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Measurement and simulation of back-reflected radiation during penetration laser welding
Horník, Petr ; Mrňa, Libor ; Šarbort, Martin ; Šebestová, Hana
The laser welding process is accompanied by a wide range of radiation, both in the visible part of the spectrum and thermal radiation of the weld pool, and last but not least, the laser radiation itself. During penetration laser welding mode, which is often used, the keyhole is created. Most of the laser radiation is absorbed by the multiple reflections inside the keyhole, but a small portion is reflected back and passes through the welding head and the optical fiber. Back-reflected laser radiation is also monitored directly in the laser to protect the resonator and other optical components. The signal is easily accessible and obtained data can be used for monitoring during the welding process. Therefore, we designed experiment in which the relationship between weld dimensions, focal position, and back-reflected laser radiation was investigated. Furthermore, the measurement results were compared with the simulation.
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Use of laser-TIG hybrid technology for boron-doped high-strength steels
Kachlíř, Jaromír ; Šebestová, Hana (referee) ; Mrňa, Libor (advisor)
This thesis deals with the usage of arc preheating for welding high strength boron enhanced steel 22MnB5 using hybrid technology known as laserTIG and also its impact on the final weld compared to welds welded by only the laser or the arc method. During the experiment I welded five sheets of the above mentioned steel 1,3 or 1,9 milimeters wide. Except for the welds fabricated by the laser and the TIG method was the only variable the electric current of the arc (I = 20, 40, or 60 A). Welds welded this way were compared based on strength limits measured by the tensile tests. Additionally were they compared according to the metalographic survey and the progress of weld hardness, calculated using the Vickers hardness test.
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Use of laser-TIG hybrid technology for welding aluminium alloys
Drápela, Petr ; Šebestová, Hana (referee) ; Mrňa, Libor (advisor)
Different problems arise from choice of setting technological parameters during welding of alluminium alloys. Choice of welding method, welding speed and material influence mechanical properties of welds. During welding of alluminium alloys come difficulties due to oxidation of thin surface layer of material. One of ways how to overcome this obtacle is to use hybrid laser-TIG welding method. In this diploma thesis is described influence of welding processes on mechanical properties of two alluminium alloys(EN AW-5754 H22, EN AW-6082 T6) and change in their microstructure during welding.
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Strength charactristics of hybrid LasTig welds of thermomechanically processed steel
Šebestová, Hana ; Horník, Petr ; Mrňa, Libor
Thermomechanically processed steels achieve their high strength properties, while maintaining good ductility, thanks to their fine-grained structure assured by micro-alloying and strictly controlled process of rolling. Low heat input welding technologies are advisable. Nevertheless, high temperature gradients accompanying laser welding can lead to the brittle microstructures formation. The cooling rate can be controlled by preheating that we have realized with the heat of electric arc. Hybrid technology combining laser welding with tungsten inert gas (TIG) welding is referred to as LasTIG. The paper presents the effect of electric current that generates arc discharge on tensile strength, toughness, and fatigue life of LasTIG welds of S460MC and S700MC steels.
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Measurement of laser welding process by high-speed camera and photodiode
Horník, Petr ; Mrňa, L. ; Šebestová, Hana
Laser welding monitoring system can be realized optically. The solution with photodiode sensing welded area has advantage of simplicity and low cost but faces many challenges. Multi-photodiode measurement show dependency of the measured intensity on the photodiode position. Subsequently, the measured values were compared with high-speed camera images. Using the correlation coefficient, the area providing the same information as photodiode measurement was determined in the images.
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Synergic effects of laser – TIG welding
Kubíček, J. ; Doležal, P. ; Mrňa, Libor ; Šebestová, Hana ; Horník, Petr
Laser welding compared to conventional arc methods is accompanied by rapid cooling rates. It can lead to the formation of undesirable microstructure of the weld metal and heat affected zone of some steel grades which has a negative impact on their mechanical properties. The preheating is quite problematic because of high speed of laser welding. The possibility of preheating by the heat of the arc discharge of the associated TIG burner has been tested. Precise holder has been fabricated to fix the burner to the laser welding head allowing TIG electrode positioning towards the laser beam and the workpiece. A number of high strength steel S460MC and S700MC welding experiments was performed. The effect of TIG current on microstructural changes has been proven. Some welding experiments were compared to the SYSWELD welding simulations.\n
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Assessment of weld defects during laser welding with beam wobbling of aluminum alloy
Slíž, Michal ; Šebestová, Hana (referee) ; Mrňa, Libor (advisor)
This bachelor thesis is aimed on assessment of weld defects during laser welding with beam wobbling of aluminum alloy. Theoretical part deals with study of main types of industrial lasers, laser modes and analysis of beam wobbling technique. Further described aluminum alloys, their weldability, weld defects and methods of their evaluation. In the experimental part, sixteen test welds are made on sheet metal from aluminum alloy AlMg3. This is followed by the evaluation of the defects and determination of optimal welding parameters.
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Study of properties of laser welds of Domex 700 MC material using arc preheating
Kosinka, Jakub ; Šebestová, Hana (referee) ; Mrňa, Libor (advisor)
This thesis deals with the study of influence of preheating/reheating by TIG arc method in the laser welding process of Domex 700 MC fine-grained steel through the evaluation of laser-welds properties, respectively properties of welds made by laser-TIG hybrid technology. The main part of this thesis is experiment, in which Domex 700 MC plates 3 mm thick were welded – first using laser itself, then using laser with arc preheating and finally using laser with arc reheating. The variable parameter during the processes preheating or reheating was distance of TIG tungsten electrode and laser beam (DLA = 1 mm, 2 mm and 4 mm). The criterion for the assessment of welds properties thus produced was tensile strength verified by the tensile test. For a more detailed study of the laser-welds properties, a macrostructure / weld microstructure analysis and a Vickers hardness test were performed.
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Properties of hybrid LasTIG welds of of S460MC steel
Šebestová, Hana ; Horník, Petr ; Mrňa, Libor
Modern structural high strength low alloy steels achieve their excellent strength properties through the microalloying and carefully controlled process of hot rolling. Welding technologies with low heat input are advisable to maintain fine-grained structure of these steels and to minimize heat distortions. Laser beam is a source of highly concentrated energy and thus very narrow heat affected zone is reached during laser welding. Unfortunately, undesirable quenching microstructures can be generated thanks to high heating and cooling rates in both weld metal and heat affected zone. Their amount can be reduced through the temperature rate decrease realized using preheating. Technology of LasTIG hybrid welding combines laser welding with the preheating by an electric arc. The contribution evaluates the effect of electric current on LasTIG weld macro and microstructure and microhardness.
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