| 1. |
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| 2. |
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| 3. |
- Bostanjoglo, Georg, et al.
(författare)
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Processing of Ni-based aero engine components with repetitively Q-switched Nd:YAG lasers
- 1996
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Ingår i: High-Power Lasers. - : SPIE. ; , s. 145-157
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Konferensbidrag (refereegranskat)abstract
- Aircraft engine industry uses free running high power Nd:YAG lasers for drilling cooling holes into nickel base alloy turbine components. A cw-pumped, Q-switched, high beam quality laser system with 400W laser power is presented. The laser is used to trepan drilling of 1.6mm. Hastelloy X sheets and ceramic coated combustion chamber tubes of the same metal. Cylindrical shape, uniformity, and reproducibility are achieved with a trepan-like drilling setup. The heat load of the workpiece as well as the process time is considerably decreased by employing high-repetition Q-switched lasers.
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| 4. |
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| 5. |
- Fällström, Karl-Evert, et al.
(författare)
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Generating and recording transient bending waves in plates by pulsed lasers
- 1996
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Ingår i: Experimental techniques (Westport, Conn.). - : Springer Science and Business Media LLC. - 0732-8818 .- 1747-1567. ; 20:1, s. 15-19
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Tidskriftsartikel (refereegranskat)abstract
- We have presented a method to generate bending waves in a plate by focusing a Q-switched Nd:YAG-laser pulse on its surface. These waves are recorded by double pulsed hologram interferometry. Evaluation of the interferograms show that the bending wave pattern is very similar to what is predicted by the Kirchhoff plate equation assuming a point impact of infinitesimally short duration. This indicates that a short Nd:YAG-laser pulse may be considered as a Dirac pulse in space and time. Future investigations will be performed with a more powerful and "cleaner" laser to get a higher energy and impulse transfer to the plate thus giving bending waves of larger amplitude. Promising preliminary experiments have also begun using a double pulsed ruby laser both for generating and recording of bending waves.
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| 6. |
- Koh, Yangsook, et al.
(författare)
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Cleaning of corroded iron artefacts using pulsed TEA CO2- and Nd:YAG-lasers
- 2003
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Ingår i: Journal of Cultural Heritage. - 1296-2074 .- 1778-3674. ; 4:Suppl. 1, s. 129-133
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Tidskriftsartikel (refereegranskat)abstract
- Archaeological iron artefacts are often covered with a crust, containing organic fibres, mineral particles, dirt, etc. Before conservation, this crust must be carefully removed. With traditional mechanical and chemical methods, there is an obvious risk of over-cleaning. These methods also increase the risk of the oxidised or primary corrosion layer breaking away which will lead to loss of information about the form of the object and other important surface details. The main advantage of using pulsed lasers for cleaning metallic archaeological artefacts is that the removal of the crust is well controlled and can be carried out layer by layer. To determine the most suitable irradiation conditions, the wavelengths and the fluence for successful cleaning must be evaluated carefully. As test samples, corroded utility articles such as nails and hand tools have been used. Depending on the composition of the crust, different lasers have been used: TEA CO2 lasers have been successfully used for removal of organic materials and rust. EO-Q-switched Nd:YAG laser at IR and at green wavelengths, which have different absorption characteristics, has also been tested. The Nd:YAG laser was able to clean the corroded samples; however, the risk of surface damage was higher than when using the TEA CO2 laser. Analysis of the surfaces cleaned by lasers has been performed with optical and scanning electron microscopy, X-ray spectrometry and Raman-spectrometry
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| 7. |
- Koh, Yangsook, et al.
(författare)
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Removal of adhesives and coatings on iron artifacts using pulsed TEA CO2 and Nd:YAG lasers
- 2001
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Ingår i: Laser Techniques and Systems in Art Conservation. - Bellingham, wash. : SPIE - International Society for Optical Engineering. - 9780819440976 ; , s. 46-53
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Konferensbidrag (refereegranskat)abstract
- Selective and precise removal of surface coatings and contaminants can be achieved using lasers with a suitable wavelength. In this study pulsed TEA CO2- and Nd:YAG- lasers have been used to remove old adhesive and coatings from iron artifacts. This laser cleaning technique can enable extremely precise removal of old coating layers without damaging the underlying metal. Cleaning test on different samples using an Nd:YAG-laser with wavelengths of 1,064 nm, 532 nm and a TEA CO2-laser with 10,600 nm have been carried out. Trial sample were treated with different kinds of adhesive and coatings used in metal conservation and then cleaned using the three lasers. The results were compared with a conventional technique, micro blasting. Comparison of the laser cleaned surfaces was performed by optical microscopy and Raman-spectroscopy. The comparative study showed that the best results were achieved with the TEA CO2 laser, with the coatings being removed entirely without damage to the substrate. The original surface of the substrate was preserved and any re-deposited particles could be removed easily using a scalpel or brush after the laser radiation treatment.
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| 8. |
- Koh, Yang Sook, et al.
(författare)
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Surface cleaning of iron artefacts by lasers
- 2005
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Ingår i: Lasers in the Conservation of Artworks. - Berlin : Encyclopedia of Global Archaeology/Springer Verlag. - 9783540229964 ; , s. 95-100
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Konferensbidrag (refereegranskat)abstract
- In this paper the general method and ethics of the laser cleaning technique for conservation are presented. The results of two experiments are also presented; experiment 1 compares cleaning of rust by an Nd:YAG laser and micro-blasting whilst experiment 2 deals with removing the wax coating from iron samples by a TEA CO2 laser. The first experiment showed that cleaning with a pulsed laser and higher photon energy obtained a better surface structure than micro blasting. The second experiment showed how differences in energy density affect the same surface.
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| 9. |
- Meijer, J., et al.
(författare)
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Phase transformations by high-intensity sub-microsecond laser pulses.
- 1992
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Ingår i: Proceedings of the laser materials processing symposium, ICALEO '92. - Orlando, Fla : Laser institute of America. - 0912035498 ; , s. 228-236
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Konferensbidrag (refereegranskat)abstract
- In certain alloys, the 'laser shocking' causes work hardening, an increase in dislocation density and phase transformations. Of the materials tested, and austenitic Hadfield manganese-alloyed steel target was found to have the strongest tendency for a martensitic phase transformation. In contrast with conventional transformation hardening, there is no tempering in the case of repeated application. Whilst most material is vaporized, some surface melting will occur. The rate of re-solidification of the molten material is such that an almost completely amorphous structure results. The martensitic transformation has been confirmed by using optical, scanning and transmission electron microscopy, OM, SEM and TEM/STEM. Two different lasers, a Q-switched Ruby and a Q-switched Nd:YAG were used for the experiments. Calculations of impact/momentum, peak pressure and peak temperature were performed using the finite difference method. The model used for simulating the process has been proved to be useful in understanding the transformation mechanism.
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| 10. |
- Miroshnikova, Natalia, et al.
(författare)
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Percussion hole drilling of metals with a fourth-harmonic Nd:YAG laser studied by defocused laser speckle correlation
- 2005
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 44:17, s. 3403-3408
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Tidskriftsartikel (refereegranskat)abstract
- Defocused speckle correlation is introduced as a tool for measuring the response in metal sheets during percussion laser drilling. For this procedure the fourth-harmonic Nd:YAG wavelength (266 nm) was used in pulsed mode. The method provides a cost-efficient and robust alternative to speckle interferometry for the study of the small deformations that appear during laser processing. The accuracy was shown to be of the order of a few tens of microradians for the tilt component that is measured, which translates to a few nanometers in deflection when the component is spatially integrated. In the measurements, deflections in the form of craters as large as 50 nm were detected on the back sides of silver and copper sheets. The diameters of the craters were 300 μm in the silver and 150 μm in the copper sheet; the output diameter of the hole was ~5 μm.
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| 11. |
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| 12. |
- Miroshnikova, N., et al.
(författare)
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Study of the interaction mechanisms between different materials and pulses from CO2- and Nd:YAG-lasers using digital speckle photography
- 2004
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5506, s. 42-50
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Tidskriftsartikel (refereegranskat)abstract
- Pulsed irradiation from CO2- and Nd:YAG lasers focused on the front side of different plates produces nearly instantaneous surface changes on the rear side of the plate. The responses of the materials depend on physical parameters such as pulse energy and duration, photon energy, the absorption and mechanical characteristics of the target material. The equipment built up for visualization of these phenomena consists of a cw. He-Ne laser, a digital CCD camera and a fast computer. The analysis is done using Digital Speckle Photography (DSP). Using focused and defocused laser speckle patterns, DSP enables measurement of in-plane strain fields, Brownian motion and residual micro-structural changes in the material caused by a laser pulse. Results are obtained at the frame rate of the digital camera and allow the creation of animated real-time or "movie" sequences. Results from CO2- and Nd:YAG pulse interaction on Al2O3 ceramics and steel plates will be presented. The Brownian motion during the relaxation phase is more or less localized to the impacted area for both materials and both wavelengths but the relaxation times differ significantly. Steel also exhibits some residual material changes and doesn't recover completely while Al2O3 returns to its initial state some time after the impact
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Sarady, Istvan, et al.
