How about the material selection and process performance of the mold?

Die material selection

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

The mold material selection needs to meet three principles, the mold meets the work needs of wear resistance, strength and toughness, the mold meets the process requirements, and the mold should meet the economic applicability.

Conditional requirement

1. Wear resistance

When the billet is plastic denaturated in the mold cavity, it flows and slides along the surface of the mold cavity, causing severe friction between the surface of the mold cavity and the billet, resulting in the 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 wear amount, and the better the wear resistance. In addition, the wear resistance is also related to the type, quantity, shape, size and distribution of carbides in the material.

2. Strength and toughness

Most of the working conditions of the mold are very bad, and some often bear a large impact load, resulting in brittle fracture. In order to prevent the sudden brittle break of the mold parts during work, the mold should have high strength and toughness.

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

3. Fatigue fracture property

In the process of mold operation, the long-term action of cyclic stress 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 die 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 higher, the hardness and strength will decrease, resulting in early wear or plastic deformation of the mold and failure. Therefore, the mold material should have a high tempering stability to ensure that the mold has a high hardness and strength at the working temperature.

5. Resistance to cold and heat fatigue

Some molds are in the state of repeated heating and cooling during the working process, so that the surface of the cavity is strained and the pressure changes the stress, causing the surface cracking and spalling, increasing the friction force, hindering the plastic deformation, reducing the dimensional accuracy, resulting in the failure of the mold. Hot and cold fatigue is one of the main failure forms of hot working die, and this kind of die should have high resistance to cold and heat fatigue.

6. Corrosion resistance

Some molds, such as plastic molds, when working, due to the presence of chlorine, fluorine and other elements in the plastic, after heat decomposition and precipitation of HCI, HF and other strong corrosive gases, erosion of the surface of the mold cavity, increase its surface roughness, exacerbate wear failure.

Process performance

The manufacture of molds generally goes 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 malleability, machinability, hardenability, hardenability and grindability. It should also have a small oxidation, decarburization sensitivity and hardening deformation cracking tendency.

1. malleability

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

2. annealability

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, low machining surface roughness.

4. Oxidation and decarbonization sensitivity

When heated at high temperature, the antioxidant capacity is good, the decarburization rate is slow, the heating medium is insensitive, and the pitting tendency is small.

5. hardenability

Uniform and high surface hardness after quenching.

6. hardenability

After quenching, a deeper hardening layer can be obtained, and the quenching medium can be hardened using a moderate quenching medium.

Seven. Hardening deformation cracking tendency

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

8. grindability

Grinding wheel relative loss is small, no burn limit grinding amount is large, not sensitive to grinding wheel quality and cooling conditions, not easy to wear and grinding cracks.