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Optimized Durability Prediction of



ompared to the conven- tional design of castings, a substantial qualitative and quantitative improvement

in assessing the real performance of cast iron materials can be realized. Te casting process has an essential

impact on the creation of the local microstructure of a casting. Tese local variations in microstructure lead to locally varying mechanical properties. Te properties of cast iron castings depend on their geometry and are mainly driven by the graphite mor- phology, microstructure, and disconti- nuities. Terefore, the chosen metal- lurgy and process control are essential parameters for the performance. Te conventional casting design

process does not consider the impact of microstructure variations on the fatigue/lifetime performance of cast- ings. Te designer lays-out castings based on established standards. Tese standards assume homogenous prop- erties throughout the entire casting. As a result, only one material dataset is considered in fatigue/lifetime predic- tion analysis tools.

Local residual stresses and micro-

structure variations are rarely recog- nized in lifetime prediction simula- tions. Tis leads to underestimating failure risks and failing to utilize the full potential of the material. Designers are uncertain how close the expected mechanical properties match the ones found in the real castings. A conservative design requires them to apply safety factors, which lead to unnecessarily high weight and result- ing costs. Metalcasting engineers suffer from

undesired consequences created by this approach as well: safety factors result in thicker walls, which increase solidification times and usually lead to decreased mechanical properties. Tey are also tougher to feed and cause increasing residual stresses within the casting during its cooling process. Coupling casting process simula-

tion with fatigue/lifetime prediction analysis is necessary to unlock the full potential of cast materials. Cast- ing process simulation tools need to provide answers to questions posed by engineers and casting designers. It

must qualitatively and quantitatively describe material and mechanical properties (Fig. 1). Integrating local properties allows the designer to customize the casting design for the specific requirements of an application. Te transfer of residual stress distributions caused by the casting 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. In 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-

April 2017 MODERN CASTING | 35

Cast Iron Based on Local Microstructure

A casting design where the application load and weight are optimized is only achievable if the designer can fully unlock the potential of the material. A research project studied how to integrate process and application simulation for

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