Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Validierung von AM-Laser-Metal-Deposition Simulationen mittels in-situ Verzugsmessungen an der aufgebauten Geometrie
    ( 2018)
    Biegler, Max
    Aufgrund der schnellen, zyklischen Aufheizung und Abkühlung tritt Verzug in Additive Manufacturing (AM) Laser Metal Deposition (LMD) Bauteilen auf und kann die Maßhaltigkeit vermindern, sowie zu Bauteilfehlern beitragen. Numerische Struktursimulation bietet das Potential, Verzug rechnerisch zu optimieren. Zur Etablierung der Simulation werden umfassende experimentelle Daten zum Abgleich, verlässliche Modelle sowie erprobte Arbeitsabläufe benötigt. In diesem Vortrag wird eine neue Messmethodik zur in-situ Verzugsmessung mittels Digital-Image-Correlation (DIC) beim additiven Aufbau einer Wandstruktur aus 1.4404 nichtrostendem Stahl demonstriert. Im Gegensatz zu etablierten Messmethoden, die den Verzug der Substratplatte betrachten, kann mittels DIC direkt an der neu aufgebauten Geometrie gemessen werden. Die gewonnenen Messdaten werden mit den Ergebnissen einer AM-Struktursimulation verglichen und die Übereinstimmungen und Abweichungen speziell im Hinblick auf zukünftige Herausforderungen im Bereich der Simulation diskutiert.
  • Publication
    Finite element analysis of in-situ distortion and bulging for an arbitrarily curved additive manufacturing directed energy deposition geometry
    ( 2018)
    Biegler, Max
    ;
    Marko, Angelina
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    With the recent rise in the demand for additive manufacturing (AM), the need for reliable simulation tools to support experimental efforts grows steadily. Computational welding mechanics approaches can simulate the AM processes but are generally not validated for AM-specific effects originating from multiple heating and cooling cycles. To increase confidence in the outcomes and to use numerical simulation reliably, the result quality needs to be validated against experiments for in-situ and post process cases. In this article, a validation is demonstrated for a structural thermomechanical simulation model on an arbitrarily curved Directed Energy Deposition (DED) part: at first, the validity of the heat input is ensured and subsequently, the model's predictive quality for in-situ deformation and the bulging behaviour is investigated. For the in-situ deformations, 3D-Digital Image Correlation measurements are conducted that quantify periodic expansion and shrinkage as they occur. The results show a strong dependency of the local stiffness of the surrounding geometry. The numerical simulation model is set up in accordance with the experiment and can reproduce the measured 3 dimensional in-situ displacements. Furthermore, the deformations due to removal from the substrate are quantified via 3D scanning, exhibiting considerable distortions due to stress relaxation. Finally, the prediction of the deformed shape is discussed in regards to bulging simulation: to improve the accuracy of the calculated final shape, a novel extension of the model relying on the modified stiffness of inactive upper layers is proposed and the experimentally observed bulging could be reproduced in the finite element model.
  • Publication
    In-situ distortions in LMD additive manufacturing walls can be measured with digital image correlation and predicted using numerical simulations
    ( 2018)
    Biegler, Max
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Distortions in Additive Manufacturing (AM) Laser Metal Deposition (LMD) occur in the newly-built component due to rapid heating and solidification and can lead to shape deviations and cracking. This paper presents a novel approach to quantify the distortions experimentally and to use the results in numerical simulation validation. Digital Image Correlation (DIC) is applied together with optical filters to measure in-situ distortions directly on a wall geometry produced with LMD. The wall shows cyclic expansion and shrinking with the edges bending inward and the top of the sample exhibiting a slight u-shape as residual distortions. Subsequently, a structural Finite Element Analysis (FEA) of the experiment is established, calibrated against experimental temperature profiles and used to predict the in-situ distortions of the sample. A comparison of the experimental and numerical results reveals a good agreement in length direction of the sample and quantitative deviations in height direction, which are attributed to the material model used. The suitability of the novel experimental approach for measurements on an AM sample is shown and the potential for the validated numerical model as a predictive tool to reduce trial-and-error and improve part quality is evaluated.