Prof. Dr. Sandro Wartzack

Chair of Engineering Design, Department of Mechanical Engineering

Research and validation of processes, methods and tools to support the design of medical technologies and interventions.

Research projects

  • Biomechanical Engineering
  • Musculoskeletal Modeling and Simulation
  • Development of Exoskeletons and Ortheses
  • Preoperative Planning of Endosurgeries
  • Analysis and Optimization of User-Product-Interaction

  • OptNeTol: Integrated, optimization-based parameter and tolerance design

    (Third Party Funds Single)

    Term: 1. July 2021 - 31. December 2023
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)

    The usage of optimization methods for optimal tolerance allocation significantly contributes to the development of least-cost and high-quality products. By formulating suitable optimization problems and solving them with the aid of powerful algorithms, nominal dimensions and tolerance values can be allocated in a way that the cost potential is fully exploited while ensuring that the stringent requirements on robustness, function and aesthetics are fulfilled. In this way, optimization-based methods successively replace purely qualitative approaches, such as simple rules of thumb or well-known theorems like "define tolerances as wide as possible, but as tight as necessary", and thereby create an undisputed competitive advantage.

    In the preceding funding phase, an important basis for the productive use of tolerance optimization in the industrial environment was established. However, it cannot effectively contribute to answering practice-relevant questions yet. This is mainly due to the deficits of efficient, valid optimization methods, the missing link between the interdisciplinary methods and their lack of focus on practical problems.

    Therefore, the aim of this research project is to enable the product developer to assign cost-optimal part dimensions and tolerances to practically relevant application cases. This implies that the obstacles to the practical application of the interdisciplinary and at the same time highly specialized methods of nominal dimension and tolerance optimization are largely eliminated. In this context, innovative methods of nominal dimension and tolerance optimization are developed addressing aspects that have not been considered so far, but are absolutely necessary for practical use, such as geometrical tolerances or the handling of missing or uncertain cost information. However, since the optimization problems can only be solved by powerful, sampling-based optimization algorithms, the focus of this research project is also on the development and combination of methods to significantly increase the efficiency in the determination of valid optimization results, such as adaptive sampling and surrogate modelling, including statistical tolerance analysis methods. Finally, the individually developed methods will be linked in a software prototype based on a common, interdisciplinary knowledge base and their applicability will be evaluated in user studies. This ensures that product developers without in-depth knowledge of optimization are supported in defining and solving practical problems as automatically as possible. Thus, currently open research gaps preventing the change from an expert tool for mere tolerance optimization to an integrated, optimization-aided tolerance management are finally closed.

  • Hybrid Models for the Development of Technical Systems for Direct Interaction with Humans - Units with Power Tools and Upper Body Support Systems as an Example

    (Third Party Funds Single)

    Term: 1. November 2020 - 30. May 2023
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    The aim of the present research project is the development of a methodology for the development of wearable and hand-held technical systems, which are in close interaction with human beings. Systems in focus are both support systems that are parallel to the human body (e.g., exoskeletal systems) as well as systems acting serial to the human body (e.g., hand-held devices such as power tools). This methodology merges methods of use-case modelling, support systems, bio-mechanical models of the human body and multi-critical optimization algorithms. Through the combination and extension of common simulation approaches with bio-mechanical models of the human body arise hybrid models for the product development of exoskeletons and power tool, one parallel and one serial to the human body. This proposed research project enables, in contrast to today, the integrative development of exoskeletons and power tools regarding the focused use-cases. Currently, the direct combination of support-system and power tools happens to be challenging for the developer. Reasons are the consideration of the complex human anatomy, the correct choosing of harmless force introduction into the human body and especially the complex human motion patterns. The current approach of intuitive evaluation of boundary conditions regarding the user is experience based knowledge of experts and engineers familiar with the topic. An evaluation during development of support-system and power tool is yet not possible since final and wearable prototypes are required. The proposed methodology aims to close this gap by providing new hybrid models for the full support during design and a continuous evaluation of the developed support-system and power tool. Therefore, methods of use-case and human body modelling are merged to create these hybrid models through co-simulation. In this proposed research project, the methodology will be developed and evaluated for an upper-body support-system (exoskeleton) with an integrated wrench for the use case bolting above the head.
  • Wälzlagertoleranzen II - FVA736II

