@misc{ZaissPowellHaasetal., author = {Zaiß, Felix and Powell, John and Haas, Michael and Wahl, Johannes and Diegel, Christian and Schricker, Klaus and Bergmann, Jean Pierre and Hummel, Marc and Spurk, Christoph and Olowinsky, Alexander and Beckmann, Felix and Moosmann, Julian and Hagenlocher, Christian and Graf, Thomas}, title = {The influence of different core-ring intensity distributions on the capillary shape and resulting weld in laser welding of steel}, series = {Optics \& laser technology}, volume = {194}, journal = {Optics \& laser technology}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0030-3992}, doi = {10.1016/j.optlastec.2025.114495}, pages = {1 -- 12}, abstract = {Laser welding was carried out using a co-axial core-ring beam, with independent control of the power to the core and the ring. The welding process was observed using high-power X-rays and high-speed imaging equipment. Adjusting the relative powers of the core and the ring beams was found to have profound effects on the shape of both the capillary created and the weld melt pool. Moderate laser power densities in the ring were found to increase the top diameter of the weld pool and reduce fluctuations in the welding process. High laser power densities in the ring led to the creation of a second capillary which largely acted independently of the capillary generated by the laser power in the core. At high power densities and welding speeds the two capillaries were almost completely separated in the direction of travel.}, language = {en} } @misc{ZaissPowellHaasetal., author = {Zaiß, Felix and Powell, John and Haas, Michael and Diegel, Christian and Schricker, Klaus and Bergmann, Jean Pierre and Spurk, Christoph and Hummel, Marc and Olowinsky, Alexander and Beckmann, Felix and Moosmann, Julian and Hagenlocher, Christian and Graf, Thomas}, title = {Core-ring laser welding : the influence of ring diameter on the capillary dynamics and the formation of pores in the resulting weld}, series = {Lasers in manufacturing and materials processing}, journal = {Lasers in manufacturing and materials processing}, publisher = {Springer Science and Business Media LLC}, address = {New York, NY}, issn = {2196-7229}, doi = {10.1007/s40516-026-00331-1}, pages = {21}, abstract = {Double-core fibers that deliver laser beams with adjustable amounts of power to the central core and the surrounding ring component of the fiber are of major interest for optimizing laser welding processes. However, the central focussed laser spot and the ring diameters are fixed by the fiber dimensions, the focusing optics, and the laser systems involved. This work investigates the influence of different ring beam diameters, with a constant central spot diameter, on the capillary dynamics and the formation of pores in the resulting welds in 1.4301 stainless steel (X5CrNi18-10, AISI 304). The different core-ring configurations were achieved using specially designed beam-shaping optics. The generation of pores during the welding process was examined by means of synchrotron X-ray imaging. The results show that different ring diameters have a profound effect on the melt pool geometry, the capillary shape and the location of the capillary collapse which gives rise to pore formation in the weld. In the examples presented here, larger ring diameters extended the melt pool in the direction of welding without contributing directly to the capillary evaporation. In this case the narrow, deep capillaries which are created by the core beam alone can bulge and collapse, trapping vapor and gas to create large pores. If, however, the ring beam has a small enough diameter, it can help to produce a wider capillary which does not trap gas and create pores in the same way. The mechanisms by which large bubbles in the melt can result in non-spherical pores in the weld are also explained.}, language = {en} } @misc{FlorianSchrickerZenzetal., author = {Florian, Tobias and Schricker, Klaus and Zenz, Constantin and Otto, Andreas and Schmidt, Leander and Diegel, Christian and Friedmann, Hannes and Seibold, Marc and Hellwig, Peter and Fr{\"o}hlich, Fabian and Nagel, Falk and Kallage, Peter and Buttazzoni, Michele and Rack, Alexander and Requardt, Herwig and Chen, Yunhui and Bergmann, Jean Pierre}, title = {Combining in situ synchrotron X-ray imaging and multiphysics simulation to reveal pore formation dynamics in laser welding of copper}, series = {International Journal of Machine Tools and Manufacture}, volume = {204}, journal = {International Journal of Machine Tools and Manufacture}, publisher = {Elsevier BV}, issn = {0890-6955}, doi = {10.1016/j.ijmachtools.2024.104224}, pages = {1 -- 22}, abstract = {Laser beam welding has emerged as a powerful tool for manufacturing copper components in electrical vehicles, electronic devices or energy storage, owing to its rapid processing capabilities. Nonetheless, the material's high thermal conductivity and low absorption of infrared light can introduce process instabilities, resulting in defects such as pores. This study employs a hybrid approach that combines in situ synchrotron X-ray imaging with compressible multiphysics process simulation to elucidate pore-forming mechanisms during laser beam welding of copper. High-speed synchrotron X-ray imaging with an acquisition rate of 20,000 images/second facilitates the identification of relevant