(1) The mold meets the requirements of the working conditions
1. When the wear-resistant
blank is plastically deformed in the mold cavity, it both flows and slides along the surface of the cavity, causing severe friction between the surface of the cavity and the blank, thus causing the mold to wear and tear. invalid. Therefore, the material’s wear resistance is one of the mold’s most basic and important properties.
Hardness is the main factor affecting wear resistance. In general, the higher the hardness of the mold parts, the smaller the amount of wear and the better the wear resistance. In addition, wear resistance is also related to the type, quantity, shape, size, and distribution of carbides in the material.
2. Most of the working conditions of strong and tough
Molds are very bad, and some often bear large impact loads, resulting in brittle fractures. In order to prevent sudden brittle fracture of mold parts 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 is often caused. 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 of the mold or plastic deformation and failure. Therefore, the mold material should have high anti-tempering stability to ensure that the mold has high hardness and strength at working temperature.
5. Heat and cold fatigue resistance
Some molds are in a state of repeated heating and cooling during the working process, so the surface of the cavity is subjected to tension, pressure, and stress, causing surface cracking and peeling, increasing friction, and hindering plastic deformation. Reduced dimensional accuracy, leading to dying failure. Hot and cold fatigue is one of the main forms of loss of hot work dies, and these dies should have high resistance to cold and heat 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, strong corrosive gases such as HCI and HF are decomposed after heating, which erodes the surface of the mold cavity and increases its surface roughness. , aggravating wear failure.
(2) The mold meets the process performance requirements
Mold manufacturing generally has to go through several processes such as forging, cutting, and heat treatment. In order to ensure the manufacturing quality of the mold and reduce the production cost, the material should have good forge ability, machinability, hardenability, hardenability, and grind ability; it should also have small oxidation, decarburization sensitivity, and quenching properties. Deformation and cracking tendency.
1. Forgeability
has low hot forging deformation resistance, good plasticity, wide forging temperature range, a low tendency for forging cracking and cold cracking, and precipitation of network carbides.
2. Annealing process
The annealing temperature range is wide, the annealing hardness is low and the fluctuation range is small, and the rate is high.
3. Machinability The cutting amount is large, the tool loss is low, and the machined surface roughness is low.
4. Sensitivity to oxidation and decarburization. When heated at a high temperature, the oxidation resistance is good, the decarburization speed is slow, it is not sensitive to the heating medium, and the tendency to produce pitting is small.
5. Hardenability
After quenching, it has a uniform and high surface hardness.
6. Hardenability After quenching, a deep hardened layer can be obtained, which can be hardened by using a mild quenching medium.
7. Quenching deformation and cracking tendency
The conventional quenching volume change is small, the shape is warped, the distortion is slight, and the abnormal deformation tendency is low. Conventional quenching has low cracking sensitivity and is not sensitive to quenching temperature and workpiece shape.
8. Grindable grinding of the wheel has a small relative loss, a large amount of grinding without burn limit, is insensitive to grinding wheel quality and cooling conditions, and is not prone to wear and grinding cracks.
(3) The mold meets the economic requirements.
When selecting the mold material, the principle of the economy must be considered to reduce the manufacturing cost as much as possible. Therefore, under the premise of satisfying the performance, first, choose the lower price, if you can use carbon steel, you don’t need alloy steel, and if you can use domestic materials, you don’t need imported materials.
In addition, the production and supply situation in the market should also be considered when selecting materials. The selected steel grades should be as few and concentrated as possible and easy to purchase.
