@article{60299,
abstract = {{Non-rotationally symmetrical joints can have different properties that can be controlled by the joint orientation. This hypothesis is tested using a Reuleaux triangle joint geometry. A tool design is carried out, followed by a numerical sensitivity analysis of the tool geometry. Initial tools were manufactured for experimental investigations and then adapted based on the findings of the sensitivity analysis. The joints are characterized by micrographs, 3D scans, shear tensile tests, head tensile tests and three-point bending tests and compared with a round geometry. The analysis confirms the hypothesis. Thus, joints with adaptable properties can be produced with one tool set.}},
author = {{Steinfelder, Christian and Acksteiner, Clemens and Brosius, Alexander}},
issn = {{0007-8506}},
journal = {{CIRP Annals}},
keywords = {{Joining, Forming, Property adjustment}},
publisher = {{Elsevier BV}},
title = {{{A new joint with versatile properties based on a Reuleaux triangle geometry}}},
doi = {{10.1016/j.cirp.2025.03.002}},
year = {{2025}},
}
@inproceedings{59907,
abstract = {{Abstract. Flow forming is recognized for its precision in producing rotationally symmetric components, but the use of metastable austenitic stainless steel (AISI 304L) introduces challenges due to uncontrolled strain-induced α’ martensite formation. Variations in factors such as eccentricity and batch inconsistencies lead to unpredictable microstructural profiles, limiting reproducibility [1,2]. This study addresses these issues by incorporating thermal actuators for cryogenic cooling and induction heating to regulate forming temperatures, enabling control of the α’-martensite content. Experimental investigations demonstrate that local tempering during thermomechanical reverse flow forming produces discernible variations in microstructure, affecting mechanical and magnetic properties [3]. Controlled local adjustments of α’-martensite content allow for customization of properties in seamless tubes, advancing manufacturing capabilities for complex, defect-free components. The results presented demonstrate promising strategies for implementation within the context of closed-loop property control in flow forming.}},
author = {{Arian, Bahman and Homberg, Werner and Kersting, Lukas and Trächtler, Ansgar and Rozo Vasquez, Julian and Walther, Frank}},
booktitle = {{Materials Research Proceedings}},
editor = {{Carlone, Pierpaolo and Filice, Luigino and Umbrello, Domenico}},
issn = {{2474-395X}},
keywords = {{Flow Forming, Thermomechanical Forming, α’-Martensite, Property Control}},
location = {{Paestum, Italy}},
publisher = {{Materials Research Forum LLC}},
title = {{{Advanced thermomechanical flow forming: A novel approach to α’-martensite control for enhanced material properties}}},
doi = {{10.21741/9781644903599-127}},
volume = {{54}},
year = {{2025}},
}
@inproceedings{49430,
abstract = {{Within the current energy and environmental crisis, new material- and energy-saving processes are needed. For this reason, this study focuses on the development of a new forming technology for Ti-6Al-4V sheet metal. It is based on combination of solution treatment by resistive heating with rapid tool-based quenching and subsequent annealing. This new “TISTRAQ” process is comparable with press-hardening already known for steels and hot die quenching known for aluminium alloys. One of the main influencing factors for this process is the heat transfer coefficient (HTC). It is an important driver for adjustment of basic parameters, as selection of tool material or the forming speed but also plays an important role while elaborating temperature distribution in the numerical model. Therefore, a new and unique test rig was developed to determine the HTC and to perform tool-based heat treatment at specimen level under laboratory conditions. The test rig was used to investigate the influence of the titanium-tool-lubricant system on HTC and cooling rate. Further the effect of heat treatment in the test rig and tool-based quenching on microstructure and mechanical properties was studied. To improve the prediction of the temperature distribution of the titanium during cooling, the HTC was integrated into the numerical process simulation}},
author = {{Kaiser, Maximilian Alexander and Höschen, Fabian and Pfeffer, Nina and Merten, Mathias and Meyer, Thomas and Marten, Thorsten and Rockicki, Pawel and Höppel, Heinz Werner and Tröster, Thomas}},
booktitle = {{IOM3. Chapter 14: Forming, Machining & Joining [version 1; not peer reviewed]}},
keywords = {{Interfacial heat transfer coefficient, Ti-6Al-4V, nonisothermal forming, thermomechanical processing, TISTRAQ process}},
location = {{Edinburgh}},
title = {{{The new TISTRAQ process: Solution treatment with rapid quenching and annealing for Ti-6Al-4V sheet metal part forming - investigation on heat transfer coefficient and influence on cooling rates}}},
doi = {{doi.org/10.7490/f1000research.1119929.1}},
year = {{2024}},
}
@inproceedings{49437,
abstract = {{The phase and TTT diagrams of the Ti-6Al-4V system allow the development of a new forming process for a more energy- and materialefficient production of sheet metal parts. This new “TISTRAQ” process is composed of two steps. In terms of process technology, the first step is comparable to a direct press-hardening process already well known for steels. In this step, the Ti-6Al-4V sheet material is resistively heated to a temperature below β-transus Tβ and, after a very short holding time, simultaneously formed and quenched by use of water cooled tools. Thereby, the β phase undergoes a martensitic transformation. The second step is a subsequent short-time annealing, which leads to a hardening of the material. In this work, a new test rig using resistive heating technique was used in order to produce
different solution treated and tool quenched (STQ) and subsequently annealed (STA) states. In this paper, the effects of heating rate, solution treatment temperature and holding time on microstructure and mechanical properties are addressed. For the characterisation, tensile testing and scanning electron microscopy were used. By the systematic variation of applied processing parameters, dominating effects on microstructure and mechanical properties were evaluated. For example, the solution treatment temperature was found to have a significant effect on microstructural features and characteristic strength and strain values. The obtained results reveal a high potential for future technical applications.}},
author = {{Pfeffer, Nina and Kaiser, Maximilian Alexander and Meyer, Thomas and Göken, Mathias and Höppel, Heinz Werner}},
booktitle = {{IOM3. Chapter 14: Forming, Machining & Joining [version 1; not peer reviewed]}},
keywords = {{Ti-6Al-4V, thermomechanical processing, resistive heating, quench-forming, process parameter-microstructure-properties relationship}},
location = {{Edinburgh}},
title = {{{The new TISTRAQ process: Solution treatment with rapid quenching and annealing for Ti-6Al-4V sheet metal part forming - the effect of processing parameters on microstructure and mechanical properties}}},
doi = {{https://doi.org/10.7490/f1000research.1119929.1}},
year = {{2024}},
}
@article{60300,
abstract = {{This study focuses on the phenomenological change in material strength caused by a specific heat treatment and the subsequent analysis of the influence on the clinching process and the resulting joint properties. For this purpose, three series of tests were performed. In the first series of tests, the influence of heat treatment up to 340 °C on the mechanical properties of an age-hardenable AlMgSi alloy was investigated. Holding time and temperature were varied and the material strength was evaluated by tensile and hardness tests. Two strength-increasing and two strength-reducing heat treatment parameters were identified. In the second series of tests, selected heat treatment parameters were applied to a larger number of specimens and the joint strength was investigated by shear and head tensile tests. In the shear tensile test, mainly the properties of the punch-side material have an influence on the resulting joint strength. A change in strength of the die-side material can be neglected. In contrast, the properties of both sheets are important in the head tensile test. The strength of the joint will only increase if the strength of both sheets is increased. In general, a strength increasing heat treatment resulted in higher joint strength. In the third series of tests, the factor of punch displacement was considered, which was demonstrated to directly influence the formation of the clinched joint geometry.}},
author = {{Steinfelder, Christian and Rempel, Dennis and Brosius, Alexander}},
issn = {{2666-3309}},
journal = {{Journal of Advanced Joining Processes}},
keywords = {{Joining by forming, Clinching, EN AW-6014, Heat treatment, Load-bearing capacity}},
publisher = {{Elsevier BV}},
title = {{{Influence of the material properties on the clinching process and the resulting load-bearing capacity of the joint}}},
doi = {{10.1016/j.jajp.2024.100263}},
volume = {{10}},
year = {{2024}},
}
@inproceedings{43044,
abstract = {{Abstract. The combination of incremental sheet metal forming and high-speed forming offers new possibilities for flexible forming processes in the production of large sheet metal components of increased complexity with relatively low forming energies. In this paper, the general feasibility and process differences between the pulse-driven high-speed forming technologies of electrohydraulic and electromagnetic forming were investigated. An example component made of EN AW 6016 aluminum sheet metal was thus formed incrementally by both processes and the forming result evaluated by an optical 3D measurement system. For this purpose, a forming strategy for electromagnetic incremental forming (EMIF) was developed, tested and adapted to the electrohydraulic incremental forming process (EHIF). The discharge energy, the tool displacement and the pressure field of the forming zone were determined as relevant parameters for the definition of an adequate tool path strategy. It was found that the EHIF process is less affected by larger distances between the tool and the blank, while this is a critical variable for force application to the component during EMIF. On the other hand, the more uniform pressure distribution of the EMIF process is advantageous for forming large steady component areas. }},
author = {{Holzmüller, Maik and Linnemann, Maik and Homberg, Werner and Psyk, Verena and Kräusel, Verena and Kroos, Janika}},
booktitle = {{Materials Research Proceedings}},
issn = {{2474-395X}},
keywords = {{Incremental Sheet Forming, Aluminium, High-Speed Forming}},
location = {{Nürnberg}},
pages = {{11--18}},
publisher = {{Materials Research Forum LLC}},
title = {{{Proof of concept for incremental sheet metal forming by means of electromagnetic and electrohydraulic high-speed forming}}},
doi = {{10.21741/9781644902417-2}},
volume = {{25}},
year = {{2023}},
}
@article{43045,
abstract = {{The pressure fields generated by two simultaneous discharges have not been investigated on any notable scale for the electrohydraulic impulse forming method. In this study, the synchronicity of two discharges is ensured by the sequential connection of two wires mounted in two spark gaps in a common volume of liquid. The objective is to experimentally confirm the equilibrium of the energies evolved in two spark gaps by means of pressure measurements. In addition, multipoint membrane pressure gauges demonstrated the feasibility of easily recording detailed pressure maps. Based on the membrane deformation mechanism and material strengthening under static and impulse conditions, the processing procedure is further developed so as to achieve better accuracy in the determination of pressure field parameters. The practical equality of the pressure fields on the left and right halves of the flat-loaded area confirms the equality of energies evolved in the two spark gaps. The direct shock waves create zones with the most intensive loading. These results provide a basis for the development of new electrohydraulic technologies involving the application of two simultaneous discharges with equal energy and pressure parameters.}},
author = {{Knyazyev, Mykhaylo and Holzmüller, Maik and Homberg, Werner}},
issn = {{2504-4494}},
journal = {{Journal of Manufacturing and Materials Processing}},
keywords = {{impulse, forming, electrohydraulic, discharge, wire, pressure gauge, pressure field}},
number = {{1}},
publisher = {{MDPI AG}},
title = {{{Investigation of Pressure Fields Generated by Two Simultaneous Discharges in Liquid Initiated by Wires}}},
doi = {{10.3390/jmmp7010040}},
volume = {{7}},
year = {{2023}},
}
@inproceedings{30292,
abstract = {{The spinning process is a flexible incremental forming process for the manufacturing of axially-symmetric sheet metal or tubular components with functionally graded properties. It is characterized by the utilization of universal tooling geometries and quite low forming forces. The process has a high potential to reduce material waste, to extend the forming limits and to achieve more complex geometries as well as favorable part properties [1]. Current research work at the Chair of Forming Technology (LUF) is focused on innovative flow-turning processes that have a high potential for producing flat components with excellent geometrical and mechanical properties while keeping process times short [2]. In combination with process-integrated local heat treatment, the new spinning process is predestined for the efficient forming of ultra-high-strength steel or tailored materials. Due to the desired field of food industry only food-safe materials such as special stainless steels are being investigated. This paper presents an innovative machine layout as well as an adequate process design for the production of high-performance circular knives with optimized mechanical hardness. In this context, particular attention is paid to various areas of temperature control as well as process-related challenges during the process.}},
author = {{Engemann, David and Homberg, Werner}},
keywords = {{Cutting blades, Flow-forming, Incremental forming, Hot Forming, High strength steels}},
location = {{Braga - Portugal}},
title = {{{Hot Spinning of Cutting Blades for Food Industry}}},
year = {{2022}},
}
@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}},
}
@inproceedings{21447,
abstract = {{Even though the spectrum of parts is expected to shift over the long term as a result of increasing e-mobility, there is still an extremely high demand for complex components made of high-strength materials which can only be produced by hydroforming technologies. The innovative combination of hydroforming processes with other forming processes, as well as the improvement of the processes themselves, offers considerable potential for improvement.
A number of promising ways of improving the hydroforming process chain are therefore the subject of this contribution. The focus of the article is on possible approaches for combining (incremental) pre- and post-forming operations, which can permit considerable improvements in both quality and features at a reduced cost. Furthermore, a novel combination of quasi-static and high-speed forming processes is presented, leading to an improved overall forming process (with a high application potential) for the production of complex parts.
}},
author = {{Wiens, Eugen and Djakow, Eugen and Homberg, Werner}},
booktitle = {{Nebu/Nehy 2020}},
keywords = {{Hydroforming, Incremental Forming, Internal Flow-turning, High-speed Forming}},
title = {{{Some ideas for the further development of hydroforming process chains}}},
year = {{2020}},
}
@proceedings{19976,
abstract = {{The aim to reduce pollutant emission has led to a trend towards lightweight construction in car body development during the last years. As a consequence of the resulting need for multi-material design, mechanical joining technologies become increasingly important. Mechanical joining allows for the combination of dissimilar materials, while thermic joining techniques reach their limits. Self-piercing riveting enables the joining of dissimilar materials by using semi-tubular rivets as mechanical fasteners. The rivet production, however, is costly and time-consuming, as the rivets generally have to be hardened, tempered and coated after forming, in order to achieve an adequate strength and corrosion resistance. A promising approach to improve the efficiency of the rivet manufacturing is the use of high-strength high nitrogen steel as rivet material because these additional process steps would not be necessary anymore. As a result of the comparatively high nitrogen content, such steels have various beneficial properties like higher strength, good ductility and improved corrosion resistance. By cold bulk forming of high nitrogen steels high-strength parts can be manufactured due to the strengthening which is caused by the high strain hardening. However, high tool loads thereby have to be expected and are a major challenge during the production process. Consequently, there is a need for appropriate forming strategies. This paper presents key aspects concerning the process design for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel. The aim is to produce the rivets in several forming stages without intermediate heat treatment between the single stages. Due to the high strain hardening of the material, a two stage forming concept will be investigated. Cup-backward extrusion is chosen as the first process step in order to form the rivet shank without forming the rivet foot. Thus, the strain hardening effects in the area of the rivet foot are minimized and the tool loads during the following process step can be reduced. During the second and final forming stage the detailed geometry of the rivet foot and the rivet head is formed. In this context, the effect of different variations, for example concerning the final geometry of the rivet foot, on the tool load is investigated using multistage numerical analysis. Furthermore, the influence of the process temperature on occurring stresses is analysed. Based on the results of the investigations, an adequate forming strategy and a tool concept for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel are presented.}},
editor = {{Kuball, Clara-Maria and Uhe, Benedikt and Meschut, Gerson and Merklein, Marion}},
keywords = {{high nitrogen steel, self-piercing riveting, joining by forming, bulk forming, tool design}},
pages = {{280--285}},
title = {{{Process design for the forming of semi-tubular self-piercing rivets made of high nitrogen steel}}},
doi = {{10.1016/j.promfg.2020.08.052}},
volume = {{50}},
year = {{2020}},
}
@proceedings{19974,
abstract = {{Due to the trend towards lightweight design in car body development mechanical joining technologies become increasingly important. These techniques allow for the joining of dissimilar materials and thus enable multi-material design, while thermic joining methods reach their limits. Semi-tubular self-piercing riveting is an important mechanical joining technology. The rivet production, however, is costly and time-consuming, as the process consists of several process steps including the heat treatment and coating of the rivets in order to achieve an adequate strength and corrosion resistance. The use of high nitrogen steel as rivet material leads to the possibility of reducing process steps and hence increasing the efficiency of the process. However, the high tool loads being expected due to the high strain hardening of the material are a major challenge during the rivet production. Thus, there is a need for appropriate forming strategies, such as the manufacturing of the rivets at elevated temperatures. Prior investigations led to the conclusion that forming already at 200 °C results in a distinct reduction of the yield strength. To create a deeper understanding of the forming behaviour of high nitrogen steel at elevated temperatures, compression tests were conducted in a temperature range between room temperature and 200 °C. The determined true stress – true strain curves are the basis for the further process and tool design of the rivet production. Another key factor for the rivet manufacturing at elevated temperatures is the influence of the process temperature on the tribological conditions. For this reason, ring compression tests at room temperature and 200 °C are carried out. The friction factors are determined on the basis of calibration curves resulting from the numerical analysis of the ring compression process. The investigations indicate that the friction factor at 200 °C is significantly higher compared to room temperature. This essential fact has to be taken into account for the process and tool design for the rivet production using high nitrogen steel.}},
editor = {{Kuball, Clara-Maria and Jung, R and Uhe, Benedikt and Meschut, Gerson and Merklein, Marion}},
keywords = {{High nitrogen steel, Self-piercing riveting, Joining by forming, Bulk forming, Strain hardening}},
title = {{{Influence of the process temperature on the forming behaviour and the friction during bulk forming of high nitrogen steel}}},
doi = {{10.1016/j.jajp.2020.100023}},
volume = {{1}},
year = {{2020}},
}
@phdthesis{15030,
abstract = {{Working-media-based forming processes (WMBF) represent a great potential regarding the production of complex sheet-metal lightweight components with excellent surface quality, shape accuracy and dimensional stability. The working-media-based forming processes characterize the sheet-metal forming process, where the sheet metal blank is formed during the forming process by means of a (quasi-)static or dynamic working media pressure into a contouring forming tool. Although the WMBF offers improved utilization of the formability of the used materials compared to conventional sheet metal forming processes, there are limits in the production of complex deeper or sharp edged components with (quasi-)static and dynamic WMBF processes, which can not be overcome by using these methods alone. In order to overcome this, multi-level WMBF process sequences for components with spherical and stepped geometries are developed in this work. Here the developed strategies combine the advantages of (quasi-)static and dynamic WMBF processes. Furthermore, based on analytical, experimental and numerical investigations, innovative process management strategies were derived, which completely compensate the local wall thickness changes, make better use of existing material resources and thus enable the safe production of mentioned geometries.}},
author = {{Djakow, Eugen}},
keywords = {{High Speed Forming}},
pages = {{188}},
publisher = {{Shaker}},
title = {{{Ein Beitrag zur kombinierten (quasi-)statischen und dynamischen Umformung von blechförmigen Halbzeugen}}},
doi = {{ISBN 978-3-8440-6723-1}},
year = {{2019}},
}