@inproceedings{36473, abstract = {{Destructive micrograph analysis (MA) is the standard method for the assessment of clinched joints. However, during the joint preparation for the MA, geometric features of the joint can change due to elastic effects and closing cracks. X-ray computed tomography (CT) is a promising alternative to investigate the joint non-destructively. However, if the material properties of similar joining partners are the same, the CT is not able to correctly resolve surfaces in the joint that are close to or pressing onto each other. These surfaces are relevant for the determination of characteristic dimensions such as neck thickness and undercut. By placing a thin, highly radiopaque tin layer between the joining partners, the interfacial area in the reconstructed volume can be highlighted. In this work, a method for the localisation of the tin layer inside the joint as well as threshold value procedures for the outer joint contour in cross section images are investigated. The measured characteristic dimensions are compared with measured values from MA of the same samples and of samples without tin layer. In addition, possible effects of the tin layer on the joining point characteristics as well as problems of the MA are discussed.}}, author = {{Busch, Matthias and Köhler, Daniel and Hausotte, Tino and Kupfer, Robert and Troschitz, Juliane and Gude, Maik }}, title = {{{Approach to Determine the Characteristic Dimensions of Clinched Joints by Industrial X-ray Computed Tomography}}}, year = {{2022}}, } @article{34215, abstract = {{Clinching as a mechanical joining technique allows a fast and reliable joining of metal sheets in large-scale production. An efficient design and dimensioning of clinched joints requires a holistic understanding of the material, the joining process and the resulting properties of the joint. In this paper, the process chain for clinching metal sheets is described and experimental techniques are proposed to analyze the process-microstructure-property relationships from the sheet metal to the joined structure. At the example of clinching aluminum EN AW 6014, characterization methods are applied and discussed for the following characteristics: the mechanical properties of the sheet materials, the tribological behavior in the joining system, the joining process and the resulting material structure, the load-bearing behavior of the joint, the damage and degradation as well as the service life and crack growth behavior. The compilation of the characterization methods gives an overview on the advantages and weaknesses of the methods and the multiple interactions of material, process and properties during clinching. In addition, the results of the analyses on EN AW 6014 can be applied for parameterization and validation of simulations.}}, author = {{Kupfer, Robert and Köhler, Daniel and Römisch, David and Wituschek, Simon and Ewenz, Lars and Kalich, Jan and Weiß, Deborah and Sadeghian, Behdad and Busch, Matthias and Krüger, Jan Tobias and Neuser, Moritz and Grydin, Olexandr and Böhnke, Max and Bielak, Christian Roman and Troschitz, Juliane}}, issn = {{2666-3309}}, journal = {{Journal of Advanced Joining Processes}}, keywords = {{Mechanical Engineering, Mechanics of Materials, Engineering (miscellaneous), Chemical Engineering (miscellaneous)}}, publisher = {{Elsevier BV}}, title = {{{Clinching of Aluminum Materials – Methods for the Continuous Characterization of Process, Microstructure and Properties}}}, doi = {{10.1016/j.jajp.2022.100108}}, volume = {{5}}, year = {{2022}}, } @article{34216, abstract = {{Mechanical joining technologies are increasingly used in multi-material lightweight constructions and offer opportunities to create versatile joining processes due to their low heat input, robustness to metallurgical incompatibilities and various process variants. They can be categorised into technologies which require an auxiliary joining element, or do not require an auxiliary joining element. A typical example for a mechanical joining process with auxiliary joining element is self-piercing riveting. A wide range of processes exist which are not requiring an auxiliary joining element. This allows both point-shaped (e.g., by clinching) and line-shaped (e.g., friction stir welding) joints to be produced. In order to achieve versatile processes, challenges exist in particular in the creation of intervention possibilities in the process and the understanding and handling of materials that are difficult to join, such as fiber reinforced plastics (FRP) or high-strength metals. In addition, predictive capability is required, which in particular requires accurate process simulation. Finally, the processes must be measured non-destructively in order to generate control variables in the process or to investigate the cause-effect relationship. This paper covers the state of the art in scientific research concerning mechanical joining and discusses future challenges on the way to versatile mechanical joining processes.