(författare)
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Aluminum welding by beam addition of cw. and repetitively Q-switched multi-kW Nd:YAG lasers
- 1997
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Ingår i: Proceedings of the Laser Materials Processing Conference. - Orlando, Fla : Laser institute of America. - 0912035560 ; , s. G229-G237
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Konferensbidrag (refereegranskat)abstract
- To ensure a stable process when welding Al, the power density must exceed a certain threshold value. An increase of power density can be achieved with Q-switched pulses. To simultaneously obtain both high average power and high welding speed, the beam of a cw. pumped, repetitively AO-Q-switched 1.7 kW Nd:YAG-laser at PRF 60 kHz was combined with the beam of a 2.0 kW cw. Nd:YAG-laser. The foci of the two lasers were coincident on the surface of the work piece. Positioning was accomplished by using two separate focusing optics. As the spot size on the work piece increases with the cosine of the tilt angle between the focusing optics, the relative movement of the work piece and optics was in the direction of the tilt angle. The beams from both lasers were delivered via o 600 mu m optical fibres.
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| 17. |
- Sarady, Istvan
(författare)
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Applications of pulsed lasers for phase transformation and welding
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work deals with the interaction of pulsed laser radiation with solid, metallic materials at moderate and very high power densities. The interaction mechanism depends upon the properties of both the laser and the target material. The wavelength, pulse energy and pulse duration of a laser can be chosen to suit a particular application whilst the physical properties of the target material are usually fixed. The reflectivity, absorptivity, thermal diffusivity and conductivity, density, specific heat, melting point, boiling point, latent heat of melting, latent heat of vaporisation, ionisation energy, plasma opacity, plasma density, etc. of the target all influence the interaction with the laser beam. In addition, the mechanical and metallurgical properties of the target can be important in certain situations, for example high pressure shock waves in some materials can lead to work hardening. This process is known as shock hardening. At very high power densities or fluxes, 109 - 1014 Wcm-2 [Jcm-2s-1], the explosion of a superheated plasma causes a high-pressure shock wave, which, in turn causes micro structural changes in certain target materials (papers I-III). Investigations into this phenomenon were performed with TEA C02, Q-switched Ruby, Nd:YAG and Iodine photo dissociation lasers. At moderate power densities or fluxes, 104 - 107 [Jcm-2s-1], the focused pulse only melts a limited volume of the metal parts involved. This is the interaction mechanism found in laser welding (papers IV-VI). These investigations were performed with an Nd:YAG laser and studied the interaction mechanism with pairs of materials usually difficult to join in industrial applications: tungsten alloys to cobalt and iron-base alloys, tungsten carbide to tool steel, aluminium to copper, etc. In some cases, the addition of filler metals was found useful to produce sound welds, forming ternary phases or a 'dispersed ensemble' during the process.
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| 18. |
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| 19. |
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| 20. |
- Sarady, Istvan, et al.
(författare)
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Investigation of interaction mechanisms in laser processing using digital speckle photography
- 2003
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Ingår i: Congress proceedings. - Orlando, Fla : Laser institute of America. - 0912035757 ; , s. 314-321
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Konferensbidrag (refereegranskat)abstract
- Digital, defocused speckle photography was used for the in-situ, real-time determination of the strain field round the focus spot of a pulsed Nd:YAG laser. These surface strains can cause cracking during laser cutting and drilling of advanced engineering ceramic materials. A CW HeNe laser was used for illumination, images being captured by CCD camera with a 633 nm band pass filter, synchronised to operate between the individual laser pulses. Targets included alumina and stainless steel.
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| 21. |
- Sarady, Istvan, et al.
(författare)
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Investigations into the welding of superalloys with a CW [continuous wave] Nd : YAG laser and dual-focusing optics
- 1999
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Ingår i: 7th NOLAMP Conference. - Lappeenranta : Lappeenrannan teknillinen korkeakoulu. - 9517643500 ; , s. 497-504
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Konferensbidrag (refereegranskat)abstract
- The use of continuous wave Nd:YAG lasers for the welding of sheet metal parts of superalloys was investigated. Laser butt welds were made in AISI 410, austenitic 18/8 stainless steel and aircraft-grade superalloys Haynes 25 and Inconel 718 (1.6, 2, 2.1 and 3.2 mm thickness) using single- and dual-focusing optics. Microstructure, appearance, porosity, weld quality and solidification were determined. Solidification of the molten material in the weld bead can be controlled using Nd:YAG continuous wave laser with special focusing optics
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| 22. |
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| 23. |
- Sarady, Istvan, et al.
