Advantages of using small gate in injection mold
The design of the gate in an injection mold has a significant impact on part quality, production efficiency, and mold costs. Small gates, a common type of gate, offer significant advantages in many injection molding scenarios. Small gates typically have a smaller cross-sectional area. Their dimensions depend on the part size and material properties, typically ranging from 0.5 to 2mm in diameter and relatively short in length. Using a small gate not only optimizes melt flow but also simplifies gate removal after molding, significantly improving the overall efficiency of injection molding production.
One of its most significant advantages is that a small gate significantly increases the melt’s shear rate, improving its fluidity. When the melt passes through a small gate, the cross-sectional area suddenly decreases, dramatically increasing its flow rate and generating a strong shearing effect. This reduces the melt’s viscosity and enhances its fluidity. This characteristic is particularly important for plastics with poor fluidity, such as polycarbonate and polyoxymethylene, helping the melt to more smoothly fill the mold cavity, especially for thin-walled parts with complex structures. For example, when molding precision electronic plastic parts as thin as 0.5mm, the high shear rate generated by a small gate allows the previously difficult-to-flow melt to fill the entire cavity, reducing defects such as underfill and weld marks. Furthermore, the high shearing effect increases the melt temperature, further reducing viscosity, enhancing filling capacity, and ensuring part quality.
Small gates facilitate sequential filling of plastic parts, reducing air entrapment and weld marks, and improving the part’s appearance quality and structural strength. In multi-cavity molds or large, complex cavities, small gates control the melt flow path, ensuring it fills the cavity in a predetermined sequence and preventing weld marks from occurring when multiple melt fronts meet simultaneously. Even if weld marks do occur, the high shear effect of the small gate raises the melt temperature, increasing the bond strength at the weld. Furthermore, sequential filling allows air in the cavity ample time to escape through the venting grooves, reducing air entrapment defects such as bubbles and burns. For example, when molding a part with multiple ribs, using a small gate allows the melt to fill the main body first, followed by the ribs, preventing air entrapment at the ends of the ribs. This ensures a reasonable distribution of weld marks across the parts and ensures strength.
Small gates can effectively shorten holding time, improve production efficiency, and reduce internal stress in plastic parts. Due to their smaller cross-sectional area, small gates cool and solidify rapidly after the holding phase, creating a “self-locking” pattern that prevents melt backflow and reduces holding time. Compared to large gates, small gates have a shorter solidification time, allowing the holding phase to end earlier and the cooling phase to begin, thus shortening the overall molding cycle. For example, a part using a small 1mm diameter gate requires only 5 seconds of holding time, while a large 3mm diameter gate requires 10 seconds. This reduces the molding cycle by nearly 10%, significantly improving production efficiency. Furthermore, the pressure imparted by a small gate during the holding phase is relatively low and more evenly distributed, reducing internal stress in the part caused by excessive holding pressure and minimizing the risk of warping and cracking after demolding.
Small gates facilitate automated production, simplify gate removal, and reduce production costs. Small gates have a small connection area with the plastic part and low strength. They can be automatically removed during or after demolding through simple mechanical methods (such as vibration and shearing), eliminating the need for manual trimming and making them suitable for automated production lines. For parts with high aesthetic requirements, small gate removal leaves minimal marks, virtually negating the impact on the part’s appearance and reducing subsequent finishing steps. For example, in the production of exterior parts such as mobile phone cases, using a small gate can keep the gate mark diameter to less than 0.5mm, meeting aesthetic requirements without the need for additional treatment. Furthermore, the small gate design simplifies the mold’s gating system structure, easing processing complexity and reducing mold manufacturing and maintenance costs.
Small gates are less sensitive to the mold’s venting system and process parameters, making them more adaptable. The high shear effect of a small gate enhances melt fluidity, reducing reliance on mold venting slots. Even if the venting system is slightly inadequate, the high melt fluidity can reduce air entrapment defects. Furthermore, small gates are insensitive to fluctuations in process parameters within a certain range. For example, small changes in injection pressure and melt temperature have little impact on part quality, facilitating stable control of the production process. This can reduce production complexity and improve product qualification rates for companies with insufficient production experience or low-precision equipment. Of course, a small gate isn’t suitable for all situations. For parts with extremely poor fluidity or an excessively large molding area, a larger gate may be required. However, in the production of most small and medium-sized plastic parts, the advantages of a small gate make it the preferred gate type.
