TY - CONF A1 - Schröpfer, Dirk T1 - Correlation of process, design and welding residual stresses in WAAM of high-strength steel components N2 - High-strength fine-grained structural steels have great potential for modern weight optimized steel construc-tions. Efficient manufacturing and further weight savings are achievable due to Wire Arc Additive Manu-facturing (WAAM). First commercial high-strength welding consumables for WAAM are already available. However, the application is still severely limited due to a lack of knowledge and guidelines for the industry regarding welding residual stresses and component safety in manufacturing and operation. Residual stresses may be critical regarding the special microstructure of high-strength steels in context with the risk of cold cracking and component performance in service. Therefore, process- and material-related influences, as well as the design effects on residual stress formation and cold cracking, are being investi-gated in a research project (IGF 21162 BG) focusing a high-strength WAAM welding consumable with yield strength of over 800 MPa. Objectives are the establish-ment of special WAAM cold cracking tests and pro-cessing recommendations allowing economical, suita-ble, and crack-safe WAAM of high-strength steels. First studies on process-related influences showed transfor-mation residual stresses arising during cooling, which significantly influence stress evolution of the compo-nent during layer-wise build-up. This has not yet been investigated for WAAM of high-strength steels. Focus of this study is on the systematic investigation of interactions of the WAAM welding process and design with cooling time, hardness, and residual stresses. Defined open hollow cuboids were welded and investi-gated under systematic variation (design of experi-ments, DoE) of the scale/dimensions (cf. Fig. 1a) and heat control (interlayer temperature Ti: 100–300 °C), heat input E: 200–650 kJ/m. The welding parameters were kept constant as possible to avoid any influence by the arc and the material transfer mode. The heat input adjusted primarily via the welding speed. The resulting different weald bead widths were considered by different build-up strategies (weld beads per layer) to ensure defined wall thicknesses. The hardness was determined on cross-sections taken from the manufac-tured hollow cuboids (Fig. 1c) and the analysis of the residual stress state was carried out by means of X-ray diffraction (XRD) at defined positions on the lateral wall (Fig. 1b). The hardness is higher at the top compared to the lower weld beads, as shown in Fig. 1c exemplarily for central test parameters of the DoE = 425 kJ/mm, Ti = 200 °C). This may be attributed to the specific heat control of the top weld beads, i.e., quenching effects, which are not tempered by weld beads above as is the case for lower weld beads implying a higher hardness. It was observed that the hardness level decreases with increasing energy per unit length, while the in-terpass temperature has a rather low influence on the hardness Residual stress analysis was performed on the lat-eral wall in the welding direction, cf. Fig. 1b, to deter-mine the influence of heat control and design. In the top area of the wall, maximum longitudinal residual stress-es of up to over 500 MPa exhibit, which corresponds to approx. 65% of the nominal yield strength of the mate-rial. The statistic evaluation of stress levels in welding direction of all test specimens show that adaption of heat input may reduce welding stresses up to 50%. In-terpass temperature has less pronounced effect on cool-ing times, microstructure, and on the residual level within parameter matrix. Overall, the results show a significant influence of heat input and component di-mensions on the residual stresses and minor effect of the interpass temperature. Hence, the properties of the specimens may be effectively adjusted via heat input. The working temperatures should be considered for global shrinkage behavior or restraints. Such investiga-tions of residual stress are necessary to further deter-mine local and global welding stresses regarding the consequences on the component safety during manu-facturing and service. T2 - 6th International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation CY - Osaka, Japan DA - 25.10.2022 KW - MAG-Schweißen KW - Additive Fertigung KW - Eigenspannungen KW - Hochfester Stahl KW - Kaltrisssicherheit KW - Wärmeführung KW - Windenergie PY - 2022 AN - OPUS4-56725 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Hensel, J. T1 - Influence of the WAAM process and design aspects on residual stresses in high-strength structural steels N2 - High-strength fine-grain structural steels have great potential for weight optimization of many modern engineering structures. Efficient manufacturing can be