TY - CONF A1 - Üstündag, Ömer A1 - Gook, S. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Hybrid laser-arc welding of thick-walled pipe segments with optimization of the end crater N2 - The study deals with the application of the high-power hybrid-laser arc welding process on up to 15 mm thick pipe segments with the intention to avoid end crater imperfections during closing of the circumferential welds, where the pipes were turned during welding in 1G- and 2G-positions. Different techniques such as laser power ramp-down, abrupt switch-off of the laser power and change of the magnification of the laser spot diameter and defocusing of the laser beam relative to the workpiece were tested to remove the laser energy from the process. It could be shown that a high defocusing of the optic system above 40 mm with a resulting beam diameter > 2.9 mm in a short overlap length of approx. 20 mm leads to the formation of a cup-shaped weld seam, which is preferred for avoidance of cracks and pores in the end crater. A laser optics with motor-driven lens system was used for the welding experiments to defocuse the laser beam without changing the position of the arc. T2 - 11th CIRP Conference on Photonic Technologies LANE 2020 CY - Online Meeting DA - 07.09.2020 KW - End crater KW - Hybrid laser-arc welding KW - Circumferential weld PY - 2020 AN - OPUS4-51634 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Üstündag, Ömer A1 - Gumenyuk, Andrey A1 - Gook, S. A1 - Rethmeier, Michael T1 - Investigation of the mechanical properties of single-pass hybrid laser-arc welded thick X120 pipeline steel plates N2 - High heat input leads to grain coarsening and softening in WM and HAZ; the tensile strength is reduced. Low heat input leads to inadmissible hardening in the WM; the impact strength is reduced. The proposed t8/5-time of 3 s to 15 s could be achieved through the reduced welding velocity. The concept of electromagnetic weld pool support system allowed single-pass welds in flat position without gravity drop-outs even for reduced welding speeds; in this way the heat input can be controlled. The adaptation of the electromagnetic weld pool support system to laser and laser hybrid welding process can dramatically increase the potential field of application of these technologies for real industrial implementation. T2 - 14th Pipeline Technology Conference 2019 CY - Berlin, Germany DA - 18.03.2019 KW - Toughness KW - Hybrid laser-arc welding KW - Pipeline steel X120 KW - Electromagnetic weld pool support KW - Mechanical properties PY - 2019 AN - OPUS4-49894 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Üstündag, Ömer A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael A1 - Churiaque, C. A1 - Sanchez-Amaya, J.M. T1 - High-power hybrid laser arc welding of thick materials with electromagnetic weld pool support N2 - In addition to the many advantages of deep penetration, increased welding speed and a low sensitivity to manufacturing tolerances such as gap and edge offset, the hybrid laser arc welding (HLAW) process is used increasingly in industrial applications such as shipbuilding or pipeline manufacturing. Nonetheless, thick-walled sheets with a wall thickness of 20 mm or more are still multi-pass welded using the arc welding process, due to increased process instability by increasing laser power. Welding at reduced speed, especially in a flat position, leads to an irregular formation of the root part such as dropping. The hydrostatic pressure exceeds the surface tension, which decreases with increasing seam width. In order to prevent gravity drop-outs, the use of a melt pool support is necessary. Usual weld pool supports such as ceramic or powder supports require time-consuming mechanical detachment. The electromagnetic weld pool support system, which is described in this study, operates without contact and based on generating Lorentz forces in the weld pool. An externally applied oscillating magnetic field induces eddy currents and generates an upward directed Lorentz force, which counteracts the hydrostatic pressure. This allows single-pass welds up to 30 mm by hybrid laser arc welding process with a 20-kW fibre laser. Moreover, it is favoured by the diminished welding speed the cooling rate which leads to an improvement of the mechanical-technological properties of the seams – the lower formation of martensite in the microstructure enables better Charpy impact toughness. The electromagnetic weld pool support extends the limitation of the laser hybrid welding process in the thick sheet area. By adapting the electromagnetic weld pool support to the laser and laser hybrid welding process, the application potential of these technologies for industrial implementation can be