In the mould manufacturing, mouldselection is a very important part of the entire mould manufacturing process.
The selection of materials for the mouldneeds to meet three principles. The mould meets the work requirements of wear resistance and toughness. The mould meets the process requirements. At the same time, the mouldshould meet the economic applicability.
1. Wear resistance
When the blank is plastically deformed in the mouldcavity, it flows and slides along the surface of the cavity, which causes intense friction between the surface of the cavity and the blank, resulting in the failure of the moulddue 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. In general, the higher the hardness of the mouldparts, the smaller the amount of wear and the better the wear resistance. In addition, wear resistance is also related to the type, number, form, size and distribution of carbides in the material.
2. Strong toughness
Most of the working conditions of the mouldare very bad, and some often bear a large impact load, which leads to brittle fracture. In order to prevent the mouldparts from being brittlely broken at work, the mouldshould have high strength and toughness.
The toughness of the mouldmainly depends on the carbon content, grain size and microstructure of the material.
3. Fatigue fracture performance
In the mouldworking process, under the long-term effect of cyclic stress, it often leads to fatigue fracture. Its forms include low energy multiple impact fatigue fracture, tensile fatigue fracture contact fatigue fracture and bending fatigue fracture.
The fatigue fracture performance of the mouldmainly depends on its strength, toughness, hardness, and the content of inclusions in the material.
4. High temperature performance
When the working temperature of the mouldis higher, the hardness and strength will be reduced, resulting in early wear or plastic deformation of the mouldand failure. Therefore, the mouldmaterial should have a higher stability against tempering to ensure that the mouldhas a higher hardness and strength at the working temperature.
5. Cold and heat fatigue resistance
Some molds are in the state of repeated heating and cooling during the work process, which causes the surface of the cavity to be pulled and the stress of the pressure changes, causing surface cracking and flaking, increasing friction, hindering plastic deformation, and reducing dimensional accuracy, resulting in mouldfailure. Hot and cold fatigue is one of the main forms of hot work die failure. This type of die should have high resistance to cold and hot fatigue.
6. Corrosion resistance
When some molds such as plastic molds work, due to the presence of chlorine, fluorine and other elements in the plastic, after heating, the strong corrosive gases such as HCI and HF are resolved, eroding the surface of the mouldcavity, increasing its surface roughness, and aggravating wear failure.