Mold material selection is a very important part of the entire mold making process.
Mold material selection needs to meet three principles. The mold meets the work requirements of wear resistance, strength and toughness, the mold meets the process requirements, and the mold should meet economic applicability.
The Condition requirements Of Mold Material Selection
1. Wear resistance
When the blank is plastically deformed in the mold cavity, it flows and slides along the surface of the cavity, causing violent friction between the surface of the cavity and the blank, which causes the mold to fail 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. 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.
The working conditions of the molds are mostly very bad, and some of them are often subjected to large impact loads, which leads to brittle fracture. In order to prevent sudden brittle fracture of mold parts during work, the mold must have high 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
In the process of mold work, under the long-term action of cyclic stress, fatigue fracture is often caused. 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 of the mold is higher, the hardness and strength 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 the working temperature.
5. Heat and cold fatigue resistance
Some molds are in a state of repeated heating and cooling during the working process, which causes the surface of the cavity to be pulled and pressure to change the stress, causing surface cracks and peeling, increasing friction, hindering plastic deformation, and reducing dimensional accuracy. Mold failure. Heat and cold fatigue is one of the main forms of failure of hot work molds, and this type of mold should have high resistance to cold and heat fatigue.
6. Corrosion resistance
When some molds such as plastic molds are in operation, due to the presence of chlorine and fluorine in the plastics, strong corrosive gases such as HCI and HF will be resolved after being heated, which will erode the surface of the mold cavity, increase its surface roughness, and aggravate wear failure.
The Process Performance Of Mold Material Selection
The manufacturing of molds generally involves several processes such as forging, cutting, and heat treatment. In order to ensure the quality of mold manufacturing and reduce production costs, the material should have good forgeability, machinability, hardenability, hardenability and grindability; it should also have small oxidation, decarburization sensitivity and quenching Deformation and cracking tendency.
It has low hot forging deformation resistance, good plasticity, wide forging temperature range, low tendency of forging cracking and cold cracking and precipitation of networked carbides.
2. Annealing processability
The spheroidizing annealing temperature range is wide, the annealing hardness is low, the fluctuation range is small, and the spheroidizing rate is high.
The cutting amount is large, the tool loss is low, and the machined surface roughness is low.
4. Sensitivity to oxidation and decarburization
When heated at high temperature, the oxidation resistance is good, the decarburization speed is slow, the heating medium is not sensitive, and the tendency of pitting is small.
After quenching, it has uniform and high surface hardness.
After quenching, a deeper hardened layer can be obtained, and it can be hardened by using a mild quenching medium.
7. Quenching deformation cracking tendency
Conventional quenching has small volume change, shape warping, slight distortion, and low tendency of abnormal deformation. Conventional quenching has low sensitivity to cracking, and is insensitive to quenching temperature and workpiece shape.
The relative wear of the grinding wheel is small, and the 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 cause abrasion and grinding cracks.