    (Third Party Funds Single)

    Term: 1. June 2020 - 30. November 2022
    Funding source: Bundesministerium für Wirtschaft und Technologie (BMWi)

    Mithilfe der Tolerierung sollen technologisch unvermeidbare geometrische Bauteilabweichungen so eingeschränkt werden, dass die Anforderungen an die Montierbarkeit, Funktionalität und Qualität der Produkte erfüllt werden können. Dabei hat das Toleranzmanagement aufgrund der hohen Kostenverantwortung eine enorme wirtschaftliche Relevanz. Zwar existieren Computer Aided Tolerancing (CAT) Softwarewerkzeuge, welche Konstrukteure bei der Bauteiltolerierung unterstützen. Diese Hilfsmittel erfordern für ihren gewinnbringenden Einsatz aber häufig eine zeit- und kostenintensive Ausbildung. Gängige CAT-Anwendungen sind zudem nicht geeignet, die komplexen Wirkzusammenhänge in Wälzlagersystemen abzubilden.

    Eine funktionsgerechte Auslegung von Wälzlagersystemen ist eine Grundvoraussetzung für die Zuverlässigkeit und Sicherheit technischer Systeme und trägt entscheidend zur Prognostizierbarkeit des Systemverhaltens bei. Ein wichtiger Aspekt bei der Auslegung von Wälzlagersystemen ist die Auswahl der Toleranz- und Lagerluftklasse des Lagers sowie die Tolerierung der Umgebungsbauteile. Für diese Aufgaben existieren zwar bereits einige Gestaltungsrichtlinien, diese haben sich jedoch trotz des technologischen Fortschritts seit mehreren Dekaden kaum verändert. Zudem ist teilweise nicht mehr bekannt, auf welcher Basis diese Gestaltungsrichtlinien erarbeitet wurden. Des Weiteren werden auch bei ihnen die komplexen Wirkzusammenhänge in Lagersystemen in der Regel nur stark vereinfacht abgebildet.Im vorliegenden Forschungsvorhaben wird eine einfach anzuwendende Methodik entwickelt, die sowohl die Komplexität der Wirkzusammenhänge in Wälzlagersystemen als auch die enormen Gestaltungsfreiheiten bei der Tolerierung von Wälzlagersystemen berücksichtigt.

  • Entwicklung und Validierung fortgeschrittener Analysemethoden für abweichungs-behaftete Wälzlagersysteme

    (Third Party Funds Single)

    Term: 1. June 2020 - 30. November 2022
    Funding source: Bundesministerium für Wirtschaft und Technologie (BMWi)
  • Customized Digital Engineering für bayerische KMU am Beispiel des Antriebsstrangs elektrischer Fahrzeuge

    (Third Party Funds Single)

    Term: 1. April 2020 - 31. March 2023
    Funding source: Bayerische Forschungsstiftung
  • Virtual and experimental tolerance analysis of deviated assembly groups

    (Third Party Funds Group – Sub project)

    Overall project: FOR 2271: Prozessorientiertes Toleranzmanagement mit virtuellen Absicherungsmethoden
    Term: 1. April 2020 - 31. March 2023
    Funding source: DFG / Forschergruppe (FOR)
    The aim of the research project is to enable a process-oriented tolerancing, which considers all geometric deviations and their various sources as well as measurement uncertainties, by providing the required methods and tools. In order to achieve this goal, particularly the research challenges regarding the best practice for process-oriented tolerance specification, regarding the integration of various kinds of geometric deviations in tolerance simulation models and regarding the use of tolerance simulation results for optimized tolerance allocation and process design are answered. The focus of the research project in the second funding period of the research unit is on the extension of the interdisciplinary process-oriented tolerance allocation with regard to the consideration of wear behavior during use. Here, the entire intended product use is virtually validated with tolerance management tools by not only taking into account process variations during product development, but also virtually mapping wear influences during operation in the simulation models. In order to validate the novel simulation models developed, experimental tolerance analysis are carried out on the test stand of the research unit, the results from which are compared with the virtual results. In addition, a tolerance optimization is to be carried out in order to meet specified quality targets over the product lifecycle while at the same time ensuring that production and measuring process-related restrictions are observed.Beside the development of virtual tools for the tolerance analysis and their validation, methods and best practices for the integrated and holistic tolerance management are provided, which consider the characteristic features of computer-aided engineering tools and which will be checked in cooperation with the partners of the research unit. Thus, the main benefit of the research project is a procedure for process-oriented tolerancing, which allows the holistic consideration of various kinds and sources of geometric deviations already during product development as well as the identification of relevant process and operating parameters. Based thereon, manufacturing and inspection processes can be systematically optimized, costs can be saved and the time-to-market can be shortened.
  • Machine Learned Dynamics – Berücksichtigung des dynamischen Verhaltens von Käfigen mittels maschinellen Lernens im Auslegungsprozess von Wälzlagerungen

    (Third Party Funds Single)

    Term: 1. March 2020 - 31. August 2022
    Funding source: Bayerische Forschungsstiftung

    Schwingungen können bei Wälzlagern zu einer Beeinflussung der Leistungsfähigkeit
    führen, wenn diese auf die Umgebung übertragen werden und Schäden hervorrufen.
    Damit die Dynamik des Wälzlagerkäfigs bewertet werden kann, sind rechenintensive
    Mehrkörpersimulationen notwendig, die nur von Expertinnen und Experten durchgeführt werden
    können. Ziel dieses Projektes ist eine einfache und zeiteffiziente Ermittlung des
    dynamischen Verhaltens von Wälzlagerkäfigen mithilfe von Machine Learning
    Algorithmen, die auf Basis von zahlreichen, validierten Mehrkörpersimulationen
    trainiert wurden. Die ermittelte Käfigdynamik kann anschließend zur Optimierung
    des Käfigs für den auszulegenden Lastfall hinsichtlich Kriterien wie Reibungs- oder
    Schwingungsverhalten verwendet werden. Aufgrund ihrer Rechenzeiteffizienz
    eignen sich solche Algorithmen für den Einsatz in Industrie 4.0 oder IoT.
    Zu Beginn des Projektes müssen alle relevanten Ein- und Ausgabeparameter für die
    Käfigauslegung wie beispielsweise Geometriemerkmale und die daraus resultierende
    Käfigdynamik identifiziert werden. Darauf aufbauend wird ein Simulationsplan
    erstellt, anhand dessen Zusammenhänge im Parameterraum untersucht werden können.
    Die Ergebnisse der anschließenden Mehrkörpersimulationen bilden die Datenbasis
    für das Machine Learning. Damit eine hochwertige Prognose des Algorithmus
    gewährleistet wird, folgt zuletzt eine Verifizierung anhand der Ergebnisse der
    Mehrkörpersimulation und eine Validierung anhand experimenteller Untersuchungen.

  • COFFEE - Collaborative Forgetting for Engineering Design

    (Third Party Funds Group – Sub project)

    Overall project: SPP 1921: Intentional Forgetting in Organisationen.Mechanismen des Vergessens als Anpassungsleistungen von Organisationen an eine Umweltstetig wachsender Informationsmengen
    Term: 1. January 2020 - 31. December 2022
    Funding source: DFG / Schwerpunktprogramm (SPP)

    In engineering, product development is a collaborative activity, within reusing and adapting existing product models could decrease effort. While capturing design rationale is effective to deal with adaptations by teams, adaptation not only requires joint extension of models, as supported by existing methods for design rationale, but also removing what is no longer relevant or in conflict. Such Intentional Forgetting (IF) is difficult, as may affect assemblages of elements, should not over- or underdelete, and may require undoing. While EVOWIPE (our phase 1 project) has successfully tackled IF, project teams require methods for Collaborative Forgetting:

    • Design Rationale and IF: Neither engineering nor computer science foresee methods to capture reasons for something that has been dismissed. Thus, team members might inadvertently reintroduce what was discarded before. How do we capture and represent design rationales behind forgetting?
    • Varying Levels of Granularity and IF: Collaborative engineering must find compromises between different requirements. How can we establish compromise by partial forgetting?
    • Cooperative Work and IF: Cooperative environments handle conflicts during model extension. Interwoven intricate forgetting is not supported in known cooperative environments. How can we concurrently add and remove designs and avoid inconsistencies?

    COFFEE constitutes basic research about novel collaborative forgetting supporting engineers in developing product models in teams with sophisticated reuse and adaptation. COFFEE will extend successful ontologybased knowledge representations of EVOWIPE.

  • TopoRestruct - Rückführung fertigungs-, beanspruchungs- und funktionsgerechter Konstruktionsgeometrie aus Ergebnissen der Topologieoptimierung in den Produktentwicklungsprozess

    (Third Party Funds Single)

    Term: 1. October 2019 - 30. September 2022
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)

    Topology optimisation (TO) methods generate ideal structures for givenobjective functions, loads and boundary conditions. A typical result of aFE-based topology optimisation is a triangulated surface mesh, which in mostcases is largely irregular and does not provide a parametrised CAD geometry.Therefore, further integration into the product development process ischallenging. Automatised, feature-based creation of parametric CAD geometrythus is the aim of “TopoRestruct".

  • Integrated computer-automated tolerance management in early design stages

    (Third Party Funds Single)

    Term: 1. October 2019 - 30. September 2022
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    In the previous research project "Tolerance management in early design stages", fundamental methods for early consideration of tolerances were developed. The results from the application of the individual approaches were linked with each other and with the conventional design process. Since the potential and applicability of these approaches strongly depend on the stored design and tolerance knowledge, the present project focuses not only on the further development of tolerance management methods but also on the specific provision of relevant data. For this purpose, robust design and tolerance management methods developed in the first phase of the project will be expanded and new ones are added in order to support the designer in the tolerance-compliant product development. The scientific challenge is the automation of the process in order to help to achieve reliable results independent of the user. The data management to be developed for this purpose allows consistent management of the product development information (from task classification to detail design) relevant to the tolerancing process. By defining rules (e.g. inferences in ontologies), relevant implicit knowledge can be used in early product development phases to automate the process. In this way, the methodology enables the tolerance concept to be verified even before the final product design without considerable additional effort. Due to the close link to the product development process this methodology improves the product design and thus contributes to avoiding costly iterations at the end of product development.
  • Konstruktive Auslegung wandlungsfähiger Fügeverbindungen

    (Third Party Funds Group – Sub project)

    Overall project: Methodenentwicklung zur mechanischen Fügbarkeit in wandlungsfähigen Prozessketten
    Term: 1. July 2019 - 30. June 2023
    Funding source: Deutsche Forschungsgemeinschaft (DFG)

