The shrinkage of sand castings occurs during the solidification process after pouring, and the mold (core) material expands with the increase of temperature, so the shrinkage of castings is hindered by the mold (core), which makes the sand castings in the solidification cooling process subject to tensile stress. The greater the stress that hinders the shrinkage of the casting, the easier the sand casting is to produce hot cracks. Therefore, the high temperature mechanical properties of the mold (core) material and the interaction between the sand casting and the mold (core) have an important impact on the stress distribution and hot cracking of the sand casting.

The interaction between sand mold casting and mold (core) is reflected in the following aspects: there is thermal resistance in the gap between the solidified watch shell and the mold of sand mold casting, which will affect the heat transfer; when the mold contacts with the solidified shell, mechanical action will be produced, and the contact and friction of the mold is also one of the sources of stress of sand mold casting; The expansion of the mold and its resistance to the shrinkage of the sand casting determine the stress level of the sand casting within the temperature range of hot crack formation.

When considering the interaction between sand casting and mold (core), the following treatment methods are usually adopted:

(1) The false shape (core) has a completely yielding property, which does not hinder the shrinkage of sand castings. The mold (core) part is omitted during the stress field simulation. This method is often used in the stress field simulation of sand casting.

(2) The false shape (core) is completely rigid, and the constraint is imposed on the normal direction of the contact part between the sand casting and the mold (core). This method is mostly used for the stress field simulation of the metal mold casting process.

(3) The mold (core) action is simplified to be an elastic body or calculated with equivalent boundary conditions.

(4) It is assumed that the sand casting is closely connected with the mold (core) and will never be separated in the simulation. Let the mold (core) participate in the calculation. (5) Use the contact element method in contact mechanics to deal with the boundary of the sand casting/core.

(6) Establish the mechanical resistance model of the mold (core), and establish the resistance calculation model through the mold resistance test of the test piece.