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  • 1.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    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 components2013Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 2.
    Al-Mashikhi, S.O
    et al.
    Salalah College of Technology, Engineering Department, Salalah, Oman and Faculty of Engineering, University of Nottingham.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    Faculty of Engineering, University of Nottingham.
    Heat affected zones and oxidation marks in fiber laser–oxygen cutting of mild steel2011Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    Atiyah, H.
    et al.
    Faculty of Engineering, The University of Nottingham.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Petring, D.
    Fraunhofer Institute for Laser Technology ILT.
    Stoyanov, S.
    Fraunhofer Institute for Laser Technology ILT.
    Voisey, T.
    Faculty of Engineering, The University of Nottingham.
    Fiber laser cutting: The use of carbon-filled acrylic as a qualitative and quantitative analysis tool2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, artikkel-id 032009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of carbon-filled black acrylic (CFBA) as a quantitative and qualitative analytical tool for fiber laser cutting is investigated. In the qualitative work, CFBA targets placed below the laser cutting zone when cutting stainless steel showed a distinctive “leaf” shaped evaporation crater which can provide information about the nature of the reflections taking place in the cut zone. Quantitative measurements have revealed a specific evaporation energy of 3.4 J/mm3 for CFBA. However, this figure is only applicable when considering intense beams when the CFBA target is stationary with respect to the laser beam.

  • 4.
    Brueckner, Frank
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology.
    Mûller, Michael
    Fraunhofer Institute for Material and Beam Technology.
    Marquardt, Alex
    Fraunhofer Institute for Material and Beam Technology.
    Willner, Robin
    Fraunhofer Institute for Material and Beam Technology.
    Seidel, André
    Fraunhofer Institute for Material and Beam Technology.
    Lopez, Elena
    Fraunhofer Institute for Material and Beam Technology.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology.
    Beyer, Eckhard
    Fraunhofer Institute for Material and Beam Technology.
    Enhanced manufacturing possibilities using multi-materials in laser metal deposition2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikkel-id 032308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing (AM) addresses various benefits as the buildup of complex shaped parts, the possibility of functional integration, reduced lead times or the use of difficult machinable materials compared to conventional manufacturing possibilities. Beside these advantages, the use of more than one material in a component would strongly increase the field of applications in typical AM branches as energy, aerospace, or medical technology. By means of multi-material buildups, cost-intensive alloys could be only used in high-loaded areas of the part, whereas the remaining part could be fabricated with cheaper compositions. The selection of combined materials strongly depends on the requested thermophysical but also mechanical properties. Within this contribution, examples (e.g., used in the turbine business) show how alloys can be arranged to fit together, e.g., in terms of a well-chosen coefficient of thermal expansion. As can be seen in nature, the multi-material usage can be characterized by sharp intersections from one material to the other (e.g., in case of a thin corrosion protection), but also by graded structures enabling a smoother material transition (e.g., in case of dissimilar materials which are joined together without defects). The latter is shown for an example from aerospace within this paper. Another possibility is the simultaneous placement of several materials, e.g., hard carbide particles placed in a more ductile matrix composition. These particles can be varied in size (e.g., TiC versus WC). Also the ratio between carbides and matrix alloy can be adjusted depending on its application. Especially, nozzle-based free form fabrication technologies, e.g., laser metal deposition, enable the utilization of more than one material. Within this contribution, possibilities to feed more than one filler material are demonstrated. In addition, results of multi-material processes are shown. Finally, this work focuses on different (potential) applications, mainly on power generation, but also for medical technology or wear resistant components.

  • 5.
    Eriksson, Ingemar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Surface tension generated defects in full penetration laser keyhole welding2014Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 1, artikkel-id 12006Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During laser keyhole welding of thin plates the melt pool is relatively wide compared to the plate thickness. Under certain conditions an elongated keyhole can be created and a permanent hole is sometimes left in the weld seam. The generation of such holes is determined by surface tension effects in the melt which can generate a self sustaining geometry at the rear of the melt pool. The geometry of the shape is known as a catenoid and has clear geometrical limits.

  • 6. Forsman, Tomas
    et al.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    Initiation and termination phenomena in laser welding of aluminum2000Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 12, nr 2, s. 81-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article investigates a defect problem related to laser welding of tailored aluminum blanks. During the initial few millimeters of welding the weld was intermittent. By applying an analytical line source model the weld was shown to experience overheating close to the starting edge. This overheating was reduced by ramping the power during the initial 100 mm and this made the defects disappear. Al sheets of 0.1mm thickness with milled edges were butt welded and bead-on-plate welded in the present investigation.

