Numerical Optimization of the Method of Cooling of a Massive Casting of Ductile Cast-Iron

Abstract

An original application of ANSYS simulating the forming of the temperature field of a massive casting from ductile cast-iron during the application various methods of its cooling using steel chills. The numerical model managed to optimize more than one method of cooling but, in addition to that, provided serious results for the successive model of structural and chemical heterogeneity, and so it also contributes to influencing the as solidified microstructure. The file containing the acquired results from both models, as well as from their organic unification, brings new and, simultaneously, remarkable findings of causal relationships between the structural and chemical heterogeneity and the local solidification time in any point of the casting. Therefore the determined relations enable the prediction of the local density of the spheroids of graphite in dependence on the local solidification time. The calculated temperature field of a two-ton (500 × 500 × 1000) mm casting of ductile cast-iron with various methods of cooling has successfully been compared with temperatures obtained experimentally. This has created a tool for the optimization of the microstructure with an even distribution of the spheroids of graphite in such a way so as to minimize the occurrence of degenerated shapes of graphite, which happens to be one of the conditions for achieving good mechanical properties of castings of ductile cast-iron. Key-words: ductile cast-iron, massive casting, cooling, temperature field, numerical model Uporaba originalnega programa ANSYS omogo~a simulacijo tvorbe temperaturnega polja v masivnem lito`eleznem ulitku pri razli~nih metodah hlajenja z jeklenimi hladilnimi telesi. Z numeri~nim modelom se lahko optimira ve~metod hlajenja, dodatno pa je mogo~izra~un pomembnih rezultatov za modeliranje strukturne in kemijske heterogenosti, kar tudi prispeva k vplivu na lito mikrostrukturo. Dobljeni rezultati obeh modelov omogo~ajo pomembne ugotovitve o odnosih med strukturno in kemijsko heterogenostjo ter lokalnim~asom strjevanja v poljubni to~ki ulitka in napoved lokalne gostote krogli~astega grafita v odvisnosti od lokalnega~asa strjevanja. Izra~unano temperaturno polje dvotonskega ulitka duktilne`elezove litine z izmerami (500 × 500 × 1000) mm je bilo v skladu z eksperimentalnimi rezultati pri razli~nih metodah hlajenja. Na podlagi teh ugotovitev je bilo izdelano orodje za optimizacijo mikrostrukture z enakomerno porazdelitvijo krogli~astega grafita, s~imer se zmanj{a pojav degeneriranih oblik grafita in se ustvarijo pogoji za dosego dobrih mehanskih lastnosti ulitkov duktilne`elezove litine. Klju~ne besede: temperaturno polje, strjevanje, ohlajanje, numeri~na optimizacija, strukturna in kemijska heterogenost

Analysis of the Influence of Boundary Condition on Simulation Accuracy of Solidification Thermokinetics Model

“…The solidification and cooling of a classically cast (i.e. gravitationally poured) casting (ingot) and simultaneous heating of the mould and chills is, from the viewpoint of thermokinetics, a very complicated case of 3D transient heat and mass transfer [1][2][3][4][5]. In systems comprising the casting (ingot), the mould, chills and environment, all three kinds of heat transfer take place.…”

Multidisciplinary Shape Optimization of Ductile Iron Castings by Considering Local Microstructure and Material Behaviour

“…The importance of considering strength variability of DI has been shown by Olofsson and Svensson (2013) and Shirani and Härkegård (2014). Kavicka et al (2010) found out correlations between local solidification time and local microstructure for large DI castings. Wessén and Svensson (1996) developed a model for ferrite growth in DI castings, and Donelan applies a method for modelling the microstructural and mechanical properties of ferritic DI to thick-walled casting (Donelan 2000).…”

Influence of the chill size on the porosity formation in ductile iron casting

“…After successful validation of a model, numerical simulation can be an efficient tool for relatively fast verification of the designed corrections in the production technology. Nowadays, by using numerical simulations, it is possible to predict the complete process, from the technology plan [7,8,9] through castings casting [10,11], including solidification [12][13][14], stress states [13][14][15][16][17], defects prediction [13,14,18,19] and resulting metallographic structure of a casting [19][20][21].…”