A Complete Guide to Injection Molding Gate Types and Applications

Table of Contents

1.Introduction

2.Common Injection Molding Gate Types

3.How to Choose the Right Gate Type for Plastic Injection Molding

4.Impact of Gate Types on Mold Design and Production

5.Common Gate-Related Issues and Optimization Tip

6.Conclusion

1.Introduction

In plastic injection molding, the gate plays a crucial role in determining part quality, mold structure, and production efficiency. As the entry point through which molten plastic flows into the mold cavity, the gate design—including its type, size, and injection molding gate location—directly influences the flow pattern, cooling rate, and cycle time.

A proper injection molding gating design not only improves part appearance and dimensional stability but also helps optimize mold structure and reduce manufacturing cost. This guide introduces the most common types of gates in injection molding, along with their advantages, disadvantages, and ideal application scenarios—helping engineers and product developers make informed decisions in early-stage mold design and boost the success of injection projects.

2.Common Injection Molding Gate Types

The injection molding gate types used in a mold greatly affect melt flow, pressure loss, part strength, surface finish, and overall production efficiency. Below are seven widely used gate designs for plastic parts, each with unique structural features and use cases.

2.1 Direct Gate

Overview:

The direct gate, also known as a sprue gate, is the simplest type, allowing molten plastic to flow directly from the sprue into the cavity. It is typically used for single-cavity or large, simple parts.

Advantages:

·Short flow path and minimal pressure loss

·Simple mold structure and lower tooling cost

Disadvantages:

·High stress around the gate area

·Visible gate mark on the part surface

·Manual gate trimming required

Applications:

Best suited for large structural components or deep-cavity parts where aesthetics are not a priority. The gate can be placed on hidden surfaces when needed.

2.2 Edge Gate

Overview:

An edge gate is positioned on the parting line, allowing melt to enter from the side of the cavity. It is a commonly used gate type in injection molding.

Advantages:

·Simple to design and machine

·Supports larger gate cross-section

·Easy gate removal by trimming

Disadvantages:

·Requires manual gate removal

·May leave visible marks on side surfaces

Applications:

Suitable for most standard parts, though not ideal for cylindrical or deep components due to ejection direction constraints.

2.3 Tab Gate

Overview:

A tab gate is an enhanced form of the edge gate, designed to reduce shear stress and jetting by spreading the melt flow. It appears as a wide, flat transition area before the melt enters the cavity.

Advantages:

·Minimizes shear-induced defects

·Improves surface finish

·Shares the benefits of an edge gate

Disadvantages:

·Requires trimming

·Visible gate witness on the part

Applications:

Ideal for flat-panel components and parts with cosmetic surface requirements, such as covers or enclosures.

2.4 Fan Gate

Overview:

The fan gate expands the flow path laterally, distributing melt evenly across a wide area, reducing warpage and stress concentration.

Advantages:

·Ensures uniform melt flow

·Minimizes air entrapment and cosmetic defects

Disadvantages:

·Large gate area may leave visible marks

·Gate must be trimmed post-molding

Applications:

Perfect for thin-wall, large-area parts or optical components made of PC, PMMA, etc., where consistent flow is critical.

2.5 Tunnel Gate / Submarine Gate

Overview:

Also known as a sub-gate, the tunnel gate enters the cavity beneath the parting line, creating a hidden gate location in injection molding.

Advantages:

·Gate separates automatically during ejection

·Minimal gate mark; good for cosmetic parts

·Suitable for both two- and three-plate molds

Disadvantages:

·Potential flash or powder at gate exit

·Higher pressure loss than direct gating

Applications:

Common in multi-cavity tools for consumer electronics, connectors, or decorative parts. Great when automatic separation is required.

2.6 Banana Gate

Overview:

A curved variation of the tunnel gate, the banana gate enables the melt to enter from behind or undercut areas of the mold cavity.

Advantages:

·Invisible gate location

·Supports automated ejection

·Preserves front-facing aesthetics

Disadvantages:

·Difficult to machine and maintain

·Not suitable for crystalline or rigid materials

Applications:

Mostly used for ABS, HIPS; not recommended for POM, PBT, PC, or PMMA due to risk of gate blockage or stress cracking.

2.7 Pin Point Gate

Overview:

A pin point gate has a very small diameter, typically placed at the center or hidden side of the molded part. It is common in multi-cavity and precision plastic parts.

Advantages:

·Very small gate mark

·Automatic gate separation

·Lower stress and good dimensional control

Disadvantages:

·Higher injection pressure needed

·Requires complex three-plate mold structure

Applications:

Used for LED lenses, optical parts, electronic housings, and intricate precision components.

