What kind of material can make a good injection mold? How to do the injection mold material selection?
Injection mold is the mother of industry. Our daily life cannot be separated from the participation of injection molds. So what kind of injection molds are qualified products that meet the requirements? What conditions do injection mold materials need to produce excellent quality injection mold products?
First, the injection mold meets the requirements of working conditions
1. Wear resistance
When the blank is plastically deformed in the injection 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 injection 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 injection 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 fractures. In order to prevent sudden brittle fracture of mold parts during work, the mold must have high strength and toughness.
The toughness of the injection mold mainly depends on the carbon content, grain size, and organization state of the material.
3. Fatigue fracture performance
In the process of injection 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 injection 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 injection mold or plastic deformation and failure. Because the injection mold material should have high anti-tempering stability, to ensure that the injection mold has a high hardness and strength at the working temperature.
5. Resistance to cold and heat fatigue
Some injection 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 are 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 injection molds such as plastic injection molds are in operation, due to the presence of chlorine and fluorine in the plastic, strong corrosive gases such as HCI and hf will be resolved after heating, which will erode the surface of the mold cavity, increase its surface roughness, and aggravate wear failure.
Second, the mold meets the process performance requirements
The manufacturing of injection molds generally involves several processes such as forging, cutting, and heat treatment. In order to ensure the quality of injection mold manufacturing and reduce production costs, the material should have good forge ability, machinability, hardenability, hardenability, and grind ability; 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, a 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 a 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 a 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. Tendency of quenching deformation and cracking
Conventional quenching has small volume change, shape warping, slight distortion, and a 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.
Third, the mold meets the economic requirements
When selecting materials for the mold, the principle of the economy must be considered to reduce the manufacturing cost as much as possible.
Therefore, under the premise of satisfying the performance, the first choice is the lower price, carbon steel can be used without alloy steel, and domestic materials can be used without 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.
Fourth, the injection molding material selection guide
It is better to use Cr12, Cr12MoV, and CrWMn for cold punching die than T8 and T10 steel. As a new type of wear-resistant steel, GM steel can replace C12 series steel grades in the field of cold work die materials and has broad application prospects.
It has been applied to the multi-station progressive die, thread rolling die, and trimming die of high-speed punch presses, and the service life of 65Nb and Crl2MoV steel is increased by more than 2-6 times.
ER5 steel is superior to Crl2 steel in strength, toughness, wear resistance, etc., and has no special requirements in forging, heat treatment, machining, electrical processing, etc.
The production and processing technology is simple and feasible, and the material cost is moderate. Carrying cold heading dies, precision cold punching dies, and other cold punching and cold forming die. Reducing heat treatment deformation is very important for complex shapes and precise molds.
The Cr2Mn2SiWMoV steel developed in my country has a heat treatment deformation rate of less than ±0.004%, which is much lower than the normal heat treatment deformation rate of ±01% to ±0.2%. Production practice has proved that: on a 100mm rectangular die, the length and width changes are ±0.01mm.
The injection mold uses 40CrMnMo7 pre-hardened plastic mold steel, X42Cr13 (stainless steel), X36CrMo17 (pre-hardened stainless steel), X38CrMo51 hot work steel, which is better than using 45# steel and T8 steel.
The die-casting mold is made of 5Cr4W5Mo2V (RM-2) steel, ωc is 5%, the total mass fraction of alloying elements is 12%, and there are more carbides, mainly Fe3W3C, which has higher thermal strength and wear resistance than 3Cr2W8V steel Sex and thermal stability.
When the hardness is 40HRC, the thermal stability can reach 700℃, but its carbide distribution is uneven and toughness is poor. It can be used as a precision forging die, hot extrusion dies, etc.
5Cr4Mo3SiMnVAl (O12Al) steel dies steel for both cold and hot work. The steel has a higher thermal hardness, thermal stability is higher than that of 3Cr2W8V steel, and thermal fatigue is much better than that of 3Cr2W8V steel.
6Cr4Mo3Ni2WV (CG-2) steel is based on the base steel of high-speed steel (6W6Mo5Cr4V low carbon M2 steel) by making appropriate improvements, increasing the amount of Ni, and reducing the amount of W and Mo, and is developed as base steel for both cold and heat.
Its room temperature and high-temperature strength and thermal stability are higher than 3Cr2W8V steel, but the high-temperature impact toughness is lower than 3Cr2W8V steel.
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