The use of molds often has failures. Starting from reality, we will focus on several failure modes. There are five main types:
1, plastic deformation failure
It is mainly due to the low level of strength of the mold material; or the incorrect heat treatment process, which fails to achieve the best toughness of the steel; local overload occurs when the mold is improperly used; and the thermoplastic deformation of the mold may be caused by the high temperature softening of the hot mold. . Failure of plastic deformation can lead to deformation of the mold, which ultimately affects the quality of the forging.
2, the mold wear failure
The root cause of die wear failure is the friction between the die and the blank. However, the specific form of wear and the wear process are related to many factors; the pressure, temperature, billet deformation speed, and lubrication conditions of the mold during the work process. For hot work molds, the wear surface of the cavity surface is softened by high temperature and the wear resistance is reduced. In addition, the oxide skin itself also acts as an abrasive, which determines that the wear process is more complicated. The wear failure of the die mainly causes wear of the forging die and affects the accuracy of the forging.
3, the fatigue failure of the mold
The root cause of mold fatigue failure is stress concentration and cyclic loading. Although the load on the mold is sometimes significantly lower than its yield strength, due to the local stress concentration, micro cracks may still form at the stress concentration under low loads. The molds are usually in service under high strength and low plasticity. When the microcracks are formed, the microcracks can easily expand under the cyclic loading of the mold and eventually lead to fatigue fracture.
4, the thermal fatigue failure of the mold
For hot work molds, due to the interaction with hot billets, the mold surface temperature often rises to the range of 600~900°C. In order not to reduce the strength of the mold, the mold must be sprayed with a cooling agent to cool it. In this way, it is a process in which the surface of the die undergoes repeated quenching and rapid heating, and a considerable amount of cyclic thermal stress is accumulated on the surface of the die, and the stress is finally released in a manner of thermal fatigue to form a cold-heat fatigue crack. As for high-temperature oxidation, corrosion of the coolant, and friction between the mold and the high-temperature billet, this process accelerates the thermal fatigue.
5. Failure under the influence of comprehensive factors
The working conditions of the mold are all intricate and complex. Therefore, the occurrence of damage occurs from time to time. Once damage is caused, they may promote each other and eventually accelerate the failure of the mold.
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