  • 7.
    Forsman, Tomas
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    Process instability in laser welding of aluminum alloys at the boundary of complete penetration2001Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 13, nr 5, s. 193-198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Intrinsic instabilities in the depth of penetration achieved when laser welding aluminum alloys were investigated in this article. Four types of weld pool configuration, resulting in different welds, were identified, only two of which are associated with full penetration. A simple phenomenological explanation of the unstable welding process at the boundary of complete penetration was proposed. The nature and cause of the instabilities were discussed and suggestions were offered for process control. Materials used: AA6016 aluminum alloy.

  • 8.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Comparison of three different arc modes for laser-arc hybrid welding steel2016Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 28, nr 2, artikkel-id 22407Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 9.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Undercut suppression in laser-arc hybrid welding by melt pool tailoring2014Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 3, s. 4-, artikkel-id 31501Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 10.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Qinglong, Pan
    Joining and Welding Research Institute, Osaka University.
    Mizutani, Masami
    Joining and Welding Research Institute, Osaka University.
    Kawahito, Yousuke
    Joining and Welding Research Institute, Osaka University.
    Katayama, Seiji
    Joining and Welding Research Institute, Osaka University.
    Effects of edge oxides from laser cutting in laser-arc hybrid welding2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 1, artikkel-id 012014Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 11.
    Frostevarg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Torkamany, Mohammad
    Department of Materials Engineering, Tarbiat Modares University.
    Powell, John
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Improving weld quality by laser re-melting2014Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 4, artikkel-id 41502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 12.
    Gedda, Hans
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Wahlström, G.
    Duroc AB.
    Li, W-B
    Luleå tekniska universitet.
    Engström, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Magnusson, Claes
    Energy redistribution during CO2 laser cladding2002Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 14, nr 2, s. 78-82Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article examines the factors that effect the efficiency of the CO sub 2 -laser powder cladding process. By theoretical calculation and experimental work it has been possible to identify how much of the original laser energy contributes to the cladding process and how much is lost to the surrounding environment by reflection, radiation, convection, etc. Every aspect of energy redistribution has been analyzed and quantified and this has led to a deeper understanding of the process. The article concludes with a number of suggestions for improving the efficiency of blown powder laser cladding.

  • 13.
    Haglund, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Eriksson, Ingemar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Surface tension stabilized laser welding (donut laser welding): A new laser welding technique2013Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new laser welding process is presented which delivers a porosity free, spatter free weld. The process involves a donut shaped melt with a central hole of the same order of magnitude as the material thickness. The laser illuminates only the leading section of this melt. The hole is kept open by the melt surface tension.

  • 14.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Vomacka, P.
    Luleå tekniska universitet.
    Acoustic emission response of soda lime glass after a single Nd-YAG laser pulse1994Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 6, nr 3, s. 153-158Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When machining brittle solids with a laser, crack formation can occur in the material around the irradiated area causing a strength reduction of the machined material. The purpose of this work was to study a well known brittle material (soda lime glass) by means of acoustic emission (AE) in order to investigate the correlation between visually observed crack formation and detected AE energy released by the crack formation in the material. During and after irradiation of soda lime glass with an Nd-YAG laser pulse, the number of hits and amount of AE energy were measured in the first 300 s using AE. It was found that it is possible to detect AE signals from cracks caused by irradiation with a single Nd-YAG laser pulse. The power of the detected signal is related to the amount of crack formation. Cracks can be minimized or avoided by choosing a suitable combination of pulse time and power density of the single laser pulse. The cracks which occur after a laser shot extend mainly in the radial direction from the irradiated area.

  • 15.
    Ion, John
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Kokkonen, J.
    Lappeenranta University of Technology.
    A comparison of gas tungsten arc and CO2 laser beam welding of AA20242001Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 13, nr 2, s. 79-83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mechanical fastening methods are used extensively to join aluminum alloys, particularly in the aerospace industries. Laser welding provides the possibility of a high productivity single-step process, with the added benefit of potential weight savings of about 10% in comparison with riveting. However, the weldability of many aluminum aerospace alloys is generally considered to be low, and little data are currently available. A procedure for CO2 laser welding of the alloy AA2024 is developed, with the use of 2319 filler wire. Weld property data are shown to achieve the requirements for the most stringent quality level of the current European workmanship standard for laser-welded joints in aluminum. Hardness and tensile strength properties are shown to be similar to those of gas tungsten arc (GTA) welds. The fatigue strength of GTA welds is superior to that of laser welds in the as-welded condition, but when the weld bead is machined flush with the plate surface the difference is reduced. The laser welds achieved the requirements of recommendations produced by the International Institute of Welding for single-sided welding of aluminum alloys. The quality of the weld toe is shown to have the greatest effect on fatigue strength.

