| 1. |
- Bang, Han-Sur, et al.
(författare)
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Effect of Tungsten-Inert-Gas Preheating on Mechanical and Microstructural Properties of Friction Stir Welded Dissimilar Al Alloy and Mild Steel
- 2016
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Ingår i: Strength of Materials. - : Springer Science and Business Media LLC. - 0039-2316 .- 1573-9325. ; 48:1, s. 152-159
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to clarify the effect of tungsten-inert-gas (TIG) welding preheating on the mechanical properties of Al6061-T6 and SS400 welded joints by friction stir welding (FSW). FSW joints with and without TIG welding preheating are characterized and compared in terms of their mechanical and microstructural properties. The results show that the TIG assisted hybrid FSW welded joints (TIG-HFSW) provide an enhanced joint strength. The transversal tensile strength of the TIG-HFSW joints exhibited approximately 104% of the Al6061-T6 base metal tensile strength and was higher than that of the FSW joints. Microstructural investigations also reveal that in the HAZ and TMAZ of TIG-HFSW joints, the grains of Al6061-T6 are smaller than those of the FSW welds
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| 2. |
- Bunaziv, I., et al.
(författare)
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Application of laser-arc hybrid welding of steel for low-temperature service
- 2019
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 102:5-8, s. 2601-2613
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Tidskriftsartikel (refereegranskat)abstract
- Laser-arc hybrid welding (LAHW) is more often used in shipbuilding and oil and gas industries in recent years. Its popularity arises due to many advantages compared to conventional arc welding processes. The laser beam source is used to achieve much higher penetration depths. By adding filler wire to the process area, by means of an arc source, the mechanical properties can be improved, e.g. higher toughness at low temperatures. Therefore, LAHW is a perspective process for low-temperature service. Applicability of LAHW is under concern due to process stability and mechanical properties related to heterogeneous filler wire distribution through the whole weld metal in deep and narrow joints. This can cause reduced mechanical properties in the weld root as well as problems with solidification cracking. The fast cooling rate in the root provides hard and brittle microconstituents lowering toughness at low temperatures. Numerical simulations and experimental observations showed that an increase in heat input from the laser beam is an effective way to reduce the cooling rate, which is also possible by applying preheating.
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| 3. |
- Bunaziv, Ivan, et al.
(författare)
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Deep penetration fiber laser-arc hybrid welding of thick HSLA steel
- 2018
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 256, s. 216-228
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Tidskriftsartikel (refereegranskat)abstract
- The present investigation addresses laser-arc hybrid welding of 45 mm thick steel with variation in a wide range of process parameters. High volume fraction of acicular ferrite formed in the upper part of the weld metal regardless process parameters. Significantly lower fraction of acicular ferrite was found in the root due to substantially increased cooling rates and the inability to deliver filler wire to this region, resulting in bainite-martensite microstructures in the root. The delivery of filler wire to the root can be enhanced by increasing the air gap between the plates. Higher heat inputs reduce cooling rates in the root which create softer and ductile microstructures, at the expense of a much wider and coarser grained HAZ. The results obtained showed high fusion line and weld metal toughness at low temperature (−50 °C).
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| 4. |
- Bunaziv, Ivan, et al.
(författare)
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Hybrid Welding of 45 mm High Strength Steel Sections
- 2017
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Ingår i: Physics Procedia. - : Elsevier. - 1875-3892. ; 89, s. 11-22
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Tidskriftsartikel (refereegranskat)abstract
- Thick section welding has significant importance for oil and gas industry in low temperature regions. Arc welding is usually employed providing suitable quality joints with acceptable toughness at low temperatures with very limited productivity compared to modern high power laser systems. Laser-arc hybrid welding (LAHW) can enhance the productivity by several times due to higher penetration depth from laser beam and combined advantages of both heat sources. LAHW was applied to join 45 mm high strength steel with double-sided technique and application of metal cored wire. The process was captured by high speed camera, allowing process observation in order to identify the relation of the process stability on weld imperfections and efficiency. Among the results, it was found that both arc power and presence of a gap increased penetration depth, and that higher welding speeds cause unstable processing and limits penetration depth. Over a wide range of heat inputs, the welds where found to consist of large amounts of fine-grained acicular ferrite in the upper 60-75% part of welds. At the root filler wire mixing was less and cooling faster, and thus found to have bainitic transformation. Toughness of deposited welds provided acceptable toughness at -50 °C with some scattering.
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| 5. |
- Bunaziv, Ivan, et al.
(författare)
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Laser-arc hybrid welding of thick HSLA steel
- 2018
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 259, s. 75-87
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Tidskriftsartikel (refereegranskat)abstract
- A standard laser-arc hybrid welding (S-LAHW) and LAHW with preplaced cut wire inside the groove before welding were studied and compared. The S-LAHW setup revealed problems with filler wire delivery to the root, resulting in substantial hardness increase due to bainitic-martensitic transformation. The applied finite element modelling confirmed significant cooling rate increase in the root area for deep penetration welds. Preplacement of cut wire prior to welding reduced hardness providing improved welds with higher homogeneity. This method was subsequently applied for multi-pass welding that revealed insufficient nucleation of acicular ferrite on non-metallic inclusions (NMIs). It is implied that a critical cooling rate has been exceeded where the NMIs become inactive, resulting in a microstructure consisting of a martensite and bainite mixture. This kind of microstructure is clearly harmful for the weld metal toughness.
