Injection Mold Gate Types Compared: Sprue, Pin-Point, Submarine & Edge

All Five Gate Types at a Glance

Direct Sprue Gate

The simplest gate type — resin flows directly from the sprue bushing into the part cavity. No runner system, no gate bushing. The entire sprue is the gate.

• Pros: Simplest mold, lowest pressure drop, best packing, cheapest mold cost
• Cons: Largest vestige (requires manual trimming), single-cavity only, cosmetically unacceptable for visible surfaces
• Use when: Prototype molds, thick-walled parts requiring maximum packing, single-cavity production where gate location is non-cosmetic

Pin-Point Gate

Uses a pin-point gate bushing to create a small-diameter gate (0.5–2.0 mm) in a three-plate mold. The gate shears automatically when the mold opens, leaving a minimal vestige.

• Pros: Smallest cold-runner vestige, automatic degating, multi-cavity capability, gate can be placed anywhere on the part surface
• Cons: Requires three-plate mold (more expensive), runner waste, limited gate diameter (< 2.0 mm)
• Use when: Multi-cavity cosmetic parts (electronics housings, consumer goods), automated production requiring no manual gate trimming

Submarine (Tunnel) Gate

An angled tunnel below the parting line that shears automatically during mold opening. Requires a submarine gate electrode to EDM the tunnel shape.

• Pros: Automatic degating in a two-plate mold (simpler than three-plate), gate vestige is on the non-cosmetic side, well-suited for two-plate multi-cavity molds
• Cons: Gate thickness limited to ≤ 2 mm for reliable shearing, tunnel can clog with high-viscosity resins, electrode wear requires periodic re-machining
• Use when: Multi-cavity production requiring automatic degating but where a three-plate mold is not justified

Edge Gate

A rectangular gate at the mold parting line. Resin enters the cavity through a rectangular slot on the part's edge surface. Manual trimming or rolling gate cut units remove the gate after ejection.

• Pros: Easy to machine (no EDM needed), good for large flat parts, adjustable gate width for fill balance, can be used with in-mold gate cut
• Cons: Gate on parting line is visible, requires manual trimming (or gate cut unit), creates a witness line on the part edge
• Use when: Flat or box-shaped parts, parts where the parting line gate is acceptable, large parts requiring wide gate cross-section for fill

Selection Decision Matrix

According to ScienceDirect's gate design reference, gate type selection should consider part geometry, cosmetic requirements, production volume, mold budget, and resin characteristics as an integrated decision.