TESTING 1-2-3
REVEALING LOCAL MECHANICAL PROPERTIES IN CGI
Fine-tuning prediction models to account for variations in
microstructure could unlock the full potential of cast materials. AN MCDP STAFF REPORT
C GmbH, Aachen, Germany 1
Background—Computer-aided lifetime prediction assumes ho- mogenous material behavior. Production related variations in the microstructure are not considered. The research team set out to integrate process simulation into computer aided lifetime prediction to achieve more accurate part layouts.
2 3
Procedure—Step casting and crankcase samples were used in numerous fatigue test runs. Using the mathematical methods of variance and regression analysis, the researchers developed a correlation between local microstructure and durability using the experimental data. Results and Conclusions—A variance and regression analysis under consideration of local graphite morphology and ferrite/pearlite ratio shows good correlation between measured and predicted durability values. A model predicting the ferrite/pearlite ratio was developed and validated.
42 | METAL CASTING DESIGN & PURCHASING | Jul/Aug 2013
omputer aided lifetime prediction of parts assumes homogenous material behavior. Production related variations in the microstructure are not considered, so designers tend to lay out the components conser- vatively to compensate for these uncertainties. A team of researchers from Magma Foundry Tech- nologies, Schaumburg, Ill.; Audi AG, Ingolstadt, Germany; and Eisenwerk Bruehl GmbH, Bruehl, Germany, set out to integrate process simulation into computer aided lifetime prediction to achieve more accurate part layouts.
ADDING IT ALL UP
“Prediction of Microstructure and Local Mechanical Properties for a CGI Crankcase”Christof Heisser, Magma Foundry Technologies, Schaumburg, Ill.; N. Zenker, Audi AG, Ingolstadt, Germany; E. Fritsche, Eisenwerke Bruehl GmbH, Bruehl, Germany; and J.C. Sturm, Magma Giessereitechnologie
Non-uniform cooling conditions
within a casting lead to locally diff erent microstructures, which result in locally diff ering mechanical properties. T ese have a signifi cant impact on the behav- ior of the parts under their application load conditions and their lifetime. Compacted graphite iron (CGI) has two strength-relevant microstructure variables: the shape and size of the graphite particles and the ferrite/pearl- ite ratio and distribution in the matrix. T e research team felt it necessary to understand and mathematically describe the metallurgical process during the solidifi cation and eutectoid transforma- tion to simulate the development of the microstructure. T e available simulation models describing the solidifi cation were expanded and a new model for the ferrite/pearlite distribution was developed. T e models were validated on test castings and the Audi 3.01 V6 CGI crankcases. T e paper, “Prediction of Microstructure and Local Mechani- cal Properties for a CGI crankcase,” by Christof Heisser and J.C. Sturm, Magma; N. Zenker, Audi; and E. Frit- sche, Eisenwerke Bruehl, compares and discusses the measured and calculated microstructure distribution and its im- pact on durability of the castings.
Question
Can casting process simulation be used to predict local microstructure?
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