(författare)
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Joining of cemented tungsten carbide to tool steel using Nd:YAG-laser and optical fibres
- 1992
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Ingår i: Proceedings of the Laser Materials Processing Symposium : ICALEO '92. - Orlando, Fla : Laser institute of America. - 0912035498 ; , s. 529-533
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Konferensbidrag (refereegranskat)abstract
- The aim of the present work was to produce tools for powder compacting by joining cemented tungsten carbide to high-quality tool steels by laser welding. The conventional method of joining such materials is by brazing or by using adhesives (glue), both of which have disadvantages: low strength and poor positional accuracy. In the case of laser welding, the components were positioned exactly in a jig or fixture, heated to 200-300°C and finally welded by using a pulsed Nd:YAG laser giving a positional accuracy in the order of a few micrometers. The laser beam was optically split and guided by optical fibers to opposite sides of the joint greatly reducing the effect of thermal distortion. The use of optical fibers also result in a smooth energy distribution in the beam spot reducing the risk of crack formation. Compressive fatigue strength of the joined components was determined. Cross-sectioned samples were examined for microstructure, microhardness and the distribution of alloying elements in the joint zone. The weld surface was also examined for evidence of microcracking. The method described can complement conventional and vacuum brazing techniques in certain applications.
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| 24. |
- Sarady, Istvan, et al.
(författare)
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Phase transformations in Fe-Mn alloys with nanosecond iodine laser pulses
- 1994
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Ingår i: Intense beams and applications. - Bellingham, Wash : SPIE - International Society for Optical Engineering. - 819414123
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Konferensbidrag (refereegranskat)abstract
- If a short laser pulse with high intensity is focused on the surface of a target in vacuum, it causes a nearly instantaneous vaporization of a limited volume of material. The rapid expansion of this material vapor produces an impact at the surface. The shock wave propagates and is absorbed in the material. In certain alloys, this causes work hardening, an increase in dislocation density, and phase transformations. While most material is vaporized, some surface melting occurs. The rate of re-solidification of the molten material is such that an almost completely amorphous structure results. The martensitic transformation in the solid target has been confirmed by using optical and transmission electron microscopy and by electromagnetic detection techniques. An iodine photodissociation laser emitting at the wavelength of 1315 nm was used for the experiments. The pulse length was typically 1 ns and the pulse energy could be varied between 1 and 30 Joules. The energy and power density in the focused spot were larger than 3 X 103 Jcm-2 and 3 X 1012 Wcm-2, respectively. Calculations of impact/momentum, peak pressure, and peak temperature were performed using the finite difference method with moving boundaries. The effects of the iodine laser pulses are compared with those of Q- switched Nd:YAG and ruby laser pulses.
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| 25. |
- Sarady, Istvan, et al.
(författare)
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Rapid tooling : en förundersökning
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Rapid Prototyping-tekniken började utvecklas för över tjugofem år sedan, med "laser cladding" som bas. Man sintrade ihop pulverformig material, levererad av enkla pulversprutor, med hjälp av en delvis fokuserade laserstråle. Dessa tidiga prototyper var tämligen klumpiga, uppnådde långt ifrån full täthet och måttnoggrannheten var låg. Den egentliga snabba prototyptillverkningen fick sitt första genombrott 1986, när processen stereolitografi introducerades. Tekniken använde en blå- eller UV-laser för att av en flytande härdplast framställa fasta, tredimensionella modeller. Där laserljuset aktiverade plasten, härdade den, på andra områden förblev den flytande. Inom två år har sådana utrustning blivit kommersiellt tillgängliga. Några år senare utvecklades selektiv lasersintring, SLS av pulverformade plastmaterial, som gav mycket högre flexibilitet, samt bättre form- och måttnoggrannhet. Även här tillverkades modellerna genom att tunna skikt "staplades" på varandra. Denna teknik vidareutvecklades både i Europa och i USA för att framställa dels funktionsdugliga komponenter av metaller, sintrade till nära nog 100% densitet, dels för att framställa verktygsinsatser för formsprutning av termoplaster och gummi samt för pressgjutning av Al-legeringar för bilindustrin. Sedan 1995 används därför begreppet Rapid Tooling, eftersom det inte bara är prototyper utan även fullt användbara komponenter och verktygsinsatser som kan tillverkas. Det är framför allt två teknik för sintring av metallpulver som torde vara av intresse för Ltu: EOSINT-M, utvecklad av EOS GmbH i Tyskland, samt Directed Material Deposition Systems, DMDS, som marknadsförs av OPTOMEC Inc. i USA. EOSINT-M lämpar sig särskilt för framställning av verktygsinsatser, medan DMDS kan användas för framställning av "near net shaped" funktionsdetaljer (enstaka eller i små serier). DMDS kan även med framgång användas för att reparera tredimensionella strukturer, såsom turbinblad, ledskenor, roterande tätningar i jetmotorer och gasturbiner, axlar, mm. Därför kan dessa två teknik anses snarare komplettera varandra än att man kan beskriva dem som konkurrerande förfaranden.
