When choosing hardware mold materials, experts suggest that the focus should be on whether it can meet the following three requirements:
(1) The mold meets the economic requirements
When selecting materials for the mold, the principle of economy must be considered to reduce the manufacturing cost as much as possible. Therefore, under the premise of satisfying the performance, the first choice is the lower price, carbon steel can be used without alloy steel, and domestic materials can be used without imported materials. In addition, the production and supply of the market should also be considered when selecting materials. The selected steel grades should be as few and concentrated as possible and easy to buy.
(2) The mold meets the requirements of working conditions
1. Strength and toughness: Most of the working conditions of the mold are very bad, and some often bear a large impact load, which leads to brittle fracture. In order to prevent sudden brittle fracture of mold parts during work, the mold must have high strength and toughness. The toughness of the mold mainly depends on the carbon content, grain size and organization state of the material.
2. Fatigue fracture performance: In the process of mold work, under the long-term action of cyclic stress, fatigue fracture is often caused. 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 mold mainly depends on its strength, toughness, hardness, and the content of inclusions in the material.
3. High temperature performance: When the working temperature of the mold is higher, the hardness and strength will decrease, leading to early wear of the mold or plastic deformation and failure. Therefore, the mold material should have a higher anti-tempering stability to ensure that the mold has a higher hardness and strength at the working temperature.
4. Resistance to cold and heat fatigue: some molds are in a state of repeated heating and cooling during the working process, which causes the surface of the cavity to be stretched and pressure to change stress, causing surface cracks and peeling, increasing friction and hindering plastic deformation , Reducing the dimensional accuracy, resulting in mold failure. Heat and cold fatigue is one of the main forms of failure of hot work molds, and this type of mold should have high resistance to cold and heat fatigue.
5. Corrosion resistance: When some molds such as plastic molds are working, due to the presence of elements such as chlorine and fluorine in the plastic, they will separate and resolve strong corrosive gases such as HCI and HF after being heated, which will erode the surface of the mold cavity and increase its surface roughness. Degree, aggravate wear failure.
6. Wear resistance: When the blank is plastically deformed in the mold cavity, it flows and slides along the surface of the cavity, causing violent friction between the surface of the cavity 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. 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.
(3) The mold meets the process performance requirements
The manufacturing of molds generally involves several processes such as forging, cutting, and heat treatment. In order to ensure the quality of mold manufacturing and reduce production costs, the material should have good forgeability, machinability, hardenability, hardenability and grindability; it should also have a small sensitivity to oxidation, decarburization and quenching Deformation and cracking tendency.
1. Hardenability: uniform and high surface hardness after quenching.
2. Machinability: large cutting amount, low tool loss, and low surface roughness.
3. Hardenability: After quenching, a deeper hardened layer can be obtained, and it can be hardened by using mild quenching medium.
4. Annealing processability: wide spheroidizing annealing temperature range, low annealing hardness and small fluctuation range, high spheroidizing rate.
5. Forgeability: It has low hot forging deformation resistance, good plasticity, wide forging temperature range, low forging cold cracking and low tendency to precipitate network carbides.
6. Sensitivity to oxidation and decarburization: It has good anti-oxidation ability when heated at high temperature, slow decarburization speed, insensitive to heating medium, and little tendency to produce pitting.
7. Grindability: The grinding wheel is relatively low in wear, and the non-burn limit grinding consumption is large. It is not sensitive to the quality of the grinding wheel and the cooling conditions, and it is not easy to cause abrasion and grinding cracks.
8. Quenching deformation cracking tendency: conventional quenching has small volume change, shape warping, slight distortion, and low abnormal deformation tendency. Conventional quenching has low sensitivity to cracking, and is insensitive to quenching temperature and workpiece shape.