@article{34000, abstract = {{Abstract This paper presents the characterization of the microstructure evolution during flow forming of austenitic stainless steel AISI 304L. Due to plastic deformation of metastable austenitic steel, phase transformation from γ-austenite into α’-martensite occurs. This is initiated by the formation of shear bands as product of the external stresses. By means of coupled microscopic and micromagnetic investigations, a characterization of the microstructure was carried out. In particular, this study shows the distribution of the strain-induced α’-martensite and its influence on material properties like hardness at different depths. The microstructural analyses by means of electron backscattered diffraction (EBSD) technique, evidence a higher amount of α’-martensite (ca. 23 %) close to the outer specimen surface, where the plastic deformation and the direct contact with the forming tool take place. In the middle area (ca. 1.5 mm depth from the outer surface), the portion of transformed α’-martensite drops to 7 % and in the inner surface to 2 %. These results are well correlated with microhardness and micromagnetic measurements at different depths. EBSD and atomic force microscopy (AFM) were used to make a detailed characterization of the topography and degree of deformation of the shear bands. Likewise, the mechanisms of nucleation of α’-martensite were discussed. This research contributes to the development of micromagnetic sensors to monitor the evolution of properties during flow forming. This makes them more suitable for closed-loop property control, which offers possibilities for an application-oriented and more efficient production.}}, author = {{Rozo Vasquez, Julian and Kanagarajah, Hanigah and Arian, Bahman and Kersting, Lukas and Homberg, Werner and Trächtler, Ansgar and Walther, Frank}}, issn = {{2195-8599}}, journal = {{Practical Metallography}}, keywords = {{Metals and Alloys, Mechanics of Materials, Condensed Matter Physics, Electronic, Optical and Magnetic Materials}}, number = {{11}}, pages = {{660--675}}, publisher = {{Walter de Gruyter GmbH}}, title = {{{Coupled microscopic and micromagnetic depth-specific analysis of plastic deformation and phase transformation of metastable austenitic steel AISI 304L by flow forming}}}, doi = {{10.1515/pm-2022-0064}}, volume = {{59}}, year = {{2022}}, } @article{33999, abstract = {{The production of complex multi-functional, high-strength parts is becoming increasingly important in the industry. Especially with small batch size, the incremental flow forming processes can be advantageous. The production of parts with complex geometry and locally graded material properties currently depicts a great challenge in the flow forming process. At this point, the usage of closed-loop control for the shape and properties could be a feasible new solution. The overall aim in this project is to establish an intelligent closed-loop control system for the wall thickness as well as the α’-martensite content of AISI 304L-workpieces in a flow forming process. To reach this goal, a novel sensor concept for online measurements of the wall thickness reduction and the martensite content during forming process is proposed. It includes the setup of a modified flow forming machine and the integration of the sensor system in the machine control. Additionally, a simulation model for the flow forming process is presented which describes the forming process with regard to the plastic workpiece deformation, the induced α’-martensite fraction, and the sensor behavior. This model was used for designing a closed-loop process control of the wall thickness reduction that was subsequently realized at the real plant including online measured feedback from the sensor system.}}, author = {{Kersting, Lukas and Arian, Bahman and Vasquez, Julian Rozo and Trächtler, Ansgar and Homberg, Werner and Walther, Frank}}, issn = {{1662-9795}}, journal = {{Key Engineering Materials}}, keywords = {{Mechanical Engineering, Mechanics of Materials, General Materials Science}}, pages = {{862--874}}, publisher = {{Trans Tech Publications, Ltd.}}, title = {{{Innovative Online Measurement and Modelling Approach for Property-Controlled Flow Forming Processes}}}, doi = {{10.4028/p-yp2hj3}}, volume = {{926}}, year = {{2022}}, } @inproceedings{36563, author = {{Rozo Vasquez, Julian and Walther, Frank and Arian, Bahman and Homberg, Werner and Kersting, Lukas and Trächtler, Ansgar}}, booktitle = {{Proceedings of the 14th International Conference on Barkhausen Noise and Micromagnetic Testing}}, location = {{Stockholm}}, title = {{{Soft sensor concept for micromagnetic depth-specific analysis of phase transformation during flow forming of AISI 304L steel.