1. Requirements of mold working conditions.
1. After grinding.
When the blank is plastically deformed in the cavity, it flows and slides along the surface of the cavity, causing severe friction between the surface of the cavity and the blank, causing the mold to wear and fail. Therefore, the grindability of the material is one of the basic and important properties of the mold.
The main factor that affects the abrasion performance is the hardness. Generally speaking, the higher the hardness of the mold parts, the smaller the amount of wear and the better the wearability. In addition, the type, quantity, shape, size and distribution of carbides in the material also have some relations.
2. Strong toughness.
The working environment of most molds is very harsh, and some molds often bear great impact loads, which leads to brittle fracture. In order to prevent sudden brittle fracture of mold parts during work, the mold is required to have high strength and high toughness.
The toughness of the casting mold mainly depends on the carbon content, grain size and organization state of the material.
3. Fatigue fracture characteristics.
In the process of mold processing, under the action of cyclic stress, fatigue fracture is often caused. It has low energy multiple impact fatigue fracture, tensile fracture contact fatigue fracture and bending fatigue fracture.
The fatigue fracture performance mainly depends on the strength, toughness, hardness of the mold and the content of inclusions in the material.
4. High temperature properties.
When the working temperature is too high, the hardness and strength of the mold will decrease, leading to early wear of the mold or plastic deformation and failure. The mold material should have high anti-tempering stability to ensure that the mold has high hardness and strength at working temperature.
5. Resistance to cold and heat fatigue.
Some molds are repeatedly heated and cooled during the working process, causing the surface of the cavity to be subjected to tensile and pressure-changing stresses, causing surface cracks and peeling, increasing friction, hindering plastic deformation, reducing dimensional accuracy, and causing mold failure. Cold and thermal fatigue is one of the main forms of hot work die failure, and the die should have high resistance to cold and thermal fatigue.
6. Corrosion resistance.
When some molds such as plastic molds are in operation, due to the elements such as chlorine and fluorine in the plastic, the heat will resolve the strong corrosive gases such as HCI and HF, which will erode the surface of the mold cavity, increase the surface roughness, and aggravate wear failure.
2. Mold process performance requirements.
Manufacturing molds generally go through multiple 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 forgeability, machinability, hardenability, and grindability; it should also have low oxidation, decarburization sensitivity and quenching deformation cracking tendency .
Its hot forging deformation ability is small, plasticity is good, forging temperature range is wide, forging cracking and cold cracking, network carbide tendency is low.
2. The manufacturability of annealing.
The spheroidizing annealing temperature range is wide, the annealing hardness is low, the fluctuation range is small, and the spheroidizing rate is high.
3. Cutting performance.
High cutting consumption, reduce tool loss, and low surface roughness.
4. Sensitivity to oxidation and decarburization.
Oxidizer resistance has good grindability at high temperature, slow decarburization speed, insensitive to heating medium, and prone to pitting.
After hardening, the surface hardness is uniform and the hardness is high.
After hardening, a deeper hardened layer can be obtained, and a slow cooling medium is used for hardening during quenching.
7. Tendency of quenching deformation and cracking.
Ordinary quenching has small volume change, low warpage, light distortion, and low tendency of abnormal deformation. It is not sensitive to the quenching temperature and the shape of the workpiece, and is sensitive to the cracking of conventional quenching.
The relative wear of the grinding wheel is small, and the upper limit of grinding without burn is large. It is not sensitive to the quality of the grinding wheel and cooling conditions, and it is not easy to produce abrasion and grinding cracks.
Third, the economic requirements of the mold.
For the selection of mold materials, the principle of economy should be considered, and the manufacturing cost should be reduced as much as possible. Therefore, under the premise of satisfying the use performance, first choose lower-priced steel. Carbon steel does not need alloy steel, and Image production material does not need imported materials. In addition, the production and supply of the market should also be considered when selecting materials, and the selected steel grades should be as few and concentrated as possible, and easy to buy.
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