Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Validierung von Methoden zur Vermeidung von Liquid Metal Embrittlement an realitätsnahen Prinzipbauteilen (IGF 21483 BG / P 1488)

2021 , Meyerdierks, Martin , Schreiber, Vincent , Böhne, Christoph , Seitz, Georg , Jüttner, Sven , Meschut, Gerson , Rethmeier, Michael

Ziel des Forschungsprojekts ist es, eine Korrelation zwischen Gleeble-Heißzug-Prüfverfahren und Widerstandspunktschweiß-basierten Prüfverfahren herzustellen. Es soll die Effektivität von Methoden zu Vermeidung von Liquid Metal Embrittlement an realitätsnahen Prinzipbauteilen bewertet werden. Weiterhin soll Kenntnis über Auswirkungen von LME Rissen auf das Tragverhalten von realitätsnahen Prinzipbauteilen gewonnen werden.

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Avoidance of End Crater Imperfections at High-Power Laser Beam Welding of Closed Circumferential Welds

2019 , Gook, Sergej , Üstündag, Ömer , Gumenyuk, Andrey , Rethmeier, Michael

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 the imperfections such as pores, cracks, excessive root-side drop-through and shrinkage cavities in the overlap area. An abrupt switch-out 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 imperfections. Cracks and pores could be effectively avoided by using defocusing techniques. A strategy for avoiding of end crater defects 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.

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Laser-plasma-cladding as a hybrid metal deposition-technology applying a SLM-produced copper plasma nozzle

2018 , Brunner-Schwer, Christian , Kersting, Robert , Graf, Benjamin , Rethmeier, Michael

Laser-Metal-Deposition (LMD) and Plasma-Transferred-Arc (PTA) are well known technologies which can be used for cladding purposes. The prime objective in combining LMD and PTA as a Hybrid Metal Deposition-Technology (HMD) is to achieve high deposition rates at low thermal impact. Possible applications are coatings for wear protection or repair welding for components made of steel. The two energy sources (laser and plasma arc) build a joint process zone and are configurated to constitute a stable process at laser powers between 0.4-1 kW (defocused) and plasma currents between 75-200 A. Stainless steel 316L serves as filler material. For this HMD process, a plasma Cu-nozzle is designed and produced by powder bed based Selective Laser Melting. The potential of the HMD technology is investigated and discussed considering existing processes. This paper demonstrates how the interaction of the two energy sources effects the following application-relevant properties: deposition rate, powder efficiency and energy input.

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Hybrides Auftragschweißen: Potentiale des laserunterstützten Plasma-Pulver-Auftragschweißens (PTA)

2018 , Brunner-Schwer, Christian , Graf, Benjamin , Rethmeier, Michael , Schreiber, Frank

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Analysis and recycling of bronze grinding waste to produce maritime components using directed energy deposition

2021 , Müller, Vinzenz , Marko, Angelina , Kruse, Tobias , Biegler, Max , Rethmeier, Michael

Additive manufacturing promises a high potential for the maritime sector. Directed Energy Deposition (DED) in particular offers the opportunity to produce large-volume maritime components like propeller hubs or blades without the need of a costly casting process. The post processing of such components usually generates a large amount of aluminum bronze grinding waste. The aim of the presented project is to develop a sustainable circular AM process chain for maritime components by recycling aluminum bronze grinding waste to be used as raw material to manufacture ship propellers with a laser-powder DED process. In the present paper, grinding waste is investigated using a dynamic image analysis system and compared to commercial DED powder. To be able to compare the material quality and to verify DED process parameters, semi-academic sample geometries are manufactured.