drastically increased. T2 - 23rd Technical Conference on Welding and Joining Technologies CY - Irun, Spain DA - 07.03.2023 KW - Laser hybrid welding KW - Thick-walled steel KW - Electromagnetic backing KW - High-power laser PY - 2023 AN - OPUS4-58613 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Üstündag, Ömer A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Analysis of microstructure and mechanical properties of single-pass laser hybrid welded thick-walled steels up to 30 mm with contactless electromagnetic backing N2 - The study deals with the influence of the heat input on the thermal cycles, the microstructure and the mechanical properties for laser-hybrid welded steels of S355J2 with thicknesses up to 30 mm using a 20-kW high-power laser with contactless electromagnetic backing. The focus is on the change of the mechanical properties over the seam thickness. Therefore, the impact toughness and tensile strength were tested in different depths. Based on the experiments, a heat input of 1.3 kJ/mm - 1.6 kJ/mm, 2 kJ/mm - 2.4 kJ/mm and 3.7 kJ/mm were recommended when single-pass welding of 20 mm, 25 mm and 30 mm with a 20-kW laser in regard to the minimum requirements of the mechanical properties, respectively. Lower heat inputs led to undesired microstructure consisting of martensite, hardening and deteriorated impact toughness, where higher heat inputs led to grain-coarsening and even loss of impact strength due to the formation of retained-austenite on the grain boundaries. T2 - EMPOrIA 2023 - International Joint Conference CY - Aachen, Germany DA - 16.05.2023 KW - Laser hybrid welding KW - Electromagnetic backing KW - Thermal cycles KW - Charpy impact toughness KW - Thick-plate welding PY - 2023 AN - OPUS4-58614 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Üstündag, Ömer A1 - Kampffmeyer, D. A1 - Wolters, M. A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of shielding gas on filler wire mixing at laser hybrid welding of thick high strength steels N2 - The laser hybrid welding process offers many advantages during welding oft hick-walled steels, such as the increased penetration depth and, thus, reduced number of layers, reduced heat input and decreased distortion compared to arc-based welding processes. Especially, when welding high-strength steels (HSS), the reduced heat input plays an essential role. However, a major challenge when laser hybrid welding of thick-walled steels is the limited filler wire mixing over the entire seam thickness, which can lead to changed mechanical properties over the depth. To overcome this issue, the add of oxygen into the shielding gas and its influence on the filler wire mixing and finally to the mechanical properties were investigated within this work. Therefore, 20 mm thick S690QL steels were laser hybrid welded in a single-pass. A contactless electromagnetic backing was used to avoid sagging. The admixture of oxygen was performed by a gas mixer, where the oxygen content was varied between 0 % and 7.2 %. The experiments were also accompanied by laser beam welding tests in steel/glass configuration, where the melt pool geometry as well as the melt flow characteristics were captured by a high-speed camera. It can be concluded, that adding of 2 % to 4 % oxygen into the shielding gas had a positive effect on the filler wire mixing, were up to a depth of 18 mm elements of the filler wire could be observed. T2 - 19th Nordic Laser Material Processing Conference CY - Turku, Finland DA - 22.08.2023 KW - Laser hybrid welding KW - Electromagnetic backing KW - Shielding gas KW - Charpy impact toughness KW - Thick-plate welding KW - Filler wire mixing PY - 2023 AN - OPUS4-58615 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Üstündag, Ömer A1 - Brunner-Schwer, C. A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Process advantages of laser hybrid welding compared to conventional arc-based welding processes for joining thick steel structures of wind tower N2 - The most common welding processes when joining thick-walled steels in the industry are arc-based welding processes such as GMAW or SAW. For this purpose, the sheets are joined in multi-layer technique, which can lead to productivity losses due to high welding times. The process-specific challenges in welding thick steels using multi-layer technique relate to the high heat input from the process. Therefore, alternative welding processes are being actively sought. A suitable alternative is provided by beam-based welding processes such as the laser beam or laser hybrid welding processes, which are characterized by deep penetration welds and lower heat input. With implementation of the laser hybrid welding process in the heavy industry, such as the wind tower