Principles of Mold Material Selection

1) Meet the requirements of working conditions

1. Abrasion 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.

1. Toughness

The working conditions of the molds are mostly very bad, and some of them are often subjected to relatively large impact loads, resulting in 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, 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 mold mainly depends on its strength, toughness, hardness, and the content of inclusions in the material.

3. High temperature performance (Guide: Hardware Knowledge: Definition of Various Molds)

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 high anti-tempering stability to ensure that the mold has high hardness and strength at the working temperature.

4. Heat and cold fatigue resistance

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, hindering plastic deformation, and reducing 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.

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, 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 Wear failure.

(2) Meet process performance requirements

The manufacturing of molds generally involves 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 forgeability, machinability, hardenability, hardenability and grindability; it should also have small oxidation, decarburization sensitivity and quenching Deformation and cracking tendency.

1. Malleability

It has low hot forging deformation resistance, good plasticity, wide forging temperature range, low forging cold cracking and low tendency to precipitate network carbides.

2. Annealing processability

The spheroidizing annealing temperature range is wide, the annealing hardness is low, the fluctuation range is small, and the spheroidizing rate is high.

3. Machinability

Large cutting amount, low tool loss and low surface roughness.

4. 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.

5. Hardenability

It has uniform and high surface hardness after quenching.

6. Hardenability

After quenching, a deeper hardened layer can be obtained, and it can be hardened by using mild quenching medium.

7. Quenching deformation cracking tendency

The volume change of conventional quenching is small, the shape is warped, the distortion is slight, and the tendency of abnormal deformation is low. Conventional quenching has low sensitivity to cracking, and is insensitive to quenching temperature and workpiece shape.

8. Grindability

The relative wear of the grinding wheel is small, the limit grinding consumption is large without burns, and it is not sensitive to the quality of the grinding wheel and cooling conditions, and it is not easy to cause abrasion and grinding cracks.

(3) Meeting economic requirements

When selecting materials for molds, the principle of economy must be considered to reduce manufacturing costs as much as possible. Therefore, under the premise of satisfying the performance, first choose the lower price, carbon steel can be used without alloy steel, and domestic materials can be used without imported materials.

In addition, when selecting materials, the production and supply of the market should also be considered. The selected steel grades should be as few and concentrated as possible, and easy to buy.

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