TY - JOUR A1 - Graf, B. A1 - Gook, S. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Combined laser additive manufacturing for complex turbine blades N2 - Laser beam processes are increasingly used in the field of additive manufacturing. Prominent methods are either powderbed-based like Laser Metal Fusion (LMF), or utilizing a powder nozzle like Laser Metal Deposition (LMD). While LMF allows the manufacturing of complex structures, build rate, part volumes and material flexibility are limited. In contrast, LMD is able to operate with high deposition rates on existing parts, and materials can be changed easily during the process. However LMD shape complexity is limited. Utilizing their respective strengths, a combination of these two additive technologies has the potential to produce complex parts with high deposition rates and increased material flexibility. In this paper, combined manufacturing with additive technologies LMF and LMD is described. Its benefit for industry with emphasis on turbomachinery is shown. As reality test for the innovation, an industrial turbine blade is manufactured. KW - Turbine blade KW - Additive manufacturing KW - Laser metal fusion KW - Laser metal deposition PY - 2016 SN - 2499-9733 VL - 3 IS - 20 SP - 34 EP - 42 AN - OPUS4-38709 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael T1 - Trends in European thin sheet welding N2 - 1. Steel Production and Processing in Europe 2. Design Trends in the Automotive Industry 3. Welding Technologies in the Automotive Industry 4. Problems while Processing AHSS/UHSS 5. Challenges in Joining Multi-Material Structures 6. Mechanical Joining Technologies 7. Thermal-Mechanical Joining Processes 8. Energy Efficiency of Welding Processes T2 - AWS Sheet Metal Welding Conference XVII CY - Livonia, MI, USA DA - 19.10.2016 KW - Lightweight concepts PY - 2016 AN - OPUS4-38763 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Na, S.-J. A1 - Han, S.-W. A1 - Muhammad, S. A1 - Zhang, L. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael A1 - Karhu, M. A1 - Kujanpa, V. T1 - Flow and Bead Formation Characteristics in High Power Laser Welding at Different Welding Positions (Invited Talk) N2 - The numerical simulations of high power laser keyhole welding at different welding positions are performed by using Volume-Of-Fluid (VOF) method. The main material is SS400. The multi-physics phenomenon is considered using several models, such as the heat flux of Gaussian heat source, the recoil pressure with Clausisus-Clapeyron equation, the Marangoni flow considering temperature gradient, the buoyancy force with Boussinesq approximation, the additional shear stress and heat source due to metallic vapor ejected through keyhole entrance, the bubble formation assumed as adiabatic bubble, and the multiple-reflection by solving proper discriminant, are used. To analyze the fluid flow pattern, the concept of streamline formed by reconstructing the value of the velocity vector is applied. Partial and full penetration cases at different welding positions are considered. The welding position seems to have only a minor influence on bead formation characteristics in both cases. This is probably due to the fact that the recoil pressure has a major influence when compared to other driving forces. The flow characteristics and fluid velocity in weld pool are analyzed to compare the gravity direction effect at different welding positions. It is observed that the clockwise flow pattern is mainly formed by the recoil pressure on the keyhole surface in the case of partial penetration. The laser energy can't maintain the whole weld pool when the weld pool size becomes too large. And then the solidification starts from the middle part of weld pool and a necked weld pool shape is formed. In the full penetration welding, the weld pool flow patterns are affected by the leakage of laser power through the full penetration keyhole and also by surface tension. Furthermore, the numerical simulation of full penetration welding with AISI316L is also performed to analyze the effect of material properties. The weld bead shapes obtained by simulations were compared with the corresponding experimental results to confirm the validity of the process models adopted and the CFD simulation tool. T2 - Lasers in Manufacturing Conference 2015 CY - München, Germany DA - 22.06.2015 KW - Macro Processing (Joining, Welding) KW - Weld pool KW - Flow pattern KW - Different welding position KW - Numerical simulation KW - High power laser keyhole welding PY - 2015 SP - 1 EP - 6 AN - OPUS4-37163 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Numerical simulation of solidification crack formation during laser beam welding of austenitic stainless steels under external load N2 - Solidification cracking phenomena taking place under controlled tensile weldability (CTW) test conditions have already been investigated both experimentally and numerically via FEA in order to get a better understanding of the mechanisms of hot crack formation during laser beam welding of austenitic steel grades. This paper develops a threedimensional finite element model employing the contact element technique to simulate the formation and propagation of solidification cracks during laser full penetration welding of fully austenitic stainless steel 1.4376. During the experimental procedure, the resulting strain and displacement directed to the laser beam in the close vicinity of the weld pool was measured at the surface of the workpiece using a digital image correlation (DIC) technique with an external diode laser as an illuminating source. Local strain fields, global loads and crack lengths predicted by the model are in good agreement with those observed in experiments. KW - Solidification cracking KW - Finite element analysis KW - Imaging KW - Laser welding KW - Austenitic stainless steels PY - 2016 DO - https://doi.org/10.1007/s40194-016-0357-1 SN - 0043-2288 SN - 1878-6669 VL - 60 IS - 5 SP - 1001 EP - 1008 PB - Springer CY - Berlin, Heidelberg AN - OPUS4-37287 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sproesser, Gunther A1 - Chang, Y.