}}}, year = {{2022}}, } @book{36412, author = {{Kersting, Lukas and Trächtler, Ansgar and Arian, Bahman and Homberg, Werner and Rozo Vasquez, Julian and Walther, Frank}}, isbn = {{978-3-948749-23-1 }}, publisher = {{Diedrich}}, title = {{{Echtzeitfähige Modellierung eines innovativen Drückwalzprozesses für die eigenschaftsgeregelte Herstellung gradierter Bauteile.}}}, year = {{2022}}, } @phdthesis{30255, author = {{Wiens, Eugen}}, isbn = {{978-3-8440-8408-5}}, publisher = {{Shaker}}, title = {{{Innendrückwalzen – Ein innovatives Umformverfahren zur inkrementellen Formgebung von wanddickenkonturierten Rohren mit lokal einstellbaren mechanischen Eigenschaften}}}, year = {{2022}}, } @article{37647, abstract = {{Mechanical joining processes are an essential part of modern lightweight construction. They permit materials of different types to be joined in a way that is suitable for the loads involved. These processes reach their limits, however, as soon as the boundary conditions change. In most cases, these elements are specially adapted to the joining point and cannot be used universally. Changes require cost-intensive adaptation of both the element and the process control, thus making production more complex. This results in high costs due to the increased number of auxiliary joining element variants required and reduces the economic efficiency of mechanical joining. One approach to overcoming this issue is the use of adaptive auxiliary joining elements formed by friction spinning. This article presents the current state of research on pre-hole-free joining with adaptive joining elements. The overall process chain is illustrated, explained and analyzed. Special attention is paid to demonstrating the feasibility of pre-hole-free joining with adaptive joining elements. The chosen mechanical parameters are subsequently listed. Finally, a comprehensive outlook of the future development potential is derived.}}, author = {{Wischer, Christian and Homberg, Werner}}, issn = {{1662-9795}}, journal = {{Key Engineering Materials}}, keywords = {{Mechanical Engineering, Mechanics of Materials, General Materials Science}}, pages = {{1468--1478}}, publisher = {{Trans Tech Publications, Ltd.}}, title = {{{Further Development of an Adaptive Joining Technique Based on Friction Spinning to Produce Pre-Hole-Free Joints}}}, doi = {{10.4028/p-1n6741}}, volume = {{926}}, year = {{2022}}, } @inbook{25448, author = {{Heggemann, Thomas and Sapli, Hüseyin and Homberg, W.}}, booktitle = {{Forming the Future}}, issn = {{2367-1181}}, title = {{{Experimental and Numerical Investigations into the Influence of the Process Parameters During the Deep Drawing of Fiber Metal Laminates}}}, doi = {{10.1007/978-3-030-75381-8_219}}, year = {{2021}}, } @article{26191, author = {{Voswinkel, Dietrich and Sapli, Hüseyin and Kloidt, Dennis and Heggemann, Thomas and Homberg, Werner and Grydin, Olexandr and Schaper, Mirko}}, issn = {{1757-8981}}, journal = {{IOP Conference Series: Materials Science and Engineering}}, title = {{{Improving the Accuracy of Deep Drawn Fiber-Metal Laminate Parts by Preliminary Surface Treatment}}}, doi = {{10.1088/1757-899x/1190/1/012028}}, year = {{2021}}, } @article{21633, abstract = {{Higher quality requirements by customers demand higher precision and accuracy from manufacturing processes. Application oriented preparation of semi-finished materials is key for subsequent forming operations, therefore, straightening machines are employed. Straightening strengthens the material by increasing plastic deformation by means of strain hardening, resulting in undesirable reduction in formability when processing high strength materials, in particular. Conventional roll-type straightening machines process either bars or strips. This is achieved upon passing material between rolls arranged in two staggered rows. However, conventional straightening processes do not adapt to the local varying distortion of coiled strips. Innovative, self-correcting process control techniques, which adapt to the initial geometric characteristics of the strip, present a promising approach to fix this issue through optimization of the leveling process. Here, an innovative strategy to improve straightening of high strength steel materials (1.4310) is presented. This implements optimized leveling, adding minimal plastic deformation and, thus, strain hardening. To operate an intelligent straightening machine, a reliable online measurement of the surface defects is fundamentally essential. The MagnaTest, which is developed for material testing, is made feasible for such purposes after calibrating for curvature measurement. Preliminary results are promising in regards to measuring the curvature online, so that the following straightening process can be close loop controlled. The bending measurement is linked to open/closed loop control, therefore providing an optimal straightening result in regards to formability, leveling, and reduced strain hardening.