Failure forms of the mold

The actual working condition of the mold is very complicated, so there will be a variety of damage forms, and they will interact with superimposed influence. Wear will promote plastic deformation and fracture, and plastic deformation will increase the rate of wear and fracture. The basic forms of mold failure are: wear, fracture, and plastic deformation.

1. Wear

The friction between the mold and the processed blank billet causes the loss of material on the surface of the mold, and the geometric shape of the mold changes and cannot continue to serve, which is wear failure.

Wear failure is manifested as dullness of the cutting edge, rounded edges and corners, flat surface depression, surface groove marks, peeling, and mucous membranes.

Influencing factors: the chemical composition and mechanical properties of the mold material and the processed blank;

The surface state of the mold material and blank (oxidized film, surface treatment);

The state of pressure, temperature, speed and lubrication in the stamping process.

The wear resistance of the mold depends on the hardness of the mold material, especially the nature, size, distribution and quantity of hardened phases such as carbides.

According to the wear mechanism, it can be divided into abrasive wear, adhesive wear, fatigue wear, cavitation and erosion wear, and corrosion wear.

2. Fracture

 The fractures are mainly brittle fracture, fatigue fracture, ductile fracture, creep fracture, and stress corrosion fracture. The main factors that cause fracture: the surface shape of the mold (abrupt grooves, sharp corners and other parts are prone to stress concentration and crack formation), material properties (metallurgical quality, fracture toughness of the material)

3. Plastic deformation

When the load on the mold exceeds the yield strength of the mold steel itself, the mold will undergo plastic deformation, changing the geometry and size of the mold. If it cannot be repaired, it will be plastic deformation failure when it is put into service again.

The main failure modes are cavity expansion, collapse, bending, and upsetting.

The plastic deformation of the mold is the yield process of the mold metal material: the local stress is greater than the yield strength of the mold.

Factors affecting mold life

There are many reasons for the end of mold failure life, such as: unreasonable mold design, poor mold material quality, improper machining, improper heat treatment system, improper surface strengthening, improper operation method, etc.