The role and function of injection mold parts
An injection mold is a complex system composed of numerous parts, each with a specific role and function. They work together to complete the plastic molding process. From the cavity and core that form the product shape, to the guide components that ensure mold precision, to the ejector components that enable product ejection, the performance and condition of each component directly impacts mold efficiency and product quality. Understanding the roles and functions of each injection mold component is crucial for mold design, manufacture, operation, and maintenance. Injection mold components can be categorized by function, including molding components, guide components, ejector components, cooling and heating components, and positioning components. Each component in this category performs a unique task.
Molding components are the core components that come into direct contact with the plastic melt and determine the shape and size of the plastic product. They primarily include the cavity, core, and inserts. The cavity, also known as the female mold, forms the outer surface of the plastic product, its internal shape identical to that of the product. The core, also known as the male mold, forms the inner surface or raised portion of the plastic product, forming a closed molding space with the cavity. During the injection molding process, the plastic melt, under pressure, fills the gap between the cavity and core. Upon cooling, the product forms a product with the same shape as the cavity and core. Molded components require high strength, hardness, and wear resistance to withstand the impact and friction of the high-temperature and high-pressure melt. They are typically manufactured from high-quality alloy tool steel (such as P20 and 718H) and undergo heat treatment processes such as quenching and tempering to enhance their mechanical properties. For products with complex shapes, molded components often adopt a mosaic structure, consisting of multiple inserts. This not only facilitates processing and manufacturing but also facilitates subsequent repair and replacement.
The primary function of guide components is to ensure the relative positioning accuracy of the fixed and movable molds during mold opening and closing, preventing misalignment or collision between the cavity and core, and ensuring product dimensional accuracy and mold safety. Guide components primarily include guide pins, guide bushings, and guide blocks, with guide pins and guide bushings being the most commonly used guide combination. The guide pin is typically fixed to one side of the movable mold, while the guide bushing is installed in the corresponding position of the fixed mold. A precise clearance fit ensures smooth movement of the movable mold along the axis of the guide pin during mold opening and closing. Guide components require extremely high precision, with clearances typically controlled between 0.01 and 0.03 mm and surface roughness below Ra0.8 μm. For large molds or those requiring particularly high precision, auxiliary guide mechanisms (such as tapered positioning blocks) are often incorporated in addition to the main guide mechanism to further enhance guiding accuracy. Guide components are also designed to withstand certain lateral forces, preventing mold deflection under load.
The function of an ejector component is to smoothly remove the cooled, molded plastic product from the core or cavity during the mold opening process, ensuring the product remains intact. Common ejector components include ejector pins, ejector plates, ejector tubes, and bevel ejectors, with different types suitable for different product shapes and structures. The ejector pin, the most commonly used ejector component, is cylindrical in shape. One end is fixed to the ejector mounting plate, while the other end passes through the core or mold plate, directly contacting the product surface. The ejector mechanism pushes the product out. The ejector plate, also known as the push plate, is a large-surface ejector component suitable for thin-walled products or those where ejector marks are unacceptable. It contacts the bottom of the product across its entire surface, ejecting it with uniform force and minimizing damage. The bevel ejector is used for undercuts within molded products. It simultaneously ejects and allows for lateral core pulling. Despite its complex structure, it offers unique functionality. Ejector components must possess sufficient strength and rigidity to avoid bending or breaking during the ejection process. They must also move flexibly and smoothly, and maintain a reasonable clearance with the mold plate to prevent leakage.
Cooling and heating components are crucial for regulating mold temperature and controlling the cooling and solidification rate of the plastic melt, significantly impacting mold quality and production efficiency. Cooling components primarily include cooling channels and cooling inserts. By creating circulating water channels within the mold plate, cavity, and core, cooling water is introduced to remove heat absorbed by the mold, enabling rapid cooling and finalization of the product, shortening the molding cycle. Cooling channels should be evenly and appropriately arranged, as close to the cavity surface as possible to maximize cooling efficiency. For complex cavities, custom-shaped cooling channels or conformal cooling inserts can be used to ensure uniform cooling. Heating components are used when elevated mold temperature is required, such as when molding crystalline or less fluid plastics. Heating tubes or heating plates are used to heat the mold to a specific temperature, improving melt flow and ensuring cavity fullness. The design of cooling and heating components requires careful calculation based on the plastic’s characteristics and product requirements, determining appropriate parameters such as cooling water volume and heating power to achieve optimal temperature control.
Locating and fastening components are auxiliary parts that ensure the assembly accuracy and joint strength of mold components. Although they are not directly involved in the molding process, they are crucial to the overall performance of the mold. Locating components, such as locating pins and locating blocks, ensure accurate relative positioning between mold plates and between the cavity and core, preventing deviation during assembly. Fastening components, primarily hexagon socket bolts and screws, securely connect the mold components together, withstanding the various forces during the injection molding process and preventing loosening or separation during operation. Locating components require high precision fit, typically employing a transition fit or interference fit. Fastening components require appropriate specifications and materials based on the forces being applied, ensuring sufficient joint strength and uniform tightening torque to prevent uneven stress on mold components and deformation. In addition, other auxiliary components are used in the mold, such as venting grooves, lifting rings, and limiter posts, which serve various functions, including venting, lifting, and limiting mold opening and closing strokes, to ensure safe and stable operation of the mold.
