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.