observed. Powder catchment trendsare explained by interpreting physical phenomena, such as the melt flow and surface tension. Distinct zones for powder catchment are categorizeddepending on the position of initial interaction between powder grains and the melt pool. Particles are introduced outside the meltpool ricochet and do not attach to the clad. Particles arriving outside the laser spot, onto the solidifying skin of the melt pool, are caught,and may incorporate. Some particles may remain on the clad surface as surface roughness on the built part. Particles interacting with thelaser-irradiated region of the melt pool tend to move toward its center and readily incorporate into the melt. Quantitative analyses of highspeedvideos are carried out to measure incorporation time of powder grains in the melt pool, their velocity, and distance traveled.

  • 291.
    Siva Prasad, Himani
    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.
    The stability of laser welding with an off-axis wire feed2019Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 264, s. 84-90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The concept using an off-axis filler wire during laser welding is introduced here in order to provide added process robustness considering gap width variations. Its stability is investigated with respect to gap width, welding speeds and powers. Geometry of the welds is analysed by tracing of weld cap edges and joint cross sections, connecting trends to weld parameters. High speed imaging and streak images are used to further study and describe sequences of events, including undercut formation. Formation of imperfections are found to be mainly correlated to wire feed position variations at the surface due to irregular melting of the wire tip.

  • 292.
    Sokolov, Mikhail
    et al.
    Lappeenranta University of Technology.
    Salminen, Antti
    Lappeenranta University of Technology.
    Somonov, Vladislav
    Saint-Petersburg State Polytechnical University.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser welding of structural steels: influence of the edge roughness level2012Inngår i: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 44, nr 7, s. 2064-2071Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser welding continues to become more extensively used in many industrial applications and in the last 10 years an increasing number of studies have examined ways to increase the efficiency of the process. This study investigates the influence of joint edge surface roughness on weld quality and penetration depth. The characteristics are investigated of welded samples of two low alloyed steels, S355 and St 3, of 20 mm thickness with various joint edge surface roughness levels in butt joint configuration. Welding was performed with different fiber lasers with a wavelength of 1070 nm at power levels from 10 to 15 kW. The absorption characteristics were evaluated at 10 kW power level using a calorimeter. There was a significant positive correlation between edge surface roughness level and the penetration depth. Optimum roughness levels to provide maximum penetration depth are presented. The highest penetration depth at power levels of 14 and 10 kW was achieved at Ra=6.3 μm.

  • 293.
    Song, Hong-Wei
    et al.
    Laboratory for Laser Intelligent Manufacturing, Institute of mechanics, Chinese Academy of Sciences.
    Yu, Gang
    Laboratory for Laser Intelligent Manufacturing, Institute of mechanics, Chinese Academy of Sciences.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Tan, Jian-Song
    College of Mechanical and Energy Engineering, Zhejiang University.
    Yu, Xiao-Li
    College of Mechanical and Energy Engineering, Zhejiang University.
    Thermal fatigue on pistons induced by shaped high power laser: Part II: Design of spatial intensity distribution via numerical simulation2008Inngår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 51, nr 3-4, s. 768-778Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the laser induced thermal fatigue simulation test on pistons, the high power laser was transformed from the incident Gaussian beam into a concentric multi-circular pattern with specific intensity ratio. The spatial intensity distribution of the shaped beam, which determines the temperature field in the piston, must be designed before a diffractive optical element (DOE) can be manufactured. In this paper, a reverse method based on finite element model (FEM) was proposed to design the intensity distribution in order to simulate the thermal loadings on pistons. Temperature fields were obtained by solving a transient three-dimensional heat conduction equation with convective boundary conditions at the surfaces of the piston workpiece. The numerical model then was validated by approaching the computational results to the experimental data. During the process, some important parameters including laser absorptivity, convective heat transfer coefficient, thermal conductivity and Biot number were also validated. Then, optimization procedure was processed to find favorable spatial intensity distribution for the shaped beam, with the aid of the validated FEM. The analysis shows that the reverse method incorporated with numerical simulation can reduce design cycle and design expense efficiently. This method can serve as a kind of virtual experimental vehicle as well, which makes the thermal fatigue simulation test more controllable and predictable.

  • 294.
    Sundqvist, Jesper
    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.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Keskitalo, M.
    University of Oulu.
    Mentyjärvi, K.
    University of Oulu.
    Influence of the metallurgy on fatigue crack propagation in welded high strength steel joints2013Inngår 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. 25-35Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A literature study of high strength steels, fatigue and fatigue assessment of welds has beenconducted and is briefly presented in this paper together with experiments on fatigue crackgrowth rates of laser welded high strength steel. It is well-known that the fatigue life ofwelded joints is heavily dependent upon the surface geometry and welding defects because ofcrack initiation from the high stress concentrations associated with these types of weldingflaws. However, the crack propagation through different weld zones of laser-welded highstrength steels and the corresponding impact from the metallurgy is not fully understood.The experiments comprise three-point bending fatigue tests on laser-welded highstrength steel with machined surfaces. Measurement of the fatigue crack propagation ratetransverse the weld and hence through the different metallurgy and hardness of the heataffected zone and of the weld can contain information on the impact of the metallurgy on thecrack propagation speed. The influence of different high strength steel grades and of differentwelding parameters on the crack propagation and fatigue life is discussed

