Factors affecting the service life of die casting die and treatment methods
- Date：2022-07-05
- Read：679
Due to the long production cycle, large investment, high manufacturing precision and high cost, die-casting dies are expected to have a high service life. However, due to the influence of a series of internal and external factors such as materials and machining, the die has been prematurely invalid and scrapped, resulting in huge waste. Today, Aoke editor in chief introduced the factors affecting the life of die-casting die and the treatment methods.
The main forms of die casting die failure are: sharp corners Cracks at corners crackle. Hot cracks (cracks) Wear Erosion, etc. The main causes of die-casting die failure are: the defects of the material itself, as well as the processing, use, maintenance and heat treatment of the die-casting die.
1、 Defects of the material itself
As we all know, the service conditions of die-casting dies are extremely poor. Taking the aluminum die-casting die as an example, the melting point of aluminum is 580-740 ℃, and the temperature of molten aluminum is controlled at 650-720 ℃. Die casting does not preheat the mold, the cavity surface temperature rises from room temperature to liquid temperature, and the cavity surface bears large tensile stress. When opening the top of the mold, the cavity surface bears a large compressive stress. After thousands of die casting, cracks and other defects appeared on the surface of the die.
It can be seen that the service condition of die casting is rapid heating and rapid cooling. The die material shall be hot die steel with high cold and hot fatigue resistance, fracture toughness and thermal stability. H13 (4Cr5MoV1Si) is a widely used material at present. It is reported that H13 is used in 80% of foreign cavities. At present, 3cr2w8vv is still widely used in China, but 3cr2w8vt_ Poor artistic performance, poor thermal conductivity, high coefficient of linear expansion, large thermal stress in work, resulting in mold cracking or even cracking, easy decarburization during heating, reducing the wear resistance of the mold. Therefore, it belongs to the elimination of steel. Maraging steel is suitable for molds with low requirements for heat crack resistance, wear resistance and corrosion resistance. Tungsten molybdenum and other heat-resistant alloys are limited to small inserts with hot cracks and serious corrosion. Although these alloys are brittle and notch sensitive, they have the advantage of good thermal conductivity, and still have good adaptability and production management for thick die-casting molds that need cooling but cannot be equipped with water channels. Therefore, H13 still has good heat treatment performance.
The materials used to manufacture the die-casting die should meet the design requirements in all aspects, so as to ensure that the die-casting die can reach the design service life under its normal use conditions. Therefore, before putting into production, a series of inspections should be carried out on materials to prevent defective materials from wasting the early scrapping and processing costs of molds. The commonly used inspection method is macro corrosion inspection. Metallographic examination. Ultrasonic examination.
(1) Macroscopic corrosion inspection. Mainly check the porosity of the material Segregation crackle. crackle. Non metallic inclusions and surface hammer cracking Seams.
(2) Metallographic examination. Mainly check the carbide segregation on the grain boundary of the material Distribution status Crystallinity and mixture between grains.
(3) Ultrasonic examination. Mainly check the internal defects and size of materials.
2、 Processing + use + maintenance of die casting die
The die design manual introduces in detail the problems that should be paid attention to in the design of die casting dies, but when determining the injection speed, the maximum speed should not exceed 100M / s. Too high speed will increase mold corrosion and deposits on the cavity and core; However, too low can easily lead to casting defects. Therefore, the minimum injection velocity of magnesium, aluminum and zinc is 27.18.12m/s, the maximum injection velocity of cast aluminum shall not exceed 53m/s, and the average injection velocity is 43M / s.
In the processing process, the thickness of thick formwork cannot be guaranteed by superposition. As the thickness of the steel plate is 1 time, the bending deformation is reduced by 85%, and the lamination can only play a superposition role. The bending deformation of the two plates with the same thickness as the single plate is 4 times that of the single plate. In addition, when processing the cooling water channel, special attention should be paid to ensuring the concentricity of both sides. If the head corners are not concentric with each other, the connecting corners will crack during use. The surface of the cooling system should be smooth, and it is best not to leave machining marks.
EDM is more and more widely used in mold cavity machining, but the machined cavity surface has a quenching layer. This is caused by the self carburization and quenching of the die surface in the processing process. The thickness of quenching layer depends on the current intensity and frequency in the machining process. Rough machining is deep and finish machining is shallow. Regardless of the depth, there is a lot of stress on the surface of the die. If the quenching layer or stress is not removed, the die surface will crack, pitting and crack during use. It can be used to eliminate quenching layer or stress relief:
① Remove the hardened layer with oilstone or grinding;
② Without reducing the hardness, the surface stress of the die cavity is greatly reduced below the tempering temperature.