}}, author = {{Bader, Fabian and Bathelt, Lukas and Djakow, Eugen and Homberg, Werner and Henke, Christian and Trächtler, Ansgar}}, journal = {{ESAFORM 2021}}, title = {{{Innovative Measurement Of Stress Superposed Steel Strip For Straightening Machines}}}, doi = {{10.25518/esaform21.2382}}, year = {{2021}}, } @inbook{23385, abstract = {{Innovative self-correcting process control techniques which adapt to the initial geometric characteristics of the strip are a promising approach to fix the local varying distortion of coiled strips by optimizing the leveling process. This paper presents an innovative strategy to improve straightening of AHSS materials (1.4310). This implies optimized leveling, adding minimal plastic deformation, and, thus, strain hardening. Therefore, an “intelligent straightening machine” is being developed which will be presented. To operate an intelligent straightening machine a reliable online measurement of the surface defects is fundamentally essential. This paper describes an approach towards the measurement of a bent steel strip for an automatic straightening process. Therefore, various ways of measuring the bending curvature are investigated. Optical, tactile, and the electromagnetic induction testing MagnaTest are compared with each other. The bending measurement is linked to open-loop control, providing an optimal straightening result in regards of formability, leveling, and reduced strain hardening.}}, author = {{Bader, Fabian and Bathelt, Lukas and Djakow, Eugen and Homberg, Werner and Henke, Christian and Trächtler, Ansgar}}, booktitle = {{Forming the Future}}, issn = {{2367-1181}}, title = {{{Self-optimized, Intelligent Open-Loop-Controlled Steel Strip Straightening Machine for Advanced Formability}}}, doi = {{10.1007/978-3-030-75381-8_1}}, year = {{2021}}, } @article{30649, abstract = {{Nowadays, the production of modern lightweight structures, like a body in white structure requires a wide variety of mechanical joining processes. To fulfill the various demands, mechanical joining processes and joining elements (JE) are used. Very often, they are adapted to the application, which leads in turn to a numerous of different variants, high costs, and loss of the process chain versatility. To overcome this drawback, an innovative approach is the usage of individually produced and task-adapted JE, the so-called friction spun joint connectors (FSJC). These connectors can be modified in shape as well as in material properties. This flexibility offers high potential for lightweight design but also increases the necessary analytical effort regarding the forming process as well as the manufactured joint's properties. Therefore, a new analysis strategy based on the Finite-Element-Method (FEM) is proposed, which numerically determines the local load bearing capacity within a given joint in order to identify the critical regions for load transfer. The process of joining element manufacturing and the analysis strategy will be described in detail and optimization results of the joints are shown. Numerical results are discussed and possible recommendations for joint manufacturing are derived.}}, author = {{Wischer, Christian and Steinfelder, Christian and Homberg, Werner and Brosius, Alexander}}, journal = {{IOP Conference Series: Materials Science and Engineering}}, pages = {{012007}}, title = {{{Joining with Friction Spun Joint Connectors – Manufacturing and Analysis}}}, doi = {{10.1088/1757-899x/1157/1/012007}}, volume = {{1157}}, year = {{2021}}, } @article{30702, author = {{Wischer, Christian and Homberg, Werner}}, journal = {{Production Engineering}}, title = {{{A contribution on versatile process chains: joining with adaptive joining elements, formed by friction spinning}}}, doi = {{10.1007/s11740-021-01094-8}}, year = {{2021}}, } @article{23469, abstract = {{The implementation of control systems in metal forming processes improves product quality and productivity. By controlling workpiece properties during the process, beneficial effects caused by forming can be exploited and integrated in the product design. The overall goal of this investigation is to produce tailored tubular parts with a defined locally graded microstructure by means of reverse flow forming. For this purpose, the proposed system aims to control both the desired geometry of the workpiece and additionally the formation of strain-induced α′-martensite content in the metastable austenitic stainless steel AISI 304 L. The paper introduces an overall control scheme, a geometry model for describing the process and changes in the dimensions of the workpiece, as well as a material model for the process-induced formation of martensite, providing equations based on empirical data. Moreover, measurement systems providing a closed feedback loop are presented, including a novel softsensor for in-situ measurements of the martensite content.