The LVMFlow software was used to simulate the solidification process of a large-sized thin-walled steel casting in a sand mold. For the computer model of such a complex casting technology, the necessary settings were selected and verified. Improving the thermos-physical properties of the mold material is the most important setting that ensures the correct computation of temperature fields. To restore the heat capacity and thermal conductivity in the technological temperature range, a method based on solving direct and inverse problems of thermal conductivity has been developed. As a result, using accurate computer simulation, an improved technology for the "side frame" casting was developed.