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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
      22  75
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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
      20  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  343
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    Item type:Publication, Access status: without files ,
    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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    Item type:Publication, Access status: with files ,
    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
      54
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    Item type:Publication, Access status: without files ,
      89
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    Item type:Publication, Access status: without files ,
    Process Monitoring Using Machine Learning for Semi-Automatic Drilling of Rivet Holes in the Aerospace Industry
    (2020-09)
    Köttner, Lars
    ;
    Mehnen, Jan Philipp
    ;
    Romanenko, Denys
    ;
    Bender, S.
    ;
    Hintze, Wolfgang
    The majority of aircraft rivet holes are drilled with semi-automatic and manually controlled, pneumatically driven machines as full automation is often unsuitable due to workspace restrictions. Lightweight materials of difficult machinability complicate drilling. This is particularly relevant when drilling stack materials, where the machining parameters are determined by the most difficult to machine material layer. To provide reliable rivet connections, drilling in multiple steps, use of minimum quantity lubrication as well as subsequent manual deburring and cleaning are indispensable. Newly developed electrically driven semi-automatic advanced drilling units (ADUs) enable intelligent process layouts and online condition monitoring by evaluating integrated sensor data. Additionally, process parameters can be adapted to suit each material in the stack.
    Publicationtype: Conference Paper
      96
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    Item type:Publication, Access status: with files ,
    Temperature field due to a moving heat source in machining orthotropic composites with arbitrary fiber orientation
    (Elsevier, 2019-12-30)
    Mehnen, Jan Philipp
    ;
    Hintze, Wolfgang
    ;
    Köttner, Lars
    ;
    Wenserski, Robert von
    Milling of fiber reinforced plastics (FRP) is challenging with respect to surface integrity and tool wear due to high process temperatures. The maximum temperatures occurring in the workpiece determine the extent of the matrix decomposition area. Improving the workpiece quality therefore requires an understanding of its internal temperature distribution during milling. However, steep temperature gradients and high mechanical stress make measurements of temperature fields in the cutting zone difficult. In addition, thermal properties change depending on the fiber orientation in the case of orthotropic FRP. In this paper, an existing model describing the temperature field for isotropic materials is extended to unidirectional, orthotropic FRP. Here, the thermal impact of an end mill upon the machined surface is represented by a strip-shaped heat source which moves with the feed velocity along a semi-infinite space. Starting with the temperature field of an instantaneous point source, multiple integration steps and a coordinate transformation lead to the temperature field of the moving strip source for orthotropic materials with arbitrary fiber orientation. Using this analytical approach, two-dimensional temperature fields within the workpiece can be calculated for various feed velocities, heat source widths and fiber orientation angles. A cross verification of the analytical solution is successfully carried out by comparing it to a numerical simulation. Furthermore, temperature measurements during end milling of carbon fiber reinforced plastics using thermocouples confirm these results for different fiber orientations. The derived model can be applied to a variety of heat flow problems relevant for orthotropic materials, e.g. other machining technologies.
    Publicationtype: Conference Paper
    Scopus© Citations 3  266  207