| 1. |
- Dizdar, Senad, et al.
(författare)
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Grey Cast Iron Brake Discs Laser Cladded with Nickel-Tungsten Carbide-Friction, Wear and Airborne Wear Particle Emission
- 2020
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Ingår i: Atmosphere. - Basel : MDPI. - 2073-4433. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- Airborne wear particle emission has been investigated in a pin-on-disc tribometer equipped with particle analysis equipment. The pins are cut out from commercial powder metallurgy automotive brake pads as with and without copper content. The discs are cut out from a commercial grey cast iron automotive brake disc as cut out and as in addition to a laser cladded with a powder mix of Ni-self fluxing alloy + 60% spheroidized fused tungsten carbide and then fine-ground. Dry sliding wear testing runs under a contact pressure of 0.6 MPa, sliding velocity of 2 m/s and a total sliding distance of 14,400 m. The test results show both wear and particle emission improvement by using laser cladded discs. The laser cladded discs in comparison to the reference grey cast iron discs do not alter pin wear substantially but achieves halved mass loss and quartered specific wear. Comparing in the same way, the friction coefficient increases from 0.5 to 0.6, and the particle number concentration decreases from over 100 to some 70 (1/cm(3)) and the partition of particles below 7 mu m is approximately halved.
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| 2. |
- Forsman, Tomas, et al.
(författare)
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Prediction of the cross-sectional geometry of Nd:YAG laser welds in aluminum alloys
- 2000
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Ingår i: Proceedings of the Laser Materials Processing Conference. - Orlando, Fla. : Laser institute of America. - 0912035609 ; , s. E156-E165
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Konferensbidrag (refereegranskat)abstract
- This paper describes an analytical model for determining the geometry of laser welds. An earlier model by Lampa and Kaplan (1997), for CO2 laser welding of stainless steel, has been further developed to cover Nd:YAG laser welding of aluminium alloys. This analytical work was followed by experimental verification using a 4 kW Nd:YAG laser. The model was found to be accurate over a wide range of process parameters
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| 3. |
- Forsman, Tomas, et al.
(författare)
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The Luleå model for laser welding simulation
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Laser welding is emerging as one of the most interesting methods for joining of metals. The process has already been proven in both high quality welding in aerospace, electronics and medical engineering as well as in applications for high volume production in automotive industry. Over the past decade a substantial amount of theoretical research has been carried out into the subject of deep penetration laser welding. Many of the models developed for the laser welding process, are highly sophisticated and demand the work of scientists for performing the modelling and interpretation of the modelling results. There is a substantial lack of "easy-to-use" models which can be handled by research and development engineers in the manufacturing industry and which will give such important data as the geometrical size and form of the welded joints. The over all objective by this work was to develop a fast and user-friendly model for the prediction of weld geometries in various engineering materials, different joint types and wavelengths in laser welding. A basic, analytical thermodynamic model, first developed by A. Kaplan and then further by C. Lampa, was expected to be a suitable base for continuing development of a laser welding model, which could be used for real joint configurations and various engineering materials, as well as for both CO2- and Nd:YAG-lasers. The project has succeeded in developing this analytical model, "The Luleå model for laser welding simulation", for predicting the geometrical dimensions of laser welds in overlap and butt configuration. The metals supported by the model are mild steels, stainless steels, aluminium alloys and titanium alloys. Welding of those materials can be simulated by using CO2- or Nd:YAG laser. A PhD-degree and a substantial amount of scientific results for a docent degree have also been achieved by this work. The analytical model has been given a user-friendly interface and is incorporated on a CD for easy access. Through the software interface, the material properties and process parameters can be changed to the liking of the user. Calculated results in form of weld shape as a function of process speed are offered and compared to experimental macrographs. The "Luleå model for laser welding simulation", was in its basic state originally developed for ELANET, the "EuroLaser Academy Network for Educational Tools". The objective of the ELANET is to make use of the numerous theoretical investigations in laser materials processing carried out in the past. Developed models, including "the Luleå model" shall be implemented into a CD for easy accessibility and distribution. The simple structure of the calculation logic of this analytical model does not require high performance computer sources. The "Luleå model for laser welding simulation" is therefore suitable for use directly on a shop floor on a standard equipped personal computer. The introduction and implementation of the model to the industry is planned to take place during year 2001 when the model will be presented and used in practical industrial tests.
