Effect of Sand Mold Constraint on Warpage Deformation of Lamellar Graphite Gray Cast Iron and Prediction by Elastoplastic-Creep Finite Element Analysis

Casting that comprises multiple parts with different thicknesses is prone to experience warpage deformation due to the non-uniform temperature distribution from the beginning of solidification to room temperature. This study is the first to investigate the effect of sand mold shake-out timing on the warpage deformation of a lamellar graphite gray cast iron casting with thick and thin geometries by both experiment and finite element analysis. It was found that warpage deformation was suppressed by 81.6% when the shakeout was performed just after A1 (austenite to ferrite) phase transformation temperature rather than after eutectic solidification temperature. The elastoplastic-creep analysis was proven to predict the warpage amount better than elastoplastic analysis, in which prediction error was reduced by 116%. The introduction of creep term that should not contribute to the work-hardening of the casting was assumed to relax the stress and suppress the warpage deformation; however, poor estimation of the creep properties at about 1000 °C to the A1 transformation temperature reduced the prediction accuracy. A sudden increase of warpage was observed and predicted during shakeout due to the release of the elastic strain that was accumulated as a result of sand mold constraint.