Advanced modeling of shrinkage porosity in castings

Abstract

Porosity due to solidification shrinkage is a troublesome defect in all types of metal castings. It limits the performance of cast components by adversely affecting the material’s strength, fatigue and creep properties. By reliably predicting porosity in casting process simulation, it can be minimized or eliminated. Here, a newly developed model for predicting porosity is presented. The model is based on the recent discovery that all shrinkage porosity nucleates and grows in regions of a casting where the solid fraction is the lowest. It calculates the feeding flows and pressure distribution in the liquid while accounting for the liquid density variation during cooling and solidification. It predicts the location, extent and amount of all types of shrinkage porosity in a casting, including riser pipes and large internal holes, surface sinks, and distributed micro-shrinkage. The model is numerically implemented in a standard casting simulation code. Comparisons to measurements in specially made steel castings demonstrate the capability of the model to accurately predict various types of shrinkage porosity.