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    Item type:Publication, Access status: without files ,
    Prozesskette zum Oberflächenschleifen von nachgiebigen Luftfahrtstrukturbauteilen aus kohlenstofffaserverstärkten Kunststoffen
    (Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V. (DGLR), 2025-11-07)
    Junghans, Sebastian
    ;
    Köttner, Lars
    ;
    Dege, Jan Hendrik
    In the production of structural components made of carbon fiber-reinforced plastics (CFRP) in aircraft manufacturing, manufacturing-related dimensional deviations can occur. These lead to gaps during assembly, which have so far been compensated by so-called shimming. For this purpose, manual filler materials are applied at the affected areas. However, this process is time-consuming and costly. A promising alternative is the automated sanding of the component surfaces, provided that designated sacrificial layers are available. The goal is to avoid shimmering by selectively removing the surface irregularities that cause the gaps. However, implementation presents particular challenges. On the one hand, process forces act during grinding, which can lead to undesired component displacement. This is especially true for thin-walled, locally supported, and thus flexible structures. On the other hand, grinding forces continuously increase with increasing tool wear. As part of the SHILA project (Shim-free assembly of thin-walled aircraft structures), the Institute for Production Management and Technology (IPMT) at the Technical University of Hamburg (TUHH), together with the project partners (Boeing Germany GmbH, Broetje-Automation GmbH, KEBA Industrial Automation Germany GmbH, 3D.aero GmbH, WZL RWTH Aachen), is investigating, among other things, a grinding process chain that addresses these challenges by compensating for component deflection. The focus is on the application case of fuselage section assembly, where the individual fuselage segments exhibit deviations from the nominal contour. For this purpose, test rigs have been set up at IPMT to examine individual elements of the process chain in both analogy experiments and under conditions close to practical application. The focus is on selecting suitable tools and processing strategies, predicting the resulting process forces while taking tool wear into account, and integrating them into a FEM model to simulate component-specific displacement. Based on the simulated deformations, the tool path can then be adjusted to minimize component displacement.
    Publicationtype: Conference Paper
      33
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    Item type:Publication, Access status: with files ,
    Zerspankraftmodellierung und Prozessgrenzen der Umrissbearbeitung von FKV-Bauteilen mit scheibenförmigen Werkzeugen
    (2025)
    Köttner, Lars
    ;
    Hintze, Wolfgang
    Machining of defined part contours is an essential step in the production of fiber-reinforced plastic (FRP) shell components. Besides milling, processes with disk-shaped tools such as abrasive cutting and sawing can be used for this purpose. In addition, Curved Circular Cutting (CCC) is a novel technology that enables the machining of curved contours with these type of tools. To date, however, there has been comparatively little research into these FRP machining processes. This results in a lack of suitable simulation models and detailed knowledge of the relevant technological process limits with regard to process design and optimization. This thesis addresses this need and provides a mechanistic cutting force model that can be used for cutting force simulations with arbitrary disk-shaped tool geometries. This model includes for the first time oblique cutting with spatial cutting phenomena at the fibers of the FRP, which can occur in the contact zone due to complex engagement conditions, especially when using the CCC technology. The resulting effect on the cutting behavior of the orthotropic material is systematically investigated by machining tests on unidirectional CFRP, mathematically modeled and integrated into the cutting force model. In addition, the results of comprehensive experimental investigations are used to identify the technological process limitations of CCC and to derive recommendations for the application.
    Publicationtype: Doctoral Thesis
      113  104
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    Item type:Publication, Access status: with files ,
    Prediction of surface profile in CFRP machining through phenomenological analysis and inverse continuous wavelet transformation
    (2024-06)
    Brouschkin, Alexander
    ;
    Köttner, Lars
    ;
    Hintze, Wolfgang
    ;
    Dege, Jan Hendrik
    Carbon fibre-reinforced polymer (CFRP) is favored for its high strength to weight ratio, outstanding direction dependent mechanical properties and the high potential for load adapted design. However, machining unidirectional CFRP is challenging due to its anisotropic behavior, resulting in variable surface quality under identical machining parameters with different fibre orientations. Recently, a universal, process-independent model describing the engagement conditions in oblique cutting of unidirectional CFRPs has been developed, introducing the spatial fibre cutting angle θ0 and the spatial engagement angle ϕ0. Milling and drilling are mostly used for machining CFRP. Since the engagement conditions are rather complex, first analogy experiments are conducted in turning with variation of the setting and inclination angles. In this study, continuous surface profiles were recorded as a function of the spatial fibre cutting angle. Phenomenological and continuous wavelet analyses can be used to describe the surface profiles as a function of the spatial engagement conditions and to accurately predict them and the surface roughness using an inverse wavelet transformation. Experimental investigations with a side milling process of CFRP validate the prediction approach and show a good agreement between the experimental and predicted surface profiles.
    Publicationtype: Conference Paper
      21  74
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    Item type:Publication, Access status: with files ,
    Prediction of surface profile in CFRP machining
    (Elsevier, 2024-05)
    Brouschkin, Alexander
    ;
    Köttner, Lars
    ;
    Hintze, Wolfgang
    ;
    Dege, Jan Hendrik
    Carbon fibre-reinforced polymer (CFRP) is favored for its high strength to weight ratio, outstanding direction dependent mechanical properties and the high potential for load adapted design. However, machining unidirectional CFRP is challenging due to its anisotropic behavior, resulting in variable surface quality under identical machining parameters with different fibre orientations. Recently, a universal, process-independent model describing the engagement conditions in oblique cutting of unidirectional CFRPs has been developed, introducing the spatial fibre cutting angle 𝜃₀ and the spatial engagement angle 𝜙₀. Milling and drilling are mostly used for machining CFRP. Since the engagement conditions are rather complex, first analogy experiments are conducted in turning with variation of the setting and inclination angles. In this study, continuous surface profiles were recorded as a function of the spatial fibre cutting angle. Phenomenological and continuous wavelet analyses can be used to describe the surface profiles as a function of the spatial engagement conditions and to accurately predict them and the surface roughness using an inverse wavelet transformation. Experimental investigations with a side milling process of CFRP validate the prediction approach and show a good agreement between the experimental and predicted surface profiles.
    Publicationtype: Conference Presentation
      19  17
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    Item type:Publication, Access status: with files ,
    Kraftmodellierung beim Schleifen von UD-CFK unter räumlichen Eingriffsbedingungen
    (2024)
    Köttner, Lars
    ;
    Jakele, Lukas
    ;
    Hintze, Wolfgang
    Endlosfaserverstärkte Faser-Kunststoff-Verbunde (FKV) spielen für Anwendungen im Leichtbau eine herausragende Rolle. Der orthotrope Aufbau dieser Werkstoffgruppe bedingt jedoch ein richtungsabhängiges Trennverhalten. Bei der spanenden Bearbeitung führt dies unter anderem zu einer Variation der Zerspankräfte im Eingriffsbereich des Werkzeugs bei ansonsten konstanten Zerspanbedingungen. In der Kraftmodellierung wird diesem Umstand üblicherweise durch die Berücksichtigung des Fasertrennwinkels θ Rechnung getragen. Der Winkel θ entspricht dabei dem eingeschlossenen Winkel zwischen der Schnittrichtung und Faserlängsrichtung innerhalb der Laminatebene des FKV. Allerdings ist der Winkel nur beim Besäumen mit Schaftwerkzeugen für eine vollständige Beschreibung der Eingriffsverhältnisse ausreichend. Bei einer Vielzahl weiterer, spanender Bearbeitungsprozesse wie dem Bohren, Kreissägen, Trennschleifen mit Trennscheibe oder dem Oberflächenschleifen lassen sich die Eingriffsverhältnisse und das Trennverhalten hingegen nicht mit nur einem Winkel beschreiben. Zur vollständigen Beschreibung und Modellierung beliebiger Eingriffsverhältnisse wurden daher der räumliche Fasertrennwinkel θ0 und der räumliche Eingriffswinkel φ0 eingeführt. Dabei entspricht der Winkel θ0 dem eingeschlossenen Winkel zwischen der Schnittrichtung und der Faserlängsrichtung und der Winkel φ0 dem eingeschlossenen Winkel zwischen der Schneidenebenennormalen und der Faserlängsrichtung. Anhand systematischer Schleifversuche an UD-CFK wird in diesem Beitrag aufgezeigt, welchen Einfluss die Variation der Winkel auf die Kräfte beim Schleifen besitzt. Aufbauend wird erstmals ein mechanistisches Kraftmodell entwickelt, welches die Berechnung der Schleifkräfte bei beliebigen räumlichen Eingriffsbedingungen ermöglicht. Die Validierung des Modells erfolgt abschließend anhand eines Trennschleifprozesses mit komplexer Werkzeuggeometrie und Prozesskinematik.
    Publicationtype: Conference Paper
      52  342
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    Model based prediction of force and roughness extrema inherent in machining of fibre reinforced plastics using data merging
    (2023)
    Hintze, Wolfgang
    ;
    Brouschkin, Alexander
    ;
    Köttner, Lars
    ;
    Blühm, Melchior Frieder
    Planning of machining operations for fibre reinforced plastics components today entails expensive trials in order to meet quality, productivity and cost requirements. The use of existing data for modeling and simulation has so far been severely limited due to the lack of universal process models that capture fundamental mechanisms in a process-independent approach and thus allow data to be merged across different cutting processes. Recently, a universal model describing the engagement conditions in oblique cutting of unidirectional FRPs has been developed. The model closes the gap described and builds the basis for cross-technology data merging from different cutting operations, which has been common practice for homogenous materials for a long time. In case of mostly thin FRP components and often poor clamping conditions the generated forces in cutting operations are crucial as they may lead to dynamic process instabilities and to unfavorable part deflections impeding part precision. Furthermore, the quality of the machined surface depends on the engagement conditions, which usually change significantly during machining. Force and quality data from different sources and across various cutting processes and FRP materials were merged using the universal engagement model to reveal generally applicable relationships. These will enable faster, more reliable and more cost-efficient planning of cutting operations for FRP components in the future.
    Publicationtype: Conference Paper
      63
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    Holistic process monitoring with machine learning classification methods using internal machine sensors for semi-automatic drilling
    (Elsevier, 2022-05-26)
    Hintze, Wolfgang
    ;
    Romanenko, Denys
    ;
    Molkentin, Lukas
    ;
    Köttner, Lars
    ;
    Mehnen, Jan Philipp
    Since one third of rivet holes during aircraft assembly are produced with semi-automatic drilling units, in this work reliable and efficient methods for process state prediction using Machine Learning (ML) classification methods were developed for this application. Process states were holistically varied in the experiments, gathering motor current and machine vibration data. These data were used as input to identify the optimal combination of five data feature preparation and nine ML methods for process state prediction. K-nearest-neighbour, decision tree and artificial neural network models provided reliable predictions of the process states: workpiece material, rotational speed, feed, peck-feed amplitude and lubrication state. Data preprocessing through sequential feature selection and principal components analysis proved to be favourably for these applications. The prediction of the workpiece clamping distance revealed frequent misclassifications and thus, was not reliable.
    Publicationtype: Journal Article
    Scopus© Citations 1  66  136
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    Item type:Publication, Access status: without files ,
      52
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    Item type:Publication, Access status: without files ,
    Curved circular cutting of lightweight structures
    (2021-12)
    Hintze, Wolfgang
    ;
    Köttner, Lars
    China-Germany-Japan Workshop on Advanced Manufacturing of New Energy Vehicles
    Publicationtype: Conference Paper not in Proceedings
      53
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    Item type:Publication, Access status: without files ,
      89