| 1. |
- Forsman, Tomas, et al.
(författare)
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Nd:YAG laser welding of aluminium : factors affecting absorptivity
- 1999
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Ingår i: Lasers in engineering (Print). - 0898-1507 .- 1029-029X. ; 8:4, s. 295-309
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the factors affecting the absorptivity during Nd:YAG laser keyhole welding of a 6xxx aluminum alloy. The influence of surface condition on absorption is shown to be negligible. Experimental absorption measurements by calorimetry are compared to analytical absorption values using a simple model based on Fresnel absorption during multiple reflections in the keyhole.
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| 2. |
- Kaplan, Alexander, et al.
(författare)
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An analysis of the heat transfer from a moving elliptical cylinder
- 1997
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 30, s. 1190-1196
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical analysis of the heat transfer from a moving elliptical cylinder is carried out and general solutions in elliptical coordinates are obtained for aspect ratios β, both β and β. The heat-flux distribution and total heat-flow rate are calculated, investigated for a wide range of parameters and presented graphically. The results obtained are useful for applications concerning thermal processes (laser cutting, welding, heat treatment and so on). A comparison of a moving circular cylinder with a numerical model of laser cutting is considered and discussed.
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| 3. |
- Kaplan, Alexander
(författare)
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An analytical model of metal cutting with a laser beam
- 1996
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 79:5, s. 2198-2208
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Tidskriftsartikel (refereegranskat)abstract
- The process of cutting metals with a laser beam is described by a mathematical model comprising a set of balance equations for mass, momentum and energy. The molten film at the cutting front is defined as the control volume. The calculation yields average values for the characteristic macroscopic state of the cutting front, such as temperature, melt film velocity and melt film thickness. All relevant parameters of the laser beam and of the process gas flow are considered in the model. Numerical evaluations of the analytical model provide explanations of the process behavior both for inert and for oxygen gas cutting. The narrowing of the kerf width with increasing speed is explained by heat conduction. Furthermore, the model shows that the evaporation temperature is reached at high velocities for thin metal sheets. Using a higher gas pressure increases the diffusion limited oxidation rate and provides higher cutting velocities, while the fraction of oxidized metal decreases substantially with increasing speed.
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| 9. |
- Kaplan, Alexander, et al.
(författare)
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Laser beam welding of aluminium alloys
- 1997
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Ingår i: Internationale Konferenz Schweißtechnik, Werkstoffe und Werkstoffprüfung, Bruchmechanik und Qualitätsmanagement (ST-W&WP-BM-QM) : Technische Universität Wien, 1997 = International Conference Welding Technology, Materials and Materials Testing, Fracture Mechanics and Quality Management (WT-M&MT-FM-QM). - Wien : Technischen Universität Wien. ; , s. 147-156
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Konferensbidrag (refereegranskat)
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| 10. |
- Kaplan, Alexander, et al.
(författare)
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Laser cutting : Fundamentals of the periodic striations and their on-line detection
- 1997
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Ingår i: Lasers in engineering (Print). - 0898-1507 .- 1029-029X. ; 6:2, s. 103-126
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Tidskriftsartikel (refereegranskat)abstract
- The burning mechanism which occurs in oxygen assisted laser cutting of mild steel and the resulting periodic cut edge striations are under consideration in this study. The average wavelength of the periodic striations is shown to be independent of the processing speed, but strongly correlates with the beam radius at the work piece surface. A theoretical approach has been developed to describe the transient oxidation process. Initially, the heated iron at the cutting front oxidizes rapidly and the oxidation front can retreat from the laser beam. The growing oxide layer acts as a barrier for diffusion, lowering the reaction rate which in turn reduces the exothermal energy gain. Consequently, after few 10 µsec the oxide layer of some microns thickness terminates the retreating motion. Typically after 10 msec the reaction is terminated until the next, periodical ignition by the laser beam occurs. In order to monitor the periodic process, the thermal emissions from the cutting front are detected by employing a photodiode and analyzing the temporal signal. An analysis algorithm suitable for on-line detection of both the roughness of the striations and the appearance of defects is presented.
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