| 1. |
- Kaplan, Alexander, et al.
(author)
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Advanced welding analysis methods applied to heavy section welding with a 15 kW fibre laser
- 2009
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In: Welding in the World. - 0043-2288 .- 1878-6669. ; 53:Special issue, s. 295-300
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Journal article (peer-reviewed)abstract
- For butt joint welding of 8 mm and of 16 mm thick stainless steel a 15 kW fibre laser was applied, achieving full penetration for a welding speed of 7 m/min and 3 m/min, respectively. Optics with a focal length ranging from 500 mm to 150 mm focus the laser beam to a spot diameter of 0.65 to 0.2 mm with a focal depth of 18 to 4 mm and a cw-power density of 4 to 48 MW/cm2. Although narrow sound welds can be achieved, heavy spatter ejection along with underfill can take place at the top and root side, particularly for high power density and for low line energy. Various advanced analysis methods were developed. Spatter was observed by high speed imaging of the weld pool surface and of the keyhole. Quantitative evaluation of the drop size and flight trajectories enabled categorisation into four spatter modes, revealing favoured conditions for spatter suppression. Modelling subsequent to the drop evaluation provided additional analysis. An illustrative theoretical description and the formulation of a standard documentation methodology were developed. This aims to generalise and transfer knowledge as a guideline for spatter suppression in other laser welding situations.
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| 2. |
- Kaplan, Alexander, et al.
(author)
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Imaging in cooperation with modeling of selected defect mechanisms during fiber laser welding of stainless steel
- 2008
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In: Congress proceedings. - Orlando, Fla : Laser institute of America. - 9780912035123 ; , s. 789-798
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Conference paper (peer-reviewed)abstract
- Fiber laser welding of stainless steel was studied for different joint configurations and gaps. The higher focusing capability of fiber lasers compared to traditional Nd:YAG and CO2 lasers creates different, usually smaller, keyhole and melt pool geometries. These geometrical aspects, accompanied by a different laser energy redistribution, are essential for the weld pool dynamics and the resulting joint, with or without defects. Typical defects identified during fiber laser welding were spatter, humping, or lack of material at the top or root. High-speed imaging enables observation of the geometry and motions of the melt pool surface and keyhole during welding. This is illuminated by an additional diode laser permitting spectral filtering and also the metal vapor dynamics can be visualized. Mathematical modeling provides the possibility to estimate and study additional phenomena that are difficult to measure, such as effects inside the melt volume or the impact of surface tension forces on dynamic melt motion. For recorded melt surface motion images, in particular, the corresponding surface tension forces and other mechanisms can be estimated by cooperative complementary modeling, enabling to draw conclusions. This advanced method was carried out for the different joint and defect cases studied, resulting in an illustrated theoretical description of the observed physical phenomena.
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| 3. |
- Kaplan, Alexander, et al.
(author)
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The impact of zinc-coating on laser hybrid welding of steel
- 2007
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In: Congress proceedings. - Orlando, Fla : Laser institute of America. - 9780912035888
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Conference paper (peer-reviewed)abstract
- Hybrid Nd:YAG/MAG welding of ultra high strength steel is studied for 1,5 mm thick sheets in I-, T- and overlap joint type configuration. Untreated and zinc-coated steels were compared, causing distinct differences in terms of process stability and welding result. For zinc coating it can be distinguished between domains of trapped zinc layers like in overlap and T-joints and free surface zinc coatings. While the former situation is critical for violent evaporation and in turn spatter in the absence of a gap, in the latter case a zinc domain outside the weld pool area evaporates due to its low boiling point, thus not disturbing the laser welding process. However, during hybrid welding arc instabilities and short circuiting were observed when changing to zinc coated steel, even for butt joints. One hypothesis is an impact of the zinc vapour atoms on the plasma, with an ionisation energy 20% higher than iron, but 40% lower than Ar. The influence was calculated by Saha's equation. The process window is much narrower than for uncoated steel. Moreover, an enhanced generation of spatter and fume can be observed. A theory for the impact of zinc-coating on hybrid welding is postulated.
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| 4. |
- Vuorinen, Esa, et al.
(author)
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Laser surface hardening of steel with ausferritic structure
- 2008
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In: SMT22.
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Conference paper (peer-reviewed)abstract
- High strength steels can be produced by austempering of Si-containing steels. High toughness and good wear resistance are properties possible to achieve. Surface hardening of this group of steels can give an additional increase of the surface hardness and wear resistance. Laser surface hardening has been used in order to increase the surface hardness of the steel 55Si7. The effect of surface hardening on the ferritic-austenitic carbide- free microstructure created for this steel has been studied. Optical as well as scanning electron microscopy has been used in the characterization of the micro-structural changes.
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| 5. |
- Wiklund, Greger, et al.
(author)
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Laser cladding of cast iron using a 12 kW CO2-laser combined with induction heating
- 2005
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In: 10th NOLAMP Conference. - Luleå : Luleå tekniska universitet. - 9163172283 ; , s. 217-224
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Conference paper (peer-reviewed)abstract
- Laser surfacing experiments were carried out using high alloy high, strength compact graphite iron Darcast (3.5%C, 2%Si, 0.85%Mn, 0.9%Cu) and ductile cast iron SS0732 (3.4-3.85%C, 2.3-3.1%Si, 0.1-0.3%Mn) substrate materials with a view to developing a crack-free surfacing process for use on piston rings. The cladding material used was a nickel based chromium carbide powder. Tracks 20 mm wide and 1-2 mm thick were created using heat input of 1700-3000 J/mm; pre- and post-heating using induction heating equipment was used to prevent cracking. Based on the experiments, parameters suitable for laser surfacing of SS0732 piston rings were selected and applied
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| 6. |
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| 7. |
- Wiklund, Martin, et al.
(author)
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»68» inför historiens domstol
- 2007
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In: Vetenskapssocieteten i Lund. Årsbok 2007. - 0349-053X. - 9789197486354 ; , s. 128-142
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Book chapter (other academic/artistic)
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