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Janna Hofmann, M.Sc.

Chief Engineer Electric Mobility
department: Machines, Equipment and Process Automation
office hours: To be agreed
room: 014, Geb. 50.36
phone: +49 1523 9502584
fax: +49 721 608 28284
Janna HofmannRvz9∂kit edu

Campus Süd



Janna Hofmann, M.Sc.

Area of Research:

 

General Tasks:

  • Contact wbk Alumni Club

 

Projects:

  • ProMoS - Umformtechnisch unterlagerte Prozessmodellierung des Linearspulenwickelprozesses
  • NeWwire - Neuartige serienflexible Wickelverfahren für die wirtschaftliche automatisierte Fertigung von hoch performanten elektrischen Maschine
  • PoLiS - Energy Storage beyond Lithium

 

Test benches:

 

Lebenslauf:

since 12/2017 Group leader for electric mobility in research group Machines, Equipment and Process Automation (MAP)
since 09/2015 Research Associate at the Institute of Production Science (wbk) at Karlsruhe Institute of Technology (KIT)
2009 - 2015 Study of mechanical engineering at Karlsruhe Institute of Technology

 

Publications

[ 1 ] Sell-Le Blanc, F.; Hofmann, J.; Simmler, R. & Fleischer, J. (2016), "Coil winding process modelling with deformation based wire tension analysis", CIRP Annals - Manufacturing Technology, vol. 1, pp. 65-68. 10.1016/j.cirp.2016.04.037
Abstract:
For electric motors, the stator designs with tooth coils are predominant. Due to their noncircular shape, the tooth coils display a challenge for highly productive winding processes with a low coil resistance. With the use of a process model a prediction of the central process parameters, like the wire tension, can be achieved. This model consists of a wire deformation based multi-body-dynamic simulation, measurements and analytic model aspects which were validated at a test stand. It can be used to optimize controller and actuator designs for wire tension control systems and enables higher winding speeds and winding quality.

[ 2 ] Hofmann, J. & Urban, N. (2016), "Industrie 4.0 im Elekromaschinenbau", industrieanzeiger, pp. 28-29.
Abstract:
Auf der Hannover Messe 2016 wurde das Leitthema „Industrie 4.0“ durch zahlreiche Aussteller mit ihren Show-Cases eindrucksvoll repräsentiert. So war es nicht verwunderlich, dass auch bei vielen Herstellern elektrischer Antriebstechnik im Rahmen der Leitmesse Industrial Automation ein Fokus auf diesem Themengebiet lag.

[ 3 ] Hofmann, J.; Sell-Le Blanc, F.; Krause, M.; Wirth, F. & Fleischer, J. (2016), "Simulation of the Assembly Process of the Insert Technique for Distributed Windings". Proceedings of 6th International Electric Drives Production Conference (E|DPC), eds. IEEE, pp. 144-148.
Abstract:
As the efficiency of electric power trains in hybrid electric vehicles should be increased and at the same time the manufacturing costs reduced, different motor designs and production concepts need to be considered. Because of the nearly sinusoidal magnetic field inside, the stator design with distributed windings, which is typically produced with the insert technique, is technically preferred. The insert technique offers a high productivity because the complete winding assembling process can be done in one step. This results in the fact, that nearly 80% of all electric motors worldwide have distributed windings. In order to enhance the possibilities for distributed windings with the insert technique, the current fill factor needs to be improved. Due to the fact that the actual wire placement cannot be measured und thus not optimized, a simulative approach with a multi-body simulation is used to understand the process interactions between the wires, the stator groove and the tool. This approach will be presented in this paper.

