TY - JOUR A1 - Ehlers, Henrik A1 - Pelkner, Matthias A1 - Thewes, R. T1 - Heterodyne Eddy Current Testing Using Magnetoresistive Sensors for Additive Manufacturing Purposes N2 - In recent years additive manufacturing technologies have become widely popular. For complex functional components or low volume production of workpieces, laser powder bed fusion can be used. High safety requirements, e.g. in the aerospace sector, demand extensive quality control. Therefore, offline non-destructive testing methods like computed tomography are used after manufacturing. Recently, for enhanced profitability and practicality online non-destructive testing methods, like optical tomography have been developed. This paper discusses the applicability of eddy current testing with magnetoresistive sensors for laser powder bed fusion parts. For this purpose, high spatial resolution giant magnetoresistance arrays are utilized for testing in combination with a single wire excitation coil. A heterodyne principle minimizes metrology efforts. This principle is compared to conventional signal processing in an eddy current testing setup using an aluminum test sample with artificial surface defects. To evaluate the influence of the powder used in the manufacturing process on eddy current testing and vice versa, a laser powder bed fusion mock-up made from stainless steel powder (316L) is used with artificial surface defects down to 100 µm. This laser powder bed fusion specimen was then examined using eddy current testing and the underlying principles. KW - Eddy current testing KW - Heterodyning KW - Laser powder bed fusion KW - Giant magnetoresistance KW - Additive manufacturing KW - 316L PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-506140 DO - https://doi.org/10.1109/JSEN.2020.2973547 SN - 1530-437X VL - 20 IS - 11 SP - 5793 EP - 5800 PB - IEEE AN - OPUS4-50614 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schridewahn, S. A1 - Spranger, F. A1 - Hilgenberg, Kai A1 - Merklein, M. T1 - Laser Implantation of Niobium and Titanium-Based Particles on Hot Working Tool Surfaces for Improving the Tribological Performance within Hot Stamping N2 - Within the scope of this work, a laser implantation process has been used, in order to improve the tribological performance of hot stamping tools. This surface engineering Technology enables the generation of dome-shaped, elevated and highly wear resistant microfeatures on tool surfaces in consequence of a localized dispersing of hard ceramic particles via pulsed laser radiation. As a result, the topography and material properties of the tool and thus the tribological interactions at the blank-die interface are locally influenced. However, a suitable selection of hard ceramic particles is imperative for generating defect-free surface features with a high share of homogenously disturbed particles. For this purpose, different niobium (NbB2 and NbC) as well as titanium-based (TiB2 and TiC) materials were embedded on hot working tool specimens and subsequently analyzed with regard to their resulting shape and mechanical properties. Afterwards, modified pin-on-disk tests were carried out by using conventional and laser-implanted tool surfaces, in order to evaluate the wear and friction behavior of both tooling systems. KW - Surface modification KW - Triobology KW - Laser implantation PY - 2020 DO - https://doi.org/10.4028/www.scientific.net/DDF.404.117 SN - 1662-9507, VL - 404 SP - 117 EP - 123 PB - Trans Tech Publications Ltd. AN - OPUS4-53690 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Charmi, Amir T1 - Mechanical anisotropy of additively manufactured stainless steel 316l: an experimental and numerical study N2 - This work aims for a yield function description of additively manufactured (AM) parts of stainless steel 316L at the continuum-mechanical macro-scale by means of so-called virtual experiments using a crystal plasticity model at meso-scale. T2 - 1st Workshop on In-situ Monitoring and Microstructure Development in Additive Manufacturing CY - BAM, Berlin DA - 10.12.2020 KW - Anisotropy KW - Crystal plasticity KW - Additive manufacturing PY - 2020 AN - OPUS4-51941 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Abdel-Wakil, W. A1 - Fahmy, Alaa A1 - Kamoun, E. A1 - Hassan, W. A1 - Abdelhai, Q. A1 - Salama, T. T1 - A New Route for Synthesis of Polyurethanevinyl Acetate Acrylate Emulsions as Binders for Pigment Printing of Cotton Fabrics N2 - Herein, two polyurethane oligomers were successfully synthesized using a prepolymer mixing process. The prepolymers were synthesized based on the step-growth addition polymerization of polypropylene glycol, Methylene diphenyl diisocyanate and 2-hydroxyethyl methacrylate or 2-hydroxyethyl acrylate. Isopropanol was functioned as the isocyanate