  • 16.
    Ivarson, Anders
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    Role of oxidation in laser cutting stainless and mild steel1991Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 3, nr 3, s. 41-45Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper gives the results of a detailed examination of the particles ejected from the cut zone during CO2 laser cutting of mild and stainless steels. Cuts were carried out over a range of material thickness at the optimum speed for each at a laser power of 900 Watts. Particles ejected from the cut zone were collected and analyzed to establish their chemical and physical characteristics. Analysis techniques included Scanning Electron Microscopy, wet chemical analysis, optical microscopy, metallography and particle sizing. The results from this extensive analysis have enabled the authors to estimate the heat generated by the oxidation process during cutting of both mild and stainless steels.

  • 17.
    Ivarson, Anders
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    Role of oxygen pressure in laser cutting mild steels1996Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 8, nr 4, s. 191-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the results of an experimental program investigating the effects of using high pressure oxygen as assist gas in combination with a pulsed laser while cutting medium thick mild steel plates. It was discovered that if the pulse conditions are optimized, the maximum cutting speed for a set average laser power could be increased by up to 10% compared to low oxygen pressure continuous wave (CW) laser cutting. The assist gas was found to have two optimum pressure ranges between which the material suffered from burning on the cut edge. The paper presents a phenomenological model to explain the changes in cut front dynamics as the oxygen pressure is increased and the role of pulsing in suppressing edge burning

  • 18.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Influence of the beam profile formulation when modeling fiber-guided laser welding2011Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During deep penetration laser welding, the focused laser beam determines the vapor capillary, called keyhole, and in turn the whole process physics. Beside spot diameter and Rayleigh length, the beam profile is another important but hardly explored part of the focused laser beam. The focusing of fiber-guided Yb:fiber, Nd:YAG or diode laser beams creates the complex situation that the beam has a top-hat profile in the focal plane but toward the far field transforms to a Gaussian beam. Such power density distribution was measured for a focused high power Yb:fiber laser beam and then approached by three different beam formulations. The beam formulations were then applied to model the keyhole shape during laser welding. Although a second order beam model approached the measured beam significantly more accurately, the first order Gaussian beam was similarly suitable to predict the keyhole shape as long as the central beam domains do not interact with the material, which occurs only for low focal plane positions. A hypothetical top-hat beam would cause a different, steeper keyhole shape. Consequently, a Gaussian beam is still a suitable formulation for a wide range of welding parameters.

  • 19.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser absorptivity on wavy molten metal surfaces: Categorization of different metals and wavelengths2014Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 1, artikkel-id 12007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The absorptivity of a laser beam interacting at grazing incidence with the processing front during laser welding, cutting, or drilling depends on the metal to be processed and on the laser wavelength. The absorptivity on a smooth processing front is homogeneously governed by the angle-dependent operating range of the corresponding Fresnel-curve. In contrast, a wavy processing front strongly modulates the absorptivity across the surface. The calculated absorptivity modulation is presented for five different metals and four laser wavelengths. A discussion based on the respective optical constants and Fresnel-curves leads to a categorization of the absorption behavior, mainly dividing into low and high electrical conductivity metals as well as into short and 10.6 μm long laser wavelength. Six categories are distinguished. In particular, highly conductive metals remain highly reflective for short laser wavelength, even for a wavy processing front. Exceptions of higher overall absorptance are Cu for 532 nm and Al for 808 or 532 nm

  • 20.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kim, Kyounghak
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Bang, Hee-Seon
    Chosun University, Department of Welding & Joining Science Engineering.
    Bang, Han-Sur
    Chosun University, Department of Welding & Joining Science Engineering.
    Näsström, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Narrow gap laser welding by multilayer hot wire addition2016Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 28, nr 2, artikkel-id 22410Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 21.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Matti, Ramiz
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Absorption peaks depending on topology of the keyhole front and wavelength2015Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, nr Suppl. 2, artikkel-id S29012Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By high speed imaging, wavy patterns were observed at the keyhole front in Yb:fibre laser welding. Despite a regular appearance of downstreaming wave flow in the movies, deeper image analysis shows that the pattern structure is complex. The observed grayscale levels of the flow pattern are likely to correspond to a combination of temperature, topology, and emissivity of the keyhole front, in turn originating from variations of the beam absorption, temperature, boiling, ablation pressure, and melt acceleration across the keyhole surface. Bright domains can fluctuate on a time scale of 10-100 mu s. For interpretation of the fundamental mechanisms, the evidence from high speed imaging analysis is accompanied by mathematical modeling of the absorption modulation, combining local absorptivity, and beam projection. The calculated results show that for a wide range of keyhole topology parameters, lasers with a wavelength of about 1 mu m induce high absorption peaks at the wave shoulders while CO2-lasers have a more homogenizing behavior. Different regimes can be distinguished

