TY - CONF A1 - Rethmeier, Michael A1 - Gook, S. A1 - Üstündag, Ö. A1 - Gumenyuk, Andrey T1 - Avoidance of end crater imperfections at high-power laser beam welding of closed circumferential welds N2 - The present work deals with the development of a strategy for the prevention of end crater defects in high-power laser welding of thick-walled circumferential welds. A series of experiments were performed to understand the influence of the welding parameters on the formation of end crater defects such as pores, cracks, excessive root-side drop-through and shrinkage cavities in the overlap area. An abrupt switch-off of the laser power while closing the circumferential weld leads to a formation of a hole which passes through the whole welded material thickness. A laser power ramp causes solidification cracks which are initiated on the transition from full-penetration mode to partial penetration. Strategies with a reduction of the welding speed shows a creation of inadmissible root sagging. Defocusing the laser beam led to promising results in terms of avoiding end crater defects. Cracks and pores in the overlap area could be effectively avoided by using defocusing techniques. A strategy for avoiding of end crater imperfections was tested on flat specimens of steel grade S355J2 with a wall thickness of 10 mm and then transferred on the 9.5 mm thick pipe sections made of high-strength steel X100Q. T2 - The 72nd IIW Annual Assembly and International Conference 2019 CY - Bratislava, Slovakia DA - 07.07.2019 KW - End crater KW - Laser beam welding KW - Circumferential welds PY - 2019 AN - OPUS4-48976 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Hildenberg, Kai A1 - Hrabe, N. T1 - Thoughts on damage tolerance and safe life design in metallic AM structures N2 - Der Vortrag bietet eine Diskussion zur Abschätzung des Schadenstoleranzverhaltens metallischer AM - Komponenten. Im Fokus stehen Probleme bei der Ermittlung repräsentativer Materialdaten, der Einfluss von Materialdefekten und Eigenspannungen. Ausgehend von derzeitigem Stand auf dem Gebiet werden Möglichkeiten der Schadenstoleranten Bauteileauslegung von AM diskutiert. N2 - The presentation provides a discussion and damage tolerant assessment of metallic AM components. In the focus are problems of the determination of representative material data, the effect of material defects and residual stresses. Starting with the actual state-of-the-art in the field, options and possibilities of a damage tolerant design for AM are discussed. T2 - BAM/NIST-Workshop on Fatigue of Additive Manufactured Metallic Components CY - Berlin, Germany DA - 16.05.2019 KW - Schadenstolerante Bauteilauslegung KW - Repräsentative Werkstoffeigenschaften KW - Defekte Eigenspannung KW - Damage tolerant component design KW - Representative material properties KW - Residual stresses PY - 2019 AN - OPUS4-48810 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael A1 - Üstündag, Ö. A1 - Gumenyuk, Andrey T1 - Single-pass Hybrid Laser Arc Welding of Thick Materials Using Electromagnetic Weld Pool Support N2 - Hybrid laser-arc welding process allows single-pass welding of thick materials, provides good quality formation of joints with minimal thermal deformations and a high productivity in comparison with arc-based welding processes. Nevertheless, thick-walled steels with a thickness of 20 mm or more are still multi-pass welded using arc welding processes, due to increased process instability by increasing laser power. One limitation factor is the inadmissible formation of gravity drop-outs at the root. To prevent this, an innovative concept of electromagnetic weld pool support is used in this study. With help of such system a stable welding process can be established for 25 mm thick steel plates and beyond. Sound welds could be obtained which are tolerant to gaps and misalignment of the welded parts. The adaptation of this system to laser and hybrid laser-arc welding process can dramatically increase the potential field of application of these technologies for real industrial implementation. T2 - Lasers in Manufacturing Conference 2019 CY - Munich, Germany DA - 24.06.2019 KW - Full Penetration KW - Hybrid Laser Arc Welding KW - Electromagnetic Weld Pool Support KW - Thick Materials PY - 2019 AN - OPUS4-48975 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Börner, Andreas A1 - Schröpfer, Dirk T1 - Ultraschallunterstützte Fräsbearbeitung/Rührreibschweißen aus Sicht des Maschinenbedieners N2 - Im Beitrag sind die Vor- und Nachteile beim Einsatz von Ultraschallunterstützung für das Zerspanen von harten und spröden Werkstoffen zusammengefasst. Des Weiteren werden aktuelle und zukünftige Analysen zum Thema ultraschallunterstütztes Zerspanen mit geometrisch bestimmter Schneide schwer zerspanbarer Materialien und Rührreibschweißen an CNC-Fräsmaschinen vorgestellt. T2 - Workshop BAM – IFW Forschungstechnik / Versuchsanlagen und Prüftechnik CY - Berlin, Germany DA - 11.09.2019 KW - Fräsen KW - Schleifen KW - Ultraschallunterstütztes Zerspanen KW - Zerspanbarkeitsanalysen KW - Abtragende Glasbearbeitung KW - Rührreibschweißen PY - 2019 AN - OPUS4-48951 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Thomas, Maximilian A1 - Vollert, F. A1 - Weidemann, Jens A1 - Gibmeier, J. A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - On the Accuracy of Standard Analysis Methods for (Trans-) Varestraint Solidification Cracking Testing N2 - Solidification cracking of metals is a well-researched topic in