Summary:
Aiming at the ubiquitous characteristics of die-casting molds that are easy to age and have a short life, it is pointed out that the selection of high-quality steel is the basic condition to ensure the life of die-casting molds. Reasonable design of castings and die-casting molds, ensuring the processing quality of die-casting molds, standardized heat treatment process, surface strengthening treatment of die-casting molds, and standardized operations during the use of die-casting molds can extend the life of die-casting molds. The statistical results of our company’s die-casting molds after long-term use of these methods show that the service life of domestic H13 steel die-casting die-casting molds can be extended from 80,000 to 120,000 molds, and the economic benefits are significant.
Keywords: Die-casting mold; Die-casting mold steel; Die-casting mold processing;
introduction
How to extend the life of die-casting molds has always been the most concerned issue for die-casting mold manufacturers and orderers. The material of the die-casting mold only accounts for about 10% of the total cost of the die-casting mold, but the benefits of using high-quality die-casting mold steel to increase the service life of the die-casting mold are very significant. In recent years, reasonable selection of materials for die-casting mold forming parts has gradually received widespread attention. In addition, standardized heat treatment, stress-relieving maintenance and maintenance of die-casting molds, and attention to operating specifications during use are of great significance to prolonging the service life of die-casting molds. .https://www.swissmachining.cn/
1 Reasonable selection of die-casting die steel
Selection of high-quality steel for production is the basic condition to ensure the life of the die-casting mold. Since the 1950s, 3CR2W8V hot-work die-casting die steel imported from the former Soviet Union has been widely used in China. Generally, hairline cracks appear in the cavity of die-casting 10,000 to 20,000 molds, and the life of the die-casting mold is about 50,000 molds. In the 1990s, high-quality steel grade H13 (4CR5MOSIV1) was introduced from the United States. Using this steel to make die-casting molds and a strict heat treatment process, the service life of the produced die-casting molds can reach 150,000 to 200,000 mold times. It is currently widely used in the production of die-casting molds. .https://ycncmachining.blogspot.com/ A variety of similar steel grades are extended on the basis of this steel grade, such as: 40CRMOV5 of International Organization for Standardization (ISO); SKD61 of Japan (JIS); STD61 of South Korea (KS); X40CRMOV5 of Germany (DIN)- 1; British (BS) BH13; Russia’s 4X5MФ1C and some commercial brands 8407, QR90, GS-344M, etc.
H13 steel is an air-cooled hardening hot work die-casting die steel with both toughness and toughness. The main features are as follows:
(1) It has high hardenability and toughness;
(2) Excellent resistance to thermal cracking, can be directly water-cooled in the workplace;
(3) With moderate wear resistance, carburizing or nitriding processes can be used to increase the surface hardness, but the thermal crack resistance will be slightly reduced;
(4) Due to its low carbon content, the secondary hardening performance during tempering is poor;https://www.infantpulseoximeter.com/
(5) It has the ability to resist softening (thermohardening) at higher temperatures, but the hardness will drop rapidly when the temperature is higher than 540℃;
(6) Good stability and small deformation during heat treatment;
(7) Good machinability;
(8) Medium resistance to decarburization.
The carbon content (mass fraction) of H13 steel is below 0.5%, and it also contains alloying elements such as CR, W, MO, and V. The content of cr in the steel is about 5.0%. The structure formed by it and other carbides makes the steel more High hardenability and hot hardness. Therefore, the steel can be hardened under air cooling conditions, and its maximum quenching hardness is around 55HRC.