achieved here above all by Wire Arc Additive Manufacturing (WAAM). First commercial high-strength welding consumables for WAAM are already available. However, due to a lack of knowledge and guidelines for the industry regarding welding residual stresses and component safety in manufacturing and operation, their application is still severely limited. Residual stresses play a crucial role here, as the sensitive microstructure of high-strength steels carries a high risk of cold cracking. For this reason, process- and material-related influences, as well as the design aspects on residual stress formation and the risk of cold cracking, are being investigated in a recent project (FOSTA-P1380/IGF21162BG). This high strength of the WAAM welding consumables is adjusted via a martensitic phase transformation. The volume expansion associated with martensite formation has a significant influence on residual stress evolution. However, this has not yet been investigated in relation to the processing of high-strength steels by WAAM. The aim of this work is to establish a WAAM cold crack test and easy-to-apply processing recommendations that will allow economical, expedient, and crack-resistant fabrication of high-strength steels, especially for SME. This paper focuses on the analysis of the effects of welding heat control and design of WAAM components on cooling conditions, microstructure, mechanical-technological properties and residual stresses. For this purpose, geometrically defined specimens (hollow cuboids) are welded fully automatically with a special, high-strength WAAM solid wire (yield strength >790 MPa). The heat control and specimen dimensions are varied within a statistical experimental design. The weld heat control is adjusted in such a way that the t8/5 cooling times are ensured within the recommended processing range (approx. 5–20 s). For this purpose, additional thermo-physical forming simulations using a dilatometer allowed the complex heat cycles to be reproduced and the resulting ultimate tensile strength of the weld metal to be determined. The WAAM welding of complex geometries with varying welding heat control and geometric factors or wall thicknesses not only has an effect on the cooling conditions, cooling times and microstructure, but also has a significant influence on the structural restraint conditions during welding. Hence, the welding experiments show significant effects of specimen scaling and heat input on the welding residual stresses, which may be detrimental regarding component properties and crack-critical tensile residual stresses. These complex interactions are analyzed within this investigation. T2 - 75th IIW Annual Assembly CY - Tokyo, Japan DA - 17.07.2022 KW - WAAM KW - Residual Stresses KW - High-strength Steels KW - Cold cracking safety KW - Heat control KW - Wind energy PY - 2022 AN - OPUS4-56713 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Waske, Anja T1 - A unique authenticator for additively manufactured parts derived from 3D microstructural information N2 - Additive manufacturing (AM) is rapidly emerging from rapid prototyping to industrial production [1]. Thus, providing AM parts with a tagging feature that allows identification, like a fingerprint, can be crucial for logistics, certification, and anti-counterfeiting purposes since nearly any geometry can be produced by AM with stolen data or reverse engineering of an original product. However, the mechanical and functional properties of the replicated part may not be identical to the original ones and pose a safety risk [2]. Several methods are already available, which range from encasing a detector to leveraging the stochastic defects of AM parts for the identification, authentication, and traceability of AM components. The most prevailing solution consists of local process manipulation, such as printing a quick response (QR) code [3] or a set of blind holes on the surface of the internal cavity of hollow components. Local manipulation of components may alter the properties. The external tagging features can be altered or even removed by post-processing treatments. Integrating electronic systems [4] in AM parts can be used to identify and authenticate components with complex or customized geometries. However, metal-based AM, especially in powder bed fusion (PBF-LB/M) techniques, has a strong shielding effect that interferes with the communication between the reader and the transponder. Our work suggests a methodology for the identification, authentication, and traceability of AM components using microstructural features in AM components. We will show a workflow that includes analysing 3D micro computed tomography data and selecting a set number of voids that fulfil the identification criteria. We will show the results this workflow produces for a series of 20 Al-based cuboid