TY - JOUR A1 - Bachmann, Marcel A1 - Avilov, Vjaceslav A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - About the influence of a steady magnetic field on weld pool dynamics in partial penetration high power laser beam welding of thick aluminium parts JF - International journal of heat and mass transfer N2 - A multi-physics numerical model was developed to investigate the influence of a steady magnetic field aligned perpendicular to the welding direction during partial penetration high power laser beam welding of aluminium in downhand position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were successfully solved with the finite element differential equation solver COMSOL Multiphysics 4.2. The implemented material model used temperature-dependent properties up to evaporation temperature. Marangoni convection in the surface region of the weld pool, natural convection due to the gravitational field and latent heat of solid–liquid phase transition were taken into account. Solidification was modelled by the Carman–Kozeny equation for porous media morphology. The flow pattern in the melt as well as the weld bead geometry were significantly changed by the induced Lorentz force distribution in the liquid metal. It reveals that the application of a steady magnetic field to laser beam welding with corresponding Hartmann numbers Ha2 ≈ 104 allows for a suppression of the characteristic wineglass-shape of the weld cross section caused by thermocapillary flow. The numerical results are in good agreement with experimental results obtained with welding of AlMg3 with a 16 kW disc laser. The steady magnetic field was delivered by permanent magnets mounted on both lateral sides of the weld specimen. The maximum magnetic flux density was around 500 mT. It shows, that the applied magnetic field has a predominant dissipating effect on the weld pool dynamics independently of its polarity. KW - Electromagnetic weld pool control KW - Hartmann effect KW - Laser beam welding KW - Lorentz force KW - Marangoni flow KW - Natural convection PY - 2013 DO - https://doi.org/10.1016/j.ijheatmasstransfer.2013.01.015 SN - 0017-9310 VL - 60 SP - 309 EP - 321 PB - Elsevier CY - Amsterdam AN - OPUS4-27655 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Avilov, Vjaceslav A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Experimental and numerical investigation of an electromagnetic weld pool support system for high power laser beam wleidng of austenitic stainless steel JF - Journal of materials processing technology N2 - A three-dimensional turbulent steady state numerical model was used to investigate the influence of an alternating current (AC) magnetic field during high power laser beam keyhole welding of 20 mm thick stainless steel AISI 304 being modeled as an ideal non-ferromagnetic material. Three-dimensional heat transfer and fluid dynamics as well as the electromagnetic field equations were solved with the finite element package COMSOL Multiphysics 4.2 taking into account the most important physical effects of the process. Namely, the thermo-capillary (Marangoni) convection at the weld pool boundaries, natural convection due to gravity and density differences in the melt volume as well as latent heat of solid–liquid phase transitions at the phase boundaries were included in the model. It is shown that the gravity drop-out associated with the welding of thick plates due to the hydrostatic pressure can be prevented by the application of AC magnetic field between 80 mT and 135 mT for corresponding oscillation frequencies between 1 kHz and 10 kHz below the weld specimen. Experimentally, a value of the magnetic flux density of around 230 mT was found to be necessary to allow for single-pass laser beam welding without sagging or drop-out of melt for a 20 mm thick combination of austenitic stainless steel AISI 304 and ferritic construction steel S235JRC at an oscillation frequency of around 2.6 kHz. KW - Electromagnetic weld pool control KW - Laser beam welding KW - Lorentz force KW - Marangoni flow KW - Natural convection PY - 2014 DO - https://doi.org/10.1016/j.jmatprotec.2013.11.013 SN - 0924-0136 SN - 1873-4774 VL - 214 IS - 3 SP - 578 EP - 591 PB - Elsevier CY - Amsterdam AN - OPUS4-29709 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Avilov, Vjaceslav A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Magnets improve quality of high-power laser beam welding JF - Welding design & fabrication KW - Laser beam welding KW - Hartmann effect KW - Marangoni flow PY - 2013 UR - http://weldingdesign.com/processes/magnets-improve-quality-high-power-laser-beam-welding SN - 0043-2253 SP - 1 EP - 3(?) PB - Penton/IPC CY - Cleveland, Ohio AN - OPUS4-29412 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Avilov, Vjaceslav A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields JF - International journal of thermal sciences N2 - Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solide-liquid phase transition was taken into account and the solidification was modelled by the Carman-Kozeny equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics. KW - Electromagnetic weld pool control KW - Hartmann effect KW - Laser beam weliding KW - Lorentz force KW - Marangoni flow KW - Natural convection KW - Aluminium PY - 2016 DO - https://doi.org/10.1016/j.ijthermalsci.2015.10.030 SN - 1290-0729 VL - 101 SP - 24 EP - 34 PB - Elsevier CY - Paris AN - OPUS4-35034 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -