Determine the gate type for injection molding
In injection molding, determining the gate type is a critical step in mold design, directly impacting part quality, production efficiency, and mold manufacturing costs. As the channel connecting the runner and cavity, the gate’s primary function is to control the melt’s flow rate, filling time, and pressure loss. It also ensures timely cooling and sealing after the melt fills the cavity to prevent backflow. Different types of gates are suitable for different part structures, material properties, and production requirements. Therefore, when determining the gate type, factors such as the part’s shape and size, wall thickness distribution, material flowability, and appearance quality should be comprehensively considered. For example, for large parts, multiple gates are often required to ensure uniform melt filling of the cavity. For parts with high aesthetic requirements, gates with minimal gate marks should be selected.
Point gate is a widely used type of gate, characterized by a small cross-sectional size, usually between 0.5-2mm in diameter. The gate position can be flexibly set, and it can automatically separate from the plastic part when the mold is opened. There is no need for subsequent processing to remove the gate marks. It is suitable for small and medium-sized plastic parts with high appearance requirements. The advantage of point gate is that the melt generates a higher shear rate when passing through a small cross-section, which can improve the fluidity of the material and facilitate the filling of thin-walled plastic parts. However, the pressure loss of point gate is large, and for materials with poor fluidity such as polycarbonate (PC), higher injection pressure may be required. When an electronics factory produces mobile phone casings, it uses a point gate design, which not only ensures the appearance quality of the casing, but also improves the fluidity of the PC material through the shear thickening effect, shortening the filling time by 15%.
Side gates, also known as edge gates, are typically located on the mold’s parting surface, feeding material from the edge of the part. Their cross-sections are often rectangular, and the gate size can be adjusted according to the size of the part, making them suitable for parts of various shapes, especially flat panels and shells. Side gates offer the advantages of a simple structure, ease of processing, low mold manufacturing costs, and the ability to control the melt flow rate and filling time by adjusting the gate width and thickness. However, side gates leave noticeable gate marks on the part’s surface, requiring subsequent processing, making them less suitable for parts with strict aesthetic requirements. For example, when a home appliance company produced a washing machine control panel, they adopted a side gate design because the panel had low aesthetic requirements. This not only reduced mold costs but also enabled more uniform melt filling by adjusting the gate size, reducing internal stress in the part.
A latent gate, also known as a tunnel gate, features a gate located on the mold core or ejector pin. The melt enters the mold cavity through a tunnel-like channel. The gate is automatically severed by the ejector pin during mold opening, leaving a gate mark on the inside or non-exterior surface of the part. This design is suitable for parts requiring high aesthetic requirements and automated production. The advantage of a latent gate is that it eliminates the need for manual gate trimming, improving production efficiency. The gate mark is also concealed, without affecting the part’s appearance. However, latent gates are difficult to manufacture, requiring high mold precision, and are not suitable for materials with poor flowability or brittleness. An automotive parts manufacturer employed a latent gate design to produce decorative trim strips. This design concealed the gate mark on the inside of the trim strip, meeting aesthetic requirements while enabling fully automated production and increasing production efficiency by 30%.
Fan gates and film gates are suitable for large, flat-plate plastic parts. Their characteristic wide gate width allows the melt to enter the mold cavity evenly and at a lower speed, reducing shear stress and orientation effects during melt flow and preventing part warping. A fan gate, with its fan-shaped cross-section that gradually expands from the runner toward the cavity, is suitable for wide parts. A film gate, however, extends along the entire edge of the part, allowing the melt to simultaneously fill the entire cavity and is suitable for ultra-thin, flat parts. A packaging materials manufacturer uses a fan gate design when producing large plastic pallets. By increasing the gate width, the melt evenly fills all corners of the pallet, reducing warping caused by uneven filling and keeping the pallet flatness within 0.5mm. For plastic film parts as thin as 0.3mm, a film gate ensures rapid and even melt filling, preventing defects such as material shortages and bubbles.
