Cooling circuit for special cores for injection molding
Special cores in injection molds refer to molded parts with complex structures and unique shapes, such as slender cores, special-shaped cores, and deep-cavity cores. Their cooling performance directly impacts part quality and production efficiency. Due to the irregular geometry of special cores, traditional cooling methods struggle to achieve uniform cooling, which can easily lead to localized overheating of the core, causing defects such as uneven shrinkage and warping in the part, while also prolonging the molding cycle. For example, insufficient cooling of slender cores during the molding process can cause them to bend and deform due to the high temperature, affecting the dimensional accuracy of the part. Deep-cavity cores also face internal heat dissipation difficulties, which can easily cause sink marks or bubbles to form on the inner wall of the part, reducing the product’s pass rate.
The design of cooling circuits for special cores must adhere to the three principles of uniformity, efficiency, and feasibility. The uniformity principle requires that the cooling circuit maintain consistent temperatures across all core components to avoid defects in the molded part caused by large temperature differences. This requires the rational layout of cooling channels based on the core’s shape to ensure adequate cooling in every area. The efficiency principle emphasizes the cooling system’s heat dissipation capacity. By optimizing the channel structure and parameters, heat transfer efficiency is improved and cooling time is shortened. The feasibility principle requires that the cooling circuit design be consistent with the mold manufacturing process, facilitating processing and maintenance while avoiding complex, difficult-to-process structures. For example, for special-shaped cores, 3D printing technology can be used to create conformal cooling channels, ensuring cooling uniformity while reducing processing complexity.
Different cooling circuit designs are required for different types of special cores. For slender cores, since their length is much greater than their diameter, traditional straight-through water channel cooling is ineffective. Instead, a central intubation cooling structure can be used. A hollow tube is inserted into the center of the core, allowing coolant to flow in from the inside of the tube and out from the gap between the tube and the core, forming a circulating cooling system. This method effectively removes heat from the core and prevents deformation due to high temperatures. For deep-cavity cores, spiral cooling water channels can be used. Cooling water pipes are spirally wound along the outer wall of the core, allowing the coolant to fully contact the core during flow, thereby improving heat dissipation efficiency. For special-shaped cores, such as those with complex curves or concave-convex structures, conformal cooling water channels can be used. That is, the shape of the water channel is consistent with the outer contour of the core. Through 3D printing technology, the water channel is formed in one piece to ensure a uniform distance between the cooling water channel and the core surface, achieving all-round uniform cooling.
Optimizing the parameters of a specialized core cooling circuit is crucial for effective cooling. Coolant velocity and flow rate are key parameters. A low velocity results in laminar flow within the coolant channel, resulting in inefficient heat transfer. A high velocity increases power consumption and may generate turbulent noise. Generally, the coolant velocity should be controlled between 1.5 and 5 m/s to ensure turbulent flow and improve heat transfer. The channel diameter should be determined based on the core size. For small cores, a channel diameter of 6 to 10 mm is typical; for large cores, a channel diameter of 10 to 16 mm is acceptable. Furthermore, the distance between the channel and the core surface should be moderate. A small distance weakens the core strength, while a large distance impairs cooling. It is generally maintained within a range of 1.5 to 3 times the channel diameter. The temperature difference between the coolant inlet and outlet should be within 5°C to avoid uneven core temperatures caused by large temperature differences.
The manufacture and maintenance of special core cooling circuits are crucial for ensuring effective cooling. During the manufacturing process, complex conformal cooling channels can be 3D printed using selective laser melting (SLM). This technology precisely shapes complex internal structures, ensuring accurate channel size and positioning. For deep holes or curved channels that are difficult to create using traditional machining, electrical discharge machining (EDM) or gun drilling can be used to ensure channel accuracy. Regarding maintenance, the cooling circuits require regular cleaning to prevent scale and impurities from clogging the channels and affecting coolant flow. Chemical cleaning can be used by injecting citric acid or a specialized descaling agent into the channels, soaking them for 2-4 hours, and then rinsing with clean water to ensure unobstructed flow. The cooling system’s sealing should also be checked to prevent coolant leaks that could affect the mold’s lifespan.