}}, author = {{Riepold, Markus and Arian, Bahman and Vasquez, Julian Rozo and Homberg, Werner and Walther, Frank and Trächtler, Ansgar}}, issn = {{2666-9129}}, journal = {{Advances in Industrial and Manufacturing Engineering}}, title = {{{Model approaches for closed-loop property control for flow forming}}}, doi = {{10.1016/j.aime.2021.100057}}, 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}}, } @inproceedings{21477, author = {{Rostek, Tim and Makeieva, Hanna and Homberg, Werner}}, booktitle = {{Proceedings of the 13th International Conference on the Technology of Plasticity}}, editor = {{Daehn, G. and Cao, J. and Kinsey, B. and Tekkaya, A. E. and Vivek, A. and Yoshida, Y}}, isbn = {{978-3-030-75380-1}}, location = {{Columbus}}, pages = {{2115--2125}}, publisher = {{Springer, Cham}}, title = {{{Cutting Blades for Food Processing Applications Manufactured Using Innovative Spin Forming}}}, doi = {{10.1007/978-3-030-75381-8_178}}, year = {{2021}}, } @inbook{22766, author = {{Dahms, Frederik and Homberg, Werner}}, booktitle = {{Forming the Future}}, issn = {{2367-1181}}, location = {{Ohio, USA, VIRTUAL EVENT}}, pages = {{2249--2259}}, publisher = {{Springer, Cham}}, title = {{{Investigations and Improvements in 3D-DIC Optical Residual Stress Analysis—A New Temperature Compensation Method}}}, doi = {{10.1007/978-3-030-75381-8_189}}, year = {{2021}}, } @inproceedings{30297, author = {{Rozo Vasquez, Julian and Arian, Bahman and Riepold, Markus and Walther, Frank and Homberg, Werner and Trächtler, Ansgar}}, booktitle = {{Proceedings of the 11th International Work­shop NDT in Progress}}, location = {{Prague}}, title = {{{Magnetic Barkhausen noise analysis for microstructural effects separation during flow forming of metastable austenite 304L.}}}, year = {{2021}}, } @inproceedings{23465, abstract = {{One of the main objectives of production engineering is to reproducibly manufacture (complex) defect-free parts. To achieve this, it is necessary to employ an appropriate process or tool design. While this will generally prove successful, it cannot, however, offset stochastic defects with local variations in material properties. Closed-loop process control represents a promising approach for a solution in this context. The state of the art involves using this approach to control geometric parameters such as a length. So far, no research or applications have been conducted with closed-loop control for microstructure and product properties. In the project on which this paper is based, the local martensite content of parts is to be adjusted in a highly precise and reproducible manner. The forming process employed is a special, property-controlled flow-forming process. A model-based controller is thus to generate corresponding correction values for the tool-path geometry and tool-path velocity on the basis of online martensite content measurements. For the controller model, it is planned to use a special process or microstructure (correlation) model. The planned paper not only describes the experimental setup but also presents results of initial experimental investigations for subsequent use in the closed-loop control of α’-martensite content during flow-forming.}}, author = {{Arian, Bahman and Homberg, Werner and Riepold, Markus and Trächtler, Ansgar and Rozo Vasquez, Julian and Walther, Frank}}, isbn = {{978-2-87019-302-0}}, keywords = {{Flow-forming, Spinning, Process Strategy, Martensite Content, Property Control, Micromagnetic Measurement, Metastable Austenitic Stainless Steel}}, location = {{Liège, Belgium}}, publisher = {{ULiège Library}}, title = {{{Forming of metastable austenitic stainless steel tubes with axially graded martensite content by flow-forming}}}, year = {{2021}}, } @inbook{30296, author = {{Wiens, Eugen and Homberg, Werner and Arian, Bahman and Möhring, Kerstin and Walther, Frank}}, booktitle = {{Forming the Future}}, isbn = {{9783030753801}}, issn = {{2367-1181}}, location = {{Virtual Event}}, publisher = {{Springer International Publishing}}, title = {{{Forming of Parts with Locally Defined Mechanical and Ferromagnetic Properties by Flow-Forming}}}, doi = {{10.1007/978-3-030-75381-8_160}}, year = {{2021}}, } @article{26082, author = {{Wischer, Christian and Wiens, Eugen and Homberg, Werner}}, issn = {{2666-3309}}, journal = {{Journal of Advanced Joining Processes}}, publisher = {{Elsevier}}, title = {{{Joining with versatile joining elements formed by friction spinning}}}, doi = {{10.1016/j.jajp.2021.100060}}, volume = {{3}}, year = {{2021}}, }