Analysis Of The Causes Of Mold Failure
From the current actual situation, there are five main reasons for mold failure: plastic deformation failure; wear failure; fatigue failure; cold and heat fatigue failure; failure under the influence of comprehensive factors.
1.Plastic deformation failure
Mainly because the strength level of the mold material is not high; or the heat treatment process is not correct, failing to reach the best toughness of the steel; improper use of the mold causes local overload; the high temperature softening of the hot mold will also cause the thermoplastic deformation of the mold. . Failure of the shape deformation can cause deformation of the mold, which ultimately affects the quality of the forging.
2. Mold wear failure
The root cause of mold wear failure is the friction between the mold and the blank. However, the specific form of wear and the wear process are related to many factors, such as the pressure, temperature, billet deformation speed and lubrication condition of the mold during the working process.
For hot working molds, the wear resistance of the cavity surface is softened due to high temperature softening, and the scale itself acts as an abrasive, which determines that the wear process is more complicated. The wear failure of the mold mainly causes the forging die to wear, which affects the precision of the forging.
3. 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 local stress concentration, microcracks are still formed at the stress concentration under low load. While the mold is usually serviced under high strength and low plasticity, when microcracks are formed, the microcracks easily expand under the cyclic load of the mold and eventually cause fatigue fracture.
4. Cold and hot fatigue failure of the mold
For the hot work die, the surface temperature of the mold often rises to the range of 600-900 ° C due to interaction with the hot billet during operation. In order not to lower the strength of the mold, it is necessary to spray a coolant on the mold after the mold release to cool it.
This cycle is repeated, the process of the mold surface repeatedly undergoes rapid cooling and rapid heat accumulation, and a considerable cyclic thermal stress is accumulated on the surface of the mold, and the stress is finally released in the form of thermal fatigue, forming a thermal fatigue crack. As for the high temperature oxidation, the corrosion of the coolant and the friction between the mold and the high temperature billet, the process of accelerating the thermal fatigue is accelerated.
5. Failure under the influence of comprehensive factors
Because the actual working conditions of the mold are extremely complicated, a variety of damage forms can often occur on a pair of molds at the same time. Once these damages occur, they may promote each other and eventually accelerate the failure of the mold.