Following the previous article: Plastic tooling evaluation (1) Equipment selectionNext, we need to determine the mold style, decide on the method of material retrieval, and consider whether to introduce automation, among other factors, to estimate costs or even provide a quotation. Therefore, the next step is to review the product, and the first step in evaluating mold design for the product is to make the gate selection. The type of gate will determine subsequent mold types, layouts, runner designs, and molding methods, among other things.
What is meant by "gate"? The gate refers to how the molten material enters the mold cavity. There are many types of gating methods, and the selection is generally determined by the structural characteristics of the product or the customer's requirements for appearance. Here, we divide the evaluation of gating into two parts: gate location and gate type.
Injection gate location
If we don't consider the customer's specified location, we need to find the most suitable gate location based on your gating type, and there are several principles to keep in mind.
1.Gate at the thickest/most uniform section: Gating at too thin a section can cause excessive pressure resistance, leading to incomplete filling of the product, while gating at overly thick sections may result in prominent jetting marks and severe shrinkage issues. Therefore, it is optimal to gate at a suitable thickness (1.5-3mm), preferably at the thickest section. It is recommended to use mold flow analysis software for thickness analysis in this regard. If the product shape is too complex or uneven, consider adding a gate at areas where incomplete filling may occur. In such cases, it is advisable to conduct mold flow analysis for verification.
As shown in the diagram, the green area has thicker wall sections.
2.Injecting at the center/symmetrical positions of the product: Plastic should flow evenly throughout the product to avoid concentrating flow in one area, which can lead to difficulty controlling product dimensions or even warping. Therefore, injection should preferably occur at the central position, and for symmetrical shapes like circles, injecting symmetrically from both sides is suitable.
As shown in the diagram, to achieve fuller injection and symmetrical dimensions for the product, symmetrical gating may be considered. However, this approach can result in knit lines at the meeting points of the two flows. Therefore, attention should be paid to the venting design, and the decision should be made based on the material and application requirements.
3.The gate should be preferably located in positions that do not affect the appearance of the plastic part, such as edges or the bottom.
As shown in the diagram, the blue surface represents the visible exterior surface, where gate marks should not be visible. Therefore, bottom gating is adopted in this case.
4.The gate location for injection molds with thin and long cores should be positioned away from the core to prevent deformation due to material flow.
As shown in the diagram, the gate indicated by the red arrow may cause bending and deformation of the central core due to impact forces. It is preferable to position the gate at the top thick section or bottom, aligned with the direction of the core, to avoid direct impact.
Gate Types
Plastic injection molding is a commonly used technique for manufacturing various plastic parts. The design of the gating system has a significant impact on the quality, production efficiency, and cost of the product. Here are several common types of gate designs:
- Direct Gate
- Advantages: Simple process, minimal injection pressure loss, suitable for large components or products requiring rapid filling.
- Disadvantages: The gate leaves marks on the product and requires post-processing trimming.
- ApplicationsLarge or thick-walled products, such as tables and chairs.
- Side Gate
- Advantages: Suitable for most standard components, easy to design and process.
- Disadvantages: Gate marks are more noticeable than direct gate, requiring post-processing trimming.
- Applications: General plastic part production, especially for irregularly shaped components.
- Pin Gate
- Advantages: Small gate marks, can automatically detach, reducing post-processing.
- DisadvantagesGreater injection pressure loss, may affect filling.
- ApplicationsMold with three-plate mold, small precision parts, such as gears, mobile phone accessories.
- Fan Gate
- Advantages: Provides more uniform material flow, reduces stress concentration.
- Disadvantages: Gate location is wider, may affect product appearance.
- Applications: Thin-walled parts, products requiring uniform filling.
- Tab Gate
- Advantages: Control material flow into the mold, beneficial for maintaining product strength.
- Disadvantages: Requires additional processing to remove the gate.
- Applications: Products requiring increased strength or controlled warpage.
- Horn Gate
- Advantages: Allows material to enter from the side of the mold, avoiding visible surface marks.
- Disadvantages: More complex structure, difficult to design and process.
- Applications: Products with high aesthetic requirements, such as transparent parts.
- Submarine Gate
- Advantages: Gate is located below the mold parting line, automatically shears off during product demolding.
- Disadvantages: Higher mold manufacturing and maintenance costs.
- Applications: Products with high aesthetic requirements.
- Disk Gate
- Advantages: Suitable for circular or cylindrical products, achieves uniform material distribution.
- Disadvantages: Limited to specific product shapes, and due to being a full-round gate, larger ejection area, more difficult.
- Applications: Outer shells, containers, and other circular products.
In addition to selecting the gate based on the criteria mentioned above, you also need to consider whether your facility has the capability to remove the gate. For instance, if the product has a thick side gate and requires trimming to maintain a smooth appearance, you'll need trimming equipment. Moreover, if you aim for mass production, automated trimming capability becomes essential.
Once you've decided on the gate location and the type of gate to use, you can roughly determine the mold pattern and layout. Therefore, for quick assessment and quoting, this is a crucial step to be decided early on. This article only introduces the key points to consider when evaluating gates. As for how to effectively design gates during mold design and their relationship with plastic materials, we'll share more detailed insights in future articles.
