Guiding and positioning mechanism of injection mold
The guiding and positioning mechanisms of injection molds are core components that ensure precise and stable mold opening and closing movements. Their performance directly impacts the dimensional accuracy of plastic parts, mold life, and production efficiency. The guiding mechanism’s primary function is to guide the movable and fixed molds along a predetermined trajectory during mold opening and closing, preventing collision or misalignment between mold components. The most common guiding elements are guide pins and guide bushings. Guide pins are typically installed on one side of the movable or fixed mold, while guide bushings are installed on the other side. A clearance fit ensures smooth movement between the two. Guide pins should be sufficiently long, extending into the guide bushing by at least 1.5 times their diameter before the mold closes, to ensure effective guidance during the initial mold closing. The guide pin’s head is typically designed with a hemispherical or conical shape to facilitate smooth entry into the guide bushing and reduce initial wear. For large molds or those requiring high precision, lubrication grooves are provided on the mating surfaces of the guide pins and bushings. Regular lubrication reduces friction and extends the life of the guiding mechanism.
The positioning mechanism primarily ensures the relative positioning accuracy of the movable and fixed molds in the closed state, ensuring accurate alignment of the mold cavity and avoiding defects such as flash and dimensional deviations in the plastic part due to misalignment. Common positioning components include locating pins, locating blocks, and tapered positioning mechanisms. Locating pins are typically cylindrical or diamond-shaped, with a transition fit to the locating holes. They are primarily used to assist guide pins in precise positioning and are particularly suitable for small and medium-sized molds. For large molds or those with complex cavity structures, tapered positioning mechanisms are more commonly used. These utilize interlocking tapered surfaces on the movable and fixed molds for positioning. Leveraging the self-locking properties of these tapered surfaces, they effectively withstand lateral forces generated during the injection molding process, improving positioning accuracy. For example, when molding parts with side-pulling cores, the mold generates significant lateral forces under the action of injection pressure. Relying solely on guide pins for guidance can cause them to bend or wear. Adding a tapered positioning mechanism distributes these lateral forces across the tapered surfaces, ensuring stable positioning of the mold.
Precision design of the guiding and positioning mechanisms is crucial to ensuring mold performance. The clearance between guide pins and guide sleeves should be appropriately determined based on the mold’s precision requirements. A clearance of H7/f7 is generally adopted, ensuring both flexible movement and adequate guiding accuracy. For precision molds, such as those used to mold electronic components and optical parts, the clearance can be reduced to H6/g5 to improve guiding accuracy. The positioning accuracy of the positioning elements is equally important. The clearance between the locating pins and locating holes is typically controlled between 0.01-0.02mm. The contact accuracy of the tapered surface of the tapered positioning mechanism should exceed 80%, ensuring that cavity misalignment does not exceed 0.01mm after mold closing. Furthermore, the installation positions of the guiding and positioning elements should be rationally distributed. Guide pins and guide sleeves are typically placed symmetrically at the four corners of the mold, while positioning elements are positioned around the cavity or in areas subject to high stress. This ensures uniform force distribution during mold opening and closing, preventing deformation or wear caused by excessive localized stress.
The material selection and heat treatment process for the guiding and positioning mechanisms significantly impact their service life and performance. Guide pins and guide bushings are typically made of materials such as 20# steel, 45# steel, or T10A. After carburizing and quenching, 20# steel can achieve a surface hardness of 58-62 HRC, while maintaining a certain toughness in the core, offering excellent wear and impact resistance, making it suitable for high-volume mold production. 45# steel, after quenching and tempering, has a hardness of 28-32 HRC, making it suitable for small- to medium-volume mold production. The working surface of the guide pin should be ground to a surface roughness of Ra ≤ 0.8μm, and the inner surface roughness of the guide bushing should be Ra ≤ 0.4μm to reduce friction and wear on the mating surfaces. Locating pins and locating blocks are often made of alloy tool steels such as Cr12MoV, achieving a hardness of 55-60 HRC after quenching to ensure sufficient strength and wear resistance, thereby preventing deformation or wear that could lead to a loss of positioning accuracy during long-term use.
In actual applications, the maintenance and care of the guiding and positioning mechanisms are important links in ensuring the long-term and stable operation of the mold. Before the mold is used, the fit of the guide pins and guide sleeves should be checked to ensure that there is no sticking or loosening. Lubricating oil should be added regularly to keep the mating surfaces well lubricated. For molds that are used for a long time, the fit clearance between the guide pins and guide sleeves should be measured regularly. If the clearance is found to be too large or the surface is severely worn, it should be replaced in time. The positioning elements should also be checked regularly. If the positioning pins are found to be loose or the conical surface is scratched or dented, they should be repaired or replaced in time to avoid affecting the positioning accuracy. In addition, during the installation and commissioning of the mold, the coaxiality of the guide pins and guide sleeves should be ensured to avoid poor guiding or inaccurate positioning due to installation errors. For molds with a side-parting core-pulling mechanism, its guiding and positioning mechanism must also be coordinated with the movement of the core-pulling mechanism to ensure that there is no interference during the core pulling and resetting process. In short, scientific and reasonable design, high-quality material selection and standardized maintenance are the key to ensuring the performance of the injection mold’s guiding and positioning mechanisms, and are also an important guarantee for improving the quality of plastic parts and production efficiency.
