(a) die to meet the requirements of working conditions
1, wear resistance
When the billet is plastic degeneration in the mold cavity, the surface of the mould is both flowing and sliding, which makes the surface of the mold cavity and the blank to produce the intense friction, which leads to the failure of the die due to abrasion. So material wear resistance is one of the most basic and most important properties.
Hardness is the main factor affecting the wear resistance. Under normal circumstances, the higher the hardness of the mold parts, the smaller the wear, the better the wear resistance. In addition, the wear resistance is related to the type, quantity, shape, size and distribution of carbides in the material.
2, strong toughness
Mold working conditions are mostly very poor, and some often bear a larger impact load, which leads to brittle fracture. In order to prevent the mold parts in the work of brittle fracture, the mold must have high strength and toughness.
The toughness of the mould is mainly determined by the carbon content, grain size and microstructure of the material.
3, fatigue fracture performance
During the working process of the mould, the fatigue fracture is often caused by the long term effect of the cyclic stress. The form has small energy multiple impact fatigue fracture, tensile fatigue fracture contact fatigue fracture and bending fatigue fracture.
The fatigue fracture behavior of the mold mainly depends on its strength, toughness, hardness, and the content of the inclusions in the material.
4, high temperature performance
When the working temperature of the mold is higher, the hardness and strength decrease, leading to the early wear of the die or the failure of the plastic deformation. Because the mold material should have the high tempering stability, in order to guarantee the mold at the working temperature, has the high hardness and the strength.
5, resistant to cold and heat fatigue performance
Some of the mold in the repeated heating and cooling in the working process, so that the cavity surface tension and pressure stress effect caused by cracking and spalling, increase the friction surface, hinder plastic deformation, reduce the size precision, which leads to the failure of die. Cold and hot fatigue is one of the main forms of failure of hot die, which should have high resistance to cold and hot fatigue.
6, corrosion resistance
Some mould such as plastic mold at work, due to the presence of chlorine, fluorine plastic, after heat decomposition precipitation of HCI and HF strong corrosive gases, erosion of the mold cavity surface, increase the surface roughness, increased wear failure.
(two) mold to meet the requirements of process performance
Mold manufacturing generally through forging, machining, heat treatment and other processes. In order to ensure the quality of mold manufacturing, reduce the production cost, the materials should have good ductility and machinability, hardenability and hardenability and grindability; should have oxidation, decarburization sensitivity and quenching cracking tendency of small deformation.
1, can be forged
With low hot forging deformation resistance, good plasticity, wide forging temperature range, cold forging, cold cracking and carbide tendency of precipitation is low.
2, annealing process
The annealing temperature range is wide, the hardness is low and the fluctuation range is small, the rate of the ball is high.
3, cutting processing
The cutting quantity is big, the cutting tool loss is low, the processing surface roughness is low.
4, oxidation and decarburization sensitivity
When heated to high temperature oxidation with good decarburization rate is slow, not sensitive to the heating medium, produce pitting tendency.
5, quenching
After quenching, the surface hardness is uniform and high.
6, quenching
The hardened layer can be obtained after quenching, and the quenching medium can be hardened by quenching.
7, quenching deformation cracking tendency
The conventional quenching volume change is small, the shape is warped, the distortion is slight, and the abnormal deformation tendency is low. The quenching cracking sensitivity is low, which is not sensitive to the quenching temperature and the shape of the workpiece.
8, grinding
The wheel is relatively small loss, no limit of grinding burn of large amount, is not sensitive to the quality of the grinding wheel and the cooling conditions, not prone to abrasion and grinding crack.
(three) mold to meet the economic requirements
In the ion of the mold, it is necessary to consider the principle of economic, as far as possible to reduce the cost of production. Therefore, in order to meet the use of the performance of the premise, the first choice of lower prices, you can use carbon steel can not be used in domestic materials can not be imported materials. In addition, the material should also be considered in the production and supply of the market, the ion of steel should be minimal and concentrated, easy to buy.
Selection of automobile stamping die materials
Because the function of various parts of the mold is different, so the requirement of the material and the ion principle are also different. Therefore, the reasonable ion of die material is also a very important work in the design of stamping die, it is not only related to the cost of the parts, but also seriously affect the production.
With the development of the automobile industry, the demand for cars is increasing, the biggest factor affecting the production is how to choose die materials.
Although the working parts of the mold used materials should be better than other parts of the materials used. Generally speaking, depending on the conditions of the use of the mold and the requirements vary, there are four main types:
1 for simple shape, stamping parts of the mold work parts. Carbon tool steels, such as T8A, T10A, etc.. 2 for the shape of complex, stamping parts of large die work parts, often with alloy tool steel or high speed tool steel, such as Cr12, CrWMn, Cr12MoV, W18Cr4V, W6MoSCr4V2, etc..

2 for stamping parts precision or die life requirements of relatively high mold work parts, commonly used carbide or steel bonded carbide, such as YG15, YG20, GW50, etc..

3 for large-scale mold (such as automobile cover parts die) working parts, commonly used ordinary cast iron or cast steel, and some are still in the edge of the edge of the weld reinforcement, such as gray cast iron HT250, cast steel 2G270-500, etc..
Selection of die materials, ion of the most important parts in addition to the work, the more prominent is the guide column and a guide sleeve parts, generally used in low carbon steel carburizing and quenching or ion of high quality carbon steel in bearing steel.
It must be pointed out that the material ion of the work parts of the mold is the most important and strict, but also including the requirements of its heat treatment industry must be reasonable.
In addition to other parts of the mold parts outside the ion for medium carbon steel carbon steel or high quality carbon steel in it.
Drawing die material for large drawing part and automobile covering part
Alloy cast iron or high strength nodular cast iron can be used. The graphite cast iron can be dipped into the lubricating oil, the graphite in the organization has the self lubrication function, can effectively reduce the friction in the drawing, and the cost is low, easy to process.
High strength nodular cast iron can be used for the isothermal quenching of the double medium delay cooling to obtain higher strength and toughness, and the hardness is 55~58HRC. You will die slowly after preheating and heating to 880~900 DEG C, after the first heat preservation air precooling, and brine quenching to 550 DEG C into cold oil, when the mold temperature ped to 250 degrees Celsius, 2~3 hours in isothermal 180~200 DEG C oil, the oil temperature ped to 170 degrees Celsius isothermal 5~7 small, finally into the air.
After alloying, heat treatment and surface treatment, nodular graphite cast iron can be used as a drawing die for automobile covering parts, and the practical application of nodular cast iron for automobile panel dies is introduced.