Injection molding guide
The guidance of the injection molding ejector is the core link in ensuring the precise movement of the ejector mechanism, directly affecting the molding quality of the plastic part and the service life of the mold. As a key component in the mold used to remove undercuts or complex structures within the plastic part, the ejector has an inclined motion trajectory and must withstand large lateral forces during ejection and resetting. Improper guidance can easily lead to jamming of the ejector, increased wear, and even problems such as part deformation and mold sticking. In the production of precision plastic parts, such as mobile phone casings and medical device components, the ejector’s guidance requires even higher accuracy, typically controlled within a range of 0.01-0.03mm to ensure dimensional stability of the plastic part. Therefore, the scientific design of the ejector’s guidance structure is a crucial aspect of mold design that cannot be ignored.
The structural form of the inclined ejector guide needs to be reasonably selected according to the complexity of the plastic part and the spatial layout of the mold. Common guide structures include integral guide and split guide. In the integral guide, the inclined ejector rod and the guide slider are designed as one body, and the motion constraint is achieved through the guide groove on the mold. This structure has good rigidity and high precision, but it is difficult to process and is suitable for occasions with short core pulling distance and small force. In the split guide, the inclined ejector rod and the guide sleeve are designed separately. The guide sleeve is fixed to the ejector plate of the mold, and the inclined ejector rod passes through the guide sleeve to achieve guidance. This structure is easy to disassemble and assemble, has low processing cost, and the guide sleeve can be replaced separately after wear. It is suitable for situations with long core pulling distance and large force. In addition, for some plastic parts with special structures, a combined guide can also be used, that is, horizontal and vertical guide devices are set at the same time to further improve the stability of the inclined ejector movement.
Controlling the guide clearance is crucial for ensuring the guiding accuracy of the ejector. Excessive clearance can cause the ejector to wobble during movement, affecting the dimensional accuracy of the plastic part and even causing it to collide with other mold components. Too little clearance can increase movement resistance due to poor lubrication or temperature fluctuations, leading to seizures or wear. Typically, the clearance between the ejector pin and the guide sleeve should be controlled between 0.02-0.05mm. For molds requiring higher precision, the clearance can be reduced to 0.01-0.03mm. When determining this clearance, the plastic’s shrinkage and the mold’s operating temperature must also be considered. For plastics with a high thermal expansion coefficient, such as polyoxymethylene (POM), the clearance should be increased to prevent seizure at high temperatures. The guide sleeve should also be appropriately designed, generally 3-5 times the ejector pin diameter, to ensure sufficient guide length and minimize deflection of the ejector.
The selection of guide materials and their surface treatment significantly impact guide performance. Inclined guide components are subject to frequent friction and impact, requiring materials with high strength, wear resistance, and good toughness. Commonly used materials include alloy structural steels (such as 40Cr) and alloy tool steels (such as Cr12MoV). After quenching and tempering, 40Cr can achieve a hardness of HRC28-32, offering excellent overall mechanical properties and suitable for general operating conditions. After quenching and tempering, Cr12MoV can achieve a hardness of HRC58-62, offering excellent wear resistance and suitable for use in high-speed, high-pressure molds. To further enhance wear resistance, guide components typically undergo surface hardening treatments such as nitriding or chrome plating. Nitriding can achieve a surface hardness exceeding HV800, forming a tough nitride layer that effectively reduces frictional losses. Chrome plating improves surface finish, reduces the coefficient of friction, and enhances corrosion resistance.
The lubrication and maintenance of the guide system are important guarantees for the long-term and stable operation of the lift mechanism. During the movement of the lift, the friction between the guide components will generate heat and wear, so lubricants such as high-temperature grease or solid lubricants need to be added regularly. For high-speed molds, it is recommended to use an automatic lubrication system to supply lubricating oil at a regular and quantitative rate to ensure that the guide surface is always in a good lubrication state. During daily maintenance, impurities and plastic debris in the guide groove need to be cleaned regularly to prevent guide failure due to foreign matter stuck. At the same time, pay close attention to the wear of the guide components, and determine whether the guide sleeve or lift rod needs to be replaced by measuring the gap change or observing the surface scratches. For key molds, a maintenance file for the guide system can be established to record the maintenance time, lubricant type and wear data to provide a basis for preventive maintenance, thereby extending the service life of the mold and improving production efficiency.