industry, economic benefits can be reached such as the increase in productivity by reducing the layer number, and the lower consumption of filler material and energy. When comparing SAW welded 25 mm thick steels in five to six layers and single-pass laser hybrid welding, the welding time can be reduced more than 80 % and the costs of filler material, flux and energy can be saved up to 90 %. However, the industrial use of the laser hybrid welding process is still limited to applications, where the material thickness does not exceed 15 mm due to some process-specific challenges such as the sagging, sensitivity to manufacturing tolerances such as gaps and misalignment, limited filler wire mixing, and deteriorated mechanical properties resulting from high cooling rates. To overcome these challenges, an electromagnetic backing was used within the framework of this work, which works contactless and is based on an externally applied AC magnetic field. Eddy currents are induced due to the oscillating magnetic field, and an upward-oriented Lorentz force is generated to counteract the droplets formed due to gravitational forces. It allows to weld up to 30 mm thick structural steels in a single-pass with a 20-kW fiber laser system. Additionally, the gap bridgeability and the misalignment of edges were increased to 2 mm when welding 20 mm thick steels. With the aid of the AC magnetic field, a vortex was formed in the weld root, which had a positive effect on the filler wire mixing. A further significant advantage of the EM backing was the possibility to expand the process parameter window to maintain desired cooling times and mechanical properties, without suffering adverse effects concerning the root quality of the weld. T2 - 19th Nordic Laser Material Processing Conference CY - Turku, Finland DA - 22.08.2023 KW - Laser hybrid welding KW - Wind energy PY - 2023 AN - OPUS4-58616 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Üstündag, Ömer A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of heat input on cooling rates and mechanical properties of laser hybrid welded thick structural steels N2 - The laser hybrid welding process offers many advantages such as the high penetration depth and high welding speed, and it is characterized by its low heat input compared to the arc-based welding processes, which makes the laser hybrid welding process as a suitable alternative process when welding thick-walled steels. However, there are some challenges when using laser hybrid welding process for thick steels. Due to the uneven cooling conditions and the inhomogeneous filler wire mixing, a typical laser hybrid weld can be divided into two different zones over the depth: the arc-dominated zone on the upper part and the laser-dominated zone in the root part. This leads to different mechanical properties in a laser hybrid welded joint. Due to the high cooling rates and the lack of filler wire in the laser-dominated zone, this area is more critical regarding the mechanical properties, especially the Charpy impact toughness. A low heat input can lead to undesired microstructure consisting of martensite, hardening and deteriorated impact toughness due to the high cooling rate, where higher heat inputs can lead to grain-coarsening and even loss of impact strength. This study deals with the influence of the welding speed and resulting heat input on the cooling rates, the microstructure and the mechanical properties of single-pass laser hybrid welded steels of S355J2 with thickness up to 30 mm. The experiments were performed with a 20-kW fibre laser system and a contactless electromagnetic weld backing on up to 30 mm thick steels in butt-joint configuration in 1G welding position. The cooling time was measured in three different locations near to fusion lines corresponding to different heights of the seam using a special configuration with pyrometers, collimators, and optical fibres. The test specimens for the Charpy impact testing and tensile testing were extracted in up to three different depths. Based on the experiments, a heat input of 1.3 kJ/mm - 1.6 kJ/mm, 2 kJ/mm - 2.4 kJ/mm and 3.7 kJ/mm were recommended when single-pass laser hybrid welding of 20 mm, 25 mm and 30 mm thick structural steels in regard to the minimum requirements of the mechanical properties, respectively. The optical measurement of the cooling times in different depths could be carried out reproducibly. T2 - Advances in Welding and Metal Additive Manufacturing Technologies 2023 CY - Istanbul, Türkiye DA - 30.10.2023 KW - Laser hybrid welding KW - Electromagnetic backing KW - Charpy impact toughness KW - Thick-plate welding KW - Thermal cycles PY - 2023 AN - OPUS4-58942 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -