First, plastic deformation. When the load borne by the die exceeds the yield strength of die steel, the die will produce plastic deformation. Such as cavity and hole expansion, corner collapse, die core upsetting, longitudinal bending and so on.

Second, wear and tear. During the use of the mold, due to the deformation and flow of metal, strong friction occurs on the surface of the mold, resulting in the loss of surface materials of the mold, changing the geometric shape and roughness of the mold, causing the shape, size and surface quality of the processed parts to be unqualified, and the mold is invalid. In addition, in the process of friction, some blank metals adhere to the working face of the die, which changes the geometry of the die and makes it impossible to continue serving, which is also regarded as wear failure. Therefore, the wear failure is characterized by edge passivation, fillet, plane subsidence, surface groove passivation, peeling and die sticking.

Third, fatigue (fracture). It means that in some parts of the mold, after a certain service period, tiny cracks begin to appear and gradually expand in depth. After the crack grows to a certain size, the bearing capacity of the die is seriously weakened, leading to fracture. Fatigue cracks originate from places with high stress, especially those with concentrated stress (size transition, notch, tool marks, grinding cracks, etc.). ).