}}, author = {{Meschut, Gerson and Merklein, M. and Brosius, A. and Drummer, D. and Fratini, L. and Füssel, U. and Gude, M. and Homberg, Werner and Martins, P.A.F. and Bobbert, Mathias and Lechner, M. and Kupfer, R. and Gröger, B. and Han, Daxin and Kalich, J. and Kappe, Fabian and Kleffel, T. and Köhler, D. and Kuball, C.-M. and Popp, J. and Römisch, D. and Troschitz, J. and Wischer, Christian and Wituschek, S. and Wolf, M.}}, issn = {{2666-3309}}, journal = {{Journal of Advanced Joining Processes}}, keywords = {{Mechanical Engineering, Mechanics of Materials, Engineering (miscellaneous), Chemical Engineering (miscellaneous)}}, publisher = {{Elsevier BV}}, title = {{{Review on mechanical joining by plastic deformation}}}, doi = {{10.1016/j.jajp.2022.100113}}, volume = {{5}}, year = {{2022}}, } @article{51192, abstract = {{ Destructive micrograph analysis (MA) is the standard method for the assessment of clinched joints. However, during the joint preparation for the MA, geometric features of the joint can change due to elastic effects and closing cracks. X-ray computed tomography (CT) is a promising alternative to investigate the joint non-estructively. However, if the material properties of similar joining partners are the same, the CT is not able to correctly resolve surfaces in the joint that are close to or pressing onto each other. These surfaces are relevant for the determination of characteristic dimensions such as neck thickness and undercut. By placing a thin, highly radiopaque tin layer between the joining partners, the interfacial area in the reconstructed volume can be highlighted. In this work, a method for the localisation of the tin layer inside the joint as well as threshold value procedures for the outer joint contour in cross section images are investigated. The measured characteristic dimensions are compared with measured values from MA of the same samples and of samples without tin layer. In addition, possible effects of the tin layer on the joining point characteristics as well as problems of the MA are discussed. }}, author = {{Busch, Matthias and Köhler, Daniel and Hausotte, Tino and Kupfer, Robert and Troschitz, Juliane and Gude, Maik}}, issn = {{1435-4934}}, journal = {{e-Journal of Nondestructive Testing}}, number = {{12}}, publisher = {{NDT.net}}, title = {{{Approach to Determine the Characteristic Dimensions of Clinched Joints by Industrial X-ray Computed Tomography}}}, doi = {{10.58286/27519}}, volume = {{27}}, year = {{2022}}, } @inproceedings{51191, abstract = {{Zur Qualitätssicherung von Clinchpunkten werden häufig ex-situ Methoden, wie etwa Schliffbildanalysen, eingesetzt. Diese ermöglichen jedoch nicht die Berücksichtigung von Phänomenen, die während der Belastung auftreten, da sich nach der Entlastung elastische Deformationen zurückbilden und Risse wieder schließen. Dagegen kann mit der in-situ Computertomographie (CT) der innere Deformationszustand des Clinchpunkts, z.B. während eines Scherzugversuchs, untersucht werden. Hierbei ist es für artgleiche Werkstoffe aufgrund der hohen Pressungen im Clinchpunkt schwierig, die Trennfläche zwischen den Fügepartnern im CT-Scan zu erkennen. Daher wird eine radioopake Zwischenschicht aus Zinn in die Trennfläche eingebracht. In dieser Arbeit wird der Einfluss der Zwischenschicht auf die in-situ CT-Scherzugprüfung untersucht. Hierzu werden sowohl Kraft-Verlängerungs-Kurven als auch die Geometrie der Clinchpunkte während der Belastung verglichen.