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Aachen, Germany

Kotas P.,Technical University of Denmark | Tutum C.,Technical University of Denmark | Hattel J.,Technical University of Denmark | Snajdrova O.,Vitkovice Heavy Machinery a.s. | And 2 more authors.
International Journal of Metalcasting | Year: 2010

This work summarizes the findings of multi-objective optimization of a gravity sand-cast steel part for which an increase of casting yield via riser optimization was considered. This was accomplished by coupling a casting simulation software package with an optimization module. The benefits of this approach, recently adopted in the foundry industry worldwide and based on fully automated computer optimization, were demonstrated. First, analyses of filling and solidification of the original casting design were conducted in the standard simulation environment to determine potential flaws and inadequacies. Based on the initial assessment, the gating system was redesigned and the chills rearranged to improve the solidification pattern. After these two cases were evaluated, the adequate optimization targets and constraints were defined. One multi-objective optimization case with conflicting objectives was considered in which minimization of the riser volume together with minimization of shrinkage porosity and limitation of centerline porosity were performed. Copyright © 2010 American Foundry Society. Source

Spangenberg J.,Technical University of Denmark | Roussel N.,University Paris Est Creteil | Hattel J.H.,Technical University of Denmark | Thorborg J.,Technical University of Denmark | And 4 more authors.
RILEM Bookseries | Year: 2010

SCC is nowadays a worldwide used construction material. However, heterogeneities induced by casting may lead to variations of local properties and hence to a potential decrease of the structure's load carrying capacity. The heterogeneities in SCC are primarily caused by static and dynamic segregation. The present paper reports property maps for a beam based on particle distributions at the end of casting derived from numerical flow simulations. A finite volume based numerical model is used to predict particle distributions at the end of casting, which are then converted into property maps using semi-empirical relations from the literature. © RILEM 2010. Source

Andriollo T.,Technical University of Denmark | Thorborg J.,MAGMA GmbH | Tiedje N.S.,Technical University of Denmark | Hattel J.,Technical University of Denmark
IOP Conference Series: Materials Science and Engineering | Year: 2015

In the present paper a micro-mechanical model for investigating the stress-strain relation of ductile cast iron subjected to simple loading conditions is presented. The model is based on a unit cell containing a single spherical graphite nodule embedded in a uniform ferritic matrix, under the assumption of infinitesimal strains and plane-stress conditions. Despite the latter being a limitation with respect to full 3D models, it allows a direct comparison with experimental investigations of damage evolution on the surface of ductile cast iron components, where the stress state is biaxial in nature. In contrast to previous works on the subject, the material behaviour in both matrix and nodule is assumed to be elasto-plastic, described by the classical J2-flow theory of plasticity, and damage evolution in the matrix is taken into account via Lemaitre's isotropic model. The effects of residual stresses due to the cooling process during manufacturing are also considered. Numerical solutions are obtained using an in-house developed finite element code; proper comparison with literature in the field is given. © Published under licence by IOP Publishing Ltd. Source

Kotas P.,Technical University of Denmark | Tutum C.C.,Technical University of Denmark | Thorborg J.,MAGMA GmbH | Hattel J.H.,Technical University of Denmark
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2012

A methodology of how to exploit the Niyama criterion for the elimination of various defects such as centerline porosity, macrosegregation, and hot tearing in steel castings is presented. The tendency of forming centerline porosity is governed by the temperature distribution close to the end of the solidification interval, specifically by thermal gradients and cooling rates. The physics behind macrosegregation and hot tears indicate that these two defects also are dependent heavily on thermal gradients and pressure drop in the mushy zone. The objective of this work is to show that by optimizing the solidification pattern, i.e., establishing directional and progressive solidification with the help of the Niyama criterion, macrosegregation and hot tearing issues can be both minimized or eliminated entirely. An original casting layout was simulated using a transient three-dimensional (3-D) thermal fluid model incorporated in a commercial simulation software package to determine potential flaws and inadequacies. Based on the initial casting process assessment, multiobjective optimization of the solidification pattern of the considered steel part followed. That is, the multiobjective optimization problem of choosing the proper riser and chill designs has been investigated using genetic algorithms while simultaneously considering their impact on centerline porosity, the macrosegregation pattern, and primarily on hot tear formation. © The Minerals, Metals &Materials Society and ASM International 2012. Source

Flender E.,MAGMA GmbH | Sturm J.,MAGMA GmbH
International Journal of Metalcasting | Year: 2010

Not many developments in recent decades have changed the understanding of the metalcasting process as fundamentally as casting process simulation has. The main intention of this paper is to provide an easy to read and attractive overview for foundrymen addressing the development, current state, and future of casting process simulation from the point of view of the European authors. Copyright © 2010 American Foundry Society. Source

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