| 1. |
- Da Silva, Adrien, et al.
(författare)
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Influence of aluminium powder aging on Directed Energy deposition
- 2022
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- The use of aluminium alloys for Additive Manufacturing is of high interest for advanced geometries and lightweight applications. In Directed Energy Deposition, a powder stock is processed with a laser beam, which offers a high process flexibility. However, aging of the powder feedstock during storage or after recycling remains fundamentally challenging for aluminium alloys because of their sensitivity to oxida-tion and porosity. In order to investigate these effects, AlSi10Mg powder batches were aged in different conditions and processed by Directed Energy Deposition. The results showed that powder aging does not significantly change the particle size or morphology, but it introduces more oxygen and hydrogen in the powder. The oxidation of the particles reduces the laser beam absorbance of the powder and increases wetting of the melt pool, which affects the track geometry. A 3.5 to 4.2 times higher porosity was observed in the material deposited from aged powder, which are most likely hydrogen pores causedby the increased hydrogen content in the aged powder. The tensile properties of the parts built with aged powder showed 19.0% lower yield strength, 14.2% lower ultimate strength and 99.2% higher elongation, which are most likely the results of the coarser microstructure and increased porosity.
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| 2. |
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| 4. |
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14th NOLAMP Conference : The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden
- 2013
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Laser is a key element in obtaining a sustainable economy in Europe. Innovative laser processes will play a significant role in future green manufacturing as they provide a precise, well-controlled and highly effective energy deposition to the workpiece. Future challenges are to increase the spectrum of laser manufacturing technologies in all sectors where the laser can offer innovative product solutions, higher product quality, less environmental impact, higher productivity and in turn cost benefits.The NOLAMP conferences address all aspects of laser materials processing from fundamental science to industrial applications. The first NOLAMP conference took place in Oslo in 1987 in a period of intense development of the laser processes and their industrial applications. The NOLAMP has continued on a biannual cycle ever since, strengthening the Nordic laser community by encouraging knowledge transfer and networking. Now, 26 years later, in the forthcoming 14th NOLAMP, the research and development of processes like laser welding, laser hybrid welding, laser cutting and laser surface treatment is still very important, as well as the development of industrial applications and equipment for laser material processing. This time the NOLAMP Conference will be held in Gothenburg, Sweden. In this highly industrialized region of Sweden and with the close distance to Denmark, Norway and Finland, we hope to attract a strong participation from industry and the scientific community. On behalf of the Nordic laser community and Luleå University of Technology, it is our great pleasure to invite you to the 14th NOLAMP conference.
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| 6. |
- Akselsen, Odd M., et al.
(författare)
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A first assessment of laser hybrid welding of 420 mpa steel for offshore structure application
- 2013
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Ingår i: 14th NOLAMP Conference. - Luleå : Luleå tekniska universitet. - 9789174396881 - 9789174396898 ; , s. 171-182
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For many years, laser hybrid welding has been used in various industries to increaseproductivity and reduce costs. One example is the adaption of the hybrid process inshipbuilding. The next natural step is to further develop the process for the oil and gasindustry, where the welded joint properties requirements are more severe, and the ability tohandle tolerance deviations is more critical. As a first attempt to develop hybrid laser processfor the use in offshore structures, the present investigation addresses preliminary weldingtrails carried out with 15 kW fibre laser with appropriate gas metal arc welding equipment,using double Y joint geometry and 20 mm thick 420 MPa steel plates. The subsequent weldtesting included both Charpy V notch impact and CTOD fracture mechanical testing at -30°C.The results indicate that the heat affected zone (HAZ) of the examined steel appeared withsatisfactory Charpy and CTOD toughness (> 200 J, > 0.2 mm) while the weld metal hadinsufficient toughness (20-40 J, < 0.2 mm). With a better welding wire, designed for lowtemperature applications, it is reasonable to suggest that laser hybrid arc welding can be usedfor applications even below a temperature of -30°C.
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| 7. |
- Akselsen, Odd Magne, et al.
(författare)
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Properties of laser hybrid butt welds of 420 MPa steel
- 2013
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Ingår i: The proceedings of the Twenty-third (2013) International Offshore and Polar Engineering Conference. - Cupertino, Calif. : International Society of Offshore and Polar Engineers. - 9781880653999 ; , s. 290-294
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Konferensbidrag (refereegranskat)abstract
- Laser hybrid welding has been used in European shipbuilding for many years due to its high productivity. In order to qualify the process for the oil and gas industry, an extensive welding and testing programme is needed, and the properties must satisfy more severe requirements than in shipbuilding. This is particularly the case when these activities are moving to the Arctic regions, where low temperature toughness may be the primary challenge. The present investigation addressed preliminary welding trials carried out with 15 kW fibre laser-gas metal arc (GMA) hybrid welding using double Y joint of 20 mm thick 420 MPa steel plates. Both Charpy V notch impact and CTOD fracture mechanical testing were included with test temperature of -30°C. The results indicate that the heat affected zone (HAZ) of the examined steel appeared with satisfactory toughness (> 200 J, > 0.2 mm) while the employed weld metal had insufficient impact properties. The weld metal CTOD toughness approached 0.2 mm. With a better welding wire, designed for low temperature applications, it is reasonable to suggest that laser hybrid arc welding can be used for applications even below -30 to -40°C
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| 8. |
- Al-Mashikhi, S.O., et al.
(författare)
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An explanation of ‘striation free' cutting of mild steel by fibre laser
- 2009
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Ingår i: Lasers in manufacturing 2009. - Stuttgart : AT-Fachverlag.
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Konferensbidrag (refereegranskat)abstract
- This paper presents the results of an experimental and theoretical investigation into the phenomenon of ‘striation free cutting', which is a feature of fibre laser cutting of thin section mild steel. The paper concludes that the creation of very low roughness edges is related to an optimisation of the cut front geometry when the cut front is inclined at angles close to the Brewster angle for the laser - material combination. For purely geometric reasons this particular type of cut front optimisation is not possible for CO2 laser cutting of mild steel.
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| 9. |
- Al-Mashikhi, S.O, et al.
(författare)
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Heat affected zones and oxidation marks in fiber laser–oxygen cutting of mild steel
- 2011
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 23:4
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Tidskriftsartikel (refereegranskat)abstract
- The effect of cutting speed and sheet thickness on surface oxidation and heat affected zones (HAZs) has been investigated for laser–oxygen cutting of mild steel sheet with a fiber laser. Optical and scanning electron micrographs were used to determine the extent of surface oxidation and HAZ from plan and cross-sectional views, respectively. The HAZ is consistently wider at the bottom of the cut compared to the HAZ at the top of the cut. With increasing speed, the width of the HAZ at the top of the cut decreases whereas the HAZ width at the bottom of the cut generally increases. No simple, direct relationship between HAZ width and surface oxidation was seen. However, it is possible to state that in each case considered here, the HAZ would be completely removed if they are machined back by a depth equal to the extent of the surface oxidation.
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| 10. |
- Alam, Md. Minhaj, et al.
(författare)
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Analysis of the rapid central melt pool flow in hybrid laser-arc welding
- 2012
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 39, s. 853-862
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid laser arc welding creates a long weld pool tail. By high speed imaging the melt velocity behind the keyhole was measured to be very high, of the order of meters per second. Fluid dynamics simulation was carried out locally in the central axial plane of the pool tail. The high speed melt layer redistributes its momentum to slow movement of the deeper bulk. The consequences of initially high melt speed and its mass flow redistribution on the formation of the central reinforcement peak are discussed.
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