}}, author = {{Köhler, Daniel and Kupfer, Robert and Troschitz, Juliane and Gude, Maik}}, booktitle = {{Tagungsband zur Werkstoffprüfung 2022}}, editor = {{Zimmermann, Martina}}, location = {{Dresden}}, title = {{{Untersuchung zum Einfluss radioopaker Zwischenschichten bei der in-situ CT geclinchter Verbindungen}}}, year = {{2022}}, } @inbook{51195, author = {{Köhler, Daniel and Kupfer, Robert and Troschitz, Juliane and Gude, Maik}}, booktitle = {{The Minerals, Metals & Materials Series}}, isbn = {{9783031062117}}, issn = {{2367-1181}}, publisher = {{Springer International Publishing}}, title = {{{Clinching in In Situ CT—A Novel Validation Method for Mechanical Joining Processes}}}, doi = {{10.1007/978-3-031-06212-4_75}}, year = {{2022}}, } @article{51197, abstract = {{Clinching is a cost efficient method for joining components in series production. To assure the clinch point’s quality, the force displacement curve during clinching or the bottom thickness are monitored. The most significant geometrical characteristics of the clinch point, neck thickness and undercut, are usually tested destructively by microsectioning. However, micrograph preparation goes ahead with a resetting of elastic deformations and crack-closing after unloading. To generate a comprehensive knowledge of the clinch point’s inner geometry under load, in-situ computed tomography (CT) and acoustic testing (TDA) can be combined. While the TDA is highly sensitive to the inner state of the clinch point, it could detect critical events like crack development during loading. If such events are indicated, the loading process is stopped and a stepped in-situ CT of the following crack and deformation development is performed. In this paper, the concept is applied to the process of clinching itself, providing a detailed three-dimensional insight in the development of the joining zone. A test set-up is used which allows a stepwise clinching of two aluminium sheets EN AW 6014. Furthermore, this set-up is positioned within a CT system. In order to minimize X-ray absorption, a beryllium cylinder is used within the set-up frame and clinching tools are made from Si3N4. The actuator and sensor necessary for the TDA are integrated in the set-up. In regular process steps, the clinching process is interrupted in order to perform a TDA and a CT scan. In order to enhance the visibility of the interface, a thin tin layer is positioned between the sheets prior clinching. It is shown, that the test-set up allows a monitoring of the dynamic behaviour of the specimen during clinching while the CT scans visualize the inner geometry and material flow non-destructively.}}, author = {{Köhler, Daniel and Stephan, Richard and Kupfer, Robert and Troschitz, Juliane and Brosius, Alexander and Gude, Maik}}, issn = {{1662-9795}}, journal = {{Key Engineering Materials}}, keywords = {{Mechanical Engineering, Mechanics of Materials, General Materials Science}}, pages = {{1489--1497}}, publisher = {{Trans Tech Publications, Ltd.}}, title = {{{Investigations on Combined <i>In Situ</i> CT and Acoustic Analysis during Clinching}}}, doi = {{10.4028/p-32330d}}, volume = {{926}}, year = {{2022}}, } @article{30659, abstract = {{In lightweight design, clinching is a cost-efficient solution as the joint is created through localized cold-forming of the joining parts. A clinch point’s quality is usually assessed using ex-situ destructive testing methods. These, however, are unable to detect phenomena immediately during the joining process. For instance, elastic deformations reverse and cracks close after unloading. In-situ methods such as the force-displacement evaluation are used to control a clinching process, though deviations in the clinch point geometry cannot be derived with this method. To overcome these limitations, the clinching process can be investigated using in-situ computed tomography (in-situ CT). However, a clinching tool made of steel would cause strong artefacts and a high attenuation in the CT measurement, reducing the significance of this method. Additionally, when joining parts of the same material, the sheet-sheet interface is hardly detectable. This work aims at identifying, firstly, tool materials that allow artefact-reduced CT measurements during clinching, and, secondly, radiopaque materials that can be applied between the joining parts to enhance the detectability of the sheet-sheet interface. Therefore, both CT-suitable tool materials and radiopaque materials are selected and experimentally investigated. In the clinching process, two aluminium sheets with radiopaque material in between are clinched in a single-step (rotationally symmetric joint without cut section). It is shown that e.g. silicon nitride is suited as tool material and a tin layer is suitable to enhance the detectability of the sheet-sheet interface. }}, author = {{Köhler, D. and Kupfer, R. and Troschitz, J. and Gude, M.}}, journal = {{ESAFORM 2021}}, title = {{{Clinching in In-situ CT – Experimental Study on Suitable Tool Materials}}}, doi = {{10.25518/esaform21.2781}}, year = {{2021}}, } @article{30661, abstract = {{As lightweight design gains more and more attention, time and cost-efficient joining methods such as clinching are becoming more popular. A clinch point’s quality is usually determined by ex situ destructive analyses such as microsectioning. However, these methods do not yield the detection of phenomena occurring during loading such as elastic deformations and cracks that close after unloading. Alternatively, in situ computed tomography (in situ CT) can be used to investigate the loading process of clinch points. In this paper, a method for in situ CT analysis of a single-lap shear test with clinched metal sheets is presented at the example of a clinched joint with two 2 mm thick aluminum sheets. Furthermore, the potential of this method to validate numerical simulations is shown. Since the sheets’ surfaces are locally in contact with each other, the interface between both aluminum sheets and therefore the exact contour of the joining partners is difficult to identify in CT analyses. To compensate for this, the application of copper varnish between the sheets is investigated. The best in situ CT results are achieved with both sheets treated. It showed that with this treatment, in situ CT is suitable to properly observe the three-dimensional deformation behavior and to identify the failure modes.}}, author = {{Köhler, D. and Kupfer, R. and Troschitz, J. and Gude, M.}}, journal = {{Materials}}, pages = {{1859}}, title = {{{In Situ Computed Tomography—Analysis of a Single-Lap Shear Test with Clinch Points}}}, doi = {{10.3390/ma14081859}}, volume = {{14}}, year = {{2021}}, } @article{30698, author = {{Gröger, B. and Köhler, D. and Vorderbrüggen, J. and Troschitz, J. and Kupfer, R. and Meschut, G. and Gude, M.}}, journal = {{Production Engineering}}, title = {{{Computed tomography investigation of the material structure in clinch joints in aluminium fibre-reinforced thermoplastic sheets}}}, doi = {{10.1007/s11740-021-01091-x}}, year = {{2021}}, } @article{30697, author = {{Lafarge, R. and Wolf, A. and Guilleaume, C. and Brosius, A.}}, journal = {{Minerals, Metals and Materials Series}}, pages = {{1461}}, title = {{{A New Non-destructive Testing Method Applied to Clinching}}}, doi = {{10.1007/978-3-030-75381-8_121}}, year = {{2021}}, } @article{30683, abstract = {{When joining lightweight parts of various materials, clinching is a cost efficient solution. In a production line, the quality of a clinch point is primarily controlled by measurement of dimensions, which are accessible from outside. However, methods such as visual testing and measuring the bottom thickness as well as the outer diameter are not able to deliver any information about the most significant geometrical characteristic of the clinch point, neck thickness and undercut. Furthermore, ex-situ destructive methods such as microsectioning cannot detect elastic deformations and cracks that close after unloading. In order to exceed the current limits, a new non-destructive in-situ testing method for the clinching process is necessary. This work proposes a concept to characterize clinch points in-situ by combining two complementary non-destructive methods, namely, computed tomography (CT) and ultrasonic testing. Firstly, clinch points with different geometrical characteristics are analysed experimentally using ex-situ CT to get a highly spatially resolved 3D-image of the object. In this context, highly X-ray attenuating materials enhancing the visibility of the sheet-sheet interface are investigated. Secondly, the test specimens are modelled using finite element method (FEM) and a transient dynamic analysis (TDA) is conducted to study the effect of the geometrical differences on the deformation energy and to qualify the TDA as a fast in-situ non-destructive method for characterizing clinch points at high temporal resolution. }}, author = {{Köhler, D. and Sadeghian, B. and Kupfer, R. and Troschitz, J. and Gude, M. and Brosius, A.}}, journal = {{Key Engineering Materials}}, pages = {{89--96}}, title = {{{A Method for Characterization of Geometric Deviations in Clinch Points with Computed Tomography and Transient Dynamic Analysis}}}, doi = {{10.4028/www.scientific.net/kem.883.89}}, volume = {{883}}, year = {{2021}}, } @article{51202, abstract = {{When joining lightweight parts of various materials, clinching is a cost efficient solution. In a production line, the quality of a clinch point is primarily controlled by measurement of dimensions, which are accessible from outside. However, methods such as visual testing and measuring the bottom thickness as well as the outer diameter are not able to deliver any information about the most significant geometrical characteristic of the clinch point, neck thickness and undercut. Furthermore, ex-situ destructive methods such as microsectioning cannot detect elastic deformations and cracks that close after unloading. In order to exceed the current limits, a new non-destructive in-situ testing method for the clinching process is necessary. This work proposes a concept to characterize clinch points in-situ by combining two complementary non-destructive methods, namely, computed tomography (CT) and ultrasonic testing. Firstly, clinch points with different geometrical characteristics are analysed experimentally using ex-situ CT to get a highly spatially resolved 3D-image of the object. In this context, highly X-ray attenuating materials enhancing the visibility of the sheet-sheet interface are investigated. Secondly, the test specimens are modelled using finite element method (FEM) and a transient dynamic analysis (TDA) is conducted to study the effect of the geometrical differences on the deformation energy and to qualify the TDA as a fast in-situ non-destructive method for characterizing clinch points at high temporal resolution.}}, author = {{Köhler, Daniel and Sadeghian, Behdad and Kupfer, Robert and Troschitz, Juliane and Gude, Maik and Brosius, Alexander}}, issn = {{1662-9795}}, journal = {{Key Engineering Materials}}, keywords = {{Mechanical Engineering, Mechanics of Materials, General Materials Science}}, pages = {{89--96}}, publisher = {{Trans Tech Publications, Ltd.}}, title = {{{A Method for Characterization of Geometric Deviations in Clinch Points with Computed Tomography and Transient Dynamic Analysis}}}, doi = {{10.4028/www.scientific.net/kem.883.89}}, volume = {{883}}, year = {{2021}}, } @article{51199, abstract = {{AbstractRecent developments in automotive and aircraft industry towards a multi-material design pose challenges for modern joining technologies due to different mechanical properties and material compositions of various materials such as composites and metals. Therefore, mechanical joining technologies like clinching are in the focus of current research activities. For multi-material joints of metals and thermoplastic composites thermally assisted clinching processes with advanced tool concepts are well developed. The material-specific properties of fibre-reinforced thermoplastics have a significant influence on the joining process and the resulting material structure in the joining zone. For this reason, it is important to investigate these influences in detail and to understand the phenomena occurring during the joining process. Additionally, this provides the basis for a validation of a numerical simulation of such joining processes. In this paper, the material structure in a joint resulting from a thermally assisted clinching process is investigated. The joining partners are an aluminium sheet and a thermoplastic composite (organo sheet). Using computed tomography enables a three-dimensional investigation that allows a detailed analysis of the phenomena in different joining stages and in the material structure of the finished joint. Consequently, this study provides a more detailed understanding of the material behavior of thermoplastic composites during thermally assisted clinching.}}, author = {{Gröger, Benjamin and Köhler, Daniel and Vorderbrüggen, Julian and Troschitz, Juliane and Kupfer, Robert and Meschut, Gerson and Gude, Maik}}, issn = {{0944-6524}}, journal = {{Production Engineering}}, keywords = {{Industrial and Manufacturing Engineering, Mechanical Engineering}}, number = {{2-3}}, pages = {{203--212}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Computed tomography investigation of the material structure in clinch joints in aluminium fibre-reinforced thermoplastic sheets}}}, doi = {{10.1007/s11740-021-01091-x}}, volume = {{16}}, year = {{2021}}, } @article{51200, abstract = {{As lightweight design gains more and more attention, time and cost-efficient joining methods such as clinching are becoming more popular. A clinch point’s quality is usually determined by ex situ destructive analyses such as microsectioning. However, these methods do not yield the detection of phenomena occurring during loading such as elastic deformations and cracks that close after unloading. Alternatively, in situ computed tomography (in situ CT) can be used to investigate the loading process of clinch points. In this paper, a method for in situ CT analysis of a single-lap shear test with clinched metal sheets is presented at the example of a clinched joint with two 2 mm thick aluminum sheets. Furthermore, the potential of this method to validate numerical simulations is shown. Since the sheets’ surfaces are locally in contact with each other, the interface between both aluminum sheets and therefore the exact contour of the joining partners is difficult to identify in CT analyses. To compensate for this, the application of copper varnish between the sheets is investigated. The best in situ CT results are achieved with both sheets treated. It showed that with this treatment, in situ CT is suitable to properly observe the three-dimensional deformation behavior and to identify the failure modes.}}, author = {{Köhler, Daniel and Kupfer, Robert and Troschitz, Juliane and Gude, Maik}}, issn = {{1996-1944}}, journal = {{Materials}}, keywords = {{General Materials Science}}, number = {{8}}, publisher = {{MDPI AG}}, title = {{{In Situ Computed Tomography—Analysis of a Single-Lap Shear Test with Clinch Points}}}, doi = {{10.3390/ma14081859}}, volume = {{14}}, year = {{2021}}, } @article{51201, abstract = {{In lightweight design, clinching is a cost-efficient solution as the joint is created through localized cold-forming of the joining parts. A clinch point’s quality is usually assessed using ex-situ destructive testing methods. These, however, are unable to detect phenomena immediately during the joining process. For instance, elastic deformations reverse and cracks close after unloading. In-situ methods such as the force-displacement evaluation are used to control a clinching process, though deviations in the clinch point geometry cannot be derived with this method. To overcome these limitations, the clinching process can be investigated using in-situ computed tomography (in-situ CT). However, a clinching tool made of steel would cause strong artefacts and a high attenuation in the CT measurement, reducing the significance of this method. Additionally, when joining parts of the same material, the sheet-sheet interface is hardly detectable. This work aims at identifying, firstly, tool materials that allow artefact-reduced CT measurements during clinching, and, secondly, radiopaque materials that can be applied between the joining parts to enhance the detectability of the sheet-sheet interface. Therefore, both CT-suitable tool materials and radiopaque materials are selected and experimentally investigated. In the clinching process, two aluminium sheets with radiopaque material in between are clinched in a single-step (rotationally symmetric joint without cut section). It is shown that e.g. silicon nitride is suited as tool material and a tin layer is suitable to enhance the detectability of the sheet-sheet interface.}}, author = {{Köhler, Daniel and Kupfer, Robert and Troschitz, Juliane and Gude, Maik}}, journal = {{ESAFORM 2021}}, publisher = {{University of Liege}}, title = {{{Clinching in In-situ CT – Experimental Study on Suitable Tool Materials}}}, doi = {{10.25518/esaform21.2781}}, year = {{2021}}, } @article{51198, author = {{Köhler, D. and Sadeghian, B. and Troschitz, J. and Kupfer, R. and Gude, M. and Brosius, A.}}, issn = {{2666-3309}}, journal = {{Journal of Advanced Joining Processes}}, keywords = {{Mechanical Engineering, Mechanics of Materials, Engineering (miscellaneous), Chemical Engineering (miscellaneous)}}, publisher = {{Elsevier BV}}, title = {{{Characterisation of lateral offsets in clinch points with computed tomography and transient dynamic analysis}}}, doi = {{10.1016/j.jajp.2021.100089}}, volume = {{5}}, year = {{2021}}, } @article{30707, author = {{Sadeghian, B. and Guilleaume, C. and Lafarge, R. and Brosius, A.}}, journal = {{Lecture Notes in Production Engineering}}, pages = {{116--124}}, title = {{{Investigation of Clinched Joints – A Finite Element Simulation of a Non-destructive Approach}}}, doi = {{10.1007/978-3-662-62138-7_12}}, year = {{2020}}, } @article{30712, author = {{Köhler, D. and Gröger, B. and Kupfer, R. and Hornig, A. and Gude, M.}}, journal = {{Procedia Manufacturing}}, pages = {{940--947}}, title = {{{Experimental and Numerical Studies on the Deformation of a Flexible Wire in an Injection Moulding Process}}}, doi = {{10.1016/j.promfg.2020.04.288}}, volume = {{47}}, year = {{2020}}, } @article{30709, author = {{Köhler, D. and Kupfer, R. and Gude, M.}}, journal = {{Journal of Advanced Joining Processes}}, pages = {{100034}}, title = {{{Clinching in in-situ CT—A numerical study on suitable tool materials}}}, doi = {{10.1016/j.jajp.2020.100034}}, volume = {{2}}, year = {{2020}}, }