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| 4. |
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| 5. |
- Lampa, Conny, et al.
(författare)
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An analytical model of laser keyhole welding
- 1997
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Ingår i: Proceedings of the 6th Nordic Laser Material Processing Conference, Luleå, Sweden, August 27-29, 1997. - Luleå : Luleå tekniska universitet. ; , s. 218-225
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Konferensbidrag (refereegranskat)
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| 6. |
- Lampa, Conny, et al.
(författare)
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An analytical thermodynamic model of laser welding
- 1997
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 30:9, s. 1293-1299
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Tidskriftsartikel (refereegranskat)abstract
- An earlier model of deep-penetration laser welding has been simplified in order to provide a useful model of process analysis. This work involves the modelling of the various energy-absorption mechanisms which determine the keyhole shape and thus the dimensions of the melt pool. The penetration depth and weld width (top and bottom) predicted by the model are shown to be in close agreement with experimental results. The widening of the top of the weld seam as a result of Marangoni flow is accurately modelled by introducing an artificially enhanced value for the workpiece's thermal conductivity towards the top of the weld. The model allows analysis of the dependence of the weld profile on the process parameters.
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| 7. |
- Lampa, Conny
(författare)
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Effektivitet vid lasersvetsning : Effectiveness of laser welding
- 1997
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Ingår i: Svetsen. - 0039-7091. ; 56:3, s. 4-5
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The effectiveness of laser welding was investigated (the efficiency with which the laser radiation is utilised for welding), and the significance of the welding speed for weld geometry was analysed. Effectiveness was found to increase with increased welding speed, which decreases penetration. The welds were performed on austenitic stainless steel with a continuous CO2 laser. The heat absorbed by the weld was found
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| 8. |
- Lampa, Conny
(författare)
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Laser welding : energy redistribution and weld geometry
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Over the past few years laser welding has developed into a process which has a wide range of application over a number of industries. Industrial growth in this area has been stimulated by improvements in production rates and quality but technologically the process is still not fully understood. This work aims to contribute to the understanding of deep penetration laser welding with emphasis on energy redistribution and weld geometry. The seven papers which make up the thesis investigate various aspects of the absorption and redistribution of energy during laser welding. Theoretical and experimental methods have been used to analyze the effects of process parameters on the geometry of the resultant welds. Considerable success has been achieved in matching theoretical predictions to actual results. This work has helped to clarify a number of features of the laser welding process including the following; 1. The effect of process parameters on the efficiency of laser welding. 2. The mechanisms of energy absorption which result in a weld. 3. The effect of an increased external pressure on the laser-material interaction. 4. The effect of thermocapillary flow and how it can be taken advantage of in industrial applications.
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| 9. |
- Lampa, Conny, et al.
(författare)
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Laser welding of copper to stainless steel
- 1997
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Ingår i: Proceedings of the Laser Materials Processing Conference : November 17-20, 1997, San Diego, CA. - Orlando, Fla : Laser institute of America. - 0912035560
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the possibility of CO2 laser welding austenitic stainless steel to copper. The experimental results show that solidification cracking may be the greatest problem in this application. It is suggested that the cracks are generated in three ways: Liquid metal embrittlement, due to the presence of copper in the solidifying steel grain boundaries. Stresses generated during solidification due to fixturing and differences in the thermal properties of the materials involved. A solidification mode change due to the rapid weld solidification involved in laser welding of austenitic stainless steel. To overcome these problems the fixturing and specimen edge preparation have to be optimized to minimize the amount of copper in the fusion zone, to reduce the stresses, and to minimize the cooling rate during solidification. These factors were taken into account and the resulting welds were of high integrity with the same strength as the original copper being welded. The role of thermocapillary or Marangoni flow in transferring heat to the copper side of the weld is also discussed
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| 10. |
- Lampa, Conny
(författare)
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Modellering av svetsdimensioner vid lasersvetsning : Modelling of weld dimensions in laser welding
- 1997
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Ingår i: Svetsen. - 0039-7091. ; 56:2, s. 20-22
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The article describes how laser welding was simulated over the whole width and depth of a weld by modelling the energy absorption mechanisms. The results compared well with experiment. The thermo-capillary flow near the weld surface was modelled by "effective heat flow" in a molten pool in a stationary state. In the lower part of the weld, where boundaries between liquid and solid phases are parallel, heat flow is mainly conductive. The effects of welding speed are explained by the model.
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