[ 4 ] Fleischer, J.; Haag, S. & Hofmann, J. (2017), "Quo Vadis Wickeltechnik?". Eine Studie zum aktuellen Stand der Technik und zur Recherche zukünftiger Trends im Automobilbau.
Abstract:
Die Elektromobilität hat nicht zuletzt durch die hohen Klimaziele der Bundesregierung und die jüngsten Abgasskandale deutscher OEMs sowie den damit verbundenen strategischen Neuausrichtungen hin zu vollelektrischen Fahrzeugen in hohen Stückzahlen eine intensive und dynamische Entwicklung angenommen. Dabei wird sich mit steigender Zahl der zu produzierenden Elektrofahrzeuge sowohl der Zulieferermarkt als auch der Herstellermarkt in den nächsten zehn Jahren stark wandeln. Die Kernkomponente des konventionellen Antriebsstranges – der Verbrennungsmotor – wird dabei durch einen oder mehrere Elektromotoren ersetzt bzw. ergänzt. Elektromotoren werden seit über 100 Jahren für die unterschiedlichsten Anwendungsfelder in Industrie und Konsumprodukten gefertigt. Allerdings stehen die Hersteller der Komponenten eines E-Motors als Traktionsantrieb für PKWs völlig neuen Herausforderungen gegenüber, wie beispielsweise den hohen Anforderungen an die Qualität der Wicklung und der Isolation sowie kurze Taktzeiten, wie sie für konventionelle Antriebsaggregate heutzutage üblich sind. Im Rahmen dieser Studie soll zuerst ein qualitativer Überblick und Vergleich der PKW-Antriebs Antriebskonzepte und den dort eingesetzten Motoren gegeben werden. Daraus abgeleitet werden die unterschiedlichen Rotor- und Statordesigns im Zusammenhang mit verschiedenen Antriebskonzepten vorgestellt. Hierbei soll beispielhaft aufgezeigt werden, welche Fahrzeugkonzepte und damit einhergehend welche Vielfalt an Elektromotoren in den aktuellen elektrischen Antriebssträngen vorherrscht. Im zweiten Teil der Studie soll darauf aufbauend die Produktion der Wicklung - als Kernkomponente des felderzeugenden Stators – näher betrachtet werden. So werden die Kernkompetenzen zur Herstellung von Wicklungen sowie die produktspezifischen Anforderungen an die Wicklungen aufgezeigt, um die Herausforderungen und Ansätze zur Fertigung dieser abzuleiten.

[ 5 ] Hofmann, J.; Flohr, L.; Kistner, J. & Fleischer, J. (2017), "Drahtschwingungen beim Linearspulenwickeln", Draht, vol. 2, pp. 1-4.
Abstract:
Drahtschwingungen sind ein Resultat der schwankenden Drahtzugkraft beim Linearspulenwickelprozess von rechteckigen Statorspulen. Um diese ausregeln zu können, müssen sie zuvor analytisch beschrieben werden. Der vorliegende Beitrag zeigt Methoden, die Drahtschwingungen zu untersuchen und zu validieren.

[ 6 ] Hofmann, J.; Bold, B.; Baum, C. & Fleischer, J. (2017), "Investigations on the Tensile Force at the Multi-Wire Needle Winding Process". Proceedings of 2017 7th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1-6.
Abstract:
The electric motor is the main component in an electrical vehicle. Its power density is directly influenced by the winding. For this reason, it is relevant to investigate the influences of coil production on the quality of the stator. The examined stator in this article is wound with the multi-wire needle winding technique. With this method, the placing of the wires can be precisely guided leading to small winding heads. To gain a high winding quality with small winding resistances, the control of the tensile force during the winding process is essential. The influence of the tensile force on the winding resistance during the winding process with the multiple needle winding technique will be presented here. To control the tensile force during the winding process, the stress on the wire during the winding process needs to be examined first. Thus a model will be presented to investigate the tensile force which realizes a coupling between the multibody dynamics simulation and the finite element methods with the software COMSOL Multiphysics®. With the results of the simulation, a new winding-trajectory based wire tension control can be implemented. Therefore, new strategies to control the tensile force during the process using a CAD/CAM approach will be presented in this paper.

[ 7 ] Storz, T.; Altvater, A.; Hofmann, J.; Scharfer, P.; Fleischer, J. & Schabel, W. (2018), "The Smart Battery Maker – a concept for automated flexible and agile production of cells". Tagungsband zur International Battery Production Conference (IBPC) 2018, eds. Prof. Dr.-Ing. Arno Kwade, pp. 18-19.
Abstract:
Present day battery production happens almost exclusively in large production lines where each machine is responsible for one step in the process chain. This results in low cycle time and low production costs per unit, but also in a largely inflexible production. With an increasing number of different applications and electric vehicle models, requirements for the battery systems and each battery cell varies in size and materials used. To test and judge the performance of a novel battery cell type before going into production, research and performance tests on ready-to-use batteries are inevitable. Prototypes are usually assembled manually at high costs, with no possibility to scale up their production and with typically low reproducibility. To handle this problem, a „Smart Battery Maker“ (SBM) pilot equipment, which produces battery cells with varying dimensions and materials, is being developed. The goals of the SBM are the proof of concept of fully automated prototype machinery that executes various production steps with a high reproducibility and the adaption of cell production steps to agile manufacturing. Different-sized pouch-cells are to be manufactured by the SBM equipment in small batches under industrial production conditions with minimal change of tools or equipment. To achieve this goal, the partners, namely KIT (wbk, TVT-TFT, IAM-ESS) and Fraunhofer ICT, will agree on different electrode and separator materials as well as different cell formats to be processed. The processability and reproducibility of overall production processes with the considered materials and cell formats have to be checked and verified. A prototype coating equipment for agile electrode production will be designed and built, as well as a compact robot cell that handles the production steps of single-sheet stacking, contacting and pre-sealing. To prevent any unwanted interactions with water, a dry room atmosphere and microenvironments will be considered for cell assembly. Electrode and separator sheets will be delivered to the SBM robot cell by a novel material transportation system that guarantees a protective microenvironment throughout transportation. Potential safety risks will be identified and quantified to ensure lawful operation. Quality assurance regarding reproducibility, safety and overall battery cell quality will be implemented. This includes a Failure Mode and Effects Analysis of all considered processes. Furthermore, the battery cells produced by the SBM will be tested on electro-thermal stability and will be compared to commercially available Lithium-Ion battery cells (e.g. by EUCAR Hazard Levels). By validating the SBM pilot equipment, the partners prepare the ground for a possible adoption of this agile concept by the battery cell industry. Production scale-up is easily manageable by using multiple robot cells, flexibility is given by the possibility to quickly adapt each equipment to different cell dimensions and materials.

[ 8 ] Weinmann, H.; Lang, F.; Hofmann, J. & Fleischer, J. (2018), "Bahnzugkraftregelung in der Batteriezellfertigung", wt Werkstattstechnik online, pp. 519-524.
Abstract:
Viele Maschinen- und Materialparameter sind für die Qualität eines Elektroden-Einzelblattes verantwortlich. Relevant für Vereinzelung und Stapelbildung ist etwa die Bahnzugkraft, mit der die Elektrodenbahn während des Stanzvorgangs beaufschlagt wird. Diese wurde in der Versuchsanlage des wbk Institut für Produktionstechnik regelbar ausgeführt, um Zusammenhänge bei der Einzelblattstapelbildung zu untersuchen. Dieser Artikel stellt Auswahl und Funktion sowie die Integration der Lösung in die Versuchsanlage und die Auswirkung verschiedener Bahnzugkräfte auf die Maßhaltigkeit der gestanzten Einzelblätter vor.

[ 9 ] Komodromos, A.; Tekkaya, E.; Hofmann, J. & Fleischer, J. (2018), "Experimental and numerical investigations of wire bending by linear winding of rectangular tooth coils". Proceedings of the 21st international ESAFORM , eds. AIP Conference Proceedings, pp. 1-6.
Abstract:
Since electric motors are becoming more important in many application fields, e. g. hybrid electric vehicles, the optimization of the linear coil winding process is an important contribution to a higher productivity and flexibility. For the investigation of the forming behavior of the winding wire the material behavior is characterized in different experimental setups using wire diameters of 0.63 mm – 3.35 mm. Numerical investigations of the linear winding process in a case study for a rectangular bobbin are carried out in order to analyze the influence forming parameters have on the resulting properties of the wound coil. Besides the numerical investigation of the linear winding method by the finite element method, a combined simulation of FEM and multi-body dynamics is carried out. The simulation is implemented by coupling the multi-body dynamics with the finite element method using the software COMSOL Multiphysics®. The multi-body dynamics is necessary to represent the movement of the bodies as well as the connection of the components during winding. The finite element method is used to represent the material behavior of the copper wire and the contact conditions. Finally, the numerical investigations are validated experimentally by bending and linear winding tests.

[ 10 ] Halwas, M.; Hofmann, J.; Fleischer, J.; Riehm, C.; Spieker, C.; Fister, M.; Stoehr, G.; Wist, A.; Sell-Le Blanc, F.; Weiße, L.; Jovanovski, J. & Kehl, N. (2018), "Entwicklung eines parallelen Technologie- und Produktentwicklungsprozesses", wt Werkstattstechnik online, no. 5, pp. 301-306. [29.05.18].
Abstract:
In dem folgenden Artikel wird die parallele Technologie- und Produktentwicklung am Beispiel der Wicklungsauslegung und -fertigung beschrieben. Diese findet im Rahmen des Förderprojektes NeWwire (Neuartige serienflexible Wickelverfahren für die wirtschaftliche automatisierte Fertigung von hoch performanten elektrischen Maschinen) statt. Ziel des Forschungsprojekts NeWwire ist die Entwicklung sowie Auslegung eines neuartigen Wickelverfahrens zur automatisierten Fertigung von Elektromotoren im Hochleistungsbereich für den automobilen Einsatz. Hierbei stellt die effektive Wicklung im Stator zur Leistungssteigerung eine besondere Herausforderung dar.

[ 11 ] Preu, R.; Rein, S.; Zimmer, M.; Weinmann, H. W.; Hofmann, J. & Fleischer, J. (2018), "Digitalisierung bei der Produktion von Solar- und Batteriezellen". Die Energiewende – smart und digital, eds. FVEE ForschungsVerbund Erneuerbare Energien, pp. 0-0.
Abstract:
-

[ 12 ] Hofmann, J.; Komodromos, A.; Fleischer, J. & Tekkaya, E. (2018), "Optimization of the Linear Coil Winding Process by Combining New Actuator Principles on the Basis of Wire Forming Analysis". Proceedings of 2018 8th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1-6.
Abstract:
Due to the electrification of the automotive drive train new challenges in production technology must be faced. One of the big challenges are the copper losses within the electric drive that can be reduced by an optimized layer structure of the winding on the coil. This paper is targeting an optimized linear coil winding process with a special focus on the first layer which is decisive for the quality of the following layers. Here, the forming influence of the wire during winding on the bobbin is examined in particular. Crucial parameters in this context are the change in diameter through bending and the development of the clearance between wire and coil bobbin including their main influencing parameters. Especially the wire guide represents a machine element which influences the clearance negatively. This paper focuses on deriving critical process points from a process model and deriving forming strategies for controlling the winding process. For the first time, two actuator principles are combined to compensate the fluctuations in wire tensile force during winding and also to minimize the influence of the wire guide by moving it according to a FE simulation. Therefore, firstly the state of the art is analyzed and characterized in order to derive systematically the selection of the actuators and the control strategy. This is done in the context of achieving a higher efficiency of the electric motor through a deeper understanding of the forming process. On the one hand the integration of a fluidic muscle is serving as a compensation of the free wire length between the wire guide and the coil bobbin for a normalization of the wire tensile force. On the other hand, a piezo actuator is preventing the pre-deformation of the wire by the wire guide for keeping the clearance at a low level.

[ 13 ] Wirth, F.; Kirgör, T.; Hofmann, J. & Fleischer, J. (2018), "FE-Based Simulation of Hairpin Shaping Processes for Traction Drives". 2018 8th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1-5.
Abstract:
Based on the present change in mobility, there are novel requirements on production technologies of electric drives regarding process reliability, ability for automation, productivity as well as mechanical and electric filling factors. Providing significant advantages compared to conventional winding technologies, the hairpin technology combined with the usage of flat copper wire is a promising opportunity to fulfill the upcoming standards. Hence, the AnStaHa project aims the qualification of the hairpin technology for application in mass production. In spite of numerous advantages, the application of the hairpin technology also shows weaknesses. In particular, the shaping of hairpins is considerably more complex than corresponding process sequences of other winding technologies. The main reasons for this are the rectangular cross section and resulting directional properties of flat copper wires, significant springback effects as well as process-related damage of the wire insulation. Therefore, basic knowledge about the deformation behavior of the wire is required for process dimensioning within the context of system design. This paper handles the numerical simulation of hairpin shaping using the commercial finite element software suite Abaqus FEA. The FE-based approach is validated by experiments for different geometries and includes the complete forming process of hairpins, which is considered to be implemented in two following steps - U-bending and 3-D-shaping. Because the numerical analysis takes wire springback into account, the results can be used for a digital evaluation of hairpin shaping processes during the period of system design.

[ 14 ] Halwas, M.; Ambs, P.; Marsetz, M.; Baier, C.; Schigal, W.; Hofmann, J. & Fleischer, J. (2018), "Systematic Development and Comparison of Concepts for an Automated Series-Flexible Trickle Winding Process". 2018 8th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1-7.
Abstract:
The electrification of the automotive powertrain leads to new challenges for the production of electric drives. The resulting requirements for efficiency and power density of electric traction drives are currently not sufficiently fulfilled. The stator as an essential component of an electric drive generates the magnetic rotary field. By virtue of this effect the stator winding has a great influence on the performance and efficiency of an electric drive. The “NeWwire” project, as a starting point of this article, is concerned with the development and design of a novel automated winding process for the production of effective stator windings in order to achieve the required improvement in efficiency and performance. Therefore the so-called trickle winding process which is currently mainly carried out manually is to be automated. The goal is the reproducible filling of stator grooves with high copper fill factors in the shortest possible cycle times. To achieve this goal, concepts for suitable plants were developed with the help of the development method according to VDI 2221. At the beginning, the manual trickle winding process was divided into its sub-steps which were examined in detail. By following suitable analogies, solutions for an automated process were found. Finally, possible solution paths of the morphological box were combined to concept ideas. The main focus of the article is on the results of the systematic development steps. For this purpose, functional samples were produced in form of prototypes, their properties analyzed regarding the wire contribution and compared in several test series. The evaluation of these test series closes the main part of the paper.

[ 15 ] Wirth, F.; Hausmann, L.; Halwas, M.; Hofmann, J.; Mayer, D.; Wößner, W. & Fleischer, J. (2019), "Optimierte Fertigung elektrischer Traktionsmotoren durch Technologien der Industrie 4.0". Future Mobility: automatisiert - vernetzt - elektrisch, eds. Technische Akademie Esslingen e.V., pp. 1-14.
Abstract:
Striktere Emissionsvorgaben der Europäischen Union sowie die Endlichkeit fossiler Energieträger werden in der kommenden Dekade zu einem steigenden Absatz elektrifizierter Antriebsstränge führen. Damit die wachsende Nachfrage nach leistungsfähigen Traktionsmotoren sowie die hohen Anforderungen bezüglich Stückzahl und Qualität erfüllt werden können, müssen die innovativen aber vielmals noch unreifen Fertigungsprozesse für den industriellen Einsatz befähigt werden. Die Integration neuartiger Technologien der Industrie 4.0 in die Produktionskette stellt einen vielversprechenden Ansatz zur Lösung dieser Probleme dar. Durch eine digitale Prozessabsicherung können Wickelverfahren vor deren hardwareseitiger Erprobung bewertet und optimiert sowie Inbetriebnahmezeiten verkürzt werden. Zudem gestattet der digitale Zwilling sowohl eine prädiktive Prozesssteuerung als auch die isolierte Betrachtung von Einflussgrößen und darauf basierende Ableitung von Regelungsstrategien. Methoden des maschinellen Lernens und intelligente Algorithmen ermöglichen die Bewertung bislang unbekannter, produktseitiger Merkmale, wie den Lagenaufbau von Leitern in den Nuten von Blechpaketen, sowie die Einhaltung enger Qualitätsvorgaben durch angepasste Montagestrategien.

[ 16 ] Wirth, F.; Hofmann, J. & Fleischer, J. (2019), "Einfluss geometrischer Materialtoleranzen auf die werkzeuggebundene Formgebung und Eigenschaften von Hairpin-Steckspulen", www.umformtechnik.net, pp. 1-18.
Abstract:
Toleranzbedingte Schwankungen des Kupferflachdrahtes stellen eine wichtige Einflussgröße bei der Formgebung von Hairpin-Steckspulen für die Fertigung elektrischer Traktionsmotoren dar. Im vorliegenden Beitrag werden die Wechselwirkungen geometrischer Toleranzen mit den charakteristischen Eigenschaften und der Konturgenauigkeit von Hairpin-Steckspulen durch analytische und numerische Methoden am Beispiel einer werkzeuggebunden Formgebung systematisch untersucht.

[ 17 ] Hofmann, J. (2019), "Advances in electric drive production for e-mobility via the integration of digital assurance processes". Proceedings of CWIEME, eds. Hyve Group, pp. 1-13.
Abstract:
E-Motor & Powertrain Tech Talks Series: Advances in electric drive production for e-mobility via the integration of digital assurance processes; E-Motor & Powertrain Tech Talks Series: Advances in electric drive production for e-mobility via the integration of digital assurance processes;

[ 18 ] Hofmann, J.; Bolender, M.; Sun, P.; Fleischer, J.; Sell-Le Blanc, F. & Köhn, H. (2019), "CAD/CAM-Schnittstelle für die Wickeltechnik", wt online, pp. 611-616.
Abstract:
Durch die erhöhte Nachfrage an elektrischen Traktionsmotoren steigen die Anforderungen an die Produktionstechnik. Die Mehrachsnadelwickeltechnik spielt dabei eine wichtige Rolle, da sie es ermöglicht Vollblechschnittstatoren vollautomatisiert zu bewickeln. Die manuelle Erstellung eines NC-Programms nimmt viel Zeit in Anspruch, was eine kritische Hürde für den Prototypenbau darstellt. In diesem Beitrag wird eine CAD/CAM-Schnittstelle vorgestellt und validiert, die es erlaubt aus den CAD-Daten sowie dem Wickelschema automatisiert ein Wickelprogramm zu erstellen.

[ 19 ] Wößner, W.; Lorenz, M.; Hofmann, J.; Jux, B.; Langheck, A.; Doppelbauer, M. & Fleischer, J. (2019), "Unwucht hochausgenutzter Synchronmaschinen", ZWF Zeitschrift für wirtschaftlichen Fabrikbetrieb, vol. 114, pp. 464-468. https://www.hanser-elibrary.com/doi/10.3139/104.112127
Abstract:
In der Hochgeschwindigkeitsbearbeitung sowie der elektrifizierten Mobilität steigt die Bedeutung der Lebensdauer hochausgenutzter elektrischer Maschinen. Eine sich im Betrieb einstellende Änderung der Rotorunwucht kann diese deutlich verkürzen. Aktuelle Herausforderungen beim Auswuchten hochausgenutzter Synchronmaschinen werden daher vorgestellt. Die Relevanz dieser Problematik wird anhand einer Industriebefragung diskutiert und ein modellbasierter Lösungsansatz vorgestellt.

[ 20 ] Hausmann, L.; Wirth, F.; Franck, C.; Förderer, M.; Karrer, M.; Hofmann, J. & Fleischer, J. (2019), "Ausbildungsfabrik Statorfertigung", ZWF Zeitschrift für wirtschaftlichen Fabrikbetrieb, vol. 10, pp. 621-626.
Abstract:
The transformation process towards electric mobility results in new requirements for product development and production technology, which require the appropriate qualification of employees. In order to enable holistic further training, the wbk Institute for Production Engineering at KIT develops high-quality training concepts for the production of stators of electric traction drives by hairpin technology based on vocational pedagogical methods and integrates them into the overall concept of the training factory stator production.

[ 21 ] Hofmann, J.; Halwas, M.; Weinmann, H.; Wößner, W.; Schäfer, J.; Hausmann, L.; Wirth, F.; Storz, T. & Schild, L. (2019), "Transformationshub Elektromobilität in Baden-Württemberg" in Auf dem Weg zur Elektromobilität – Wettbewerbsfaktor Produktionstechnik , eds. Fleischer, J.; Lanza, G.; Schulze, V. & , ., Shaker, Berlin, pp. 1-29. ISBN/ISSN: 978-3-8440-6953-2
Abstract:
Die Automobilindustrie steckt in einem Transformationsprozess un-geahnten Ausmaßes und Ausgangs. Ob durch striktere europäische Abgasgrenzwerte, den Zwang lokaler Emissionsfreiheit oder den Druck des chinesischen Marktes beim Kampf um eine neue Vorherrschaftsrolle - die Gründe deutscher Automobilisten zur Elektrifizierung sind vielschichtig und die Folgen kaum abschätzbar. Die Frage, ob neue Antriebstechnologien in den Markt eingeführt wer-den, stellt sich mittlerweile kein Automobilhersteller mehr, stattdessen verbleibt die Frage nach dem „wie“. Mit der diesjährigen wbk Herbsttagung „Auf dem Weg zur Elektromobilität – Wettbewerbsfaktor Produktionstechnik“ wollen wir die vorhandenen Chancen im Bereich der Produktionstechnik für die Elektromobilität aufzeigen und einen Beitrag dazu leisten, dass diese auch genutzt werden. Hochkarätige Impulsvorträge aus Industrie und Forschung schaffen die Diskussionsbasis für einen Informationsaustausch zur Elektromobilität. Die wbk-Herbsttagung bietet dabei eine Plattform für den Dialog zwischen Politik, Anwendern, Produzenten, Anlagenbauern sowie dem wbk als Forschungspartner vor Ort.

[ 22 ] Schaefer, J.; Singer, R.; Hofmann, J. & Fleischer, J. (2019), "Challenges and solutions in automated disassembly and condition-based remanufacturing of lithium-ion battery modules for a circular economy". GCSM, eds. Elsevier, pp. 614-619.
Abstract:
This paper proposes a systematic approach for both, a remanufacturable battery module and an automated remanufacturing station. In the beginning the joints in a battery module are investigated and categorized, followed by an evaluation of alternatives. Based on the evaluation, a novel battery module and an automated remanufacturing station are presented. As a result, it is possible to replace an individual battery cell while maintaining the integrity of the battery module, leading to a value added product that can be brought back to market.

[ 23 ] Wößner, W.; Peter, M.; Hofmann, J. & Fleischer, J. (2019), "Model-based assembly optimization for unbalance-minimized production automation of electric motors". Advances in Production Research, eds. Schmitt, R. & Schuh, G., pp. 551-562.
Abstract:
Existing electric motors of higher power are optimized for driving stationary systems and are therefore generally too heavy, too large and too expensive for use in vehicles. New production processes are needed to ensure the cost efficient production of light-weight electric drives. This article presents an approach to reduce the rotor mass of permanently excited synchronous motors (PSM) by using a model-based optimized assembly procedure for rotor components. It aims to create savings in weight and winnings in dynamics by omitting the use of balancing discs that are usually needed to store mass for a costly balancing process. Investigations on two separate rotor designs are carried out to analyse whether the required balancing grade can be reached through an optimized assembly of the rotor components. For the first rotor design, an analysis of the unbalance state of all main rotor components (shaft, rotor discs and magnets) was carried out in order to validate the prediction of the resulting unbalance of the complete rotor. Improvement measures regarding the description of measuring and assembly deviations are listed and put into practice for the preparation of new investigations with a rotor design that sets higher demands to the desired residual rotor unbalance.

[ 24 ] Sell-Le Blanc, F.; Halwas, M.; Jäger, D.; Weiße, L.; Jovanski, J.; Kehl, N.; Hofmann, J. & Fleischer, J. (2019), "Feasibility Study for Enameled Round Copper Wire Compression within Slots of Electrical Machines". 2019 9th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1-9.
Abstract:
This paper discusses the compression of round magnet wires. The feasibility of forming operations within grooves of electrical machines after the winding process is investigated using a scientific methodology. This approach is motivated with the need for higher fill factors, comparable to the ones of hairpin technology. By using individual parallel conductors with higher number of turns, however, it is also possible to reduce frequency-dependent losses in higher drive speed ranges. In addition, the insulation layer quality for round wires is superior to the ones of profile wire due to the coating process, with the exception of extrusion insulations. This results in a better applicability of round wires for compression and higher voltage applications as well. At first, current state of technology is presented and applicable winding test procedures as well as a test setup is introduced. For experimental validation a model groove was designed and built. Possible groove design parameters are introduced and chosen according to a Design of Experiment approach (DoE). Different metrology approaches for the characterization of the insulation quality after processing and the resulting wire deformations are discussed. Significant input variables are pressing force, wire insulation thickness (measured in grades), number of turns per coil as well as wire diameter. Key output variables are the achieved fill factor improvement, the partial discharge voltage and the electrical resistance of the coil. The experimental plan, according to a full- factorial DoE, the chosen methodology and concluding results are being discussed based on main effect diagrams. In the outlook, the further investigation topics are outlined. It can be shown that the compression process of enameled round copper wires is well suited, up to a quality critical limit, for the production improvement of coils in grooves of electrical machines. The process therefore represents a promising approach to increase the fill factor, taking into account the electrical insulation properties of the winding. This first investigation can show that some electrical properties, such as partial discharge features, can even be improved in certain areas.

[ 25 ] Halwas, M.; Sell-Le Blanc, F.; Jux, B.; Doppelbauer, M.; Wirth, F.; Hausmann, L.; Hofmann, J. & Fleischer, J. (2019), "Coherences Between Production Technology and Performance of Electric Traction Drives". 2019 9th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1-9.
Abstract:
Coherences between production technology and performance of electric traction drives are published or based on experiential knowledge. The content of this paper shall represent an essential basis for intentions of improving future research and development purposes of production technologies for traction drives, but also of electric machine designs in general. The basic ambition of engineering a new manufacturing technology is to improve the performance of a product, taking several boundary conditions into account, like costs or cycle times. It has to be considered that the conflict area of production and performance are connected by physical characteristics, which are determined by the geometric and material compositions of the electric machine in this context. It is evident that the physical characteristics have a direct impact on the performance of electric machines. However, the production technology has a straight and unavoidable influence on the physical characteristic. An example for this is the slot fill factor, which is determined by the winding technology, but influences the performance of the machine significantly. First, known coherences between physical characteristics and performance of electric machines are considered. Therefore, an extensive summary of technical literature and publications at the current state of the art in science applications is used as a starting point. To give the best possible overview, a summary and visualization dependency matrix is created, in which the various elements of physical characteristic and the resulting performance of the electric machine are compared against each other. Next, the main influences of the different manufacturing processes on the characteristics of electric machines are presented, especially focusing on the winding technology. These contents are also transferred into the dependency matrix.

[ 26 ] Hofmann, J.; Blanc, F.; Wößner, W.; Vishnuram, E.; Köhn, H.; Lepold, A.; Weber, T.; Schüttler, T.; Busch, P. & Fleischer, J. (2019), "Development of a new model based servo-controlled wire tensile force control for stator winding applications". Proceedings of 2019 9th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1-6.
Abstract:
Due to the electrification of the automotive powertrain new challenges in production technology must be faced. For direct winding processes of non-circular bobbins, the control of the wire tensile force is crucial for the winding quality and displays one of the greatest challenges. Within this paper a new approach to control the tensile force along the winding trajectory will be introduced. As a first use case, the application of this approach for linear winding technology is presented. The potential of the model based servo-based wire tensile force control is demonstrated through systematic winding experiments. Since the control strategy does not solely rely on a measurement of the wire tensile force but also on the modeled behavior of the wire length, precision winding schemes can be achieved at significantly increased winding speeds. Secondly the transfer of this technology to the more complex multi axis needle winding kinematics will be presented. Finally the implementation of the control strategy in the needle winding machine will be shown and a validation with winding experiments is provided.

[ 27 ] Wößner, W.; Uhl, E.; Hofmann, J. & Fleischer, J. (2019), "Sensitivity Analysis and Validation of the Intelligent Assembly Process for Permanent Magnet Rotors with the Balancing Grade G 2.5". 2019 9th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 15-20.
Abstract:
An increased range of electric vehicles not only sets high demand to the chosen concept for energy storage but also implies that electric motors with high power-to-weight ratio need to be employed. A possible approach for weight reduction in a permanent magnet synchronous machine is an intelligent assembly of the rotor components followed by a positive balancing process. This approach allows to predict and minimize the rotor unbalance, resulting in a reduction in size of balancing discs that can account for up to 10 % of the rotor mass. A higher potential in reduction of the rotor mass lies in the ability to dispense entirely with balancing discs and the subsequent balancing process. This paper analyses whether a balancing grade of G 2.5 can be achieved through intelligent assembly. In a first step, the required measuring and mounting steps are presented. Possible measuring and mounting uncertainties are identified and quantified through literature, simulation and experimental results, allowing a sensitivity analysis of the entire process chain. The results of this analysis are used to identify the measuring and mounting steps with the highest influence on the deviation between an expected and measured rotor unbalance. For magnet assembly, a good model validity is achieved. Errors in perpendicularity between lamination stacks and shafts are found to have a high influence on the reachable rotor unbalance and therefore offer room for further improvement of the approach.

[ 28 ] Mayer, D.; Hausmann, L.; Maul, N.; Reinschmidt, L.; Hofmann, J. & Fleischer, J. (2019), "Systematic investigation of the grooving process and its influence on slot insulation of stators with hairpin technology". 9th International Electric Drives Production Conference (E|DPC) - Proceedings, eds. IEEE, pp. 161-167.
Abstract:
Due to the increasing electrification of the automotive drive train, production systems for electric motors grow in importance. In order to produce the required quantities at reasonable costs there is a particular need for developing new stator production plants. A trend towards using shaped coils in stators, so called hairpins, is emerging as this technology promises great automation potentials as well as high copper fill factors. Due to the axial insertion of the hairpins into the lamination stack the requirements for the slot liner shape change in contrast to the widely used winding technologies. Thus, new slot liner shapes, such as ‘B’-, ‘O’- or ‘S’-shapes, can be used. The shapes replace the previous ‘U’- shaped slot liner as well as the slot cover. In order to maintain a high fill factor, the shapes have to fit closely to the lamination stack. For this purpose, the insulation paper must be grooved and then folded into the desired shape. To map the new slot liner shapes, the grooving process and its influence on slot insulation must be understood in detail. In this paper the grooving process and its effect on breakdown voltage of the slot liner are examined. First, an overview about different insulation materials for slot liners is given. Second, a test rig setup to adjust different depths and widths of grooving is introduced. Additionally, a further test rig setup for conducting breakdown voltage tests on slot liners is presented. Based on these test rigs, experiments are carried out to determine how the grooving process parameters affect the breakdown voltage of the slot liners. As a result of the investigation a characterization of the grooving process regarding the breakdown voltage for the examined insulation paper is presented.

[ 29 ] Wirth, F.; Nguyen, C.; Hofmann, J. & Fleischer, J. (2020), "Characterization of Rectangular Copper Wire Forming Properties and Derivation of Control Concepts for the Kinematic Bending of Hairpin Coils". Procedia Manufacturing, eds. Elsevier Ltd., pp. 678-685.
Abstract:
As a result of the continuously growing demand for electric vehicles, innovative production technologies must be developed to fulfill the high automotive requirements for productivity and quality in the manufacturing of electric drives. By providing advantages regarding the degree of automation, the productivity as well as the attainable filling factors in comparison to established round wire winding technologies, the hairpin technology shows a high potential for meeting the requested specifications but also technological weaknesses, especially concerning the process reliability. The referring production process of stators is normally based on the spatial forming of open, hairpin-shaped coils of enameled flat copper wire as well as subsequent joining and contacting processes. Consequently, the hairpin coils represent the elementary components of the process chain and can be either shaped by robust tool-bound or flexible kinematic bending processes that enable the shaping of different contours at moderate tool costs. In this paper, the essential mechanical forming and product properties of flat copper wires with different dimensions and insulation coatings are characterized by means of uniaxial tensile tests as well as metallographic analyses of the material structure, at first. Subsequently, the identified forming properties are correlated to the applied manufacturing processes drawing, rolling as well as continuous extruding and considered as limits of possible material variations. To evaluate the effect of fluctuating wire qualities on the robustness of kinematic hairpin bending processes, the fabrication tolerances are analyzed by finite element simulations, using the example of elementary kinematic bending operations and modeled changes of the material properties. Based on the knowledge of material-based process tolerances, different control concepts for the kinematic bending of hairpin coils are derived and compared based on technical as well as economic aspects.