  • 22.
    Kaplan, Alexander
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Spatter in laser welding2011Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spatter, the ejection of melt from a weld pool, is a major problem whenever it occurs in a welding process. The ejection of droplets from the weld metal results in a weld with underfill, undercuts, craters, blowholes, or blowouts-all of which can have a detrimental effect on the mechanical properties of the weld. This paper presents a systematic description of the different types of spatter phenomena which occur during laser welding. A categorization system is proposed to facilitate the comparison and combination of research findings on spatter. This should allow researchers in this area to act as a more effective team in future

  • 23.
    Kledwig, Christian
    et al.
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten 87459, Germany.
    Perfahl, Holger
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten 87459, Germany.
    Reisacher, Martin
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten 87459, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology IWS, Dresden 01277, Germany.
    Bliedtner, Jens
    SciTec Department, Ernst-Abbe-Hochschule Jena, Jena 07745, Germany.
    Leyens, Christoph
    Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology IWS, Dresden 01277, Germany. Institute of Materials Science, Technische Universität Dresden, Dresden 01062, Germany.
    Image-based algorithm for nozzle adhesion detection in powder-fed directed-energy deposition2020Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 32, nr 2, artikkel-id 022021Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rapidly growing technological innovation of directed energy deposition leads to an increase in part complexity as well as quality and mechanical properties of manufacturable components. However, the variety of process parameters and influencing factors still requires skilled operators, who observe the machine tools. For an unobserved use of deposition welding machines, well parametrized and validated monitoring systems have to analyze the process to detect irregularities and finally initiate a machine stop. This study focuses on nozzle adhesions that frequently occur when tool or high-speed steels are processed. This effect leads to decreasing quality or ultimately to a failure of the whole welding process. In this work, the authors present an algorithm and the corresponding parametrization to automatically detect nozzle adhesions based on images from a coaxial camera, integrated in the laser head. The algorithm is based on a detailed image analysis from which temporal and spatial patterns are derived. In particular, the algorithm calculates a nozzle adhesion indicator based on the heat intensity distribution in an experimentally derived shaped area on the inner nozzle boundary. It is parametrized in such a way that process-critical adhesions are detected. The algorithm was parametrized using an experimental setup with four materials: stainless steel (X2CrNiMo17-12-2), tool steel (X35CrMoMn7-2-1), high-speed steel (HS6-5-2C), and the nickel-based alloy NiCr19NbMo.

  • 24.
    Koh, Y.S.
    et al.
    Kiruna Center for Conservation of Cultural Property.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Removal of layers of corrosion from steel surfaces: a qualitative comparison of laser methods and mechanical techniques2007Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 19, nr 2, s. 99-106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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

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

  • 26.
    Lopez, Elena
    et al.
    Fraunhofer Institute for Material and Beam Technology.
    Felgueiras, Tomás
    Fraunhofer Institute for Material and Beam Technology.
    Crunert, Christian
    Fraunhofer Institute for Material and Beam Technology.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology.
    Seidel, André
    Fraunhofer Institute for Material and Beam Technology.
    Marquardt, Alex
    Fraunhofer Institute for Material and Beam Technology.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology.
    Beyer, Eckhard
    Fraunhofer Institute for Material and Beam Technology.
    Evaluation of 3D-printed parts by means of high-performance computer tomography2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikkel-id 032307Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Conventional tactile and optical testing methods are not capable to detect complex inner geometries or complex surface shapes. Detecting porosities in parts is also not possible with those nondestructive methods. Among other material parameters, geometrical accuracy is essential to determine part's quality. Additive manufacturing processes also have to be optimized regarding geometry deviations caused by distortion or unfavorable orientation in the build chamber. For additive manufactured parts that incorporate previously mentioned features, high-performance computer tomography is the more suitable nondestructive testing method. Components of different materials such as plastics, ceramics, composites, or metals can be completely characterized. This nondestructive testing method was used for porosity analysis regarding the shape and local distribution of pores in an additive manufactured part to find correlations concerning the most suitable process conditions. The measured part data were also compared to original CAD files to determine zones of deviation and apply specific process strategies to avoid distortion. This paper discusses the results of integrating high-performance computer tomography (power: 500 W, max. part size: Ø 300 mm, 300 × 430 mm2) in a productionlike environment of additively manufactured parts for a wide range of technologies (i.e., electron beam melting and selective laser melting). I. INTRODUCTION

