(I) the mold meets the requirements of working conditions
1. Wear resistance
When the blank is plastic in the mold cavity, it flows and slides along the surface of the mold cavity. So material wear resistance mold is the most basic, one of the most important properties.
Hardness is the main factor affecting wear resistance. Generally speaking, the higher the hardness of die parts, the less the wear, 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
The working conditions of the die are often very bad, some often bear a large impact load, resulting in brittle fracture. In order to prevent the die parts from breaking suddenly, the die should have high strength and toughness.
The toughness of the die mainly depends on the carbon content, grain size and microstructure of the material.
3. Fatigue fracture performance
In the working process of die, fatigue fracture is often caused by cyclic stress. Its forms include small energy multiple impact fatigue fracture, tensile fatigue fracture contact fatigue fracture and bending fatigue fracture.
The fatigue fracture performance of die mainly depends on its strength, toughness, hardness, and inclusion content.
4. High temperature performance
When the working temperature of the mold is higher, the hardness and strength will decrease, leading to early wear or plastic deformation of the mold and failure. Therefore, the mold material should have a higher tempering stability, to ensure that the mold at the working temperature, has a higher hardness and strength.
5. Heat and cold fatigue resistance
Some die in the process of work in the state of repeated heating and cooling, so that the cavity surface under tension, pressure stress, cause surface cracking and peeling, increase friction, resistance to plastic deformation, reduce dimensional accuracy, resulting in mold failure. Hot and cold fatigue is one of the main forms of failure of hot working die.
6. Corrosion resistance
When some molds, such as plastic molds, are working, due to the presence of chlorine, fluorine and other elements in the plastics, HCI, HF and other strong corrosive gases are decomposed and separated after heating, eroding the surface of mold cavity, increasing its surface roughness and aggravating wear failure.
(ii) the mold meets the process performance requirements
Die manufacturing generally through forging, cutting, heat treatment and other procedures. In order to ensure the manufacturing quality of the mold and reduce the production cost, the material should have good forgability, machinability, hardenability, hardenability and grindability; It should also have small oxidation, decarburization sensitivity and quenching deformation and cracking tendency.
1. Malleability
It has low deformation resistance of hot forging, good plasticity, wide forging temperature range, low tendency of cold cracking and precipitates network carbide.
2. Annealing processability
Spheroidizing annealing temperature range is wide, annealing hardness is low and fluctuation range is small, spheroidizing rate is high.
3, machinability
Large cutting amount, low tool loss and low machining surface roughness.
4. Sensitivity to oxidation and decarbonization
High temperature heating, good antioxidant capacity, slow decarbonization, insensitive to heating medium, small tendency to pitting.
5. Hardening
It has uniform and high surface hardness after quenching.
6. Hardenability
A deeper hardening layer can be obtained after quenching and can be hardened by using a mild quenching medium.
7. Hardening deformation and cracking tendency
The volume change of conventional quenching is small, the shape warping and distortion are slight, and the abnormal deformation tendency is low. Conventional quenching has low cracking sensitivity and is insensitive to quenching temperature and workpiece shape.
8. Grindability
Grinding wheel relatively small loss, no burn limit grinding consumption is large, it is not sensitive to grinding wheel quality and cooling conditions, it is not easy to occur grinding injury and grinding crack.
(iii) the mold meets the economic requirements
In selecting material for the mould, we must consider the principle of economy and reduce the manufacturing cost as much as possible. Therefore, under the premise of meeting the use of performance, choose the lower price first, can use carbon steel without alloy steel, can produce materials without import materials. In addition, the selection of materials should also consider the production and supply of the market, the selected steel should be as little as possible and concentrated, easy to buy.