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| 6. |
- Bunaziv, Ivan, et al.
(författare)
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Porosity and solidification cracking in welded 45 mm thick steel by fiber laser-MAG process
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 36, s. 101-111
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Tidskriftsartikel (refereegranskat)abstract
- Porosity and solidification cracking in joining of thick sections are very common issues in deep penetration keyhole laser-arc hybrid welding (LAHW). In the present work, 45 mm thick high strength steel was joined by a double-sided technique. With combined use of fast welding speeds and larger air gap between plates, higher amount of porosity was found because of the dynamic behavior of the keyhole walls. Solidification cracking formed at the centerline in the bottom of the weld due to high-depth-to-width geometrical ratio. Numerical simulations have been performed and showed very high cooling rate and stresses occurred in the root of the deep welds, which corresponds with higher cracking tendency.
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| 7. |
- Bunaziv, Ivan, et al.
(författare)
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Process stability during fiber laser-arc hybrid welding of thick steel plates
- 2018
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Ingår i: Optics and lasers in engineering. - : Elsevier. - 0143-8166 .- 1873-0302. ; 102, s. 34-44
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Tidskriftsartikel (refereegranskat)abstract
- TThick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources.
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| 8. |
- Bunaziv, Ivan, et al.
(författare)
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The penetration efficiency of thick plate laser-arc hybrid welding
- 2018
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 97:5-8, s. 2907-2919
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Tidskriftsartikel (refereegranskat)abstract
- Double-sided fiber laser-arc hybrid welding was used to join 45 mm thick high strength steel over a wide range of parameters in order to investigate the efficiency of the process. Air gap size, I- and Y-groove type preparation, pulsed and cold metal transfer pulsed arc modes, arc-laser setup, and travel speeds were compared, and in all cases, sufficient filler material was provided to fully fill the gap. The welds were investigated using high speed imaging and cross-sectional analysis to identify penetration depths, morphology, and imperfections. Larger joint air gaps were found to contribute most to weld penetration depth. Surprisingly, increased line energy decreased penetration efficiency in most cases. The laser-arc interdistance was also investigated, revealing an arc size and melt flow dependency for achieving higher penetration depth for a leading arc. It was found that, although penetration can be optimized, solidification cracking can be a limiting factor in the application of deep penetration hybrid welding for thick steel section joining.
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| 9. |
- Frostevarg, Jan, 1982-, et al.
(författare)
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45 mm thick steel section joining for cold climate applications by applyinglaser-arc hybrid welding
- 2018
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Ingår i: 71st IIW International Conference.
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Konferensbidrag (refereegranskat)abstract
- Production and joining of components for energy industries(wind, oil and gas) for cold climate applications is achallenging task. Joining of thick steels is usually performedby using arc techniques such as submerged arc welding(SAW) or Gas Metal Arc Welding (GMAW). To fill thicksections, wide gap preparation is made and gradually filled inseveral weld passes. To reduce the number of weld passes,high power laser-arc hybrid welding (LAHW) is a promisingalternative, but can also weld at higher travel rates therebyreducing the total heat input and reduced filler material.LAHW is applied using a metal-cored wire, demonstratingwelding in 45 mm thick steel sheets. Setup and selection ofprocess parameters are essential for obtaining high processstability, penetration efficiency and material mixingthroughout the depth of the weld. Each weld where repeatedand performed on 500x200x45 mm (x,y,z) steel sheets withmilled joint edges. Using LAHW and selected materials, largeamounts of acicular ferrite was formed in the upper half of thejoint, gradually having increasingly more bainitic structurescloser to the weld root. From these results, it is concluded thatLAHW has high potential for increased production efficiencyand lowered costs, potentially replacing arc welding for thesetypes of applications.
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| 10. |
- Frostevarg, Jan, 1982-, et al.
(författare)
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The formation of osseointegrating surfaceson titanium by laser irradiation
- 2018
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Ingår i: 71st IIW General Assembly, C-IV.
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Konferensbidrag (refereegranskat)abstract
- Pulsed lasers can be used to modify the surface of medical implants in order to accelerate bone growth(osseointegration). Here, it is used to create a surface that is beneficial for rapid osseointegration, also calledBioHelix™, having ridges and covered in attached droplets of diameters between 1 and 20 μm. This paper presentsthe results of an experimental program in which a range of laser parameters were used to create different surfacetextures on titanium substrates. The resulting surfaces were analyzed by scanning electron microscope and MicroComputer Tomography. The paper explains how different types of surface are created by the laser-materialinteraction under different conditions. It is shown that optimization of the laser parameters results in a robustprocess which produces a surface that is fundamentally different from those created by other methods
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