-J. A1 - Pittner, Andreas A1 - Finkbeiner, M. A1 - Rethmeier, Michael T1 - Life cycle assessment of welding technologies for thick metal plate welds N2 - Life Cycle Assessment (LCA) is applied in evaluating environmental impacts of state-of-the-art welding technologies. Manual Metal Arc Welding (MMAW), Laser Arc-Hybrid Welding (LAHW) and two Gas Metal Arc Welding (GMAW) variants are used to join a plate of 20 mm thick structural steel. The LCA results indicate that for 1 m weld seam, MMAW causes the highest environmental impacts in global warming potential (GWP), eutrophication potential (EP), acidification potential (AP), and photochemical ozone creation potential (POCP) among the selected processes, and the LAHW variant performances the least. Filler material and electricity consumptions generally dominate the impacts and reach shares of up to 80% and 61% in the respective impact categories. However, electrode coating consumption in MMAW remarkably contributes impacts on AP and EP, for instance 52% of AP and 76% of EP. Strategies for improvement of the applied welding technologies are discussed. KW - Life Cycle Assessment (LCA) KW - Arc welding KW - Laser arc-hybrid welding KW - Resource efficiency PY - 2015 DO - https://doi.org/10.1016/j.jclepro.2015.06.121 SN - 0959-6526 VL - 108 IS - Part: A SP - 46 EP - 53 PB - Elsevier Science CY - Amsterdam AN - OPUS4-34969 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel A1 - Kunze, R. A1 - Avilov, Vjaceslav A1 - Rethmeier, Michael T1 - Finite element modelling of an AC electromagnetic weld pool support in full penetration laser beam welding of thick duplex stainless steel plates N2 - An electromagnetic weld pool support system for 20 mm thick duplex stainless steel AISI 2205 was investigated numerically and compared to experiments. In our former publications, it was shown how an AC magnetic field below the process zone directed perpendicular to the welding direction can induce vertically directed Lorentz forces. These can counteract the gravitational forces and allow for a suppression of material drop-out for austenitic stainless steels and aluminum alloys. In this investigation, we additionally adopted a steady-state complex magnetic permeability model for the consideration of the magnetic hysteresis behavior due to the ferritic characteristics of the material. The model was calibrated against the Jiles-Atherton model. The material model was also successfully tested against an experimental configuration before welding with a 30 mm diameter cylinder of austenitic stainless steel surrounded by duplex stainless steel. Thereby, the effects of the Curie temperature on the magnetic characteristics in the vicinity of the later welding zone were simulated. The welding process was modelled with a 3D turbulent steady-state model including heat transfer and fluid dynamics as well as the electromagnetic field equations. Main physical effects, the thermo-capillary (Marangoni) convection at the weld pool boundaries, the natural convection due to gravity as well as latent heat of solid–liquid phase transitions at the phase boundaries were accounted for in the model. The feedback of the electromagnetic forces on the weld pool was described in terms of the electromagneticinduced pressure. The FE software COMSOL Multiphysics 4.2 was used in this investigation. It is shown that the gravity drop-out associated with the welding of 20 mm thick duplex stainless steel plates due to the hydrostatic pressure can be prevented by the application of AC magnetic fields between around 70 mT and 90 mT. The corresponding oscillation frequencies were between 1 kHz and 10 kHz and the electromagnetic AC powers were between 1 kW and 2.3 kW. In the experiments, values of the electromagnetic AC power between 1.6 kW and 2.4 kW at oscillation frequencies between 1.2 kHz and 2.5 kHz were found to be optimal to avoid melt sagging or drop-out of melt in single pass fullpenetration laser beam welding of 15 mm and 20 mm thick AISI 2205. T2 - ICALEO 2015 - 34th International congress on applications of lasers & electro-optics CY - Atlanta, GA, USA DA - 2015-10-18 KW - Electromagnetic weld pool support KW - Laser beam welding KW - FE simulation KW - Duplex stainless steel PY - 2015 SN - 978-1-940168-05-0 SP - 650 EP - 659 AN - OPUS4-35036 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 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 - TY - CONF A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael A1 - Bakir, Nasim T1 - Comparative study of hot cracking susceptibility for laser welded joints by means of a self- restraint and an externally loaded hot cracking tests N2 - Over the past decade, laser beam welding has significantly evolved and established itself as an efficient tool in the industry. Solidification cracking and the weldability of materials have been highly contentious issues for many years. Today, there are many self and externally loaded tests to investigate the hot cracking resistance of steels. The purpose of this paper is to compare the susceptibility of three stainless steel grades to hot cracking by using an externally loaded hot cracking test (CTW) and a self-restraint test in accordance with SEP-220-3. The repeatability and effectiveness of the results are discussed. The experimental results are widely