Requirements for mold working conditions
1. Wear resistance
When the blank undergoes plastic deformation in the mold cavity, it flows and slides along the cavity surface, causing severe friction between the cavity surface and the blank, which causes the mold to fail due to wear. Therefore, the wear resistance of the material is one of the most basic and important properties of the mold.
Hardness is the main factor affecting wear resistance. Generally speaking, the higher the hardness of the mold parts, the smaller the wear and the better the wear resistance. In addition, wear resistance is also related to the type, quantity, form, size and distribution of carbides in the material.
2. Strength and toughness
Most of the mold working conditions are very bad, and some often bear large impact loads, resulting in brittle fracture. In order to prevent the mold parts from suddenly breaking during operation, the mold must have high strength and toughness. The toughness of the mold mainly depends on the carbon content, grain size and organizational state of the material.
3. Fatigue fracture performance
During the working process of the mold, under the long-term action of cyclic stress, fatigue fracture often occurs. Its forms include small energy multiple impact fatigue fracture, tensile fatigue fracture, contact fatigue fracture and bending fatigue fracture. The fatigue fracture performance of the mold mainly depends on its strength, toughness, hardness, and the content of inclusions in the material.
4. High temperature performance
When the working temperature of the mold is high, the hardness and strength will decrease, resulting in early wear or plastic deformation of the mold and failure. The mold material should have a high tempering resistance to ensure that the mold has a high hardness and strength at the working temperature.
5. Cold and hot fatigue resistance
Some molds are in a state of repeated heating and cooling during the working process, which makes the surface of the cavity tensile and pressure variable stress, causing surface cracking and peeling, increasing friction, hindering plastic deformation, and reducing dimensional accuracy, thus leading to mold failure. Cold and hot fatigue is one of the main forms of failure of hot working molds. This type of mold should have a high resistance to cold and hot fatigue.
6. Corrosion resistance
When some molds, such as plastic molds, are working, due to the presence of chlorine, fluorine and other elements in the plastic, after heating, they decompose and precipitate strong corrosive gases such as HCI and HF, which corrode the surface of the mold cavity, increase its surface roughness, and aggravate wear failure.