process regimes concerning pore formation during laser beam welding of copper with a wavelength of 1070 nm. Furthermore, in situ observations with high temporal and spatial resolution present a unique database for extensive validation of a multi-physics process simulation based on welding processes using different concentric intensity distributions. These validated simulation results enable thorough comprehension of process-related pore formation based on the interaction between keyhole, melt pool and resulting flow field. The findings show that pore formation is driven by four different mechanisms: bulging, spiking, upwelling waves at the keyhole rear wall and melt pool ejections. The synergy of high- speed synchrotron X-ray imaging and multi-physics modeling provides a fundamental understanding of the chronological sequence of events leading to process-related pore formation during laser beam welding of copper.}, language = {en} } @misc{DiegelSchrickerSchmidtetal., author = {Diegel, Christian and Schricker, Klaus and Schmidt, Leander and Seibold, Marc and Friedmann, Hannes and Hellwig, Peter and Fr{\"o}hlich, Fabian and Nagel, Falk and Kallage, Peter and Rack, Alexander and Requardt, Herwig and Chen, Yunhui and Bergmann, Jean Pierre}, title = {In situ characterization of keyhole behavior and spatter formation in full penetration laser beam welding with local gas flow using high-speed synchrotron X-ray imaging}, series = {Optics \& laser technology}, volume = {191}, journal = {Optics \& laser technology}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0030-3992}, doi = {10.1016/j.optlastec.2025.113367}, pages = {1 -- 17}, abstract = {Spatter formation is a major issue at welding speeds above 8 m/min for full penetration laser beam welding of high-alloyed steels. In experiments using a local gas flow directed at the keyhole rear wall, a reduction in spatter formation on the specimen top side was observed for welding of AISI 304. However, the interaction between gas flow and keyhole behavior with respect to the mechanisms and locations of spatter detachment, especially on the bottom side, is not yet fully understood. High-speed synchrotron X-ray imaging enables detailed insights into the keyhole behavior and the spatter formation to obtain a deeper understanding of the underlying mechanisms. During the reference experiments welding without shielding gas flow, the spatter detach from a melt pool swelling behind the keyhole aperture on both sides of the sheet. A gas flow with a low flow rate of 4.8 L/min reduces the spatter formation on the top side and the keyhole length due to the absence of oxygen affecting the surface tension. A swelling also forms on the keyhole front on the bottom side and small spatter detach undirected. Increasing the flow rate to 12.8 L/min elongates the keyhole, particularly on the specimen top side. The increased momentum transfer of the gas flow results in a periodic keyhole oscillation on the specimen top side. In combination with an elongated melt pool, the oscillation is directly correlated with the hump formation, caused by melt being pushed over the already solidified weld seam. In addition, spatter does not detach from the top side due to the changed melt flow and only detach from the keyhole front on the bottom side.}, language = {en} } @misc{SchrickerSchmidtNageletal., author = {Schricker, Klaus and Schmidt, Leander and Nagel, Falk and Diegel, Christian and Friedmann, Hannes and Seibold, Marc and Hellwig, Peter and Fr{\"o}hlich, Fabian and Kallage, Peter and Chen, Yunhui and Requardt, Herwig and Rack, Alexander and Bergmann, Jean Pierre}, title = {A comprehensive study on the influence of spatial power distribution on time-dependent keyhole behavior in laser beam welding of copper by means of high-speed synchrotron X-ray imaging}, series = {Optics \& laser technology}, volume = {192, Part E}, journal = {Optics \& laser technology}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0030-3992}, doi = {10.1016/j.optlastec.2025.113999}, pages = {1 -- 15}, abstract = {This paper examines the impact of spatial power distributions on the time-dependent keyhole behavior during laser beam welding of copper using high-speed synchrotron X-ray imaging. The experimental setup utilized a COHERENT HighLight FL8000-ARM fiber laser with concentric intensity distribution created by an optical fiber cable. The European Synchrotron Radiation Facility (ESRF, beamline ID19) was used to conduct high-speed synchrotron imaging at 20,000 images per second to study the spatio-temporal keyhole behavior. Keyhole geometries were extracted through advanced image processing techniques, allowing quantification of parameters like depth, aperture, bulging, and determination of related oscillation frequencies. The results showed that core-dominated processes exhibit significant variations in keyhole geometry. In contrast, ring-dominated processes exhibited reduced penetration depths but increased melt pool dynamics due to altered absorption conditions and increased temperatures within the melt pool. A stabilized core-ring power distribution minimized fluctuations, resulting in improved process stability. The findings were summarized in a model concept describing three characteristic keyhole regimes: core-dominated, ring-dominated, and stabilized core-ring processes.}, language = {en} }