Journal: International Journal of Material Forming

Abbreviation

Int. j. mater. form.

Publisher

Springer

Journal Volumes

ISSN

1960-6206
1960-6214

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Publications 1 - 10 of 17
  • Modeling of localization and fracture phenomena in strain and stress space for sheet metal forming
    Item type: Journal Article
    Gorji, Maysam; Berisha, Bekim; Hora, Pavel; et al. (2016)
    International Journal of Material Forming
  • Enhanced material models for the process design of the temperature dependent forming behavior of metastable steels
    Item type: Journal Article
    Krauer, Jürg; Hora, Pavel (2012)
    International Journal of Material Forming
  • Surface defect classification and detection on extruded aluminum profiles using convolutional neural networks
    Item type: Journal Article
    Neuhauser, Felix M.; Bachmann, Gregor; Hora, Pavel (2020)
    International Journal of Material Forming
    © 2019, Springer-Verlag France SAS, part of Springer Nature. For decades, aluminum extrusion has been successfully applied in the manufacturing of profiles for the applications ranging from locomotives to skyscrapers. In recent years however, increasing profile complexity and the need for rapid production have lead to greater challenges for manufactures seeking rapid and robust production procedures. As a consequence, the occurrence of defects in extruded profile surfaces continues to create difficulties often requiring disposal of entire components. Hence, quality inspection of the profiles must be performed prior to packing in order to identify and appropriately manage defect-containing extrusions. Up until now, quality control in extrusion factories is primarily performed by the human eye due to its high performance in discriminating defect varieties. But human performance is cost intensive and furthermore prone to failure, especially when applied in high-throughput environments. On that account this paper proposes an approach in surface defect classification and detection, whereby a simple camera records the extruded profiles during production and a neural network architecture distinguishes between immaculate surfaces and surfaces containing a variety of common defects (surface defect classification). Furthermore, a neural network is employed to point out the defects in the video frames (surface defect detection). In this work, we show that methods from artificial intelligence are highly compatible with industrial applications such as quality control even under common industry constraints such as very limited data set sizes for training a neural network. Data augmentation as well as transfer learning are the key ingredients for training networks that meet the high requirements of modern production facilities in detecting surface defects, particularly when access to training sets is limited. Accuracies of 0.98 in the classification and mean average precisions of 0.47 in the detection setting are achieved whilst training on a data set containing as little as 813 images. Real-time classification and detection codes are implemented, and the networks perform reliably despite changes in lighting conditions and camera orientation.
  • On the efficiency and accuracy of stress integration algorithms for constitutive models based on non-associated flow rule
    Item type: Journal Article
    Hippke, Holger; Manopulo, Niko; Yoon, Jeong Whan; et al. (2018)
    International Journal of Material Forming
    Constitutive models based on non-associated flow rule enable the accurate description of complex anisotropy phenomena by using distinct, but relatively simple, mathematical description for yield function and plastic potential. The computational complexity of stress integration procedure may thus be significantly reduced. The amount by which this advantage is reflected to the total computation time is, however, a function of the nonlinearity of the problem at hand. The present work aims to make a systematic comparison of two different stress integration algorithms, used in conjunction to non-associated flow rule. A fully explicit and semi-implicit integration scheme are analyzed in terms of accuracy and speed. The implemented yield model is Yld2000-2d with isotropic hardening. The validity of the stress-integration approaches is assessed based on the ability to reproduce stress-ratios, r-values and tensile test results. Additionally, measured earing profiles in cup drawing experiments are compared. The fully explicit implementation shows significant advantages in terms of speed.
  • A dislocation based material model for warm forming simulation
    Item type: Journal Article
    Berisha, Bekim; Hora, Pavel; Wahlen, Arne; et al. (2008)
    International Journal of Material Forming
  • A strain rate dependent anisotropic hardening model and its validation through deep drawing experiments
    Item type: Journal Article
    Peters, Philip; Manopulo, Niko; Lange, Christian; et al. (2014)
    International Journal of Material Forming
    In the present work, a modified version of the widely used Yld2000-2d yield function and its implementation into the commercial FE-code LS-Dyna is presented. The difference to the standard formulation lies in the dependency of the function parameters on the equivalent plastic strain. Furthermore, strain rate dependency is incorporated. After a detailed description of the model and the identification of the parameters, the numerical implementation i.e., the stress-update algorithm used for the implementation is explained. In order to validate the model, two different materials, namely Formalex™5x, a 5182-based aluminum alloy and a DC05 mild steel were characterized. The results of the tensile and hydraulic bulge tests are presented and used for the parameter identification. The experimental curves are reproduced by means of one element tests using the standard and modified model to demonstrate the benefit of the modifications. For validation purposes, cross die geometries were drawn with both materials. The outer surface strains were measured with an optical measurement system. The measured major and minor strains were compared to the results of simulations using the standard and the modified Yld2000-2d model. A significant improvement in prediction accuracy has been demonstrated.
  • Numerical modelling, validation and analysis of multi-pass sheet metal spinning processes
    Item type: Journal Article
    Rentsch, Benedikt; Manopulo, Niko; Hora, Pavel (2017)
    International Journal of Material Forming
    Conventional sheet metal spinning is an incremental forming process which typically involves the cost-effective and high-quality manufacturing of axissymmetric parts. The process is usually executed by highly skilled and experienced personnel which is able of optimizing the process parameters during production. Numerical simulation of the process can substantially help discovering systematic methodologies for optimal parameter determination and thus enable the full automation of the process using CNC machines. The present work aims to assess the quality of numerical modelling techniques by a direct comparison with metal spinning experiments. Based on the geometry and thickness distribution of intermediate and final stages of a spinned component, which are measured using the Optical 3D Digitization technique, the quality and validity of different numerical modeling approaches are assessed. Subsequently, deformation mechanisms occurring during process are identified, analysed and discussed.
  • Temperature dependent friction modeling for sheet metal forming
    Item type: Conference Paper
    Grüebler, Reto; Hora, Pavel (2009)
    International Journal of Material Forming
  • A dual-mesh strategy for the 3d simulation of fineblanking processes
    Item type: Conference Paper
    Manopulo, Niko; Tong, Longchang; Karadogan, Celaletin; et al. (2009)
    International Journal of Material Forming
  • Damage dependent stress limit model for failure prediction in bulk forming processes
    Item type: Journal Article
    Hora, Pavel; Tong, Longchang; Berisha, Bekim; et al. (2011)
    International Journal of Material Forming
Publications 1 - 10 of 17