In the actual application, the factory often determines that the mold has failed when the cost of re-maintenance reaches about 1/3-1/2 of the re-production cost, and then the repair is often not worth the loss. The failure of the mold is divided into abnormal failure and normal failure.

Abnormal failure (early failure) means that the mold cannot be used when it has not reached the industry’s recognized life.

Normal failure means that the mold cannot be used continuously after being used in large quantities due to slow plastic deformation or relatively uniform wear or fatigue fracture.

Despite the wide variety of molds, the working conditions are very different, and the damaged parts are different, but according to the failure form, it can be divided into three types: wear failure, fracture failure and plastic deformation failure.

(1) Wear is caused by the relative movement of the surface, and the contact surface gradually loses material;

(2) Fracture, which is divided into plastic fracture and brittle fracture, and brittle fracture can be divided into one-time fracture and fatigue fracture;

(3) Plastic deformation, when the stress of a part of the mold exceeds the yield limit of the mold material at the current temperature, plastic deformation occurs due to lattice slip, twinning, grain boundary slip, etc. Geometric shape or size, and can not be repaired and re-serviced, showing up, bending, swelling, collapse and so on. The plastic deformation of the mold is the yielding process of the mold metal material.

The service life of the mold is related to the mold design level, the mold structure, the heat treatment of the mold material, the material selection, the machining process, and the smoothness of the mold. According to the analysis and statistics of a large number of failed molds, among the various factors causing the mold failure, the mold failure is caused by the unreasonable mold structure, which accounts for about 25%. Therefore, the reasonable mold structure is designed to improve the quality and service life of the mold. Will play a multiplier role. Reasonable mold structure design should make the mold work evenly, not easy to be biased, and the stress concentration is small.

Regardless of the type of mold, the formwork should have good rigidity, and the formwork should not be too thin. When the working machine space is sufficient, the thickness should be increased as much as possible, not only to meet the strength requirements of the formwork, but also to consider the rigidity of the formwork. Judging from the large-scale imported molds, the phenomenon of thinner templates is common in domestic molds. The main reason is the lack of understanding of the rigidity of the mold base.

For multi-station molds, it is often difficult to ensure the accuracy of the guide by two guide pillar guides. Four guide pillar guides should be used, and six guide pillar guides should be considered for large molds. When using multiple guide pillars, the positional accuracy of the relevant parts should be given special attention.

For the forming part of the mold, the radius of the corner of the working part not only affects the molding process and the quality of the part, but also affects the failure form and life of the mold. Under the premise of meeting the requirements of the product, try to increase the size. The working part transitions the fillet radius, which has an unexpected effect on increasing the life of the mold. For occasions where the fillet radius cannot be increased and the complicated structure of the die, the insert structure can be considered, which also reduces the stress concentration.

For the stamping die, under the premise of ensuring the dimensional accuracy of the workpiece, the gap between the convex and concave molds is reasonably increased to improve the stress state of the working part of the punch, so that the punching force, the unloading force and the pushing force are reduced, and convex The die edge wear is reduced, thereby increasing the life of the mold.

Multi-station high-speed progressive stamping die should pay attention to the problem of scrapback of the scrap, and increase the corresponding measures in the structure to avoid the phenomenon of micro-slack rebound caused by the instantaneous vacuum effect during high-speed stamping, so that the scrap enters the working area and the convex die blade The mouth is cracked.

For high-temperature molds such as hot forging dies, heat dissipation and cooling are not negligible in structural design. Local temperature should be avoided and plastic deformation of the mold material should be avoided.