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Welding of Al-Si coated high-strength steel 22MnB5
Šebestová, Hana ; Horník, Petr ; Mikmeková, Šárka ; Novotný, Jan ; Mrňa, Libor
Al-Si-based coatings are widely used as surface protection of steel sheets against high-temperature oxidation during the hot stamping process. Laser welding is a suitable technology for hardened components joining because it does not produce a wide heat-affected zone with a degraded microstructure. The highly concentrated energy of the laser beam is responsible for rapid heating and subsequent rapid cooling of material which results in insufficient homogenization of the weld metal. In Al-rich areas (Al originates from the coating), ferritic bands are formed in the dominantly martensitic matrix. These bands decrease the strength of laser weld by more than one third compared to the base metal. The low-power electric arc placed immediately behind the laser beam can help to achieve a slower cooling of the weld metal, reduce the ferritic bands and increase the strength of weld joints up to 90 % of base metal tensile strength.
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Aplication of picosecond laser micromachinning for manufacturing of reflective DOE for CW power lasers
Mrňa, Libor ; Novotný, Jan ; Kolařík, Vladimír
Reflective optical elements are advantageous in terms of ease of cooling, where even a less efficient element can be easily operated without damage by a simple cooling system. When material interacts with the ultrashort pulses, the interaction is largely non-thermal and the material can be removed in a very defined manner without affecting the surrounding area. Direct ablation with ultrashort laser pulses enables fast and flexible fabrication of diffractive optical elements (DOEs). Ultrashort pulses can also be used to machine difficult-to-machine materials with conventional lasers and easily create spatial structures on the order of tens of micrometers.
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Spatial distribution of backreflecteded laser radiation during laser welding
Horník, Petr ; Mrňa, Libor ; Šebestová, Hana ; Novotný, Jan
Laser sources commonly used in industry are usually equipped with a backscattered detector, which prevents potentially dangerous situations from turning off the laser in the event of too much backscatter. However, the laser radiation is never completely absorbed by the material and to some extent is always reflected in the laser welding. This detector can also be used to monitor the welding process. The output is the intensity value returned by the optical fiber. To better understand which parts of the process contribute most to the backscatter value, an optical assembly with a camera scanning the wavelength of the process laser was designed.
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