The casting process should be strictly controlled during the use of the mold. Within the scope of process permission, try to reduce the casting temperature, injection speed and mold preheating temperature of molten aluminum. The preheating temperature of aluminum die-casting mold is increased from 100~130 ℃ to 180~200 ℃, and the service life of the mold can be greatly improved.
The main forms of die casting die failure are: sharp corners Cracks at corners crackle. Hot cracks (cracks) Wear Erosion, etc. The main causes of die-casting die failure are: the defects of the material itself, as well as the processing, use, maintenance and heat treatment of the die-casting die.
1、 Defects of the material itself
As we all know, the service conditions of die-casting dies are extremely poor. Taking the aluminum die-casting die as an example, the melting point of aluminum is 580-740 ℃, and the temperature of molten aluminum is controlled at 650-720 ℃. Die casting does not preheat the mold, the cavity surface temperature rises from room temperature to liquid temperature, and the cavity surface bears large tensile stress. When opening the top of the mold, the cavity surface bears a large compressive stress. After thousands of die casting, cracks and other defects appeared on the surface of the die.
It can be seen that the service condition of die casting is rapid heating and rapid cooling. The die material shall be hot die steel with high cold and hot fatigue resistance, fracture toughness and thermal stability. H13 (4Cr5MoV1Si) is a widely used material at present. It is reported that H13 is used in 80% of foreign cavities. At present, 3cr2w8vv is still widely used in China, but 3cr2w8vt_ Poor artistic performance, poor thermal conductivity, high coefficient of linear expansion, large thermal stress in work, resulting in mold cracking or even cracking, easy decarburization during heating, reducing the wear resistance of the mold. Therefore, it belongs to the elimination of steel. Maraging steel is suitable for molds with low requirements for heat crack resistance, wear resistance and corrosion resistance. Tungsten molybdenum and other heat-resistant alloys are limited to small inserts with hot cracks and serious corrosion. Although these alloys are brittle and notch sensitive, they have the advantage of good thermal conductivity, and still have good adaptability and production management for thick die-casting molds that need cooling but cannot be equipped with water channels. Therefore, H13 still has good heat treatment performance.
The materials used to manufacture the die-casting die should meet the design requirements in all aspects, so as to ensure that the die-casting die can reach the design service life under its normal use conditions. Therefore, before putting into production, a series of inspections should be carried out on materials to prevent defective materials from wasting the early scrapping and processing costs of molds. The commonly used inspection method is macro corrosion inspection. Metallographic examination. Ultrasonic examination.
(1) Macroscopic corrosion inspection. Mainly check the porosity of the material Segregation crackle. crackle. Non metallic inclusions and surface hammer cracking Seams.
(2) Metallographic examination. Mainly check the carbide segregation on the grain boundary of the material Distribution status Crystallinity and mixture between grains.
(3) Ultrasonic examination. Mainly check the internal defects and size of materials.
2、 Processing + use + maintenance of die casting die
The die design manual introduces in detail the problems that should be paid attention to in the design of die casting dies, but when determining the injection speed, the maximum speed should not exceed 100M / s. Too high speed will increase mold corrosion and deposits on the cavity and core; However, too low can easily lead to casting defects. Therefore, the minimum injection velocity of magnesium, aluminum and zinc is 27.18.12m/s, the maximum injection velocity of cast aluminum shall not exceed 53m/s, and the average injection velocity is 43M / s.
In the processing process, the thickness of thick formwork cannot be guaranteed by superposition. As the thickness of the steel plate is 1 time, the bending deformation is reduced by 85%, and the lamination can only play a superposition role. The bending deformation of the two plates with the same thickness as the single plate is 4 times that of the single plate. In addition, when processing the cooling water channel, special attention should be paid to ensuring the concentricity of both sides. If the head corners are not concentric with each other, the connecting corners will crack during use. The surface of the cooling system should be smooth, and it is best not to leave machining marks.
EDM is more and more widely used in mold cavity machining, but the machined cavity surface has a quenching layer. This is caused by the self carburization and quenching of the die surface in the processing process. The thickness of quenching layer depends on the current intensity and frequency in the machining process. Rough machining is deep and finish machining is shallow. Regardless of the depth, there is a lot of stress on the surface of the die. If the quenching layer or stress is not removed, the die surface will crack, pitting and crack during use. It can be used to eliminate quenching layer or stress relief:
① Remove the hardened layer with oilstone or grinding;
② Without reducing the hardness, the surface stress of the die cavity is greatly reduced below the tempering temperature.
The casting process should be strictly controlled during the use of the mold. Within the scope of process permission, try to reduce the casting temperature, injection speed and mold preheating temperature of molten aluminum. The preheating temperature of aluminum die-casting mold is increased from 100~130 ℃ to 180~200 ℃, and the service life of the mold can be greatly improved.
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