Views: 0 Author: Site Editor Publish Time: 2025-05-21 Origin: Site
The gate is the small opening that connects the runner system to the mold cavity. It controls:
✔ Flow rate – How quickly plastic enters the cavity.
✔ Pressure – Ensures proper filling and packing.
✔ Cooling & solidification – Affects part ejection and final properties.
A poorly designed gate can lead to defects like warping, sink marks, or jetting.
Design: Large opening directly from the nozzle to the part.
Pros: Low pressure loss, good for thick parts.
Cons: Leaves a visible mark, requires trimming.
Use Case: Large, simple parts (e.g., buckets, containers).
Design: Located at the parting line, rectangular or round.
Pros: Easy to machine, adjustable.
Cons: May leave a witness mark.
Use Case: Consumer products (e.g., toys, appliance housings).
Design: Tiny (0.5–2mm), automatically breaks off.
Pros: Minimal marks, no post-processing.
Cons: High pressure required, wears faster.
Use Case: Small, high-precision parts (e.g., connectors, medical devices).
Design: Angled tunnel that shears off during ejection.
Pros: Hidden gate, good for automation.
Cons: Complex design, higher maintenance.
Use Case: Automotive interiors, electronics.
Design: Widens gradually to distribute flow.
Pros: Reduces stress and jetting.
Cons: More material waste, needs trimming.
Use Case: Flat parts (e.g., panels, covers).
Design: Uses heated nozzles, no cold runner.
Pros: No waste, faster cycles.
Cons: Expensive, requires precise temp control.
Use Case: High-volume production (e.g., medical disposables).
| Factor | Consideration |
|---|---|
| Location | Avoid cosmetic surfaces; minimize weld lines. |
| Size | Too small → short shots; too large → sink marks (~50-80% of wall thickness). |
| Shape | Round (low resistance) vs. rectangular (controlled flow direction). |
| Number | Multiple gates for complex parts (but may increase weld lines). |
| Material | High-viscosity plastics (e.g., PC) need larger gates than low-viscosity (e.g., PP). |
Cause: High-speed injection causing turbulent flow.
Fix: Use a fan gate or reduce injection speed.
Cause: Insufficient packing pressure.
Fix: Increase hold pressure or reduce gate size.
Cause: Uneven cooling or gate design.
Fix: Optimize gate angle or raise mold temperature.
Medical: Pin gates (clean break, minimal contamination risk).
Automotive: Hot runner gates (efficiency for high volumes).
Optical Parts: Diaphragm gates (prevents flow marks).
✅ Simulate first – Use Moldflow analysis to predict flow behavior.
✅ Start small – Adjust gate size based on initial trials.
✅ Balance multi-cavity molds – Ensure even filling across all cavities.
The gate may be small, but it plays a huge role in injection molding success. Choosing the right type and optimizing its design can mean the difference between flawless parts and costly defects.