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Automated tool-path generation for rapid manufacturing and numerical simulation of additive manufacturing LMD geometries

2019 , Biegler, Max , Wang, Jiahan , Graf, Benjamin , Rethmeier, Michael

In additive manufacturing (AM) Laser Metal Deposition (LMD), parts are built by welding layers of powder feedstock onto a substrate. Applications for steel powders include forging tools and structural components for various industries. For large parts, the choice of tool-paths influences the build-rate, the part performance and the distortions in a highly geometry-dependent manner. With weld-path lengths in the range of hundreds of meters, a reliable, automated tool path generation is essential for the usability of LMD processes. In this contribution, automated tool-path generation approaches are shown and their results are discussed for arbitrary geometries. The investigated path strategies are the classical approaches: ""Zig-zag-"" and ""contour-parallel-strategies"". After generation, the tool-paths are automatically formatted into g-code for experimental build-up and ASCII for a numerical simulation model. Finally, the tool paths are discussed in regards to volume-fill, microstructure and porosity for the experimental samples. This work presents a part of the IGF project 18737N ""Welding distortion simulation"" (FOSTA P1140)

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Orbital hybrid laser arc welding using a high power fibre laser for pipeline construction

2018 , Gook, Sergej , Gumenyuk, Andrey , Rethmeier, Michael

Recently developed fibre lasers provide multi-kilowatt beam power with high quality at impressive energy efficiency. Combined with gas metal arc welding (GMAW) equipment these lasers can be used in a hybrid process to weld thick-walled constructions single-pass, that are currently welded using multi-pass techniques. The main benefits are a reduction of heat induced distortions, due to the low heat input, as well as savings in filler material and process time. Probable applications can be found in power generation, ship building and pipeline constructions. An orbital (girth) laser-hybrid process using a 20 kW fibre laser and a GMAW torch is currently examined at the BAM, Berlin. The aim of this research is to obtain a stable and crack free girth welding process and to demonstrate its application in pipeline construction. The experiments are carried out on 16 mm thick plates as well pipe rings with 36" (914 mm) pipe diameter of X65. Particular welding parameters, such as welding speed, GMAW power, arc length are varied and their influence on the appearance of the weld in the different welding positions is analyzed. Even though issues remain that demand further research it could already be shown that the rings can be welded using a girth hybrid process that is divided into two half girth processes in downward direction.

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Automated Tool-Path Generation for Rapid Manufacturing of Additive Manufacturing Directed Energy Deposition Geometries

2020 , Biegler, Max , Wang, Jiahan , Kaiser, Lukas , Rethmeier, Michael

In additive manufacturing (AM) directed energy deposition (DED), parts are built by welding layers of powder or wire feedstock onto a substrate with applications for steel powders in the fields of forging tools, spare parts, and structural components for various industries. For large and bulky parts, the choice of tool-paths influences the build rate, the mechanical performance, and the distortions in a highly geometry-dependent manner. With weld-path lengths in the range of hundreds of meters, a reliable, automated tool-path generation is essential for the usability of DED processes. This contribution presents automated tool-path generation approaches and discusses the results for arbitrary geometries. So-called “zig-zag” and “contour-parallel” processing strategies are investigated and the tool-paths are automatically formatted into machine-readable g-code for experimental validation to build sample geometries. The results are discussed in regard to volume-fill, microstructure, and porosity in dependence of the path planning according to photographs and metallographic cross-sections.

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Hybrid laser arc welding of 25 mm thick materials using electromagnetic weld pool support

2018 , Üstündag, Ömer , Avilov, Vjaceslav , Gumenyuk, Andrey , Rethmeier, Michael

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 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 25 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.

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Assessing the predictive capability of numerical additive manufacturing simulations via in-situ distortion measurements on a LMD component during build-up

2018 , Biegler, Max , Graf, Benjamin , Rethmeier, Michael

Due to rapid, localized heating and cooling, distortions accumulate in additive manufactured laser metal deposition (LMD) components, leading to a loss of dimensional accuracy or even cracking. Numerical welding simulations allow the prediction of these deviations and their optimization before conducting experiments. To assess the viability of the simulation tool for the use in a predictive manner, comprehensive validations with experimental results on the newly-built part need to be conducted. In this contribution, a predictive, mechanical simulation of a thin-walled, curved LMD geometry is shown for a 30-layer sample of 1.4404 stainless steel. The part distortions are determined experimentally via an in-situ digital image correlation measurement using the GOM Aramis system and compared with the simulation results. With this benchmark, the performance of a numerical welding simulation in additive manufacturing is discussed in terms of result accuracy and usability.

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