Design of die-casting guide parts
Die-casting guide components serve as the “navigation system” that ensures mold closing accuracy. Their primary function is to precisely align the movable and fixed molds during the closing process, preventing collisions between the cavity and the core. They also withstand the lateral forces generated during mold opening and closing, ensuring the dimensional stability of the die-casting. These components, including guide pins, guide bushings, guide pins, and guide plates, must be designed to meet high-precision, high-wear, and high-temperature requirements to withstand the frequent movement and high-temperature environments of the die-casting process. The quality of the guide system’s design directly impacts mold life and die-casting part yield, requiring tailored design based on mold size, complexity, and production batch size.
As a core component of the guide system, the guide pin’s structure and material selection must balance guiding accuracy and service life. Guide pins are available in headed and shouldered configurations. Small and medium-sized molds generally use headed guide pins, which offer a simple structure and easy assembly and disassembly. Large molds utilize shouldered guide pins, whose positioning improves installation accuracy and prevents axial movement when the guide pin is subjected to load. The guide pin’s diameter is determined by the mold size, generally 1/20 to 1/25 of the maximum mold width. The length must ensure that, when the mold is closed, the guide pin extends beyond the guide sleeve by at least 1.5 times its diameter, ensuring sufficient guiding length when the mold is opened. The material used is 20CrMnTi, which is carburized and quenched, achieving a surface hardness of 58 to 62 HRC and a core toughness of 25 to 30 HRC, providing both wear and impact resistance. The guide pin’s working surface is ground to a roundness of ≤0.005mm and a surface roughness of Ra ≤0.4μm to minimize friction and wear against the guide sleeve.
The guide sleeve must be designed to precisely mate with the guide pin while also exhibiting excellent wear resistance and self-lubrication. The inner diameter of the guide sleeve utilizes a clearance fit with the guide pin, achieving an H7/f7 accuracy. This clearance value is determined by the mold temperature: 0.01–0.03 mm for normal-temperature molds and 0.03–0.05 mm for high-temperature molds (>200°C) to prevent thermal expansion and seizure. The guide sleeve length is generally 1.5–2 times its inner diameter. Excessive length increases machining difficulty and assembly errors, while excessive shortness compromises guide stability. For large molds, a stepped design can be used to increase the mating area with the sleeve plate and enhance mounting security. Tin bronze ZCuSn10Pb1 is used, offering excellent wear resistance and self-lubricating properties, ensuring smooth sliding without the need for additional lubrication. Alternatively, a powder metallurgy guide sleeve with internal oil holes for lubricant storage is suitable for high-speed mold opening and closing. The guide sleeve is installed with interference fit, with an interference of 0.01~0.02mm. After assembly, the end face must be flush with the sleeve plate plane, with a flatness error of ≤0.01mm.
The layout of the guide system must be optimized based on the mold’s structural characteristics to ensure uniform guidance and balanced forces. For rectangular molds, guide pins are typically placed symmetrically at the four corners. The diagonal spacing between guide pins should be as large as possible to improve guiding stability. For example, for a 1000mm x 800mm mold, the guide pin spacing can be 900mm x 700mm. For circular molds, guide pins should be evenly distributed along the circumference, with a minimum of three, forming an equilateral triangle or square layout. If the mold has a lateral core pulling mechanism, auxiliary guide pins should be added in the direction of the core pulling to prevent lateral forces generated during core pulling from damaging the main guide system. The distance between the guide pins and the cavity should be greater than 50mm to prevent the sleeve from being too thin near the guide pins, resulting in insufficient strength. Furthermore, guide pins should be positioned away from components such as the gate and ejector mechanism to ensure non-interference between mold systems. The distance between the center of the guide pin and the mold edge should be no less than 1.5 times the guide pin diameter.
Precision guides and auxiliary guides are crucial for improving mold closing accuracy. For die-castings with extremely high precision requirements (dimensional tolerances ≤ IT6), additional precision positioning mechanisms, such as tapered locating blocks and locating pin bushings, are required in addition to the main guide system. These locating blocks typically have a taper of 1:50-1:100 and a clearance of ≤0.005mm. Installed around or at the center of the mold parting surface, they eliminate positioning errors caused by guide pin clearance and keep cavity misalignment within 0.01mm. For large molds, guide keys can be installed to mate with guide grooves. These keys are made of quenched 45 steel with a hardness of 40-45 HRC and a clearance of 0.01-0.02mm with the guide grooves, further limiting lateral mold movement. Furthermore, the guide pin head should be designed with a hemispherical or tapered transition, with a taper angle of 30°-45°, to facilitate smooth entry into the guide sleeve during mold closing and reduce initial impact and wear.
Maintenance and lifespan management of the guide system are critical to ensuring long-term guiding accuracy. During mold assembly, the clearance between the guide pin and guide sleeve must be checked, and the contact area must be inspected using a color-coating method to ensure uniform contact and no sticking. During use, the guide surface must be regularly cleaned of oil and impurities. The guide sleeve must be removed and cleaned at least once a month and inspected for wear. If the clearance between the guide pin and sleeve exceeds 0.1mm, it must be replaced promptly. For high-temperature die-casting molds, a molybdenum disulfide coating can be sprayed on the guide pin surface to improve lubrication and reduce friction at high temperatures. The lifespan of guide components is typically set at 1/3 to 1/2 of the total mold lifespan. For example, for a mold with 500,000 cycles, the guide components should be replaced between 150,000 and 250,000 cycles to prevent mold damage due to guide failure. A sound maintenance and replacement strategy ensures that the guide system is always in optimal working condition, providing a stable guarantee for die-casting quality.
