Technical requirements for Mold manufacturing

In the manufacturing process of molds, the choice of mould materials economy must be considered, as much as possible to reduce manufacturing costs. Therefore, under the premise of satisfying the performance of the use, the first choice of low price raw materials, carbon steel can be used instead of alloy steel, and domestic materials can be used instead of imported materials. In addition, when selecting materials, the production and supply of materials in the market should also be considered. The selected steel grades should be as few and concentrated as possible, and easy to purchase and deliver.

Pay attention to the following aspects in the manufacturing process of abrasive tools:

（一）The working conditions of the mold 

1. Wear resistance

When the blank is plastically deformed in the mold cavity, it flows and slides along the surface of the cavity, causing severe friction between the surface of the cavity and the blank, which leads to the mold to fail 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. 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.

2. Strength

The working conditions of the molds are mostly very bad, and some often bear a large impact load, which leads to brittle fracture. In order to prevent the mold parts from suddenly brittle fracture at work, the mold should have higher strength and toughness.

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

3. Fatigue fracture performance

Fatigue fracture is often caused by cyclic stress in the process of die work. 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.

4. High temperature performance

When the working temperature is high, the hardness and strength of the mold 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 working temperature.

5. Heat and cold fatigue resistance

For some molds, such as plastic molds, strong aggressive and corrosive gases are decomposed and precipitated after heated due to the presence of chlorine, fluorine and other elements in the plastic during work, which will erode the surface of the mold cavity, increase its surface roughness, and aggravate wear failure.

Some molds ,such as plastic molds are in a state of repeated heating and cooling during the working process, causing the surface of the cavity to be subjected to the overlapping effects of tension, pressure and variable stress, causing surface cracks and peeling, increasing friction, hindering plastic deformation, and reducing dimensional accuracy .

（二）Process performance requirements for the mold

In the manufacturing process, molds are generally processed several procedures, such as forging, cutting, and heat treatment. In order to ensure the manufacturing quality of the mold and reduce production costs, the selected material should have good forgeability, machinability, hardenability, quenching degree and grindability; it should also have slight oxidation, decarburization sensitivity and quenching Deformation and cracking tendency.

1. Forgeability

　　Low hot forging deformation resistance, good plasticity, wide forging temperature range, forging cracking cold cracking and low tendency to precipitate mesh carbide.

2. Annealing processability

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

3. Machinability

　　Available for large feed cutting amount,  have low tool loss, low machining surface roughness.

4. Sensitivity to oxidation and decarburization

　　 Good oxidation resistance when heated at high temperature, slow decarburization speed, insensitive to heating medium and small tendency to 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 a mild quenching medium.

7. Tendency of quenching deformation and cracking

　　 The volume change of conventional quenching is small, the warping and distortion shape are slight, and the tendency of abnormal deformation is low. Conventional quenching has low cracking sensitivity and is not sensitive to quenching temperature and workpiece shape.

8. Grindability

　　The grinding wheel is relatively low wear, no burn limit, large grinding amount, insensitive to the quality of the grinding wheel and cooling conditions, and it is not easy to cause abrasion and grinding cracks.

(三) Economic requirements of molds

When selecting mold materials, the principle of economic applicability should be taken into consideration while meeting the requirements for use, and the manufacturing cost should be reduced as much as possible.