3.How to Choose the Right Gate Type for Plastic Injection Molding

Selecting the appropriate injection molding gate type is essential for part quality and mold performance. Below are key factors to consider when determining how to choose gate type for plastic injection molding:

3.1 Selecting Gate Types Based on Part Geometry and Size

The geometry and size of a plastic part play a critical role in determining the appropriate injection molding gate types. For large, thick-walled, or complex components, direct gates are recommended to reduce pressure loss and ensure complete cavity filling. For flat, thin-walled parts with a wide surface area, fan gates or tab gates offer better flow distribution and improved fill balance. In the case of long, narrow, or deep cylindrical parts, side gates should be avoided—pin point gates or tunnel gates are more suitable options due to their favorable injection molding gate location and ease of ejection. Choosing the right types of gates in injection molding based on part geometry is essential in achieving an optimized injection molding gating design, improving part quality, and minimizing injection molded part defects due to gating.

3.2 Aesthetic Requirements vs. Cost

A part’s cosmetic requirements are a key factor in selecting appropriate injection molding gate types. For visible parts such as consumer electronics housings or automotive interior panels, it's essential to avoid noticeable gate marks. In such cases, tunnel gates, banana gates, or pin point gates are ideal, as they allow hidden injection molding gate locations and clean automatic separation during ejection. On the other hand, for structural or internal components where appearance is not critical, edge gates or direct gates offer simpler injection molding gating design and lower tooling costs—striking a better balance between functionality and cost-efficiency.

3.3 Demolding and Automation

As automated injection molding becomes more widespread, selecting injection molding gate types that allow easy part ejection and automatic gate separation has become increasingly important. Pin point gates and tunnel gates offer excellent auto-degating performance, making them ideal for high-speed, fully automated production with no manual trimming. In contrast, traditional gate options like edge gates or tab gates require manual removal, making them less suitable for automation. Therefore, injection molding gating design should be closely aligned with the demolding method and automation requirements to maximize production efficiency.

3.4 Material Considerations

Different plastic materials have unique flow characteristics, crystallinity, and thermal sensitivity, all of which directly influence the suitable injection molding gate types. For transparent and rigid materials like PC or PMMA, fan gates or tunnel gates are recommended to prevent issues like flow lines or silver streaks caused by jetting. Crystalline materials such as POM and PBT cool quickly and are not suitable for banana gates, as they are prone to gate blockage. For low-flow materials like PA or glass-filled resins, direct gates with short flow paths and minimal resistance are more effective. Ultimately, injection molding gating design should be carefully matched to the material properties to ensure consistent part quality and efficient molding.

Type	PVC	PE	PP	PC	PA	POM	ABS	PMMA
Direct	●	●	●	●	●	●	●	●
Edge	●	●	●	●	●	●	●	●
Tab						●	●	●
Fan			●			●	●
Tunnel					●	●	●
Banana			●			●	●	●
Pin		●	●	●	●	●	●

3.5 Production Volume

In high-volume production, the choice of injection molding gate types must account not only for part quality but also for efficiency and cycle time. Pin point gates and tunnel gates allow automatic gate separation, significantly improving productivity and making them ideal for multi-cavity molds and automated systems—especially when annual output exceeds one million parts. For low-volume or custom products, simpler options like edge gates or direct gates are more cost-effective and easier to modify. When evaluating how to choose gate type for plastic injection molding, it’s essential to balance order volume, mold flexibility, and production speed to achieve optimal efficiency and cost control.

4.Impact of Gate Types on Mold Design and Production

In the injection molding process, injection molding gate types not only determine the flow path of molten plastic but also directly influence mold complexity, defect control, and long-term maintenance costs. A well-designed injection molding gating design can improve part quality, extend mold life, and enhance overall production efficiency. Below are four key factors to consider:

4.1 Gate Location and Flow Direction Control

The injection molding gate location dictates where and how the melt enters the cavity, which directly affects filling balance and part quality. Poor gate placement can result in long flow paths, uneven fill, or dead zones, causing short shots or pressure imbalances. For instance, fan gates promote uniform distribution across wide surfaces, preventing underfill in thick central areas. Pin point gates and tunnel gates allow precise flow control and minimize directional interference. Accurate gate positioning, supported by Moldflow analysis, should be considered early in the gate design for plastic parts to ensure balanced and efficient filling.