  • 27.
    Mishra, Pragya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Energy efficiency contributions and losses during selective laser melting2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikkel-id 032304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 28.
    Moradi, Mahmoud
    et al.
    Department of Mechanical Engineering, Faculty of Engineering, Malayer University.
    Salimi, Nahid
    Department of Computer Engineering, Malayer Branch, Islamic Azad University.
    Ghoreishi, M.
    Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Tehran.
    Abdollahi, Hadi
    Department of Mechanical Engineering, Urmia University of Technology.
    Shamsborhan, Mahmoud
    Department of Engineering, Mahabad Branch, Islamic Azad University.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Ilar, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Parameter dependencies in laser hybrid arc welding by design of experiments and by a mass balance2014Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 26, nr 2, artikkel-id 22004Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 29.
    Moritz, J.
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Seidel, A.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Braun, B.
    Space Structures GmbH, Berlin, Germany.
    Brandao, A.
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Pambaguian, L.
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Köhler, B.
    Fraunhofer Institute for Ceramic Technologies and Systems, Dresden, Germany.
    Barth, M.
    Fraunhofer Institute for Ceramic Technologies and Systems, Dresden, Germany.
    Riede, M.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, E.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Leyens, C.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.Institute of Materials Science IfWW, Technische Universität Dresden, Dresden, Germany.
    Functional integration approaches via laser powder bed processing2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing design rules are different from those of conventional fabrication techniques. These allow geometries that would not be possible to achieve otherwise. One example of application is the integration of functional parts as part of the manufacturing process. Conceivable applications range from mechanical functions like integration of moving parts or thermodynamic functions, for example, cooling channels or incorporation of electric circuits for electrical functionalization [J. Glasschroeder, E. Prager, and M. F. Zaeh, Rapid Prototyping J. 21, 207–215 (2015)]. Nevertheless, the potential of functional integration using powder-bed processes is far from being exhausted. The present approach addresses the generation of inner cavities and internal structures of titanium-based parts or components by the use of selective laser melting. This paper focusses on the investigation of voids and cavities regarding their capabilities to add new functions to the material. To this end, comprehensive characterization is performed using destructive as well as nondestructive testing methods. These include 3D scanning, computed tomography, and surface roughness measurements as well as microscopic analysis. Voids and cavities were filled with different thermoplastic materials, followed by the qualitative assessment of the mold filling and resulting material properties. Finally, applications are derived and evaluated with respect to the field of lightweight design or damping structures.

  • 30.
    Mueller, Michael
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany. Technische Universität Dresden, Dresden, Germany.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Eberle, Sebastian
    Kampf Telescope Optics GmbH, Munich, Germany.
    Reutlinger, Arnd
    Kampf Telescope Optics GmbH, Munich, Germany.
    Brandão, Ana D.
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Pambaguian, Laurent
    European Space Research and Technology Centre, ESTEC, Noordwijk, Netherlands.
    Seidel, André
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, Elena
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Beyer, Eckhard
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany. Technische Universität Dresden, Dresden, Germany.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany. Technische Universität Dresden, Dresden, Germany.
    Microstructural, mechanical, and thermo-physical characterization of hypereutectic AlSi40 fabricated by selective laser melting2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 02232Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The powder bed additive manufacturing process selective laser melting (SLM) enables designers and engineers to overcome restrictions of conventional manufacturing technologies. The potential of fabricating complex lightweight structures and processing advanced materials is a key feature for enhancing further development of high performance components for space applications. Due to a high specific stiffness and a thermal expansion coefficient very close to electroless nickel, which is an advantageous optical coating material, the hypereutectic aluminum-silicon alloy AlSi40 shows great potential for the manufacturing of optical mirrors for space applications. In prior investigations, Hilpert et al.showed the feasibility to process AlSi40 by SLM [E. Hilpert and S. Risse, Materials Science & Technology Conference and Exhibition MS&T'15, Columbus, Ohio, 4–8 October 2015(Association for Iron & Steel Technology, Warrendale, PA, 2015) and E. Hilpert, “Struktur und Eigenschaften von additiv gefertigten hypereutektischen Aluminum-Siliciumlegierungen,” in Werkstoffwoche 2017, Dresden, Germany28 September 2017 (Deutsche Gesellschaft für Materialkunde e.V., Berlin, 2017)]. Nevertheless, in order to qualify this material for space applications, the manufacturing process and fabricated samples need to be thoroughly investigated in terms of microstructural, mechanical, as well as thermo-physical characterization. The authors present results of the SLM process development for manufacturing dense AlSi40 samples with a relative density above 99.50%. The effect of various process parameters, such as hatch distance, preheating, and scanning strategy, on the formation of defects was investigated by destructive [e.g., optical microscopy (OM)] and nondestructive (e.g., computed tomography) testing. In addition, the effect of several thermal post-treatments on the AlSi40 microstructure was profoundly analyzed by multiple methods such as OM, scanning electron microscopy, and energy dispersive x-ray spectroscopy analysis. Moreover, mechanical and thermo-physical testing of manufactured specimens was conducted to provide material characteristics for component design. In conclusion, the determined material properties of AlSi40 samples fabricated by SLM were compared to bulk material properties. The gained knowledge and testing data were evaluated in order to identify correlations and dependencies.

