Casting stress can be divided into thermal stress and shrinkage stress according to the different reasons.

(1) Thermal stress

During the solidification and cooling process of the casting, the stress caused by the unbalanced shrinkage of different parts is called thermal stress. The thermal stress causes the slow cooling thick wall to be stretched, and the fast cooling thin wall or surface to be compressed. During directional solidification, due to the inconsistent cooling rate of each part of the casting, the resulting thermal stress is large, and the casting is prone to deformation and cracks.

(2) Shrinkage stress

When the casting shrinks in the solid state, the stress generated due to the obstruction of external forces such as the mold, core, and pouring riser is called shrinkage stress. , Generally, after the casting is cooled to an elastic state, shrinkage stress will be generated when the shrinkage is blocked. Shrinkage stress is often expressed as tensile stress. Once the cause of formation is eliminated (for example, after the casting falls out or the gate is removed), the shrinkage stress is also eliminated, so the shrinkage stress is a temporary stress. However, before the falling sand, if the shrinkage stress and thermal stress of the casting work together and the instantaneous stress is greater than the tensile strength of the casting, cracks will occur in the casting.