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| 26. |
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| 27. |
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| 28. |
- Sarady, Istvan, et al.
(författare)
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The manufacture of high precision parts by Nd:YAG laser welding
- 1994
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Ingår i: Proceedings of the Laser Materials Processing Conference. - Orlando, Fla : Laser institute of America. - 0912035528 ; , s. 396-404
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Konferensbidrag (refereegranskat)abstract
- The mechanisms of laser welding are explained and three examples are described to illustrate the flexibility of Nd:YAG laser welding in production of small components. Explanations are given of the principles of condition-limited welding, deep penetration welding and braze welding. The production line examples given relate to: cutting, laser seam welding and laser spot welding of stainless steel housings of gyros for aeronautical navigation; laser spot welding a cobalt alloy torsion spring onto a stainless steel gyro housing; and braze welding of a tungsten alloy to an iron-cobalt alloy, involving melting the latter to make the joint. Workpieces, procedures and results obtained are detailed
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| 29. |
- Sjödahl, Mikael, et al.
(författare)
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Laser hole drilling process studied using laser speckle correlation
- 2006
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Ingår i: Speckle06. - Bellingham, Wash. : SPIE - International Society for Optical Engineering. - 9780819464262 ; , s. 63412M-
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Konferensbidrag (refereegranskat)abstract
- This paper revisits defocused speckle correlation as a tool for measuring the response in metal sheets during percussion laser drilling processing. For the processing the 4th harmonic Nd:YAG wavelength (266 nm) was used in pulsed mode. It is shown that the method provides a cost efficient and robust alternative to speckle interferometry for the study of the small deformations that appear during laser processing. The accuracy was shown to be in the order of a few tens of μrads for the tilt component being measured which translates to a few nm in deflection when being spatially integrated. In the measurements deflections up to 50 nm was detected on the backside of silver and a copper sheet, respectively.
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| 30. |
- Yalukova, O., et al.
(författare)
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Investigation of interaction mechanisms in laser drilling of thermoplastic and thermoset polymers using different wavelengths
- 2006
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 66:10, s. 1289-1296
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a comparison of the percussion drilled holes in fiber reinforced polymer and non-reinforced thermoplastic sheets using three wavelengths, 1064, 532 and 266 nm is presented. At near infrared and visible wavelengths, 1064 and 532 nm, most of the bulk thermoplastic and thermoset polymers are partially transparent. The degree of transparency is dependent upon the degree of crystallinity. The most amorphous thermoplastics, such as PMMA have the highest transparency. In comparison, the fibre reinforced thermosets - graphite fibre reinforced epoxy - have low transparency. If the IR or visible laser beam is strongly focused, it can cause thermally induced degradation and sometimes burning and other damages (cracking, boiling, etc.) around the focused laser spot and the interaction zone. By using the fourth harmonics ultraviolet light (266 nm) of a diode-pumped and AOQ-switched Nd:YAG-laser with pulse duration of about 100 ns, the hole drilling process was significantly improved and the risk for thermal damage has been significantly reduced for both materials. Around the irradiated spot or drilled holes the material is influenced. This was investigated by both scanning electron microscopy and optical microscopy. There was clear evidence of a change in the interaction mechanism if UV light with high enough photon energy was used. By using UV light, bond breaking rather than thermal material removal occurred, i.e., a change from thermal to photo-chemical dissociation or photo-ablation becomes the dominant interaction mechanism.
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| 31. |
- Yalukova, O., et al.
(författare)
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Investigation of laser percussion hole drilling by use of speckle correlation
- 2005
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 44:30, s. 6338-44
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Tidskriftsartikel (refereegranskat)abstract
- In this paper speckle correlation is introduced as a tool to investigate the heat-influenced area during material processing with laser light. Two materials were investigated, a pure silver sheet and a sheet of SiC-diamond composite. The processing laser used in the experiments was a diode-pumped acousto-optical Q-switched Nd:YAG laser that allowed percussion hole drilling to be performed using green light through a second-harmonic crystal. The measurements were performed using a continuous-wave He-Ne laser and a digital camera. The experimental results show that the heat-influenced area is ~5000 times larger than the actual hole being drilled and that it reaches a steady-state condition toward the end of the processing cycle
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