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Injection Mold Gate Types Reference

The gate controls how plastic enters the cavity, so gate type changes cosmetics, stress, warpage and cycle time. This table compares common gate types and where each is normally used, so you can discuss options with your toolmaker.

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Gate type	Description	Best for	Advantages	Drawbacks	Gate removal
Sprue gate	Melt flows directly from the sprue into the cavity	Single cavity, large or thick parts, round parts	Low pressure loss, simple tool, good pack	Large gate vestige, needs manual removal, stress at the gate	Manual cut or trim
Edge gate	Rectangular gate at the parting line feeding the edge of the part	Flat parts, multi-cavity tools, general purpose parts	Easy to machine and modify, good packing, flexible location	Gate mark on part edge, runner must be removed	Manual or automatic trim
Fan gate	Edge gate that widens like a fan across the cavity edge	Wide flat parts, thin panels, reducing warpage	Even flow front, lower shear, less orientation	Larger vestige to trim	Trim
Film (flash) gate	Very wide thin gate along the full part edge	Thin flat parts, lenses, parts needing low warpage	Uniform fill, low orientation and stress	Large gate area to remove, hard to trim cleanly	Trim or die cut
Tab gate	Small tab between gate and part to move shear away from the part	Parts sensitive to gate stress, clear resins, jetting prevention	Moves gate stress and jetting off the part, good surface	Extra step to remove tab	Manual trim
Pin-point gate (three-plate)	Small round gate fed by a runner between two plates	Multi-cavity tools, center gating of cup-shaped parts	Small vestige, automatic degating, center gating possible	Three-plate mold is more complex, runner waste, higher pressure loss	Automatic when mold opens
Submarine (tunnel) gate	Gate angled below the parting line into the part	Small to medium parts, automatic degating of runner	Automatic degating, small mark, no separate trim	Not for brittle or very stiff resins, gate wear, needs ejector design	Automatic at ejection
Cashew (banana) gate	Curved submarine gate that enters from the ejector side	Parts that need gating on an inside surface, hidden gates	Gate mark can be hidden, automatic degating	Complex to machine, limited resin suitability	Automatic at ejection
Ring gate	Melt flows around a core through a ring before entering the cavity	Cylindrical or tubular parts	Even filling around the part, reduces weld lines and eccentricity	Needs trimming of the ring, more material	Machined or trimmed off
Diaphragm gate	Disc-shaped gate across the inside of a hollow part	Round hollow parts such as bottle caps or gears, concentric parts	Uniform concentric fill, no weld lines, good roundness	Disc must be removed, cut mark inside	Machined or punched off
Hot tip gate	Hot runner nozzle with heated tip directly gating the part	High-volume parts, runnerless molding	No runner scrap, short cycle, good pack	Gate vestige or blemish, needs temperature control, not for heat sensitive resins without care	None (runnerless)
Valve gate	Hot runner nozzle with a pin that opens and closes the gate	Cosmetic parts, large parts, sequential valve gating	Clean gate mark, control of open and close timing, helps weld line control	Higher tool cost, more maintenance, more components	None (runnerless)

Gate type and location are best decided with flow simulation and the tool designer. This table gives general guidance and does not replace a design review.

Tool records and shot counts from your ERP

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How to pick a gate

Start with the part shape and where a gate mark is acceptable. A cosmetic outer surface needs a hidden or very small gate, a flat panel may need a fan or film gate for even flow, and a round hollow part often uses a diaphragm or ring gate. Then consider volume and automation: if you need unattended running, a submarine or hot runner gate removes the gate without manual work. Finally check resin: brittle or glass-filled materials can break at a submarine gate and may need an edge or hot tip gate.

Gate near the thickest section so pack reaches it
Aim the gate at a wall to avoid jetting
Keep flow length within what the resin and wall can fill

Size, shear and freeze time

Gate size sets shear rate and freeze time. A gate that is too small raises shear, causes blush and degrades the melt, while a gate that is too large leaves a large vestige and may not freeze quickly enough to limit pack. The gate should freeze after the part is packed but before the cycle is wasted waiting. Gate seal studies, which increase hold time and weigh the part until weight stops rising, show exactly when the gate freezes.

Hot runner and valve gates

Hot runner systems keep plastic molten up to the gate, which removes runner scrap and shortens cycle. Valve gates add a mechanical pin for clean gate marks and sequential filling, helpful for large parts and weld line control. They cost more and add maintenance, so they pay back mainly in high volume or cosmetic work. Watch for leaking, thermocouple faults and heater failures, and log these in your maintenance system.

Common mistakes

Typical errors include placing the gate where the part will be loaded and warping, gating a thin wall into a thick section so the thick area has no pack, and ignoring where weld lines will form. Changing gate size later by welding and re-cutting steel is possible but must be tracked. Document gate type, size and location on the tool drawing and the process sheet so repairs return it to the qualified condition.

Frequently Asked Questions

Which gate type avoids a visible gate mark?

Submarine and cashew gates on a hidden surface, and hot runner valve gates, leave small or hidden marks. The right choice depends on the part geometry, the resin and acceptable cosmetic standards.

What is the purpose of a tab gate?

A tab gate moves the high shear and jetting at the gate away from the functional surface of the part. The tab is removed after molding, which adds a trimming step but improves surface quality and reduces stress.

How do I know when the gate has frozen?

Run a gate seal study: increase hold time in steps and weigh the parts. When part weight stops increasing, the gate has frozen. Use a hold time slightly above that point to avoid wasting cycle time.

Why choose a three-plate mold?

Three-plate molds allow pin-point gating almost anywhere on the part surface and automatic separation of the runner. They cost more and generate runner scrap, so teams compare them with hot runners.

If you want gate seal, scrap and cycle data from the press tied to the tool record in your ERP, Netray can help you build that reporting inside your own environment.

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