4.2 Weld Lines and Air Trap Issues

Weld lines and air traps are common injection molded part defects due to gating, typically occurring where flow fronts meet or where air is poorly vented. The chosen injection molding gate type affects melt convergence angles and pressure, impacting weld line strength and appearance. Edge or tab gates may cause prominent weld lines if melt flows meet from opposite sides. In contrast, multi-point gating or centralized pin gate layouts help melt flow outward from the center, minimizing these defects. Fan gates and hot runner systems also improve flow consistency and air evacuation, reducing surface defects like bubbles or splay. Proper gate design must consider venting and flow direction to optimize appearance and consistency.

4.3 Residual Stress and Warpage Control

Gate type and location significantly affect cooling dynamics and internal stress distribution. For example, direct gates offer efficient filling but may cause high residual stress near the gate, leading to warpage or cracking over time. Conversely, fan gates or tab gates distribute flow more broadly, reducing localized stress and improving dimensional stability. For parts with tight flatness or geometric tolerance requirements, gates that balance cooling and pressure—along with optimized holding time and cooling profiles—can effectively reduce deformation risk.

4.4 Maintenance and Replacement Cost of Gate Components

Each injection molding gate type correlates with a certain level of mold complexity, which influences maintenance and repair costs. Simpler cold runner designs like edge and tab gates are easier to machine and clean, though they may require manual degating. Tunnel, banana, and pin point gates enable automatic separation and greater production efficiency but demand higher machining precision and more complex tooling. If the gate area wears out or becomes blocked, repairs can be time-consuming and costly. Hot runner systems, while efficient, require regular inspection of heaters and nozzles to maintain precise temperature control. For high-frequency, high-volume production, it's wise to adopt standardized, modular gate components to reduce long-term operating costs.

5.Common Gate-Related Issues and Optimization Tips

In injection molding projects, choosing and optimizing the right injection molding gate types is critical for improving part quality and manufacturing efficiency. Even with proper early-stage design, several common issues can still arise during production, such as visible gate marks, unbalanced flow in multi-gate systems, or evaluating the ROI of hot runner systems. Below are practical insights and recommendations for addressing these challenges:

5.1 How to Minimize Gate Marks?

Gate marks are visible defects caused by improper trimming or shear during gate separation—often seen on glossy, transparent, or high-aesthetic surfaces. To reduce these injection molded part defects due to gating, choose concealed gate types such as pin point gates, tunnel gates, or banana gates that allow hidden injection molding gate locations and automatic separation during ejection. Gate size must be carefully controlled based on material type and wall thickness: oversized gates may leave bumps, while undersized gates risk flash or short shots. Also, optimize packing time and mold temperature to prevent stringing and whitening caused by premature gate break-off. Through thoughtful gate design for plastic parts and process tuning, surface appearance can be significantly improved.

5.2 How to Balance Flow in Multi-Gate Designs?

Multi-gate layouts are common in large parts or multi-cavity molds to boost fill efficiency—but they can introduce flow imbalance. If resistance varies between gates, certain cavities may overfill, leading to flash, weld line shift, or short shots. To address this, Moldflow or similar simulation tools should be used to analyze pressure distribution, melt front timing, and runner balance. Flow paths can then be adjusted by modifying runner lengths, diameters, or adopting flow restrictors. For precision parts, interchangeable gate inserts or flow control pins may be added to fine-tune the system. While multi-gating increases efficiency, maintaining dynamic balance is essential for consistent quality.

5.3 Is a Hot Runner System Worth the Investment?

Hot runner systems maintain melt temperature through heated nozzles, eliminating cold runners, reducing material waste, and improving cycle time. For mid- to high-volume or multi-cavity production, a hot runner is often a worthwhile investment. Though initial tooling cost is higher, long-term benefits include lower part cost, less scrap, reduced labor, and better product consistency. From a process perspective, hot runners improve flow balance and reduce weld lines—especially valuable for parts with complex geometry or uneven wall thickness. However, for low-volume or highly customized parts, cold runner systems may offer better cost-efficiency. When evaluating whether to adopt hot runners, consider annual production volume, material costs, maintenance capability, and automation needs, along with the expected ROI.

6.Conclusion

The selection of injection molding gate types is more than a technical detail—it plays a critical role in product performance, molding efficiency, and overall production cost. Each gate design for plastic parts offers unique advantages in minimizing gate marks, balancing flow pressure, and enabling automated degating. Therefore, the choice must be based on a comprehensive understanding of project-specific requirements.

With 23 years of experience in custom mold manufacturing, Alpine Mold is committed to delivering tailored injection molding gating design solutions based on customer needs. Leveraging advanced mold design expertise and flow simulation capabilities, we help global clients optimize both part quality and production performance. Whether you're developing high-precision consumer electronics or complex automotive components, we’re here to support your success with professional, efficient, and reliable service.

Feel free to contact us to explore your next injection molding project.