Injection Moulding Gate Types: Edge, Tunnel, Pin, Hot Tip & Valve Gates

Every injection-moulded part carries a small scar where plastic entered the cavity — the gate witness. Choosing the gate type is a three-way trade between how big that scar is, how much the tool costs, and whether parts separate from the runner automatically. This guide compares the common gate types and explains why gate location is a design decision, not a toolmaker afterthought.

What are the common gate types?

Gate type	Runner	Witness mark	Degating	Tool cost impact	Best for
Sprue (direct)	Cold	Large, at part centre	Manual/machine trim	Lowest	Large single-cavity parts, prototypes
Edge (side)	Cold	Medium rectangle on edge	Manual trim	Low	Flat parts, multi-cavity two-plate tools
Fan	Cold	Wide, thin mark	Manual trim	Low	Wide flat parts needing even fill
Tab	Cold	Medium, on added tab	Trim with tab	Low	Shear-sensitive resins (PC, PVC), low jetting
Tunnel (submarine)	Cold	Small dot on edge/underside	Automatic at ejection	Low-medium	Small parts, automated two-plate tools
Pin	Cold (3-plate)	Tiny dot, ~0.5-1.5 mm	Automatic	Medium (three-plate tool)	Multi-cavity small parts, centre gating
Cashew / banana	Cold	Small, hidden	Automatic	Medium	Gating onto inner faces of curved parts
Hot tip	Hot	Small dot, ~0.5-1.5 mm	Automatic	High (hot runner)	Medium-high volumes, good cosmetics
Valve gate	Hot	Smoothest — small flush dot	Automatic	Highest	Large cosmetic parts, sequential fill, family tools

How do the cold-runner workhorses compare?

The edge gate is the default: a rectangular channel cut into the parting line feeding the part edge. Cheap to machine and easy to enlarge, but it leaves a trimmed rectangle on the part edge and needs manual or robotic separation.

The tunnel gate solves the separation problem. Its tapered channel dives under the parting surface and shears off cleanly at ejection, so parts drop free with a small mark on a non-visible edge — the reason most automated small-part tools use it. Gate diameter typically runs 0.5-1.5 mm; shear-sensitive or glass-filled materials may need larger tunnels to avoid fibre damage.

The pin gate gates into the top of the part through a three-plate tool, leaving a tiny dot and allowing balanced centre-gating of many cavities at once. The trade is a more complex tool with a floating runner plate.

When are hot-runner gates the right answer?

Hot-tip gates keep the melt liquid to the cavity face and freeze only a small vestige — a dot about 0.5-1.5 mm that can sit on a visible surface when necessary. Valve gates add a mechanical pin that seals the gate each cycle, giving the cleanest witness in the industry plus independent control of every drop.

Valve gating earns its premium on large cosmetic parts (sequential filling to eliminate weld lines), family tools with unbalanced cavities, and shear- or heat-sensitive resins where precise fill control matters. The full cost comparison against cold runners is in the hot runner vs cold runner guide.

Why does gate location matter as much as gate type?

Location decides the flow. Four rules cover most parts: fill from thick sections toward thin, so packing pressure reaches shrinking material; balance flow lengths so all regions fill at the same pressure; aim weld lines away from snap hooks, sealing beads, load paths and A-surfaces; and in glass-filled grades, gate so fibre orientation works with the load direction, not against it.

Gate position also sets the cosmetic outcome. Jetting — a worm-like flow pattern — appears when a small gate fires into an open cavity instead of landing against a wall or pin. Blush and splay concentrate near gates. A gate moved 15 mm at DFM stage can be the difference between a cosmetic pass and a texture change.

What should you specify as a buyer?

Three things on the 2D drawing or in the RFQ: which faces are cosmetic (A-surfaces), where a gate witness is acceptable, and any features a weld line must not cross. With those fixed, the toolmaker can propose gate type and location, and the proposal is reviewed before steel. Nordmould includes a gate-location proposal with witness-mark placement in every DFM review, because moving a gate after T1 sampling costs from hundreds to thousands of euros.