dispersed, implying a low predictive value for the self-restraint test. On the other hand, the results from the externally loaded test exhibit excellent repeatability and provide a quantitative characterization of the susceptibility of steels to hot cracking. T2 - The 5th International Conference on Steels in Cars and Trucks CY - Amsterdam-Schiphol, Netherlands DA - 19.06.2017 KW - Externally loaded test KW - Hot cracking test KW - SEP-1220-3 KW - CTW test KW - Self-restraint test PY - 2017 SP - 1 EP - 8 AN - OPUS4-41174 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - RPRT A1 - Vollertsen, F. A1 - Grünenwald, S. A1 - Rethmeier, Michael A1 - Gumenyuk, Andrey A1 - Reisgen, U. A1 - Olschock, S. T1 - Welding thick steel plates with fibre lasers and GMAW N2 - The results of a collaborative research project on laser beam weldability of carbon steels of high sheet thickness are presented. That includes single and multiple pass welding of 16 mm and 20 mm thick plates, as well as the investigation of acceptable tolerances i.e. gap bridgeability and edge misalignment. For the welding experiments fibre lasers with 8 kW, 20 kW laser power and different MAG-techniques were used in various applications. With the 20 kW fibre laser 16 mm plates could be welded with a single pass, 20 mm required a seam preparation or alternatively preheating of the material. For multi pass welding with 8 kW laser power a joint preparation with a single V-butt joint with a broad root face (Ygroove) was applied. The root pass was always welded with a hybrid process, the filler passes with a hybrid process as well as a MAG process which produced the best results. T2 - 61th IIW Annual Assembly CY - Graz, Austria DA - 2008-07-06 KW - Hybrid Welding KW - Carbon Steels KW - Single pass welding KW - Multi pass welding PY - 2008 IS - IV-965-08 SP - 1 EP - 14 PB - International Institute of Welding CY - Paris AN - OPUS4-18678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - RPRT A1 - Pittner, Andreas A1 - Weiss, D. A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - Fast temperature field generation for welding simulation and reduction of experimental effort N2 - The quality of welding processes is governed by the occurring induced distortions yielding an increase in production costs due to necessary reworking. Especially for more complex specimens it is difficult to evaluate the optimal configuration of welding sequences in order to minimise the distortion. Even experienced welding operators can solve this task only by trial and error which is time and cost consuming. In modern engineering the application of welding simulation is already known to be able to analyse the heat effects of welding virtually. However, the welding process is governed by complex physical interactions. Thus, recent weld thermal models are based on many simplifications. The state of the art is to apply numerical methods in order to solve the transient heat conduction equation. Therefore, it is not possible to use the real process parameters as input for the mathematical model. The model parameters which allow calculating a temperature field that is in best agreement with the experiments cannot be defined directly but inversely by multiple simulations runs. In case of numerical simulation software based on finite discretisation schemes this approach is very time consuming and requires expert users. The weld thermal model contains an initial weakness which has to be adapted by finding an optimal set of model parameters. This process of calibration is often done against few experiments. The range of model validity is limited. An extension can be obtained by performing a calibration against multiple experiments. The focus of the paper is to show a combined modelling technique which provides an efficient solution of the inverse heat conduction problem mentioned above. On the one hand the inverse problem is solved by application of fast weld thermal models which are closed form solutions of the heat conduction equation. In addition, a global optimisation algorithm allows an automated calibration of the weld thermal model. This technique is able to provide a temperature field automatically that fits the experimental one with high accuracy within minutes on ordinary office computers. This fast paradigm permits confirming the application of welding simulation in an industrial environment as automotive industry. On the other hand, the initial model weakness is compensated by calibrating the model against multiple experiments. The unknown relationship between model and process parameters is approximated by a neural network. The validity of the model is increased successively and enables to decrease experimental effort. For a test case it is shown, that this approach yields accurate temperature fields within very short amount of time for unknown process parameters as input data to the model contributing to the requirement to construct a substitute system of the real welding process. KW - Welding simulation KW - Temperature field generation KW - Short calculation time KW - Multiple experiments KW - Inverse heat conduction problem KW - Neural networks PY - 2009 IS - SC-Auto-32-09 SP - 1 EP - 11 PB - International Institute of Welding CY - Paris AN - OPUS4-19744 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pittner, Andreas A1 - Schwenk, Christopher A1 - Rethmeier, Michael A1 - Weiß, D. T1 - Automated generation of temperature fields for numerical welding simulation KW - Welding simulation KW - Temperature field generation KW - Optimization KW - Neural networks PY - 2009 SN - 0288-4771 VL - 27 IS - 2 SP - 219 EP - 224 CY - Tokyo, Japan AN - OPUS4-19826 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -