| 31. |
- Eriksson, Ingemar, et al.
(författare)
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Ultra high speed camera investigations of laser beam welding
- 2010
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Ingår i: Congress proceedings ICALEO. - Anaheim, CA : Laser institute of America. - 9780912035611 ; , s. 172-178
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With the help of high speed camera equipment, researchers can now directly observe melt flow phenomena which only could be imagined or simulated in the past. In this paper the motion of the molten metal inside the keyhole has been observed at frame rates as high as 180000 fps to provide useful information about the laser beam welding process. This paper describes two different cases where high speed imaging has given new insights into the laser beam welding process: A. In pulsed welding the melt pool oscillations can create ripples on the solidified weld surface. With the help of a high speed camera this phenomenon was analyzed, and the pulse shape was adjusted to reduce the ripple amplitude to a minimum. B. In Zn-coated steel edge welding it could be seen that blowouts were sometimes created in the melt pool at some distance behind the keyhole. Direct slowmotion observation has led to the formulation of a phenomenological model of this effect.
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| 32. |
- Fedina, Tatiana, et al.
(författare)
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A comparative study of water and gas atomized low alloy steel powders for additive manufacturing
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- This work reports a study of the differences between laser processing of water and gas atomized low alloy steel powders with a focus on powder behavior and performance in additive manufacturing. Material packing densities were measured to establish a relationship between powder packing and track formation. The results showed that the track height when using water atomized powder was 15% lower than the value achieved for the gas atomized powder. High-speed imaging was utilized to observe the material behavior and analyze the powder particle movement under laser irradiation. It was found that water atomized powder has less particle entrainment due to its tendency towards mechanical interlocking. The occurrence of powder spattering and melt pool instabilities was also studied. More frequent spatter ejection is believed to be due to the higher amount of oxygen in the water atomized powder.
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| 33. |
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| 34. |
- 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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| 35. |
- Frostevarg, Jan, et al.
(författare)
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Improving weld quality by laser re-melting
- 2014
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 26:4
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 36. |
- 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.
-
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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| 37. |
- Gavin, Michael C., et al.
(författare)
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Toward a Mechanistic Understanding of Linguistic Diversity
- 2013
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Ingår i: BioScience. - : Oxford University Press (OUP). - 0006-3568 .- 1525-3244. ; 63:7, s. 524-535
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Tidskriftsartikel (refereegranskat)abstract
- Our species displays remarkable linguistic diversity. Although the uneven distribution of this diversity demands explanation, the drivers of these patterns have not been conclusively determined. We address this issue in two steps: First, we review previous empirical studies whose authors have suggested environmental, geographical, and sociocultural drivers of linguistic diversification. However, contradictory results and methodological variation make it difficult to draw general conclusions. Second, we outline a program for future research. We suggest that future analyses should account for interactions among causal factors, the lack of spatial and phylogenetic independence of the data, and transitory patterns. Recent analytical advances in biogeography and evolutionary biology, such as simulation modeling of diversity patterns, hold promise for testing four key mechanisms of language diversification proposed here: neutral change, population movement, contact, and selection. Future modeling approaches should also evaluate how the outcomes of these processes are influenced by demography, environmental heterogeneity, and time.
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| 38. |
- Haglund, Peter, et al.
(författare)
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Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses
- 2018
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Ingår i: Optics and Laser Technology. - : Elsevier. - 0030-3992 .- 1879-2545. ; 100, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.
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| 39. |
- Hashemzadeh, M., et al.
(författare)
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The Application of Specific Point Energy Analysis to Laser Cutting with 1 μm Laser Radiation
- 2014
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 56, s. 909-918
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Tidskriftsartikel (refereegranskat)abstract
- Specific point energy (SPE) is a concept that has been successfully used in laser welding where SPE and power density determine penetration depth. This type of analysis allows the welding characteristics of different laser systems to be directly compared. This paper investigates if the SPE concept can usefully be applied to laser cutting. In order to provide data for the analysis laser cutting of various thicknesses of mild steel with a 2 kW fibre laser was carried out over a wide range of parameter combinations. It was found that the SPE concept is applicable to laser cutting within the range of parameters investigated here.
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| 40. |
- Kaplan, Alexander F. H., et al.
(författare)
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Laser induced reduction of iron ore by silicon
- 2023
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Ingår i: Journal of Alloys and Metallurgical Systems. - : Elsevier. - 2949-9178. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Iron ore powder accompanied by Si-powder as a reducing agent, was melted using a high-power laser beam. During laser melting of the two different powder beds placed next to each other, silicon merged and diffused into the iron ore, forming a ternary melt phase Fe-O-Si of around 30–60–10 at%. High speed imaging of the laser melting process as well as subsequent SEM-analysis of the generated nuggets showed the formation of droplets that merge with the surrounding Si- or ore-powder and form distinct domains. Under certain circumstances, the solidifying nuggets, of the order of 0.5–5 mm in size, generated numerous small domains, up to 25 µm, of high purity iron, 90 + at%, surrounded by a matrix of the above mentioned slag. Many of these Fe-domains were created in the vicinity of regions of high Si-content.
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