    Das Teilprojekt B05 verfolgt das Ziel, eine ganzheitliche Konstruktionsmethode bereitzustellen, die den Produktentwickler befähigt, in der Entwurfsphase sowohl die Gestalt von Fügeteil und Fügestelle festzulegen als auch die Fügeverbindung selbst auszuwählen und rechnerisch zu dimensionieren. Dafür wird ein für den Konstrukteur handhabbares, analytisches Formelwerk sowie ein wissensbasierter Gestaltungsprozess erforscht werden, mit dem die Anforderungen der Fertigung, aber auch der Beanspruchungsgerechtheit berücksichtigt werden können. Unterstützt wird hierdurch vor allem die frühe Phase der Produktentwicklung, noch vor der gestaltgebenden Phase bzw. dem Vorliegen ausdetaillierter CAD-Produktmodelle. Die zentrale wissenschaftliche Herausforderung des Teilprojekts besteht darin, die Methode zur konstruktiven Auswahl und Auslegung mechanischer Fügeverbindungen einerseits handhabbar zu halten und andererseits so anpassungsfähig zu gestalten, um auch verschiedene Fügeverfahren flexibel und robust in wandlungsfähigen Prozessketten auslegen zu können. Um dies zu erreichen, sind Methoden zu erarbeiten, die es erlauben, aus mathematischen Metamodellen analytische Auslegungsformeln abzuleiten. Grundlegend untersucht wird zudem die Erzeugung von aussagekräftigen mathematischen Metamodellen auf Basis experimentell und simulativ gewonnener Daten. Dies stellt aufgrund der Begrenztheit der zugrundeliegenden Daten gegenüber der bekannten, auf großen Datenmengen basierenden Metamodellierung eine besondere Herausforderung dar. Aus Sensitivitäts- und Robustheitsanalysen an den Metamodellen ergeben sich relevante und nicht-relevante Parameter als Basis für die Modellreduktion. Diese sind ferner abzugrenzen in vom Konstrukteur direkt beeinflussbare Parameter (Merkmale) und sich daraus ergebende Parameter (Eigenschaften). Neben der Ermittlung der relevanten Konstruktionsparameter stellt die Betrachtung der geometrischen Gestaltung einen weiteren Fokus des Teilprojekts dar. Die geometrischen Gestaltungsmöglichkeiten und -restriktionen, die sich beispielsweise aus den Anforderungen der Fertigung, aber auch für eine kraftflussgerechte Gestaltung ergeben, sollen dazu in eine Wissensbasis überführt werden. Auf den Ergebnissen der Parameterabstraktion und der Gestaltungsrestriktionen aufbauend ist ein konstruktionsmethodischer Entwicklungsprozess zu strukturieren, der die relevanten Auslegungskriterien wie beispielsweise Steifigkeit, Festigkeit oder Korrosionsbeständigkeit der Verbindung gewichtet und die vom Konstrukteur zu unternehmenden Schritte definiert. Zur Kontrolle der Zielerreichung wird der erarbeitete Konstruktionsprozess am Beispiel des Clinchens zweier gleichartiger Metalle unter statischer Last auf seine Handhabbarkeit hin evaluiert. Nach Abschluss des Vorhabens steht damit eine Konstruktionsmethode zur Verfügung, welche der Wandlungsfähigkeit mechanischer Fügeverbindungen sowie der Robustheit und Übertragbarkeit auf weitere Verfahren Rechnung tragen kann.

  • SPP 2074 Fundamental multiscale investigations for improved calculation of the service life of solid lubricated rolling bearings

    (Third Party Funds Single)

    Term: 1. April 2019 - 31. March 2022
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)

    The project aims at gathering the fundamental knowledge required for improving the calculation of the service life of solid lubricated rolling bearings, which are typically used in vacuum pumps and rotating
    anodes of medical X-Ray devices. The project will specifically focus on MoS2 tribological coatings. The only service life calculation model available up to date relies on an empirical approach, based on the assessment of the wear rate from macroscopic contact parameters such as load and sliding distance. This model does not capture important processes, such as the progressive transfer and redeposition of coating material onto the uncoated counterpart. The proposed investigations will enable the development of a mechanistic model taking into account the influence of the microstructure, texture and stoichiometry of the coating and relying only marginally on empirical parameters. The primary challenge consists into identifying the fundamental mechanisms governing the deformation of the coating during rolling contact and understanding the consequences in term of material removal, as well as its transfer and deposition onto the uncoated counter-part. This goal will be met by implementing a multi-scale approach closely combining experimental
    characterizations with computer simulations. The investigations will focus on two different MoS2 PVD coatings: the first one featuring a strongly basal texture associated with a coarse microstructure and the
    second one a weak texture associated with a fine columnar microstructure. The tribological behavior of these coatings will be investigated at the macroscopic scale by twin-disc tests performed under realistic service conditions. Interrupted monitoring by electron microscopy and atom probe tomography will allow assessing the structural and crystallographic evolution of the coating at the micro and nanoscale as a function of the loading duration. Micromechanical testing will furthermore provide direct insights into the associated deformation and material removal processes. The underlying fundamental mechanisms will finally be revealed by atomistic simulations. As these account for the observed transformation of the coating, they are ultimately responsible for its lifetime, which impliesthat their knowledge will enable formulating a mechanistic model for the service life prediction of MoS2 solid lubricated rolling bearings. The success odds of this project are very high, as the combined expertise of the project partners reaches from tribological
    characterization to material characterization, micromechanics, as well as atomistic simulations of surface chemical processes and deformation.

