Guide for die-casting mold ejection mechanism
The guidance system of the die-casting mold ejection mechanism is crucial for ensuring precise and smooth ejection. Its design quality directly impacts the release of the die-casting and the lifespan of the mold. In die-casting production, the ejection mechanism must perform reciprocating motion under high pressure and high temperature. Inadequate guidance can easily cause bending and deformation of components such as the ejector rod and ejector tube, potentially scratching the die-casting surface or damaging the mold cavity. Therefore, the guide system must be designed to meet the requirements of accurate positioning, smooth movement, wear resistance, and durability, ensuring a stable motion trajectory for the ejection mechanism.
Common guide forms for ejection mechanisms include guide pin and sleeve guidance, guide plate guidance, and guide rail guidance. The guide pin and sleeve guidance is the most widely used method, creating a sliding fit constraint by placing guide pins and sleeves between the ejector plate and the mold base. Guide pins are typically manufactured from structural alloy steels such as 20CrMnTi. After carburizing and quenching, their hardness can reach HRC58-62, and their surface roughness is controlled below Ra0.4μm to reduce friction. Guide sleeves are constructed from wear-resistant materials such as tin bronze, and their inner bores are honed to ensure a clearance between the guide pins and 0.01-0.03mm. The guide pins are arranged symmetrically, typically at each corner of the ejector plate. Their diameter is determined by the plate’s dimensions, typically ranging from 16-30mm, and their length must cover the entire ejection stroke to ensure effective guidance throughout the ejector plate’s motion.
Guide plate guidance is suitable for large push plates or applications requiring significant lateral force. Wear-resistant guide plates are installed on either side of the push plate, utilizing sliding contact between the two plates to achieve guidance. The guide plates are manufactured from T8A tool steel and, after quenching and tempering, achieve a hardness of HRC50-55. The mating surface with the push plate is precision ground to a surface roughness of Ra0.8μm or less, with a clearance of 0.02-0.05mm. The guide plates can be secured with either screws or a dovetail groove. The dovetail groove allows for micro-adjustments of the guide plates, facilitating clearance elimination during assembly . This type of guidance offers the advantages of a large contact area and excellent guiding stability, but it requires a relatively high level of installation space and is therefore suitable for medium-sized and larger die-casting molds.
Guide rail guidance is often used in core-pulling and ejection composite mechanisms. The linear motion guidance of the ejection mechanism is achieved through the rolling or sliding cooperation of the guide rail and the slider. Rolling guides use balls or rollers as rolling elements, with a low friction coefficient and high motion precision, suitable for high-speed ejection applications; sliding guides rely on direct contact guidance with the guide rail surface, with a strong load-bearing capacity, suitable for heavy-load ejection mechanisms. The guide rail material is usually 40Cr steel, which reaches a hardness of HRC45-50 after tempering and surface quenching. The guide rail surface needs to be ground and scraped to ensure that the flatness error is no more than 0.01mm/m. The advantages of guide rail guidance are high guiding precision and low motion resistance, but the structure is complex and the manufacturing cost is high. It is mainly used in precision die-casting molds.
The lubrication and maintenance design of the guide system are also crucial to ensuring the long-term stability of the ejector mechanism. Lubrication lines or oil tanks should be installed at mating points, such as guide pins, guide bushings, and guide rails, and regularly filled with high-temperature grease to reduce friction and wear. For molds in continuous production, an automatic lubrication system can be used to ensure proper lubrication of the guide parts through a timed and metered oil supply. Furthermore, the sealing design of the guide components is crucial. Dust seals should be installed at the ends of the guide bushings to prevent metal debris and dust generated during the die-casting process from entering the mating clearance, thereby preventing increased wear and causing motion seizures. During mold maintenance, guide components should be regularly inspected for wear. If the mating clearance exceeds 0.05mm, the guide pins, guide bushings, or guide rails should be replaced promptly to ensure that the guide accuracy consistently meets operational requirements. With the advancement of die-casting technology, the use of new wear-resistant materials and self-lubricating guide components has further improved the reliability and service life of the ejector mechanism’s guide system, providing a strong guarantee for efficient and precise die-casting production.
