| 1. |
- Frostevarg, Jan, et al.
(författare)
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Effects of edge oxides from laser cutting in laser-arc hybrid welding
- 2018
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 30:1
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Frostevarg, Jan, et al.
(författare)
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Investigation of laser-arc hybrid welding utilizing CMT, effects upon oxygen and nitrogen contents as well as the weld stability due to oxygen contents of the shielding gas and gap oxides
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study, the effects upon weld arc stability and contents of oxygen and nitrogen inside the weld is investigated for laser-arc hybrid welding (LAHW) using the CMT arc mode. CMT is a controlled short arc technique that is here expected to be less sensitive to oxygen levels in the shielding gas. Having oxides or nitrogen inside the weld region is also known to alter the fluid mechanics such as surface tension, but also a cause for porosity. The gap preparation prior to welding is typically carried out by thermal cutting, water jet cutting or grinding. These edges are then placed to form the joint to be welded. In the case of thermal cutting, oxides are usually formed on the cut edge, adding oxygen into the melt pool when welding is conducted. The effects are studied by macroscopy, HSI and chemical analysis. The arc stability and oxygen and nitrogen levels in the welds are more affected by the oxides remaining from the laser cut edges than the oxygen in the shielding gas when the cutting oxides are removed.
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| 3. |
- Kaplan, Alexander, et al.
(författare)
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Unbounded keyhole collapse and bubble formation during pulsed laser interaction with liquid zinc
- 2002
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 35:11, s. 1218-1228
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Tidskriftsartikel (refereegranskat)abstract
- Suppression of pore defects in keyhole laser spot welding demands for a theoretical description of the fundamental process. Investigating the unbounded keyhole collapse in liquid Zn instead of a solid provided a simplified situation offering several advantages. Improved high speed x-ray transmission imaging due to an enlarged keyhole in the absence of violent melt motion was enabled, which also facilitated the development of a semi-analytical mathematical model. Good correspondence between the experimentally and theoretically obtained transient keyhole and bubble shape permitted physical analysis by the model. Characteristic timescales were identified for post-vaporization, vapour relaxation, cooling, collapse, bubble contraction, oscillations and buoyancy. Recondensation due to rapid cooling turns out to be responsible for shielding gas flow into the keyhole, finally maintaining a spherical bubble. Creation of a convergent keyhole is a possibility to avoid bubbles.
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