2 Reasonably design castings and die-casting moldshttps://itsoug.com/
The unreasonable design of the casting structure results in a thin section in the die-casting mold (see Figure 2) and uneven wall thickness of the casting (see Figure 3), which often causes early cracks in the die-casting mold. Unreasonable design of the slope value will cause scratches when picking up parts after core pulling and mold opening. The small chamfer at the junction of the cavity wall will cause stress concentration cracks. In the design of the gating system, improper control such as flow direction, cross-sectional area, and injection speed will cause erosion of the cavity or core. Due to excessive emphasis on cost control and saving steel, the rigidity of the die-casting mold is insufficient, leading to early deformation or fracture of the die-casting mold components from time to time.https://cncturning.biz/ Because the assembly size is too tight, it is easy to form a larger pre-stress, and the die-casting mold bursts during the die-casting production process (see Figure 4). In the die-casting mold manufacturing process, the matching accuracy level of each component is not properly selected, and the aluminum liquid enters during the die-casting, which causes the die-casting mold to lose its due accuracy prematurely.
In the design of the die-casting mold, as much as possible to reduce the mosaic, can significantly enhance the rigidity of the cavity as a whole. Taking into account the complex and harsh working conditions of the die-casting mold, it is very important to ensure the thermal balance of the working state of the die-casting mold. In order to stabilize the working temperature of the die-casting mold, it is necessary to design a reasonable cooling system on the moving and fixed molds (see Figure 5 and Figure 6). In the same production cycle, the temperature of the die-casting mold also experiences sharp rises and drops. Due to the difference in the wall thickness of the castings, the equilibrium temperature is generally controlled at 35% to 45% of the alloy casting temperature.https://www.cncmachiningptj.com
3 Ensure the quality of die casting mold processing
The frictional heat generated during the grinding process of the die-casting mold will cause grinding cracks on the surface. In addition, due to the presence of grinding stress, the thermal fatigue resistance of the die-casting mold will also be reduced. The surface of the mold cavity, especially the rough surface of the runner or the place with a small amount of scratches and scribe marks on the mold surface, are potential sources of cracks. In the process of finishing using the EDM machine, due to the local high temperature forming the tempered area under the surface, the structure and chemical composition of this area are different from the matrix, the hardness is high, and the surface residual stress exists, the polishing treatment may not be in place. Micro cracks are formed in the early stages of die-casting mold use (see Figure 7). The installation accuracy between the die-casting mold and the die-casting machine, including parallelism and perpendicularity, https://www.ptjmachining.com/may cause abnormal wear of the guide or difficulty in ejecting, affecting the appearance of the casting (see Figure 8) and causing damage to the die-casting mold.
4 Reasonably standardize the heat treatment process
The material of the die-casting die should have high thermal strength and tempering stability, so that it is possible to obtain high thermal fatigue resistance and wear resistance. In addition, due to the difference in the precision and complexity of the die-casting mold, in the heat treatment process arrangement, the quenching process can be used after the first stress relief annealing to eliminate quenching deformation and cracks through subsequent processing (see Figure 9, Figure 10).
When die-casting zinc, aluminum, and magnesium alloys, the parts in the contact part of the die-casting mold and the molten metal generally have a heat treatment hardness of 44-48HRC, and the hardness of die-casting copper alloys is 38-42HRC. Die-casting molds need to undergo stress relief treatment before use. Our company uses H13 material as the core die-casting mold.https://cncmachining.jp Generally, the first stress relief tempering is performed between 5000-10000 mold times, and the stress relief treatment is performed every 15000-20000 mold times. The fire temperature is 30-50 lower.
5 Surface strengthening treatment of die-casting mold
Surface strengthening treatment is to apply extremely high energy to the surface of the material to cause physical-chemical changes to achieve the purpose of strengthening. Its main features are: simple process, rapid process, small deformation of parts and high production efficiency. Among them, the use of electric spark surface strengthening process is one of the effective ways to reduce surface erosion, prevent metal and die surface from occluding, and prolong service life. During the surface strengthening process, the pulse circuit discharges, so that the positive and negative (metal workpiece) poles of the connected circuit make periodic contact, causing air gap discharge, forming sparks and high temperatures. Under the action of high temperature, the sublimated positive electrode material completes the process of remelting, deposition, diffusion, compounding and hardening on the surface of the workpiece, so that a layer of uniform composition, dense structure and high hardness is formed on the surface of the coated workpiece. The deposition layer and the substrate are firmly bonded, impact-resistant, and not easy to peel off, and because the workpiece is in a cold state during the strengthening treatment, the discharge point is small, the time is short, and there is no annealing and deformation. https://china-turning.com/By comparing two sets of surface-strengthened die-casting molds with ordinary die-casting molds, our company has shown better results and longer service life in terms of corrosion resistance, heat resistance and wear resistance, which can be extended The service life of the die-casting mold is about 10,000 to 10,000 mold times.
6 Die-casting mold operation specifications
6.1 Die-casting mold preheating and maintaining thermal balance
The magnitude of the stress in the die-casting mold is proportional to the temperature gradient in the die-casting mold, so it is very necessary to appropriately increase the preheating temperature. However, an excessively high preheating temperature reduces the yield strength of the surface material of the cavity, which is detrimental to the thermal fatigue resistance of the die-casting mold. In addition, during the production process of die-casting molds, maintaining thermal equilibrium is an important means to prolong the life of die-casting molds, improve production efficiency and ensure the compactness of castings. The use of cooling water must be continuous, and it is forbidden to open or close the cooling water suddenly during the production process. https://beryllium-copper.com/Rhythm and continuity in the operation process can create conditions for maintaining the best thermal balance of the die-casting mold.
6.2 Use of die-casting mold coating
The use of coatings plays an important role in protecting die casting mold materials. The places where the paint is not evenly applied are often the places where the erosion is the most serious. When the paint is sprayed into the high-temperature mold cavity, it will generate high steam pressure, causing separation and splashing, and it is not easy to adsorb on the molding surface and fully wet the molding surface. The best solution is to increase the spraying pressure, so that the droplets get higher kinetic energy during spraying, overcome the condensation of the droplets, and achieve the goal of uniform coating profile.
6.3 Overhaul and maintenance of die-casting molds
Regular maintenance of the die-casting mold during use is very important. In the production process, the deformation of the support plate, the sleeve plate, the core-pulling mechanism, the push-out mechanism, etc., and the loosening of the fastening bolts all lead to the early destruction of the die-casting mold. important reason.https://cncturning.biz/
6.4 Installation and operation specifications of die-casting mold
(1) Before using the die-casting mold, first read the instructions and precautions attached to the die-casting mold materials to understand the basic structure of the die-casting mold, especially the movement sequence of each slider on the die-casting mold.
(2) Open the movable and fixed molds of the new die-casting mold, clean the dirt and rust on the die-casting mold, check whether the inner wall of the cavity is not completely polished; check the movable parts of the die-casting mold, such as: slider, push rod, reset Whether the position of the rod is accurate, whether there is tilt phenomenon, whether there is relative movement of the fixed parts; check the profile, core, guide post, inclined guide post and cylinder, etc., and there should be no defects such as bumps, dents, cracks, etc.
(3) Connect the cooling water, check whether the cooling water pipeline is unblocked and see if there is any leakage; check whether the connection between the oil cylinder and the sliding block (see Figure 11) is installed correctly, the structure is reliable, and the action is flexible.https://www.diecastingcompany.com/
(4) The die-casting mold must be preheated before use. Our company generally uses liquefied gas for filling, and heats the die-casting mold through a flame spray gun. It is not allowed to directly pour the alloy liquid into the mold for heating, and the preheating temperature is controlled at 180～220℃.
(5) When disassembling the movable parts or small cores of the die-casting mold, only soft copper, aluminum, lead rods or rubber hammers are allowed to tap lightly to avoid damaging the mold cavity.
(6) When the die-casting mold is not used for a long time, the aluminum skin attached to the die-casting mold should be cleaned,https://titanium-machining.com/ the surface should be scrubbed, and the parts should be coated with anti-rust oil.
(7) After die-casting to a certain number of times, the die-casting mold should be subjected to stress relief treatment on a regular basis.