Time to read: 6 min
Is your injection molding project ready for success? Sure, you’ve thought about most of theinjection molding manufacturing process。您已经谨慎地设计了模具，研究并选择了正确的材料，并完成了CAD文件或部分绘图。
But have you considered the type of injection molding gate to use? A gate might seem like a small detail, but it affects tooling costs, cycle times, and part quality. The good news is that this article will help you to choose the right injection molding gate for your next project.
What is an Injection Molding Gate?
注射成型力熔融塑料朝向和通过门，这是一个使材料进入霉菌腔的开口。Sprues和跑步者允许这种材料流动，但它是控制进入成型的地方的大门。由于栅极的尺寸会影响塑料的压力，因此适当的栅极尺寸至关重要。
If the gate in an injection mold is too large, molten plastic fills the cavity unevenly, and makes defects such as shrinking and weld lines more likely. If the gate is too small, short shots and high levels of residual stress at the gate may result. The shape of the gate also affects the flow and can contribute to or help minimize part defects.
In addition to size and shape, injection molding gates differ in terms of thickness. Typically, large, thick-walled plastic parts require thicker gates to accommodate a higher volume of flow. Smaller injection molded parts usually require thinner gates, but not at the expense of adequate pressure.
注射成型Gate Basics
大门可以沿着模具分开线或沿霉菌腔的各个点位于位置。这些开口可以宽或狭窄，并且可能具有锥形或一致的尺寸以帮助控制流动。因为门从模具延伸，所以门也有一个深度。腔中的大门及其复杂性有助于霉菌成本。大门还会影响循环时间和零件的外观外观。
During injection molding, most of the molten plastic material cools and solidifies inside of the mold cavity to form the finished part. However, some plastic solidifies at the gate and protrudes from the part’s surface. De-gating, the process of trimming this excess material, is important for part quality and can be performed either manually or automatically.
手动与自动修剪门
With gates that aremanually trimmed, a worker separates the molded parts from the runners after each production cycle. This increases labor costs and may result in inconsistent cycle times. With gates that are trimmed automatically, human intervention is not required. Instead, excess gate material is sheared from the runner when the part is ejected.
Different types of gates are designed specifically for manual or automatic trimming, and while gates that are automatically trimmed might always seem like the best choice, sometimes they aren’t. For example, thick gates require manual trimming because they’re susceptible to damage from the shearing associated with automatic trimming.
Manually Trimmed Injection Molding Gates
Manually trimmed gates include edge, fan, tab, direct, disc, ring, and spoke gates.
- Edge or standard gatesare recommended for flat parts. The gate’s cross-section is rectangular and can be tapered between the part and the runner.
- 风扇大门have a large opening with a variable thickness. They permit the rapid filling of large parts and fragile mold sections.
- 标签门与需要低剪切应力的薄扁平零件一起使用。类似标签的特征将这些应力限制在栅极区域。
- Direct or sprue gatesare used with large, cylindrical parts. A sprue feeds material directly and rapidly into the cavity.
- 椎间盘或隔膜大门与需要同心性的圆形或圆柱零件一起使用。通常，这些注入成型门很难卸下，修剪成昂贵。
- Ring gatesallow material to flow freely before moving into a uniform, tube-like extension for mold filling.
- Spoke gatesare round gates that have a cross in the middle. They’re used to produce tube-shaped parts, but perfect concentricity is difficult to achieve.
Automatically Trimmed Gates
Automatically trimmed gates include hot tip, submarine or sub gates, and pin gates.
- Hot tip gatessupport conical or round shapes that require uniform flow into the mold cavity. They are used in hot runner systems that keep the plastic in a molten state until it enters the cavity.
- 潜艇或子门有一个锥形通道，可以帮助隐藏门斑点。这些开口有时被称为tunnel gatesinstead.
- Pin gatesare used with fast-flowing resins and when a part’s cosmetic appearance is important. Pin gates are used typically with parts that cannot have vestiges on either side of the parting line.
Depending on the mold system, other types of gates can be used instead. For example, hot runner systems can use阀门机械作用会导致阀杆移动，然后密封门开口。阀门的成本比其他类型的门更高，但可以通过减少证人标记等缺陷来提高零件质量。阀门门也提高了生产率，因为它们支持自动修剪速度更快的周期时间。
Choosing Gate Location, Size and Geometry
注塑浇口的位置影响part quality. For best results, gates should be placed away from pins or cores because these obstructions can cause molten plastic to flow around them and form weld marks. To ensure complete filling of the mold cavity, it’s best to locate gates closest to the thick-walled areas of parts. However, because gates may leave blemishes, you should avoid placing openings near visible part surfaces.
不同类型的门也需要不同的位置。许多门可以位于模具分开线附近，但热门门通常位于零件的顶部。海底大门也可以从分节线中移开，这在模具设计过程中提供了额外的灵活性。销门通常在弹出销位置的模具的B侧发现。
门尺寸是另一个重要的考虑因素。通常，门的宽度基于霉菌腔的体积，门的深度基于标称壁的大小。但是，由于不同的材料的流速不同，因此塑料类型是一个因素。例如，由于聚乙烯（PE）和聚丙烯（PP）容易流动，因此栅极深度可能仅基于零件壁厚的50％。
The geometry, or shape of the gate also affects performance. For example, cashew-shaped sub gates are commonly used but not always the best choice in terms of flow restriction and fill pressure. For best results, gates should always taper down to the orifice to avoid flow restrictions. Otherwise, you may get flow imbalances and an increase in fill pressures.
Additional Considerations: Injection Speeds
High injection speeds through a gate can cause friction-induced increases in temperature, and if there’s enough additional heat, damage to the molecular structure of the plastic may occur. Yet slowing down the injection speed to avoid degradation may reduce a part’s mechanical strength and result in weld lines. Plus, slower cycle times mean fewer parts per hour and higher processing costs.
Knowing when to increase or decrease the injection speed isn’t just about gate size, however, which is why injection molders use arelative viscosity vs. shear rate curve找到正确的平衡。
优化您的大门并设置您的项目成功
Injection molding gates do more than affect fill rates. They also help drive tooling costs, cycle times, and part quality. For designers and engineers, it’s important to understand how injection molders can optimize the gates that connect sprues and runners to mold cavities. Gate type, trimming method, location, size, and geometry also determine quality and performance.
Fictiv has the application experience and technical expertise to optimize the gates in your injection molds, and you canlearn all about our injection molding capabilities here。不管你是刚刚开始with injection molding or have been shooting plastic for years, we’re ready to help you manage the entire process to deliver quality injection molded parts on time.Create an account和get a quote today!