  • Reibungsoptimierung von Gleit- und Wälzkontakten durch Kohlenstoff- sowie katalytisch aktive Schichten in Kombination mit niedrigviskosen Schmierstoffen

    (Third Party Funds Group – Sub project)

    Overall project: Projekt zur Reibungs-Optimierung von Motoren durch Einsatz von triboaktiven Hochleistungskohlenstoff- sowie Eisenbasisschichten und Schmierstoffen
    Term: 1. January 2019 - 31. December 2022
    Funding source: Bundesministerium für Wirtschaft und Technologie (BMWi), Industrie

    Ziel des Projektes ist das grundlagenorientierte Verständnis für Reibung und Verschleiß in Wechselwirkungen mit Schmierstoffen. Besonderes Augenmerk liegt hierbei auf metallischen Oberflächen, die mit amorphen Kohlenstoffschichten beziehungsweise metallbasierten Hartstoffschichten versehen sind und mit den jeweiligen Schmierstoffadditven niedrigviskoser Motorenöle wechselwirken. Als Anwendung wird der tribologische Kontakt Nocken/beschichter Tassenstößel aus dem Ventiltrieb von Verbrennungskraftmaschinen als Vertreter eines höher belasteten Gleit-Wälz-Linienkontaktes herangezogen. Zudem soll eine rechnerunterstützte Simulationsmethode entwickelt werden, die sowohl Schicht- als auch Systementwickler dabei unterstützt, auf Basis der vorliegenden Kontaktzustände im genannten tribologischen System die relevanten reibungs- und verschleißreduzierenden Maßnahmen stringent umzusetzen.

  • FOR 2271: Prozessorientiertes Toleranzmanagement mit virtuellen Absicherungsmethoden

    (Third Party Funds Group – Overall project)

    Term: 1. June 2016 - 31. December 2019
    Funding source: DFG / Forschergruppe (FOR)

    The comprehension of geometric part deviationsand their manufacturing and assembly related sources as well as the investigationof their effects on the function and quality of technical products builds theframework for the planned research group “process-oriented tolerance managementbased on virtual computer-aided engineering tools”. The aim of this researchgroup is the provision of holistic methods and efficient tools for thecomprehensive management of geometric deviations along the product originationprocess, which are to be validated in a model factory. In doing so, aparticular focus is set on the development of a procedure for the fruitfulcooperation of all departments involved in geometric variations management,from product development, to manufacturing, to assembly and to metrology, whichwill enable companies to quickly specify functional tolerances, which aremanufacturable and measurable, and consequently to save costs and to reduce thetime to market.

    In this regard, the vision of the researchgroup is to enable the close collaboration of product development,manufacturing, assembly and metrology in computer-aided tolerancing, i. e.the joint formulation of functional tolerances, which are manufacturable andmeasurable. By enabling this close collaboration, all manufacturing andassembly related sources of later problems regarding the product function andquality can be considered already during early phases of virtual product andprocess development. As a consequence, tolerances can be specified efficientlyand optimized inspection plans as well as robust manufacturing and operatingwindows can be identified, which allows the development of robust products tobe manufactured and measured at low costs.  

    Since geometric part deviations are inevitableand affect the function and quality of technical products, their managementalong the product origination process is essential for the development offunctioning products, which conform to the quality and usage requirements ofcustomers and are successful on international markets. As a consequence,tolerance management is a fundamental task in product development and reachesvarious fields of industry, from consumer to industrial goods. Due to steadilyincreasing requirements on quality and efficiency, it strongly gains importancenot only with large, but also small and medium-sized enterprises. In thiscontext, the industrial application of the scientific findings of the researchgroup will contribute to the success of the German economy.  




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