samples with identical processing parameters and discuss their prospects and limitations. The workflow can help to establish a non-tamperable connection between an additively manufactured part and its digital data and hence link the physical and the digital world. T2 - MSE Konferenz CY - Darmstadt, Germany DA - 24.09.2024 KW - Additive Manufacturing KW - Fingerprint KW - Computed tomography PY - 2024 AN - OPUS4-62288 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Maierhofer, Christiane A1 - Altenburg, Simon A1 - Scheuschner, Nils ED - Meyendorf, N. ED - Ida, N. ED - Singh, R. ED - Vrana, J. T1 - In Situ Real-Time Monitoring Versus Post NDE for Quality Assurance of Additively Manufactured Metal Parts N2 - In this chapter, the current state-of-the-art of in situ monitoring and in situ NDE methods in additive manufacturing is summarized. The focus is set on methods, which are suitable for making statements about the quality and usability of a component currently being manufactured. This includes methods which can be used to determine state properties like temperature or density, other physical properties like electrical or thermal conductivity, the microstructure, the chemical composition, the actual geometry, or which enable the direct detection of defects like cracks, voids, delaminations, or inclusions. Thus, optical, thermographic, acoustic, and electromagnetic methods, as well as methods being suitable for investigating particle and fume emission are presented. The requirements of in situ monitoring methods with a focus on thermographic methods are discussed by considering different additive manufacturing processes like laser powder bed fusion (PBF-LB/M) and direct energy deposition (DED-LB/M). Examples of the successful implementation and applications of such monitoring methods at BAM are given. The in situ monitoring and NDE methods are compared against post-process NDE methods. The advantages and challenges of in situ methods concerning real-time data analysis and the application of AI algorithms are addressed and discussed. KW - Additive manufacturing KW - In situ monitoring KW - In situ NDE KW - Post NDE KW - Thermography KW - Laser powder bed fusion KW - Direct energy deposition PY - 2021 SN - 978-3-030-48200-8 DO - https://doi.org/10.1007/978-3-030-48200-8_51-1 SP - 1 EP - 37 PB - Springer Nature Switzerland AG CY - Cham, Switzerland ET - 1 AN - OPUS4-52824 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Altenburg, Simon T1 - Introduction to ProMoAM N2 - A brief introduction to the project ProMoAM is given. T2 - 2nd Workshop on In-situ Monitoring and Microstructure Development in Additive Manufactured Alloys CY - Online meeting DA - 19.04.2021 KW - Additive Manufacturing KW - Process monitoring KW - ProMoAM PY - 2021 AN - OPUS4-52513 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Altenburg, Simon T1 - Unraveling thermal radiation by multispectral thermography: Real temperatures in LMD N2 - Additive manufacturing of metals offers the opportunity to build parts with a high degree of complexity without additional costs, opening a new space for design optimization. However, the processes are highly complex and due to the rapid thermal cycles involved, high internal stresses and peculiar microstructures occur, which influence the parts mechanical properties. To systematically examine the formation of internal stresses and the microstructure, in-process spatially resolved measurements of the part temperature are needed. If the emissivity of the inspected part is known, its thermodynamic temperature can be reconstructed by a suited radiometric model. However, in additive manufacturing of metals, the emissivity of the part surface is strongly inhomogeneous and rapidly changing due to variations of, e.g., the degree of oxidation, the material state and temperature. Thus, here, the applicability of thermography in the determination of thermodynamic temperatures is limited. However, measuring the process thermal radiation at different wavelengths simultaneously enables one to separate temperature and emissivity spatially resolved to obtain further insight into the process. Here, we present results of an initial study using multispectral thermography to obtain real temperatures and emissivities in the powderfree LMD process. T2 - 2nd Workshop on In-situ Monitoring and Microstructure Development in Additive Manufactured Alloys CY - Online meeting DA - 19.04.2021 KW - Additive Manufacturing KW - Process monitoring KW - Multispectral thermography KW - Laser metal deposition KW - TES KW - LMD KW - Temperature emissivity separation PY - 2021 AN - OPUS4-52514 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Altenburg, Simon T1 - Towards the determination of real process temperatures in the LMD process my multispectral thermography N2 - Due to the rapid thermal cycles involved in additive manufacturing of metals, high internal stresses and peculiar microstructures occur, which influence the parts mechanical properties. To systematically examine their formation, in-process measurements of the temperature are needed. Since the part emissivity is strongly inhomogeneous and rapidly changing in the process, the applicability of thermography for the determination of thermodynamic temperatures is limited. Measuring the thermal radiation in different wavelengths simultaneously, temperature and emissivity can be separated. Here, we present results of a preliminary study using multispectral thermography to obtain real temperatures and emissivities in directed energy deposition (DED) processes. T2 - Thermosense: Thermal Infrared Applications XLIII CY - Online meeting DA - 12.04.2021 KW - Additive Manufacturing KW - Process monitoring KW - Multispectral thermography KW - Laser metal deposition KW - TES KW - LMD KW - Temperature emissivity separation PY - 2021 DO - https://doi.org/10.1117/12.2587881 AN - OPUS4-52515 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Altenburg, Simon T1 - Improving additive manufacturing technologies by in-situ monitoring: Thermography N2 - Additive manufacturing of metals gains increasing relevance in the industrial field for part production. However, especially for safety relevant applications, a suitable quality assurance is needed. A time and cost efficient route to achieve this goal is in-situ monitoring of the build process. Here, the BAM project ProMoAM (Process monitoring in additive manufacturing) is briefly introduced and recent advances of BAM in the field of in-situ monitoring of the L-PBF and the LMD process using thermography are presented. T2 - Anwenderkonferenz Infratec GmbH CY - Online meeting DA - 04.11.2021 KW - Additive Manufacturing KW - Process monitoring KW - Thermography PY - 2021 AN - OPUS4-54026 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Maierhofer, Christiane T1 - Summary of in-situ monitoring in additive manufacturing - ProMoAM N2 - The quality of additively manufactured components is significantly influenced by the process parameters used during production. Thus, sensors and measuring systems are already commercially available for process monitoring, at least in metal-based additive manufacturing. However, it is not yet possible to detect defects and inhomogeneities directly or indirectly during the building process. The aim of the project ProMoAM is to develop spectroscopic and non-destructive testing methods for the in-situ evaluation of the quality of additively manufactured metal components in laser- or arc-based AM processes. In addition to passive and active methods of thermography, this includes optical tomography, optical emission spectroscopy, eddy current testing, laminography (radiography), X-ray backscattering, particle emission spectroscopy and photoacoustic methods. T2 - 2nd Workshop on In-situ Monitoring and Microstructure Development in Additive Manufactured Alloys CY - Online meeting DA - 19.04.2021 KW - In-situ monitoring KW - Additive manufacturing KW - Metals KW - Thermography PY - 2021 AN - OPUS4-52539 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Oster, Simon T1 - Multispectral in-situ monitoring of a L-PBF manufacturing process using three thermographic camera systems N2 - The manufacturing of metal parts for the use in safety-relevant applications by Laser Powder Bed Fusion (L-PBF) demands a quality assurance of both part and process. Thermography is a nondestructive testing method that allows the in-situ determination of the thermal history of the produced part which is connected to the mechanical properties and the formation of defects [1]. A wide range of commercial thermographic camera systems working in different spectral ranges is available on the market. The understanding of the applicability of these cameras for qualitative and quantitative in-situ measurements in L-PBF is of vital importance [2]. In this study, the building process of a cylindrical specimen (Inconel 718) is monitored by three camera systems simultaniously. These camera systems are sensitive in various spectral bandwidths providing information in different temperature ranges. The performance of each camera system is explored in the context of the extraction of image features for the detection of defects. It is shown that the high temporal and thermal process dynamics are limiting factors on this matter. The combination of different spectral camera systems promises the potential of an improved defect detection by data fusion. T2 - LASER SYMPOSIUM & ISAM 2021 CY - Online meeting DA - 07.12.2021 KW - Laser Powder Bed Fusion KW - Thermography KW - In-situ Monitoring KW - Defect detection PY - 2021 AN - OPUS4-54141 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -