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M.Sc. Janna Hofmann

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 HofmannNff5∂kit edu

Campus Süd



M.Sc. Janna Hofmann

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

 

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 ] Weinmann, H. W.; 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.

[ 8 ] 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.

[ 9 ] 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.

[ 10 ] 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.

[ 11 ] 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.

[ 12 ] 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:
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[ 13 ] 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.

[ 14 ] 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.

[ 15 ] 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.

[ 16 ] 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.