Mold selection is an important part of the whole process of mould making.
The mold selection needs to meet the three principles, the mold meets wear-resisting, toughening and other work demands, the mold meets the technical requirements, and the mould should meet the economic application.
The mold meets the working conditions
1. Abrasion resistance
When the blank is moulded in the mold cavity, the surface of the cavity flows and slides along the surface of the cavity, causing a sharp friction between the cavity surface and the billet, resulting in the failure of the mold due to wear.Therefore, the wear-resisting of the material is one of the most basic and important energy of the mould.
Hardness is the main factor that affects wear-resisting.Generally, the hardness of the mold parts is higher, the wear quantity is smaller, wear-resisting is better.In addition, wear-resisting is also related to the type, quantity, shape, size and distribution of carbide in the material.
The working conditions of the die are very poor, some of them often bear a large impact load, which leads to brittle fracture.In order to prevent the sudden break of the mold parts in the work, the mold should have high degree and toughness.
The toughness of the mould depends on the carbon content, grain size and state of the material.
3. Fatigue fracture energy
In the process of mould working, the fatigue fracture is often caused by the long-term effect of cyclic stress.Its form has small energy multiple impact fatigue fracture, tensile fatigue fracture contact fatigue fracture and bending fatigue fracture.
The fatigue fracture of the mould depends on its degree, toughness, hardness and inclusions in the material.
4. High temperature energy
When the working temperature of the mold is higher, the hardness and degree of the die will be reduced, resulting in the early wear of the mold or the production of plastic deformation.Therefore, the mould material should have high anti-tempering stability to ensure that the mould has a high hardness and degree in working temperature.
5. Thermal fatigue resistance
Some mold in the process of work is in a state of repeated heating and cooling, the cavity surface tension, pressure and stress effect, cause surface cracking and spalling, increase the friction, obstacles to plastic deformation, reduces the dimension precision, resulting in the mould failure.Cold and heat fatigue is one of the main forms of thermal die failure.
6. Corrosion resistance
Some mould such as plastic die on the job, as a result of the elements such as chlorine, fluorine plastics, thermal decomposition after precipitation erosion gas such as HCI, HF, erosion surface of mould cavity, increasing its surface roughness, aggravate the wear failure.
(2) mold meets technological requirements
The manufacture of mold is usually made of forging, cutting and processing, heat treatment and other processes.In order to ensure the quality of the mould and reduce the production cost, the material should have good forging, cutting, hardening, quenching and grinding.There should also be small oxidation, decarburization sensitivity and quenching deformation cracking tendency.
With low thermal forging deformation resistance, the forging temperature range is wide, the forging crack cold crack and the precipitation reticular carbide tendency are low.
2. Annealing process
The spherification annealing temperature range is wide, the annealing hardness is low and the fluctuation range is small, the spherification rate is high.
Large cutting amount, low cutting tool loss, low roughness of machining surface.
4. Oxidation and decarburization sensitivity
High temperature heat resistance is good, decarbonization speed is slow, it is not sensitive to heating medium, it has a small tendency of flax.9 n2] & J0 E $s/g6 U $E
It has uniform and high surface hardness after quenching.
After quenching, a deeper hardening layer can be obtained and the quenching medium can be hardened.
7. Quenching deformation and cracking tendency
The conventional quenching volume is small, the shape warps, the distortion is slight, the abnormal deformation tendency is low.The conventional quenching and cracking sensitivity is low, which is insensitive to quenching temperature and workpiece shape.
The grinding wheel has small relative loss, no burn limit grinding, and is not sensitive to the quality and cooling conditions of the grinding wheel. It is not easy to have grinding and grinding cracks.