Numerical Simulation Study On Forecasting The Shrinkage Defects In Ductile Iron Castings

Ductile iron has the advantages of high strength,high toughness and low production cost.As one of the most widely used casting materials,it is important to industries such as automobiles,ships,agricultural machinery,and rail transit.However,due to the unique paste-like solidification and the graphitization expansion,shrinkage defects such as shrinkage cavities and porosity become difficult problems in the ductile iron castings.Numerical simulation technology can help engineers to analyze the formation of defects in cast iron parts,so as to design a better process scheme.This paper studies the calculation of thermo-physical properties of ductile iron,numerical simulation of temperature field during solidification and prediction of shrinkage defects.The main contents include:(1)Based on the thermo-physical properties calculation theory,the accurate thermo-physical properties of ductile iron is obtained using JMatPro software.(2)Starting from the basic energy equation of fluid mechanics,the mathematical model of solidification temperature field under variable physical parameters is derived,and it is discretized by the finite volume method to realize the numerical calculation of solidification temperature field of actual castings under complex assembly conditions.(3)The graphitization expansion is quantitatively characterized by the density-temperature curve of ductile iron.The local contractions of the casting are determined based on the net expansion rate of the isolated feeding region,and the shrinkage defects are quantitatively predicted with a porosity distribution model.(4)A solidification simulation program was developed and applied to predict the shrinkage defects of a simple cylinder ingot and a ductile iron pedestal casting,and the correctness of the developed numerical simulation system was verified by comparing the simulation results with the actual production results.In this study,the quantitative characterization method and porosity distribution model of graphitization expansion are proposed based on the accurate mathematical model of thermo-physical parameters and solidification temperature field of ductile cast iron,and the quantitative prediction of shrinkage defects in ductile iron castings is realized.The simulation system can effectively assist engineers to design the casting process scheme for ductile iron castings.