    Fulltekst (pdf)
    FULLTEXT01
  • 295.
    Sundqvist, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Eriksson, Ingemar
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Keskitalo, Markku
    University of Oulu, University of Oulu, Oulu Southern Institute.
    Mäntyjärvi, Kari
    University of Oulu.
    Granström, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Sundin, Karl-Gustaf
    Measuring the influence of laser welding on fatigue crack propagation in high strength steel2013Inngår i: ICALEO, 32nd International Congress on Applications of Lasers & Electro-Optics: October 6-10, 2013, Hyatt Regency Miami, Miami, FL USA, Orlando, Fl.: Laser institute of America , 2013Konferansepaper (Fagfellevurdert)
  • 296.
    Sundqvist, Jesper
    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.
    Sensitisation behaviour of drop-deposited 11% Cr ferritic stainless steel2018Inngår i: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, s. 487-495Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For low-chromium ferritic stainless steel, a recently developed laser-driven drop-deposition technique enabled the building of three adjacent tracks on a substrate sheet of the same alloy, to study its risk for sensitisation from certain sequences of thermal cycles. The process was recorded by high-speed imaging to understand the drop-deposition mechanisms. Higher beam power resulted in a smoother track. The added layer was fully martensitic, achieving an elevated hardness of 320 HV. For a temperature peak just below austenitisation, the thermal cycle from a subsequent track affected the former track through tempering. Etching revealed a continuous region of ditched grain boundaries around the interface between the melted and heat affected zones. In the melted zone, the network became discontinuous approaching the surface, meaning that the specimen was immune to sensitisation, in contrast to transformation hardening results in the solid state. Additive manufacturing can induce manifold sequences of thermal cycles, but from the here generalized knowledge, strategies against sensitisation can be derived.

  • 297.
    Sundqvist, Jesper
    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.
    Granström, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Sundin, Karl-Gustaf
    Keskitalo, Markku
    University of Oulu, University of Oulu, Oulu Southern Institute.
    Mäntyjärvi, Kari
    University of Oulu.
    Ren, Xiaobo
    SINTEF Materials and Chemistry, Trondheim.
    Identifying residual stresses in laser welds by fatigue crack growth acceleration measurement2015Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, nr 4, artikkel-id 42002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During laser welding, residual stresses are thermally induced. They can have strong impact on the fatigue behavior and fatigue life. A standardized measurement method for the fatigue crack growth rate was expanded to identify residual stress along the cracking path. The second derivative of the measured crack opening and in turn the crack acceleration corresponded well with distinct acceleration maxima and minima and accordingly with tensile and compressive stress, as was basically proven by numerical simulation. The method is simple and extendable. It provides valuable information, as was demonstrated for various situations.

  • 298.
    Sundqvist, Jesper
    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.
    Kong, Choon Yen
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Assuncao, Eurico
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Quintino, Luisa
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Blackburn, Jon
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Numerical sensitivity analysis of single pulse laser welding with a C-shaped beam2015Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, nr Suppl. 2, artikkel-id S29010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Even though Gaussian and top-hat beam profiles are suitable for most laser welding applications, for certain cases other beam distributions can be favored in terms of weld quality or performance. One promising method to generate a tailored beam shape is diffractive optical elements. A numerical model on the temperature field generated by specific beam shapes is therefore under development to iteratively identify desired beam shapes for specific applications. The present study is based on two thin steel sheets that are conduction welded in a lap joint mode by a C-shaped single laser pulse. The main aim is to ensure a specified weld width along the C-weld shape at the overlap interface between the two sheets in a robust manner. The sensitivity of main criteria like the interface weld width and phase changes at the workpiece top and bottom is studied and discussed in a systematic manner by applying a numerical heat transfer model for various parameters and conditions.

  • 299.
    Sundqvist, Jesper
    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.
    Kong, Choon Yen
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Blackburn, Jon
    TWI Ltd., Granta Park, Great Abington, Cambridge.
    Assuncao, Eurico
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Quintino, Luisa
    LAETA, IDMEC, Instituto Superior Técnico, Universidade de Lisboa.
    Heat conduction modelling to optimize the laser beam profile for pulsed conduction mode welding2015Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    FULLTEXT01
  • 300.
    Sundqvist, Jesper
    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.
    Shachaf, L.
    Holo/Or Ltd.
    Kong, Choon Yen
    TWI Ltd, Granta Park, Great Abington, Cambridge .
    Analytical heat conduction modelling for shaped laser beams2017Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 247, s. 48-54Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Conduction mode laser spot welding and laser spot hardening usually employ Gaussian or top-hat-like beam modes. One main requirement of these techniques is the avoidance of overheating in the centre of the laser-material interaction zone. Process flexibility can be improved by spatially and/or temporally shaping the beam, which can enable higher process quality, robustness or speed. A desired spatial beam shape can be achieved by a suitably designed diffractive optical element. However, the prediction of a suitable beam shape for a particular process can be complex. A simplified analytical heat conduction model has been developed that can rapidly calculate the temperature field and cooling behaviour for almost any spatial and temporal beam shape. The potential and limits of the model are demonstrated and discussed by calculating and analysing temperature profiles for several cases of multi-spot welding

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