blocking agent. Thereafter, different terpolymer emulsions were prepared by the emulsion graft copolymerization with the vinyl acetate monomer in presence of 2-ethylhexyl acrylate as a vinyl monomer. The chemical structures of the synthesized oligomeric monomers were probed by FTIR spectroscopy and found to vary with the content of acrylic monomer used in the oligomer synthesis phase (i.e.hydroxyethyl acrylate or hydroxyethyl methacrylate). The topography, thermal stability, and particle size of terpolymers were investigated by SEM, TGA, and zeta potential, respectively. The TGA results demonstrated marked enhancement in thermal stability of the synthesized terpolymers up to ca. 600°C, which was concurrent with enhanced surface homogeneity and film properties as evidenced by the SEM images. These terpolymers showed also property enhancement as binders for textile pigment printing in terms of rubbing resistance, color strength and fastness to washing when compared to the commercial binders. These judgments would provide a new competent synthesis route by introducing polyurethane acetate vinyl acrylate as the binder for use in pigment printing of cotton fabrics. KW - Vinyl monomer KW - Polyurethane acetate vinyl acrylate KW - Surface coating KW - Terpolymer KW - Textile binder PY - 2020 DO - https://doi.org/10.21608/ejchem.2020.21712.2292 VL - 63 IS - 3 SP - 1063 EP - 1073 AN - OPUS4-52300 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Werner, Tiago T1 - Short fatigue crack propagation in L-PBF 316L stainless steel N2 - Fracture mechanics is a key to fatigue assessment in AM metal components. Short fatigue cracks are initiated at defects and pronounced surface roughness intrinsic to AM. The subsequent crack-propagation is strongly influenced by microstructural interactions and the build-up of crack-closure. The aim of the present study is to give an insight into short-crack propagation in AM-metals. Fatigue crack propagation resistance curves were determined experimentally for AISI 316L manufactured by Laser Powder Bed Fusion (L-PBF) which was heat treated at three different temperatures. Differences in the build-up of the fatigue-crack propagation threshold in between the L-PBF specimens and compared to wrought material are due to the residual stress states, a pronounced roughness of the crack-faces in the L-PBF specimens and phase transformation in the vicinity of the crack-tip, resulting in increased crack-closure. This, together with crack-branching found along the crack path, enhances the resistance to the propagation of fatigue cracks. T2 - ASTM International Conference on Additive Manufacturing 2020 CY - Online meeting DA - 16.11.2020 KW - Additive Manufacturing KW - Cyclic R-Curve KW - Component assessment KW - L-PBF KW - 316L KW - Residual Stress KW - Fatigue Crack Growth PY - 2020 AN - OPUS4-51585 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Werner, Tiago T1 - Damage tolerant design of metallic AM parts N2 - Additive Manufacturing (AM) opens new possibilities in the design of metallic components, including very complex geometries (e.g. structures optimized for certain loads), optimization of materials (e.g. gradient materials) and cost-effective manufacturing of spare parts. In the recent years, it has been used for the first safety-relevant parts, but the consideration of cyclic mechanical behavior in AM is still at the very beginning. The reason for this is the complexity of mechanical material properties, i.e. inhomogeneity, anisotropy and a large number of defects frequently textured and characterized by large scattering in size. Additionally, high surface roughness and residual stresses with complex distributions are typical of AM. Due to these reasons, the transferability of experimentally determined properties from specimens to components is a challenge. This presentation provides an overview of the questions concerning the application of AM to safety-relevant components. Possible strategies for the fatigue design of such components are presented. Besides the Kitagawa-Takahashi-diagram method and the cyclic R-curve analysis as approaches for damage-tolerant design, the identification of critical locations, the problem of representative material properties and the handling of residual stresses are addressed. T2 - 4th international symposium on Fatigue Design and Material Defects CY - Online meeting DA - 26.05.2020 KW - Additive Manufacturing KW - Cyclic R-Curve KW - Component assessment PY - 2020 AN - OPUS4-50938 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - El-Sari, B. A1 - Biegler, M. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Distortion-based validation of the heat treatment simulation of Directed Energy Deposition additive manufactured parts N2 - Directed energy deposition additive manufactured parts have steep stress gradients and an anisotropic microstructure caused by the rapid thermo-cycles and the layer-upon-layer manufacturing, hence heat treatment can be used to reduce the residual stresses and to restore the microstructure. The numerical simulation is a suitable tool to determine the parameters of the heat treatment process and to reduce the necessary application efforts. The heat treatment simulation calculates the distortion and residual stresses during the process. Validation experiments are necessary to verify the simulation results. This paper presents a 3D coupled thermo-mechanical model of the heat treatment of additive components. A distortion-based validation is conducted to verify the simulation results, using a C-ring shaped specimen geometry. Therefore, the C-ring samples were 3D scanned using a structured light 3D scanner to compare the distortion of the samples with different post-processing histories. KW - Directed Energy Deposition KW - Additive Manufacturing KW - Heat Treatment KW - Numerical Simulation KW - Finite Element Method PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-513153 DO - https://doi.org/10.1016/j.procir.2020.09.146 VL - 94 SP - 362 EP - 366 PB - Elsevier B.V. AN - OPUS4-51315 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Biegler, M. A1 - Wang, J. A1 - Kaiser, L. A1 - Rethmeier, Michael T1 - Automated Tool-Path Generation for Rapid Manufacturing of Additive Manufacturing Directed Energy Deposition Geometries N2 - 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 toolpaths 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. Socalled “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. KW - Porosity KW - Path planning KW - Mechanical properties KW - Laser metal deposition KW - Additive manufacturing PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-510454 DO - https://doi.org/10.1002/srin.202000017 VL - 91 IS - 11 SP - 2000017 PB - WILEY-VCH Verlag GmbH & co. KGaA CY - Weinheim AN - OPUS4-51045 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Altenburg, Simon A1 - Straße, Anne A1 - Gumenyuk, Andrey A1 - Maierhofer, Christiane T1 - In-situ monitoring of a laser metal deposition (LMD) process: comparison of MWIR, SWIR and high-speed NIR thermography N2 - Additive manufacturing offers a range of novel applications. However, the manufacturing process is complex and the production of almost defect-free parts with high reliability and durability is still a challenge. Thermography is a valuable tool for process surveillance, especially in metal additive manufacturing processes. The high process temperatures allow one to use cameras usually operating in the visible spectral range. Here, we compare the results of measurements during the manufacturing process of a commercial laser metal deposition setup using a mid wavelength infrared camera with those from a short wavelength infrared camera and those from a visual spectrum high-speed camera with band pass filter in the near infrared range. KW - Additive Manufacturing KW - Process monitoring KW - Thermography KW - LMD KW - Metal KW - MWIR KW - SWIR KW - NIR PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-516318 DO - https://doi.org/10.1080/17686733.2020.1829889 VL - 19 IS - 2 SP - 97 EP - 114 PB - Taylor & Francis Group CY - London, UK AN - OPUS4-51631 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Biegler, M. A1 - Elsner, B. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Geometric distortion-compensation via transient numerical simulation for directed energy deposition additive manufacturing N2 - Components distort during directed energy deposition (DED) additive manufacturing (AM) due to the repeated localised heating. Changing the geometry in such a way that distortion causes it to assume the desired shape – a technique called distortion-compensation – is a promising method to reach geometrically accurate parts. Transient numerical simulation can be used to generate the compensated geometries and severely reduce the amount of necessary experimental trials. This publication demonstrates the simulation-based generation of a distortioncompensated DED build for an industrial-scale component. A transient thermo-mechanical approach is extended for large parts and the accuracy is demonstrated against 3d-scans. The calculated distortions are inverted to derive the compensated geometry and the distortions after a single compensation iteration are reduced by over 65%. KW - DED KW - Welding simulation KW - Dimensional accuracy KW - Additive manufacturing KW - Laser metal deposition KW - LMD PY - 2020 DO - https://doi.org/10.1080/13621718.2020.1743927 SP - 1 EP - 8 PB - Taylor & Francis AN - OPUS4-50877 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -