Mold material selection is a very important part in the whole process of mold making.

Mold material selection needs to meet three principles, mold to meet wear resistance, strong toughness and other work requirements, mold to meet the process requirements, and mold should meet the economic applicability.

requirements

1. Wear resistance

When the blank is plastic denudation in the mold cavity, it flows and slides along the cavity surface, causing severe friction between the cavity surface and the blank, which leads to the failure of the mold due to wear. So 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. Generally, the higher the hardness of the mold parts, the smaller the amount of wear, wear resistance is also better. In addition, the wear resistance is also related to the type, amount, shape, size and distribution of carbides in the material.

2. Strong toughness

Most of the working conditions of the die are very bad, some of them often bear a large impact load, which leads to brittle fracture. In order to prevent die parts from breaking suddenly when working, the die should have high strength and toughness.

The toughness of the mould mainly depends on the carbon content, grain size and microstructure of the material.

3. Fatigue fracture property

In the process of die working, fatigue fracture is often caused by the long-term action of cyclic stress. It has the forms of multiple impact fatigue fracture of small energy, contact fatigue fracture of tensile fatigue fracture and bending fatigue fracture.

The fatigue fracture performance of the die mainly depends on its strength, toughness, hardness, and the content of inclusions in the material.

4. The high temperature performance

When the working temperature of the mold is higher, the hardness and strength will decrease, resulting in early mold wear or plastic deformation and failure. Therefore, the mold material should have a high tempering stability, to ensure that the mold in the working temperature, has a high hardness and strength.

5. Thermal and cold fatigue resistance

Some moulds are in the state of repeated heating and cooling in the working process, which causes the surface of the cavity to be pulled and stressed by pressure, causing the surface to crack and peel off, increasing the friction force, preventing the plastic deformation, reducing the dimensional precision and leading to the failure of the mould. Cold and hot fatigue is one of the main forms of hot die failure.

6. The corrosion resistance

Some molds, such as the plastic mold, work because of the presence of chlorine, fluorine and other elements in the plastic, hot decomposition of HCI, HF and other strong erosive gas, erosion of the mold cavity surface, increase its surface roughness, increase wear failure.

Process performance

Mold manufacturing is generally through forging, cutting, heat treatment and other processes. In order to ensure the manufacturing quality of the mold and reduce the production cost, the material should have good malleability, machinability, hardenability, hardenability and grindability; There should also be a small oxidation, decarbonization sensitivity and quenching deformation cracking tendency.

1. malleability

It has low deformation resistance of hot forging, good plasticity, wide forging temperature range, low tendency of forging cracking, cold cracking and net carbide precipitation.

2. Annealing process

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

3. machinability

Large cutting parameters, low tool loss, low surface roughness.

4. Sensitivity to oxidation and decarbonization

When heated at high temperature, the oxidation resistance is good, the decarburization speed is slow, is not sensitive to the heating medium, produces pitting tendency is small.

5. hardenability

It has uniform and high surface hardness after quenching.

6. hardenability

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

7. Quenching deformation cracking tendency

The normal quenching volume changes little, the shape warps slightly, the distortion is slight, the abnormal deformation tendency is low. Conventional quenching cracking is insensitive to quenching temperature and workpiece shape.

8. Grinding can be

The grinding wheel is relatively small in loss, without burn limit grinding consumption is large, the grinding wheel quality and cooling conditions are not sensitive, not easy to wear and grinding cracks.