the field of welding science. A material’s susceptibility to solidification cracking can be tested using numerous different specialized test procedures, one of which is the Modified Varestraint-/Transvarestraint test (MVT). It was developed at BAM in 1982 and is internationally standardised. Over the decades, this test has been extensively used to characterise the solidification cracking resistance of many different materials. The present study was conducted to further investigate the influences of the standardised MVT testing parameters, as well as the characteristics of evaluation methods on the results. Several different high alloyed martensitic LTT (low transformation temperature) filler materials, CrNi and CrMn type, were used. In previous pilot studies, these alloys have shown a rather distinctive solidification cracking behaviour. First, the effects of different process parameter sets on the solidification cracking response were measured using the standard approach. Subsequently, μCT scans were performed on the specimens. The results consistently show sub surface cracking, to significant, yet varying extents. Different Primary solidification types were found using WDX-analysis, an aspect that is regarded to be the main difference between the CrNi- and CrMn-type materials and their cracking characteristics. Results show that when it comes to testing of modern high-performance alloys, one set of standard MVT testing parameters might not be equally suitable for all materials. Also, to properly accommodate different solidification types, sub-surface cracking has to be taken into account. T2 - 72th International Assembly of the International Institute of Welding (IIW) CY - Bratislava, Slovakia DA - 08.07.2019 KW - Heißriss KW - Erstarrungsriss KW - Hot Cracking KW - Solidification Cracking KW - MVT KW - Varestraint KW - Low Transformation Temperature KW - LTT PY - 2019 AN - OPUS4-48752 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Üstündag, Ö. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Experimental and Numerical Study on the Influence of the Laser Hybrid Parameters in Partial Penetration Welding on the Solidification Cracking in the Weld Root N2 - In this study, the influence of the welding speed, the arc power and the laser focal position on the solidification crack formation for partial penetration laser hybrid welded thick-walled plates were investigated. Experimentally, a direct correlation between the welding speed and the crack number was observed. That is by reducing the welding velocity the crack number was decreased. The focal position shows also a significant influence on the crack number. Since by focusing the laser on the specimen surface, the crack number has been significantly diminished. The wire feed speed showed a very slight influence on the crack formation. That is due to the large distance between the critical region for cracking and the arc region. The numerical model shows a high-stress concentration in the weld root for both components (vertical and transversal). Numerically, the reduced welding speed showed a strong impact on stress, as the model demonstrated a lower stress amount by decreasing the welding speed. The solidification cracking in the weld root is a result of interaction between metallurgical and geometrical and thermomechanical factors. T2 - The 72nd IIW Annual Assembly and International Conference 2019 CY - Bratislava, Slovakia DA - 07.07.2019 KW - Laser hybrid welding KW - Solidification cracking KW - Thick-walled steels KW - Partial penetration KW - High-power laser beam PY - 2019 AN - OPUS4-48736 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Biltgen, J. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of Partial Penetration Laser Hybrid Welding Parameters on the Solidification Cracking for Thick-Walled Structures N2 - In this study, the influence of the welding speed and the arc power on the solidification crack formation for partial penetration laser hybrid welded Thick-Walled plates were investigated. Experimentally, a linear correlation between the welding velocity and the crack number was observed. That is by reducing the welding velocity the crack number was reduced. The reduced welding velocity showed a strong impact on stress, as the model demonstrated a very lower stress amount in comparison to the reference case. The reduction of the welding speed could be a helpful technique to reduce the hot cracking. The wire feed speed showed a very slight influence on the crack formation. That can be returned to the large distance between the critical region for cracking and the arc region. T2 - Lasers in Manufacturing Conference 2019 CY - Munich, Germany DA - 24.06.2019 KW - Solidification cracking KW - Partial penetration laser hybrid welding KW - Numerical simulation PY - 2019 AN - OPUS4-48731 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stankevich, S. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael A1 - Straße, Anne T1 - Measurement of thermal cycle at multi-pass layer build-up with different travel path strategies during DLMD process N2 - The shape of the parts, created by the technology of direct laser metal deposition (DLMD), is influenced by various parameters, for example, the power and diameter of the laser source spot. The contribution of energy from the laser affects the temperature distribution in the formed layers. The changing temperature in the working area entails a change in the geometry of the layers and affects the stability of the process. In this paper, experiments on the measurement of temperature cycles in the DLMD process with different directions of the filling track are carried out. An infrared camera was used to measure thermal cycles. The calibration of the acquired data (i.e. correspondence table between the intensity of thermal radiation of the material and the absolute temperature) was done with help of two-color pyrometer ex situ and in situ measurements. The experiments are carried out on two materials 316L and Inconel 718. The effect of the maximum temperature on the layer height is shown, and thermal cycles in the formation of layers for different filling strategies are presented. T2 - Laser in Manufacturing CY - Munich, Germany DA - 24.06.2019 KW - Thermography KW - Direct Laser Metal Deposition PY - 2019 AN - OPUS4-48715 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng A1 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Numerical analysis of weld pool behavior in wire feed laser beam welding with oscillating magnetic field N2 - The introduction of an external magnetic field in laser beam welding can bring a lot of beneficial effects e. g. a homogeneous element distribution and grain refinement. However, the physical mechanism has not been fully revealed because it is difficult to describe the weld pool behavior quantitatively. In this work, the influence of an oscillating magnetic field in wire feed laser beam welding is studied using a three-dimensional transient multi-physical model. The magnetohydrodynamics, heat transfer, fluid flow, keyhole dynamics and element transport are all taken into consideration. Under suitable electromagnetic parameters, a significant electromagnetic stirring can be produced in the weld pool by the induced Lorentz force. It shows important influence on the keyhole stability and the fluid flow. The keyhole collapses more frequently at the upper part under the oscillating magnetic field. The forward and downward flow along the central plane of the weld pool is enhanced, which can bring the additional element from the filler wire to the root of the weld pool. There is a good agreement between the numerical results and the experiment results from the high-speed imaging, the optical micrograph and the energy dispersive X-ray spectroscopy. This work provides a fundamental understanding of the relationship between electromagnetic control, weld pool behavior and weld property. T2 - 72nd IIW Annual Assembly CY - Bratislava, Slovakia DA - 07.07.2019 KW - Numerical simulation KW - Weld pool behavior KW - Elemenet transport KW - Magnetic field PY - 2019 AN - OPUS4-48486 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kromm, Arne A1 - Lausch, T. A1 - Schröpfer, Dirk A1 - Rhode, Michael A1 - Kannengießer, Thomas T1 - Influence of welding stresses on relaxation cracking during heat treatment of a creep-resistant 13CrMoV steel N2 - Over the past years economic and environmental considerations have led to a markedly increased demand for efficiency and flexibility in petrochemical plants. The operational temperatures and pressures required today can only be achieved by using new creep-resistant grades of steel. The modified 13CrMoV9-10 vanadium steel shows a good resistance against creep and compressed hydrogen and has been in use for the construction of petrochemical reactors since the mid-1990s. Nevertheless, processing of this type of steel requires extreme care during the welding procedure. This is due to its low toughness and high strength in the welded state when not post weld heat treated combined with increased susceptibility to cracking during stress relaxation. Previous research into crack formation in creep-resistant steels has largely focused on thermal and metallurgical factors; however, little knowledge has been gathered regarding the influence of the welding procedure on crack formation during post weld heat treatment considering real-life manufacturing conditions. The influence of heat control on the mechanical properties has been investigated by simulating the welding and subsequent post weld heat treatment operations during the construction of petrochemical reactors using a special 3-D testing facility on the laboratory scale. This work is subdivided in two parts. In part I of this study the stresses resulting from preheating, welding, dehydrogenation heat treatment and the final post weld heat treatment were analyzed during experiments under varied heat control. In all experiments stress relief cracks formed during post weld heat treatment could be observed. The total crack lengths correlated with the welding induced stresses. Part II of this work is dedicated to the characterization of the cracks and the microstructure. The application of a special acoustic emission analysis indicated that the cracks formed in a temperature range between 300 °C and 500 °C during the post weld heat treatment. In comparison to small scale specimens welded without additional shrinkage restraint, the toughness of the restrained welds was significantly decreased. SEM and TEM analyses of all samples revealed accelerated aging due to early precipitation of special carbides during post weld heat treatment under component relevant restraint. T2 - IIW Annual Assembly CY - Bratislava, Slovakia DA - 08.07.2019 KW - Welding KW - Creep-resistant steel KW - Post weld heat treatment KW - Stress relief cracking PY - 2019 AN - OPUS4-48580 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -