@article{57699,
abstract = {{The optimization of process parameters in powder Directed Energy Deposition (DED) is essential for achieving consistent, high-quality bead geometries, which directly influence the performance and structural integrity of fabricated components. As a subset of additive manufacturing (AM), the DED process, also referred to as laser metal deposition (LMD), enables precise, layer-by-layer material deposition, making it highly suitable for complex geometries and part repair applications. Critical parameters, such as the laser power, feed rate, powder mass flow, and substrate temperature govern the deposition process, impacting the bead height, width, contact angle, and dilution. Inconsistent control over these variables can lead to defects, such as poor bonding, dimensional inaccuracies, and material weaknesses, ultimately compromising the final product. This paper investigates the effects of various process parameters, specifically the substrate temperature, on bead track geometry in DED processes for stainless steel (1.4404). A specialized experimental setup, integrated within a DED machine, facilitates the controlled thermal conditioning of sample sheets. Using Design of Experiments (DoE) methods, individual bead marks are generated and analyzed to assess geometric characteristics. Regression models, including both linear and quadratic approaches, are constructed to predict machine parameters for achieving the desired bead geometry at different substrate temperatures. Validation experiments confirm the accuracy and reliability of the models, particularly in predicting the bead height, bead width, and contact angle across a broad range of substrate temperatures. However, the models demonstrated limitations in accurately predicting dilution, indicating the need for further refinement. Despite some deviations in measured values, successful fabrication is achieved, demonstrating robust bonding between the bead and substrate. The developed models offer insights into optimizing DED process parameters to achieve desired bead characteristics, advancing the precision and reliability of additive manufacturing technology. Future work will focus on refining the regression models to improve predictions, particularly for dilution, and further investigate non-linear interactions between process variables.}},
author = {{Chalicheemalapalli Jayasankar, Deviprasad and Gnaase, Stefan and Lehnert, Dennis and Walter, Artur and Rohling, Robin and Tröster, Thomas}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{additive manufacturing, direct energy deposition, laser metal deposition}},
number = {{12}},
publisher = {{MDPI AG}},
title = {{{Effect of Substrate Temperature on Bead Track Geometry of 316L in Directed Energy Deposition: Investigation and Regression Modeling}}},
doi = {{10.3390/met14121353}},
volume = {{14}},
year = {{2024}},
}
@article{56089,
abstract = {{Additive manufacturing (AM) technologies enable near-net-shape designs and demand-oriented material usage, which significantly minimizes waste. This points to a substantial opportunity for further optimization in material savings and process design. The current study delves into the advancement of sustainable manufacturing practices in the automotive industry, emphasizing the crucial role of lightweight construction concepts and AM technologies in enhancing resource efficiency and reducing greenhouse gas emissions. By exploring the integration of novel AM techniques such as selective laser melting (SLM) and laser metal deposition (LMD), the study aims to overcome existing limitations like slow build-up rates and limited component resolution. The study’s core objective revolves around the development and validation of a continuous process chain that synergizes different AM routes. In the current study, the continuous process chain for DMG MORI Lasertec 65 3D’s LMD system and the DMG MORI Lasertec 30 3D’s was demonstrated using 316L and 1.2709 steel materials. This integrated approach is designed to significantly curtail process times and minimize component costs, thus suggesting an industry-oriented process chain for future manufacturing paradigms. Additionally, the research investigates the production and material behavior of components under varying manufacturing processes, material combinations, and boundary layer materials. The culmination of this study is the validation of the proposed process route through a technology demonstrator, assessing its scalability and setting a benchmark for resource-efficient manufacturing in the automotive sector.}},
author = {{Chalicheemalapalli Jayasankar, Deviprasad and Gnaase, Stefan and Kaiser, Maximilian Alexander and Lehnert, Dennis and Tröster, Thomas}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{additive manufacturing (AM), selective laser melting (SLM), laser metal deposition (LMD), hybrid manufacturing, process optimization, 316L, 1.2709}},
number = {{7}},
publisher = {{MDPI AG}},
title = {{{Advancements in Hybrid Additive Manufacturing: Integrating SLM and LMD for High-Performance Applications}}},
doi = {{10.3390/met14070772}},
volume = {{14}},
year = {{2024}},
}
@article{48082,
author = {{Yang, Keke and Meschut, Gerson and Seitz, Georg and Biegler, Max and Rethmeier, Michael}},
issn = {{2075-4701}},
journal = {{Metals (Special Issue Embrittlement Phenomena in Steel Metallurgy)}},
number = {{10}},
publisher = {{MDPI}},
title = {{{The Identification of a New Liquid Metal Embrittlement (LME) Type in Resistance Spot Welding of Advanced High-Strength Steels on Reduced Flange Widths}}},
doi = {{10.3390/met13101754}},
volume = {{13}},
year = {{2023}},
}
@article{34252,
abstract = {{Clinching is the manufacturing process of joining two or more metal sheets under high plastic deformation by form and force closure without thermal support and auxiliary parts. Clinch connections are applicable to difficult-to-join hybrid material combinations, such as steel and aluminum. Therefore, this technology is interesting for the application of AISI 304 components, as this material is widely used as a highly formable sheet material. A characteristic feature of AISI 304 is its metastability, i.e., the face-centered cubic (fcc) γ-austenite can transform into a significantly stronger body-centered cubic (bcc) α’-martensite under plastic deformation. This work investigates the effect of heat treatment—a process that involves the formation of an oxidation layer on the sheet surface—on the forming process during joining and the resulting mechanical properties of clinch joints made from AISI 304. For this purpose, different joints made from non-heat treated and heat-treated sheets were examined using classical metallography and advanced SEM techniques, accompanied by further investigations, such as hardness and feritscope measurements. The shear tensile strength was determined, and the fracture behavior of the samples was investigated. Clear influences of heat-treatment-induced surface roughness on the joint geometry and strength were observed.}},
author = {{Zeuner, André Till and Ewenz, Lars and Kalich, Jan and Schöne, Sebastian and Füssel, Uwe and Zimmermann, Martina}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{General Materials Science, Metals and Alloys}},
number = {{9}},
publisher = {{MDPI AG}},
title = {{{The Influence of Heat Treatment on the Microstructure, Surface Roughness and Shear Tensile Strength of AISI 304 Clinch Joints}}},
doi = {{10.3390/met12091514}},
volume = {{12}},
year = {{2022}},
}
@article{34251,
abstract = {{Joining by forming operations presents powerful and complex joining techniques. Clinching is a well-known joining process for use in sheet metalworking. Currently, clinched joints are focusing on mechanically enhanced connections. Additionally, the demand for integrating electrical requirements to transmit electrical currents will be increased in the future. This integration is particularly important, for instance, in the e-mobility sector. It enables connecting battery cells with electrical joints of aluminum and copper. Systematic use of the process-specific advantages of this joining method opens up the possibility to find and create electrically optimized connections. The optimization for the transmission of electrical currents will be demonstrated for clinched joints by adapting the tool geometry and the clinched joint design. Based on a comparison of the electrical joint resistance, the limit use temperature is defined for the joining materials used based on the microstructural condition and the aging condition due to artificial aging. As a result of the investigations carried out, reliable current transmission at a constant conductor temperature of up to 120 °C can be achieved for clinched copper–copper joints. In the case of pure aluminum joints and mixed joints of aluminum and copper, long-term stable current transmission can be ensured up to a conductor temperature of 100 °C.}},
author = {{Kalich, Jan and Matzke, Marcus and Pfeiffer, Wolfgang and Schlegel, Stephan and Kornhuber, Ludwig and Füssel, Uwe}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{General Materials Science, Metals and Alloys}},
number = {{10}},
publisher = {{MDPI AG}},
title = {{{Long-Term Behavior of Clinched Electrical Contacts}}},
doi = {{10.3390/met12101651}},
volume = {{12}},
year = {{2022}},
}
@article{31360,
abstract = {{The adaptive joining process employing friction-spun joint connectors (FSJC) is a promising method for the realization of adaptable joints and thus for lightweight construction. In addition to experimental investigations, numerical studies are indispensable tools for its development. Therefore, this paper includes an analysis of boundary conditions for the spatial discretization and mesh modeling techniques, the material modeling, the contact and friction modeling, and the thermal boundary conditions for the finite element (FE) modeling of this joining process. For these investigations, two FE models corresponding to the two process steps were set up and compared with the two related processes of friction stir welding and friction drilling. Regarding the spatial discretization, the Lagrangian approach is not sufficient to represent the deformation that occurs. The Johnson-Cook model is well suited as a material model. The modeling of the contact detection and friction are important research subjects. Coulomb’s law of friction is not adequate to account for the complex friction phenomena of the adaptive joining process. The thermal boundary conditions play a decisive role in heat generation and thus in the material flow of the process. It is advisable to use temperature-dependent parameters and to investigate in detail the influence of radiation in the entire process.}},
author = {{Oesterwinter, Annika and Wischer, Christian and Homberg, Werner}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{General Materials Science, Metals and Alloys}},
number = {{5}},
publisher = {{MDPI AG}},
title = {{{Identification of Requirements for FE Modeling of an Adaptive Joining Technology Employing Friction-Spun Joint Connectors (FSJC)}}},
doi = {{10.3390/met12050869}},
volume = {{12}},
year = {{2022}},
}
@article{30885,
abstract = {{High-speed forming processes such as electromagnetic forming (EMF) and electrohydraulic forming (EHF) have a high potential for producing lightweight components with complex geometries, but the forming zone is usually limited to a small size for equipment-related reasons. Incremental strategies overcome this limit by using a sequence of local deformations to form larger component areas gradually. Hence, the technological potential of high-speed forming can be exploited for large-area components too. The target-oriented process design of such incremental forming operations requires a deep understanding of the underlying electromagnetic and electrohydraulic forming processes. This article therefore analyzes and compares the influence of fundamental process parameters on the acting loads, the resulting course of deformation, and the forming result for both technologies via experimental and numerical investigations. Specifically, it is shown that for the EHF process considered, the electrode distance and the discharge energy have a significant influence on the resulting forming depth. In the EHF process, the largest forming depth is achieved directly below the electrodes, while the pressure distribution in the EMF depends on the fieldshaper used. The energy requirement for the EHF process is comparatively low, while significantly higher forming speeds are achieved with the EMF process.}},
author = {{Heggemann, Thomas and Psyk, Verena and Oesterwinter, Annika and Linnemann, Maik and Kräusel, Verena and Homberg, Werner}},
issn = {{2075-4701}},
journal = {{Metals}},
number = {{4}},
title = {{{Comparative Analysis of Electrohydraulic and Electromagnetic Sheet Metal Forming against the Background of the Application as an Incremental Processing Technology}}},
doi = {{10.3390/met12040660}},
volume = {{12}},
year = {{2022}},
}
@article{29357,
abstract = {{Friction-spinning as an innovative incremental forming process enables high degrees of deformation in the field of tube and sheet metal forming due to self-induced heat generation in the forming area. The complex thermomechanical conditions generate non-uniform residual stress distributions. In order to specifically adjust these residual stress distributions, the influence of different process parameters on residual stress distributions in flanges formed by the friction-spinning of tubes is investigated using the design of experiments (DoE) method. The feed rate with an effect of −156 MPa/mm is the dominating control parameter for residual stress depth distribution in steel flange forming, whereas the rotation speed of the workpiece with an effect of 18 MPa/mm dominates the gradient of residual stress generation in the aluminium flange-forming process. A run-to-run predictive control system for the specific adjustment of residual stress distributions is proposed and validated. The predictive model provides an initial solution in the form of a parameter set, and the controlled feedback iteratively approaches the target value with new parameter sets recalculated on the basis of the deviation of the previous run. Residual stress measurements are carried out using the hole-drilling method and X-ray diffraction by the cosα-method.}},
author = {{Dahms, Frederik and Homberg, Werner}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{General Materials Science, Metals and Alloys}},
number = {{1}},
publisher = {{MDPI AG}},
title = {{{Manufacture of Defined Residual Stress Distributions in the Friction-Spinning Process: Investigations and Run-to-Run Predictive Control}}},
doi = {{10.3390/met12010158}},
volume = {{12}},
year = {{2022}},
}
@article{29196,
abstract = {{In biomedical engineering, laser powder bed fusion is an advanced manufacturing technology, which enables, for example, the production of patient-customized implants with complex geometries. Ti-6Al-7Nb shows promising improvements, especially regarding biocompatibility, compared with other titanium alloys. The biocompatible features are investigated employing cytocompatibility and antibacterial examinations on Al2O3-blasted and untreated surfaces. The mechanical properties of additively manufactured Ti-6Al-7Nb are evaluated in as-built and heat-treated conditions. Recrystallization annealing (925 °C for 4 h), β annealing (1050 °C for 2 h), as well as stress relieving (600 °C for 4 h) are applied. For microstructural investigation, scanning and transmission electron microscopy are performed. The different microstructures and the mechanical properties are compared. Mechanical behavior is determined based on quasi-static tensile tests and strain-controlled low cycle fatigue tests with total strain amplitudes εA of 0.35%, 0.5%, and 0.8%. The as-built and stress-relieved conditions meet the mechanical demands for the tensile properties of the international standard ISO 5832-11. Based on the Coffin–Manson–Basquin relation, fatigue strength and ductility coefficients, as well as exponents, are determined to examine fatigue life for the different conditions. The stress-relieved condition exhibits, overall, the best properties regarding monotonic tensile and cyclic fatigue behavior.}},
author = {{Hein, Maxwell and Kokalj, David and Lopes Dias, Nelson Filipe and Stangier, Dominic and Oltmanns, Hilke and Pramanik, Sudipta and Kietzmann, Manfred and Hoyer, Kay-Peter and Meißner, Jessica and Tillmann, Wolfgang and Schaper, Mirko}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{General Materials Science, Metals and Alloys, laser powder bed fusion, Ti-6Al-7Nb, titanium alloy, biomedical engineering, low cycle fatigue, microstructure, nanostructure}},
number = {{1}},
publisher = {{MDPI AG}},
title = {{{Low Cycle Fatigue Performance of Additively Processed and Heat-Treated Ti-6Al-7Nb Alloy for Biomedical Applications}}},
doi = {{10.3390/met12010122}},
volume = {{12}},
year = {{2022}},
}
@article{24131,
abstract = {{Glass/carbon fiber reinforced plastic (GFRP/CFRP) and hybrid components have attracted increasing attention in lightweight applications. However, residual stresses induced in the manufacturing process of these components can result in warpage and, eventually, negatively affect the mechanical performance of the composite structures. In the present work, GFRP, CFRP, GFRP/steel and CFRP/steel hybrid components were manufactured through the prepreg-press-technology always employing the same process parameters. The residual stresses of these components were measured through the hole drilling method (HDM), based on an adequate formalism to evaluate the residual stresses for orthotropic materials including the calculation of the calibration coefficients via finite element analysis (FEA). In FEA, the real material lay-up and mechanical properties of the samples were considered. The warpage induced by residual stresses was measured after the samples were removed from the tool. The measured residual stresses and warpage of four different types of samples were compared and results were analyzed in depth. The results obtained can be extended to other hybrid materials and even could be used for designing multi-stable laminates for application in adaptive structures. Moreover, the effects of the drilling process parameters of HDM, e.g., the drilling speed, the drilling increment and the zero-depth setting, on the resulting residual stresses of GFRP were investigated. The reliability of residual stress measurements in GFRP using HDM was validated through mechanical bending tests. The conclusions concerning the choice of optimal drilling parameters for GFRP could be directly applied for other types of samples considered in the present work.}},
author = {{Wu, Tao and Tinkloh, Steffen Rainer and Tröster, Thomas and Zinn, Wolfgang and Niendorf, Thomas}},
issn = {{2075-4701}},
journal = {{Metals}},
title = {{{Measurement and Analysis of Residual Stresses and Warpage in Fiber Reinforced Plastic and Hybrid Components}}},
doi = {{10.3390/met11020335}},
year = {{2021}},
}
@article{21064,
author = {{Tinkloh, Steffen Rainer and Wu, Tao and Tröster, Thomas and Niendorf, Thomas}},
issn = {{2075-4701}},
journal = {{Metals}},
title = {{{The Effect of Fiber Waviness on the Residual Stress State and Its Prediction by the Hole Drilling Method in Fiber Metal Laminates: A Global-Local Finite Element Analysis}}},
doi = {{10.3390/met11010156}},
year = {{2021}},
}
@article{24535,
abstract = {{Implementing the concept of mixed construction in modern automotive engineering requires the joining of sheet metal or extruded profiles with cast components made from different materials. As weight reduction is desired, these cast components are usually made from high-strength aluminium alloys of the Al-Si (Mn, Mg) system, which have limited weldability. The mechanical joinability of the cast components depends on their ductility, which is influenced by the microstructure. High-strength cast aluminium alloys have relatively low ductility, which leads to cracking of the joints. This limits the range of applications for cast aluminium alloys. In this study, an aluminium alloy of the Al-Si system AlSi9 is used to investigate relationships between solidification conditions during the sand casting process, microstructure, mechanical properties, and joinability. The demonstrator is a stepped plate with a minimum thickness of 2.0 mm and a maximum thickness of 4.0 mm, whereas the thickness difference between neighbour steps amounts to 0.5 mm. During casting trials, the solidification rates for different plate steps were measured. The microscopic investigations reveal a correlation between solidification rates and microstructure parameters such as secondary dendrite arm spacing. Furthermore, mechanical properties and the mechanical joinability are investigated.}},
author = {{Neuser, Moritz and Grydin, Olexandr and Andreiev, Anatolii and Schaper, Mirko}},
issn = {{2075-4701}},
journal = {{Metals}},
title = {{{Effect of Solidification Rates at Sand Casting on the Mechanical Joinability of a Cast Aluminium Alloy}}},
doi = {{10.3390/met11081304}},
year = {{2021}},
}
@article{21635,
abstract = {{Modern forming processes often allow today the efficient production of complex parts. In order to increase the sustainability of forming processes it would be favorable if the forming of workpieces becomes possible using production waste. At the Chair of Forming and Machining Technology of the Paderborn University (LUF) research is presently conducted with the overall goal to produce workpieces directly from secondary aluminum (e.g., powder and chips). Therefore, friction-based forming processes like friction spinning (or cognate processes) are used due to their high efficiency. As a pre-step, the production of semi-finished parts was the subject of accorded research work at the LUF. Therefore, a friction-based hot extrusion process was used for the full recycling or rework of aluminum chips into profiles. Investigations of the recycled semi-finished products show that they are comparable to conventionally produced semi-finished products in terms of dimensional stability and shape accuracy. An analysis of the mechanical properties of hardness and tensile strength shows that a final product with good and homogeneously distributed properties can be produced. Furthermore, significant correlations to the friction spinning process could be found that are useful for the above-mentioned direct part production from secondary aluminum.}},
author = {{Borgert, Thomas and Homberg, Werner}},
issn = {{2075-4701}},
journal = {{Metals}},
title = {{{Friction-Induced Recycling Process for User-Specific Semi-Finished Product Production}}},
doi = {{10.3390/met11040663}},
year = {{2021}},
}
@article{23913,
abstract = {{Implementing the concept of mixed construction in modern automotive engineering requires the joining of sheet metal or extruded profiles with cast components made from different materials. As weight reduction is desired, these cast components are usually made from high-strength aluminium alloys of the Al-Si (Mn, Mg) system, which have limited weldability. The mechanical joinability of the cast components depends on their ductility, which is influenced by the microstructure. High-strength cast aluminium alloys have relatively low ductility, which leads to cracking of the joints. This limits the range of applications for cast aluminium alloys. In this study, an aluminium alloy of the Al-Si system AlSi9 is used to investigate relationships between solidification conditions during the sand casting process, microstructure, mechanical properties, and joinability. The demonstrator is a stepped plate with a minimum thickness of 2.0 mm and a maximum thickness of 4.0 mm, whereas the thickness difference between neighbour steps amounts to 0.5 mm. During casting trials, the solidification rates for different plate steps were measured. The microscopic investigations reveal a correlation between solidification rates and microstructure parameters such as secondary dendrite arm spacing. Furthermore, mechanical properties and the mechanical joinability are investigated.}},
author = {{Neuser, Moritz and Grydin, Olexandr and Andreiev, Anatolii and Schaper, Mirko}},
issn = {{2075-4701}},
journal = {{Metals}},
title = {{{Effect of Solidification Rates at Sand Casting on the Mechanical Joinability of a Cast Aluminium Alloy}}},
doi = {{10.3390/met11081304}},
year = {{2021}},
}
@article{24573,
abstract = {{Al-Li based alloys are attractive materials for the aerospace industry. The twin-roll casting of such materials could provide properties not achievable by conventional direct-chill casting and downstream processing methods due to significantly higher solidification rates. An Al-Li-Cu-Mg-Zr alloy was twin-roll cast with the same alloy containing a small addition of Sc. The microstructure of as-cast materials and the influence of Sc on the behavior of the alloy at elevated temperatures were studied by means of light and electron microscopy and by resistivity measurements. A fine-grained structure was formed during twin-roll casting, but several surface and internal defects were found on the strips, which should be suppressed by a further adjustment of the casting conditions. The addition of Sc had a positive effect on grain size uniformity and microstructure stabilization at elevated temperatures, as shown by the precipitation of a fine dispersion of coherent Sc- and Zr-containing precipitates.}},
author = {{Grydin, Olexandr and Stolbchenko, Mykhailo and Schaper, Mirko and Belejová, Sára and Králík, Rostislav and Bajtošová, Lucia and Křivská, Barbora and Hájek, Michal and Cieslar, Miroslav}},
issn = {{2075-4701}},
journal = {{Metals}},
number = {{8}},
title = {{{New Twin-Roll Cast Al-Li Based Alloys for High-Strength Applications}}},
doi = {{10.3390/met10080987}},
volume = {{10}},
year = {{2020}},
}