Gate Types in Injection Moulding: How to Choose the Right Gate for Part Quality
Gate design is one of the most influential — yet frequently overlooked — elements of injection mould tooling. As the entry point where molten plastic flows into the cavity, the gate directly impacts fill behavior, packing efficiency, cosmetic appearance, and dimensional stability.
Selecting the appropriate gate type is not simply a tooling decision; it is a strategic engineering choice that affects the entire manufacturing process.
When optimised correctly, gate design promotes consistent production and reduces defect risk.
What Is a Gate?
A gate is the small opening that allows molten polymer to transition from the runner system into the mould cavity.
Although compact, it plays several critical roles:
- Controls material flow
- Influences cooling behavior
- Determines packing effectiveness
- Affects surface finish
- Impacts post-mould trimming
Poor gate decisions often surface later as quality issues.
Why Gate Selection Matters
The right gate supports balanced filling and predictable shrink behavior. The wrong one can introduce stress, visible marks, or incomplete filling.
Key engineering considerations include:
- Part geometry
- Wall thickness
- Material viscosity
- Cosmetic expectations
- Production volume
Common Injection Mould Gate Types
Edge Gate
One of the most widely used options, positioned along the parting line.
Advantages:- Simple to machine
- Reliable filling
- Cost-effective tooling
- Requires trimming
- Gate vestige may remain visible
Pin Gate
Typically used in multi-cavity or hot runner systems.
Advantages:- Small vestige
- Cleaner appearance
- Supports automated production
- Less suitable for very thick sections
Submarine (Tunnel) Gate
Feeds the cavity below the parting line and shears automatically during ejection.
Advantages:- Minimal manual trimming
- Improved cycle efficiency
- More complex tooling
Fan Gate
Designed to distribute material across a wider entry point.
Advantages:- Reduces flow stress
- Helps minimise warping
- Ideal for large or flat components
Hot Tip Gate
Common in hot runner systems where material remains molten.
Advantages:- Reduced material waste
- Shorter cycle times
- Often improves cosmetic quality
- Higher tooling investment
How Gate Location Influences Part Quality
Placement is often as important as gate type.
Proper positioning helps:
- Prevent weld lines
- Reduce internal stress
- Promote uniform packing
- Improve dimensional stability
Experienced tool designers evaluate flow paths carefully before finalising location.
Signs of Poor Gate Design
- Warping
- Sink marks
- Air traps
- Flow hesitation
- Visible cosmetic defects
These issues frequently trace back to early tooling decisions.
Collaborate Before Tooling Begins
Gate strategy should be discussed during the design phase — not after the tool is cut.
Early collaboration allows engineers to balance aesthetics, manufacturability, and cost before changes become expensive.
Frequently Asked Questions
What is a gate in injection moulding?
It is the opening where molten plastic enters the mould cavity.
Why is gate selection important?
It directly affects flow behavior, packing, and defect risk.
Can poor gate design cause defects?
Yes — improper gate strategy often leads to warping and uneven filling.