Several principles of mold selection

(I) Molds meet working conditions

1, wear resistance

When the billet plastically degenerates in the cavity of the mold, it flows and slides along the surface of the cavity, causing violent friction between the surface of the cavity and the blank, resulting in 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 the main factor affecting wear resistance. Under normal circumstances, 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, number, morphology, size, and distribution of carbides in the material.

2, toughness

Most of the working conditions of the mold are very harsh, and some often suffer from a large impact load, resulting in brittle fracture. In order to prevent the mold parts from suddenly breaking during work, the mold must have high strength and toughness. The toughness of the mold depends mainly on the carbon content, grain size, and microstructure of the material.

3, fatigue fracture performance

During the working of the mold, under the long-term effect of cyclic stress, fatigue fracture often occurs. In the form of small energy multiple impact fatigue fracture, tensile fatigue fracture contact fatigue fracture and bending fatigue fracture. The fatigue fracture properties of a mold depend primarily on its strength, toughness, hardness, and inclusion content in the material.

4, high temperature performance

When the working temperature of the mold is higher, the hardness and strength will be reduced, 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 higher hardness and strength at working temperature.

5, cold and hot fatigue resistance

Some molds are in a state of repeated heating and cooling during the working process, which causes the stress on the surface of the cavity to be pulled and the stress changes, causing cracking and flaking of the surface, increasing the frictional force, impeding the plastic deformation, and reducing the dimensional accuracy, thereby resulting in Mold failure. Hot and cold fatigue is one of the main forms of failure of hot work molds, and these types of molds should have high resistance to hot and cold fatigue.

6, corrosion resistance

Some molds such as plastic molds work, due to the presence of chlorine in the plastic, fluorine and other elements, after heat analysis of HCI, HF and other aggressive gases, erosion mold cavity surface, increase its surface roughness, increase wear and tear failure.

(B) mold to meet the process performance requirements

The manufacture of molds generally has to undergo several processes such as forging, cutting, and heat treatment. In order to ensure the quality of molds and reduce production costs, the materials should have good forgeability, machinability, hardenability, hardenability, and grindability; it should also have small oxidation, decarburization sensitivity, and quenching. Deformation cracking tendency.

1, forgeability

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

2, annealing process

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

3, cutting processability

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

4 oxidation, decarburization sensitivity

Antioxidation is good at high temperature heating, the decarburization rate is slow, and it is not sensitive to the heating medium, resulting in a small pitting tendency.

5, hardenability

Quenched with a uniform and high surface hardness.

6, hardenability

After quenching, a deeper hardened layer can be obtained, which can be quenched with a mild quenching medium.

7, quenching deformation cracking tendency

The conventional quenching volume changes little, the shape is warped, the distortion is slight, and the abnormal deformation tends to be low. Conventional quench cracking susceptibility is low, insensitive to quenching temperature and workpiece shape.

8. Grindability

The relative loss of the grinding wheel is small, there is no large amount of grinding limit for grinding, and it is not sensitive to the quality of the grinding wheel and the cooling conditions. It is not easy to cause grinding and grinding cracks.

(three) mold to meet the economic requirements

In the selection of materials for molds, the principle of economy must be taken into account and manufacturing costs should be reduced as much as possible. Therefore, under the premise of satisfying the use performance, the first choice of low-cost, can use carbon steel will not use alloy steel, can use domestic materials do not have imported materials.

In addition, when selecting materials, the production and supply of the market should also be taken into account. The selected steel types should be as small and concentrated as possible and easy to purchase.