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

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

  • 32.
    Näsström, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Multipass laser hot-wire welding: Morphology and process robustness2017Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 29, nr 2, artikkel-id 022014lArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 33. Ohlsson, L.
    et al.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Ivarson, Anders
    Luleå tekniska universitet.
    Magnusson, Claes
    Comparison between abrasive water jet cutting and laser cutting1991Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 3, nr 3, s. 46-50Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper is intended to demonstrate the advantages and disadvantages of laser profiling techniques as compared with the Abrasive Water Jet (AWJ). The growth of AWJ as a cutting tool has provided engineers with a new profiling technique which often offers great technical and commercial advantages over more traditional methods. However, AWJ cutting is not the best solution to all profiling problems. There are a number of techniques which compete with or complement the process and the optimum profiling method can be difficult to identify. The following paper serves as a general guide-line comparing two competitive cutting methods (CO2 laser cutting and Nd: YAG laser cutting) with AWJ cutting. The subject of cutting covers a great many more processes than can be reviewed in one article but the techniques to be discussed were chosen because they all involve profiling using an axially symmetric energy beam of some sort

  • 34.
    Olsson, Rickard
    et al.
    Lasernova AB.
    Powell, John
    Laser Expertise Ltd..
    Frostevarg, Jan
    Normal vector distribution as a new classification tool for rough surfacesInngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387Artikkel i tidsskrift (Fagfellevurdert)
  • 35.
    Olsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Laser Nova AB.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Palmquist, A.
    Department of Biomaterials, University of Gothenburg.
    Brånemark, R.
    Department of Orthopaedic Surgery, University of California, San Francisco.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The production of osseointegrating (bone bonding) surfaces on titanium screws by laser melt disruption.2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 4, artikkel-id 042009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 36.
    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.

  • 37.
    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.

  • 38.
    Polenz, S.
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Seidel, A.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Moritz, J.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Kunz, W.
    Fraunhofer Institute for Ceramic Technologies and Systems IKTS, Dresden, Germany.
    Riede, M.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, E.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Leyens, C.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.Technische Universität Dresden, Dresden, Germany.
    Wavelength dependent laser material processing of ceramic materials2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022316Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the future, ceramic materials will find even more applications in aerospace, energy, and drive technology. Reasons for this are the comparatively low density and good long-term stability at high temperatures for applications for components exposed to high temperatures, e.g., of engines. By using increasing combustion temperatures through the use of ceramics increases the efficiency of modern drive systems [Ohnabe, Masaki, Onozuka, Miyahara, and Sasa, Compos. Part A Appl. Sci. Manuf. 30, 489–496 (1999)]. Despite the high interest of the aviation industry to increase the use of ceramic materials, the time- and energy-consuming classical production of these materials and the concomitant limiting factors in terms of shape and size are still a drawback [Krenkel, Ceramic Matrix Composites Fiber Reinforced Ceramics and their Applications (WIY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2008)]. This paper follows a new approach to producing ceramic matrix composites (CMCs). The laser material deposition (LMD) and selective laser melting techniques were used to investigate the coupling of different laser wavelengths into ceramic materials. By combining different energy sources and utilizing wavelength-dependent energy coupling, the additive manufacturing application of ceramic materials to metallic substrates was tested. With the knowledge gained from wavelength-dependent energy coupling, the potential for the production of CMCs should be demonstrated by means of LMD

  • 39. 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

  • 40.
    Powell, John
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Ivarson, Anders
    Luleå tekniska universitet.
    Magnusson, Claes
    Laser cutting of steels: a physical and chemical analysis of the particles ejected during cutting1993Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 5, nr 1, s. 25-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper is a continuation of work published in an earlier edition of this journal[1]. Both papers deal with the results of a detailed analysis of the particles ejected from the cut zone during laser cutting of mild and stainless steels. The earlier paper presented the thermochemical data and discussion generated by the experimental investigation. This paper concentrates on the physical characteristics and metallography of the particles. Analysis techniques used included: scanning electron microscopy, optical microscopy, metallography and particle sizing. The results from this extensive analysis have enabled the authors to postulate oxidation histories for the particles. In addition to this, it has been possible to explain the variation in particle size for various material thicknesses

