an application. Te transfer of residual stress distributions caused by the cast- ing process or heat treatment and their consideration as additional load in stress analysis runs is easily accom- plished and already standard operating procedure during the development of, for example, cylinder heads. Unfortu- nately, the recognition of local prop- erty variations’ impact on the durabil- ity of a cast component is rudimentary. Te correlation of local properties and fatigue/lifetime prediction has only been done experimentally for specific components, which makes it difficult to transfer the findings to other parts. Within a German research project,
“MABIFF,” the link between casting process simulation and cyclic material properties was established for different cast iron materials for the first time. Te concept of this research project was to couple the varying micro- structures of cast irons (GJS-400 and GJV-450), predicted by casting process simulation, with the lifetime predic- tion for castings. Experiments were used to derive S–N curves (Woehler curves), which resulted in the develop- ment of a closed chain between casting process and the prediction of the final lifetime of a cast component. Local properties driven by the production
Fig. 1. The conventional computer-aided engineering design process is shown surrounded by a blue dashed line. This shows the potential integration of casting process simulation in the design process.
process of a casting now can be trans- ferred into and considered by lifetime prediction tools.
Microstructure Prediction for Cast Iron
Metallurgy and alloying compo-
nents have an essential influence on the final microstructure and resulting mechanical properties of a casting. Te chemical composition and inclu- sions, the melt treatment (charge materials, melting method, treatment, and inoculation), as well as the local cooling conditions are of utmost im- portance. Foundry engineers use these
process variables to dial in the desired microstructure (graphite form, ferrite/ pearlite ratio) and avoid undesired defects (i.e., porosity or dross) and microstructures (i.e., graphite defor- mations or chill). Simulation programs need to be
able to predict the kinetics of the creation of the different phases locally during the entire solidification and cooling process. Tis requires, besides the consideration of alloying elements, the consideration of the inocula- tion and melt treatment process. Te impact of these is usually overlapped with the local cooling conditions within the casting. Te calculation of the plain macroscopic solidification and cooling behavior cannot consider these parameters. Microstructure simulation is required to calculate at any time in any location inside the casting, the amount and type of phase created based on the parameters. Besides the gating and riser system
Fig. 2. Test piece locations for a ductile iron bedplate (a), test casting (b), CGI crankcase (c), and step casting (d) are depicted.
24 | METAL CASTING DESIGN & PURCHASING | Mar/Apr 2017
and geometry of the casting, cast- ing process simulation considers the chemical composition, melt treatment, and inoculation, as well as other rel- evant process parameters. Te program utilizes these input parameters and local cooling conditions to calculate the locally available inoculation sites, growth of all phases, impact of segre- gation to calculate the solidification process and resulting local microstruc- ture, and its properties. Te calculation of all phases during the solidification process allows for the prediction of the final microstructure when the casting is completely so-
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