Last updated: 2026-09-05 · 5 min read
Gate Vestige in Injection Molding — How Much Protrusion Is Acceptable, Which Gate Types Leave the Smallest Mark and What Can You Do to Minimize It?
Gate vestige is the residual bump or depression left after the gate is trimmed. For an edge gate, vestige height is 0.1–0.3mm. For a submarine gate, 0.05–0.15mm. For a hot runner valve gate, 0.02–0.05mm — nearly flush. On Class A cosmetic surfaces, any vestige above 0.1mm requires secondary trimming. Gate type, size and trim method determine whether the vestige is acceptable as-is.
Key Facts
- Gate vestige height depends on gate type and break-off design. An edge gate leaves 0.1–0.3mm protrusion because the gate fractures above the part surface. A submarine gate (below the parting line) breaks off below — vestige 0.05–0.15mm, often acceptable without trimming. A pin gate (hot runner) leaves a circular mark where the pin contacts the part — vestige 0.02–0.05mm, essentially flush.
- On cosmetic surfaces, vestige above 0.05mm is visible under overhead lighting. Class A surfaces (automotive exterior, electronics housing) require vestige below 0.05mm — only a hot runner valve gate or a manually trimmed pin gate qualifies. Class B surfaces (interior, non-visible) tolerate up to 0.3mm. If the budget does not allow a hot runner, specify a pin gate with a 0.3mm diameter and a break-off design that leaves the vestige below the surface.
- Secondary trimming methods: hand trimming (±0.05mm, $0.01–0.03/part), CNC machining (±0.02mm, $0.05–0.15/part), laser trimming (±0.01mm). Hand trimming is cheapest but inconsistent — the operator’s angle and pressure vary. CNC is precise but adds cost and cycle time. Laser trimming is the most precise with a clean edge, but the equipment cost ($50,000–150,000) only justifies for high-volume cosmetic parts (500,000+ pieces/year).
How Does Gate Vestige Compare Across Gate Types and Trim Methods?
| Gate Type | Vestige Height | Trim Required? | Cost Impact | Best For |
|---|---|---|---|---|
| Edge gate | 0.1–0.3mm | Yes (hand trim) | +$0.01–0.03/part | Non-cosmetic, thick walls |
| Submarine gate | 0.05–0.15mm | Sometimes | +$0.005–0.02/part | General purpose, mid-cosmetic |
| Pin gate (cold runner) | 0.05–0.10mm | Often | +$0.01–0.03/part | Small parts, multi-cavity |
| Hot runner valve gate | 0.02–0.05mm | No | +$0.02–0.05/part (system) | Class A cosmetic surfaces |
| Hot runner thermal gate | 0.05–0.10mm | Sometimes | +$0.01–0.03/part (system) | Mid-cosmetic, lower cost |
For consumer electronics housings (phones, tablets, remotes), the gate is almost always on a cosmetic surface — vestige must be below 0.05mm. A hot runner valve gate is the only option that avoids secondary trimming. The system costs $10,000–30,000, but for a 4-cavity mold running 500,000 parts/year, savings on hand trimming ($0.02/part × 500,000 = $10,000/year) pay for the hot runner in 1–3 years.
Class A surface — any exterior or user-visible surface that must be free of visible defects under normal lighting conditions. Automotive exterior panels, phone housings and appliance fronts are Class A. On Class A surfaces, gate vestige above 0.05mm is visible under overhead lighting and requires secondary trimming. Class B surfaces (interior, non-visible) tolerate up to 0.3mm. The hot runner vs. cold runner cost guide covers when a valve gate system pays for itself on Class A parts.
What Three Design Strategies Minimize Gate Vestige?
- Move the gate to a non-cosmetic surface whenever possible — the easiest fix is a design change. If the gate can be relocated to an internal rib, a snap-fit face or a mating surface that is never visible, the vestige is hidden regardless of height. This requires the mold designer to route the melt path from the non-visible area — which may increase flow length or create a weld line in a visible area. Run a mold flow analysis to confirm the new gate location fills without creating weld lines on cosmetic surfaces. The corner radius guide covers how gate placement interacts with part geometry at corners.
- Use a break-off groove at the gate base — this controls where the gate fractures. A break-off groove is a small undercut (0.1–0.2mm deep, 0.1mm wide) machined at the gate base where it meets the part surface. When trimmed, the fracture occurs at the groove — not randomly above or below the surface. This reduces vestige from ±0.15mm (random fracture) to ±0.03mm (controlled fracture). The groove must be on the gate side (not the part side) to ensure the vestige is below the part surface.
- Specify the vestige height on the drawing — not just the gate location. If the drawing does not state a vestige requirement, the molder defaults to “as molded” — 0.1–0.3mm for an edge gate. For cosmetic parts, specify: “Gate vestige ≤0.05mm, flush with surrounding surface.” This forces the molder to select the appropriate gate type and trim method. Without the specification, the molder may use a standard edge gate and charge extra for hand trimming — or deliver parts with 0.2mm vestige that fail inspection.
Automatic degating — a mold feature that breaks the gate from the part automatically during ejection, without manual trimming. A submarine gate uses a tapered land that fractures at a controlled point; a pin gate uses a shearing action against the core. Automatic degating eliminates labor cost ($0.01–0.03/part for hand trimming) but vestige varies by ±0.05mm depending on gate land wear. After 50,000–100,000 shots, the gate land rounds and vestige increases — the gate location guide explains how wear affects gate performance.
Gate vestige: edge gate 0.1–0.3mm, submarine 0.05–0.15mm, valve gate 0.02–0.05mm. Class A surfaces need ≤0.05mm — hot runner valve gate only. Break-off groove reduces vestige to ±0.03mm. Specify vestige height on the drawing or get “as molded” by default.
- Gate on non-cosmetic surface when possible — hidden vestige needs no trimming regardless of height.
- Break-off groove at gate base — controls fracture point, reduces vestige to ±0.03mm.
- Vestige height specified on drawing — “≤0.05mm flush” for cosmetic; otherwise “as molded” default.
- Hot runner valve gate for Class A — 0.02–0.05mm, no secondary trimming needed.
- Gate land inspected every 50k shots — wear rounds the edge, vestige increases from 0.05 to 0.15mm.
Frequently Asked Questions
Why does my gate vestige vary from part to part even in the same mold?
Two causes: inconsistent gate break-off and mold wear. For manually trimmed gates, the operator’s angle and force vary — some gates break cleanly, others tear above the surface. Switch to a break-off groove or automatic degating to make the fracture consistent. For automatic submarine gates, the gate land wears after 50,000–100,000 shots — the sharp edge becomes rounded, and vestige increases from 0.05mm to 0.15mm.
The second cause is process variation — if the mold temperature or injection speed drifts, the gate freezes at a different point, changing where the fracture occurs. Monitor the gate vestige height at the start of each production run and after every 10,000 shots — if it increases, the gate land needs re-machining.
Can gate vestige be eliminated entirely on a cosmetic surface?
Not entirely — but a hot runner valve gate reduces it to 0.02–0.05mm, nearly invisible under normal lighting. The valve gate has a mechanically actuated tip that shuts off the flow cleanly — when the valve closes, it shears the gate flush with the surface. The residual mark is a small circular depression only visible under magnification or at a grazing angle.
For parts where even 0.02mm is unacceptable (optical lenses, transparent covers), the gate must be moved to a non-visible surface or the part must be post-machined. Laser trimming can bring the vestige to 0.01mm — essentially invisible — but at $0.05–0.10/part, it adds significant cost. For most consumer electronics, 0.05mm from a valve gate is the practical limit.
How does gate vestige affect assembly with ultrasonic welding or adhesive bonding?
A gate vestige above 0.1mm creates a gap between mating surfaces — for ultrasonic welding, this gap prevents the energy director from contacting evenly, and the weld fails at the gate location. For adhesive bonding, the vestige creates a local stress concentration that reduces bond strength by 20–30%. If the gate is in the weld or bond joint area, specify vestige ≤0.05mm — or move the gate out of the joint area. The DFM review should flag any gate in a weld or bond zone.
Key Takeaways
- Edge gate: 0.1–0.3mm. Submarine: 0.05–0.15mm. Valve gate: 0.02–0.05mm.
- Class A surfaces: ≤0.05mm — hot runner valve gate only.
- Break-off groove: reduces vestige to ±0.03mm (controlled fracture).
- Specify vestige height on the drawing — or get “as molded” by default.
Send the part drawing with the cosmetic surface designation and the vestige requirement — the DFM review recommends the gate type, location and trim method needed to meet the vestige specification.
Sources: Plastics Technology — Gate Vestige Reduction and Cosmetic Surface Requirements · Plastics Technology Online — Hot Runner Valve Gate Vestige Performance · Society of Plastics Engineers (SPE) — Gate Design and Vestige Technical Papers · Synventive — Valve Gate Technology and Cosmetic Gate Vestige Data · YUDO — Hot Runner Systems and Gate Vestige Specifications
— Arthur, Tooling Engineer at aCatMould