  • 41.
    Powell, John
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Tan, W.K.
    Division of Manufacturing, Engineering and Operations Management, University of Nottingham.
    Maclennan, P
    V & S Scientific (London) Ltd.
    Rudd, D.
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Wykes, C.
    Division of Manufacturing, Engineering and Operations Management, University of Nottingham.
    Engström, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser cutting stainless steel with dual focus lenses2000Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 12, nr 6, s. 224-231Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article the performance of a new type of lens is compared with traditional meniscus lenses for CO sub 2 laser cutting of medium ( > 5 mm) section stainless steel. Dual Focus lenses produce two focus spots, one above the other. This type of optic was found to be capable of higher cutting speeds and better quality cuts. A phenomenological model is presented which explains the superior performance of Dual Focus lenses. The model concentrates upon the fact that during high speed cutting of medium section metals, the laser does not irradiate the lower portion of the cut zone. This lower part of the cut is heated by the melt flowing over it, which has been previously heated by the laser. This melt preheating involves narrower kerfs and higher cut speeds if a dual focus lens is used.

  • 42.
    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
  • 43.
    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.

  • 44.
    Schneider, J.
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.Department of Materials Technology, Technische Universität Dresden, Dresden, Germany.
    Seidel, A.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Gumpinger, J.
    ESA/ESTEC, European Space Research and Technology Centre, Noordwijk, The Netherlands.
    Riede, M.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, E.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Leyens, C.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.Department of Materials Technology, Technische Universität Dresden, Dresden, Germany.
    Advanced manufacturing approach via the combination of selective laser melting and laser metal deposition2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022317Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing processes are frequently discussed in a competitive manner instead of being considered synergetically. This is particularly unfavorable since advanced machining processes in combination with additive manufacturing can be brought to the point that the results could not be achieved with the individual constituent processes in isolation [K. Gupta, R. F. Laubscher, and N. K. Jain, Hybrid Machining Processes—Perspectives on Machining and Finishing (Springer, New York, 2016), p. 68]. On that basis, boundary conditions from selective laser melting (SLM) and laser metal deposition (LMD) are considered in mutual contemplation [A. Seidel et al., in Proceedings of 36th International Congress on Applications of Laser & Electro-Optics, Atlanta, GA, 22–26 October 2017(Fraunhofer IWS, Dresden, 2017), pp. 6–8]. The present approach interlinks the enormous geometrical freedom of powder-bed processing with the scalability of the LMD process. To demonstrate the potential of this approach, two different strategies are pursued. Firstly, a hollow structure demonstrator is manufactured layer wise via LMD with powder and subsequently joined with geometrically complex elements produced via SLM. Afterward, possibilities for a microstructural tailoring within the joining zone via the modification of process parameters are theoretically and practically discussed. Therefore, hybrid sample materials have been manufactured and interface areas are subjected to microstructural analysis and hardness tests. The feasibility of the introduced approach has been demonstrated by both fields of observation. The process combination illustrates a comprehensive way of transferring the high geometric freedom of powder-bed processing to the LMD process. The adjustment of process parameters between both techniques seems to be one promising way for an alignment on a microstructural and mechanical scale.

  • 45.
    Seidel, A.
    et al.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Davids, A.
    Technische Universität Dresden, Dresden, Germany.
    Polenz, S.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Straubel, A.
    Technische Universität Dresden, Dresden, Germany.
    Maiwald, T.
    Technische Universität Dresden, Dresden, Germany.Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Moritz, J.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Schneider, J.
    Technische Universität Dresden, Dresden, Germany.Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Marquardt, A.
    Technische Universität Dresden, Dresden, Germany.Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Saha, S.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Riede, M.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Lopéz, E.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Leyens, C.
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.Technische Universität Dresden, Dresden, Germany.
    Surface modification of additively manufactured gamma titanium aluminide hardware2019Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, nr 2, artikkel-id 022517Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A major part of additive manufacturing focuses on the fabrication of metallic parts in different fields of applications. Examples include components for jet engines and turbines and also implants in the medical sector. Titanium alloys represent a material group which is used cross-sectoral in a large number of applications. The present paper addresses the titanium aluminides in particular. These materials have a low density in combination with a comparatively high-temperature resistance [G. Sauthoff, Intermetallics (Wiley-VCH Verlag, Weinheim, Germany, 2008)]. Nevertheless, the laser material processing is rather challenging because of their distinct tendency to lamellar interface cracking. This requires tailored processing strategies and equipment [C. Leyens et al., in Ti-2015: The 13th World Conference on Titanium, Symposium 5. Intermetallics and MMCs, 16–20 August 2015, San Diego, CA (The Minerals, Metals & Materials Society, Pittsburgh, PA, 2016)]. This work focusses on tailored processing of titanium aluminides with focus on the process-dependent surface characteristics. This includes the as-built status for powder bed processing and direct laser metal deposition but also the surface modification via post and/or advanced machining. Finally, comprehensive characterization is performed using destructive as well as nondestructive testing methods. The latter includes 3D scanning, computed tomography, microscopic analysis, and, in particular, surface roughness measurements.

