The principle of material selection of molds
1) Abrasion resistance
When the blank is plastically deformed in the mold cavity, it flows and slides along the surface of the mold cavity, causing severe friction between the mold cavity surface and the blank, resulting in the failure of the mold due to wear. Therefore, the wear resistance of the material is one of the most basic and important properties of the mold.
Hardness is a major factor affecting wear resistance. Generally speaking, the higher the hardness of the mold parts, the smaller the amount of wear and the better the wear resistance. In addition, abrasion resistance is also related to the material.
2) Strength and toughness
Most molds work in very harsh conditions, and some molds are often subjected to large impact loads, resulting in brittle fractures. In order to prevent the mold parts from breaking suddenly while working, the mold should have high strength and toughness.
The toughness of the mold is mainly determined by the carbon content, grain size and microstructure of the material.
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3) Fatigue fracture properties
During the working process of the mold, under the long-term action of cyclic stress, it often leads to fatigue fracture. Its forms include low-energy multi-impulse fatigue fracture, tensile fatigue fracture, contact fatigue fracture and bending fatigue fracture.
The fatigue fracture properties of a mold are mainly determined by its strength, toughness, hardness and the amount of inclusions in the material.
4) High temperature performance
When the working temperature of the mold is higher than Ag, the hardness and strength of the mold will decrease, resulting in premature wear or plastic deformation of the mold and failure. Therefore, the mold material should have high tempering stability to ensure that the mold has high hardness and strength at the working temperature.
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5) Resistance to cold and heat fatigue
Some molds are in a state of repeated heating and cooling in the working process, which changes the stress on the surface of the cavity under the action of tension and compression, causing surface cracking and peeling, increasing friction, hindering plastic deformation, and reducing dimensional accuracy, resulting in mold failure. Hot and cold fatigue is one of the main failure forms of hot work molds, so this kind of molds should have high resistance to cold and hot fatigue.
6) Rotting resistance
When some molds such as plastic molds are working, due to the presence of chlorine, fluorine and other elements in the plastic, corrosive gases such as Hci and Hf will be resolved after heating, which will erode the surface of the mold cavity, increase its surface roughness, and aggravate the wear and failure.
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