  • 46.
    Seidel, André
    et al.
    Fraunhofer Institute for Material and Beam Technology.
    Straubel, Ariane
    Technische Universität Dresden.
    Finaske, Thomas
    Fraunhofer Institute for Material and Beam Technology.
    Maiwald, Tim
    Fraunhofer Institute for Material and Beam Technology.
    Polenz, Stefan
    Fraunhofer Institute for Material and Beam Technology.
    Albert, Maximillian
    Fraunhofer Institute for Material and Beam Technology.
    Näsström, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Marquardt, Alex
    Fraunhofer Institute for Material and Beam Technology.
    Riede, Mirko
    Fraunhofer Institute for Material and Beam Technology.
    Lopez, Elena
    Fraunhofer Institute for Material and Beam Technology.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology.
    Beyer, Eckhard
    Fraunhofer Institute for Material and Beam Technology.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology.
    Added value by hybrid additive manufacturing and advanced manufacturing approaches2018Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, nr 3, artikkel-id 032301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to lead to a competitive advantage, there is the need to carefully consider the pros and cons of state-of-the-art manufacturing techniques. This is frequently carried out in a competitive manner, but can also be done in a complementary way. This complementary approach is often used for the processing of difficult-to-machine materials with particular regard to high-tech parts or components. Hybrid machining processes or, more general, advanced machining processes can be brought to the point that the results would not be possible with the individual constituent processes in isolation [Hybrid Machining Processes Perspectives on Machining and Finishing (Springer International Publishing AG, 2016)]. Hence, the controlled interaction of process mechanisms and/or energy sources is frequently applied for a significant increase of the process performance [Advanced Machining Processes of Metallic Materials: Theory, Modelling, and Applications, 2nd ed. (2016)] and will be addressed within the present paper. A via electron beam melting manufactured gamma titanium aluminide nozzle is extended and adapted. This is done via hybrid laser metal deposition. The presented approach considers critical impacts like processing temperatures, temperature gradients, and solidification conditions with particular regard to crucial material properties like the phenomena of lamellar interface cracking [Laser-Based Manufacturing of Components using Materials with High Cracking Susceptibility (Laser Institute of America–LIA), pp. 586–592; Ti-2015: The 13th World Conference on Titanium, Symposium 5]. Furthermore, selected destructive and non-destructive testing is performed in order to prove the material properties. Finally, the results will be evaluated. This will also be done in the perspective of other applications.

  • 47.
    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.

  • 48.
    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.

  • 49.
    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.

  • 50.
    Tuominen, J.
    et al.
    Tampere University of Technology, Department of Materials Science.
    Näkki, J.
    Tampere University of Technology, Department of Materials Science.
    Poutala, J.
    Tampere University of Technology, Department of Engineering Design.
    Miettinen, J.
    Tampere University of Technology, Department of Engineering Design.
    Peltola, T.
    Technology Centre KETEK Ltd..
    Vuoristo, P.
    Tampere University of Technology, Department of Materials Science.
    Rasehorn, I.
    Centria University of Applied Sciences, Kokkola.
    Alam, M. M.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Department of Engineering Sciences and Mathematics, Luleå University of Technology.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Department of Engineering Sciences and Mathematics, Luleå University of Technology.
    Fatigue behavior of laser clad round steel bars2015Inngår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 27, nr 1, artikkel-id 12006Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser cladding is an overlay welding method to manufacture high performance, fusion bonded metal, and metal matrix composite coatings on metallic substrates with low dilution. Owing to steep thermal gradients, rapid solidification, and possible mismatch in coefficients of thermal expansion between the coating and the substrate, laser cladding induces large tensile residual stresses in coating layer, potentially affecting the service life of clad component under external load-induced stresses. In this study, four-point bending and torsion fatigue tests were conducted on relatively large round laser clad steel bars to determine the effect of laser cladding on fatigue strength. Quenched and tempered 42CrMo4 steel clad with Inconel 625 and S355 structural steel clad with Stellite 21 were subjected to various stress levels for relatively large number of cycles with and without postweld heat treatment (PWHT). The results indicated that Stellite 21 decreased the fatigue life of S355 at all the applied loads, whereas Inconel 625 increased the fatigue life of 42CrMo4 at high loads but decreased at low loads. Applied PWHT did not show any positive influence on fatigue life.

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