Last updated: 2026-09-04 · 5 min read
Gate Vestige Control — How Do You Minimize the Gate Mark on Cosmetic Injection Molded Parts Without Sacrificing Fill Quality?
Gate vestige is the bump, mark or discoloration left where the gate met the cavity surface. Every gate leaves one — the question is size. A valve gate leaves 0.02–0.1mm (near-invisible); a sprue gate leaves 0.5–2.0mm (clearly visible). The fix hierarchy: select the right gate type at DFM, optimize gate dimensions (depth 30–70% of wall, land 0.5–1.5mm), then tune process parameters. Once the mold is cut, relocating a gate costs $1,000–8,000 in welding and re-machining.
Key Facts
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Cavity — The hollow space inside the mold that forms the part shape. Multi-cavity molds produce multiple parts per shot. Cavity count determines production output but also mold cost and complexity. Each cavity must be balanced for uniform fill. The related guide covers adjacent topics.
How Do You Select the Right Gate Type for Your Cosmetic Requirement?
Five gate types, matched to vestige tolerance:
| Gate Type | Vestige Height | Visibility | Best Application |
|---|---|---|---|
| Valve gate (hot runner) | 0.02–0.1mm | Near-invisible — flush with surface | Cosmetic enclosures, automotive interior trim |
| Pin-point gate (submarine) | 0.1–0.3mm | Low — small dot, breaks off automatically | Multi-cavity molds, general-purpose |
| Hot runner open-tip | 0.1–0.3mm | Low — small bump on surface | High-volume production, engineered resins |
| Edge gate (tab gate) | 0.2–0.5mm | Moderate — visible on edge, can be trimmed | Flat parts, panels, plates |
| Direct sprue gate | 0.5–2.0mm | High — visible bump and stress mark | Non-cosmetic parts, thick sections |
The valve gate is the only gate that produces a near-invisible vestige. The shut-off pin closes the gate opening before the melt solidifies — the gate is trimmed cleanly at the part surface. The cost: $3,000–8,000 per drop for the hot runner valve gate system. For high-volume cosmetic parts (enclosures, automotive trim), the investment is justified by zero secondary trimming.
The pin-point gate and open-tip hot runner leave a small bump (0.1–0.3mm) — visible on glossy surfaces but hidden by texture (SPI C2–D1). For parts with a textured surface, either gate is acceptable. For glossy or Class A surfaces, only a valve gate meets the requirement.
What Design Rules and Process Adjustments Minimize Vestige?
Four design rules, in order of importance:
- Gate location on non-cosmetic surface. Place the gate inside, on an edge, or in a recessed area (textured zone, rib intersection). If the gate must be on a cosmetic surface, use a valve gate — no other gate type produces an acceptable vestige on a Class A surface.
- Gate depth: 30–70% of wall thickness. Below 30%: flow restriction causes injection stress, creating a shiny or discolored ring around the gate. Above 70%: excess material must be removed, increasing vestige height. For a 2.0mm wall: 0.6–1.4mm depth.
- Gate land length: 0.5–1.5mm for pin-point gates, 0.2–0.5mm for valve gates. A longer land increases vestige (more material solidifies in the gate, break point is further from the surface). A shorter land reduces vestige but risks gate freeze (short shots or sink marks).
- Add a 0.1–0.3mm radius at gate entry. A sharp corner creates stress concentration and a visible stress mark. A radius distributes the stress and reduces vestige visibility. This radius is machined into the cavity — not adjustable after mold build.
Four process adjustments, balanced to avoid fill defects:
| Adjustment | Effect on Vestige | Risk if Wrong |
|---|---|---|
| Increase melt temp (+10–20°C) | Reduces vestige — melt flows more easily, less stress | Too high: degradation, burn marks, longer cooling |
| Reduce injection speed at gate | Reduces vestige — less shear stress at entry | Too slow: jetting, flow marks, short shots |
| Reduce hold pressure (−10–20%) | Reduces vestige — less material packed at gate | Too low: sink marks, voids, shrinkage |
| Increase mold temp (+10–20°C) | Reduces vestige — melt stays fluid longer | Too high: longer cycle, part sticking, warpage |
The adjustments must be balanced. Reducing hold pressure reduces vestige but risks sink marks. Reducing injection speed at the gate reduces stress marks but risks jetting. The optimal settings are found at T1–T2 by running a DOE that varies melt temperature, injection speed and hold pressure — vestige height is measured after each trial, and the settings that produce the smallest vestige without fill defects are locked into the process sheet.
Shrinkage — The dimensional reduction from mold cavity to cooled part. Amorphous resins: 0.4–0.7% (uniform). Semi-crystalline: 1.0–2.5% (directional). Mold makers apply shrinkage factor when machining cavity. Actual shrinkage varies with wall thickness, gate location and packing pressure. The related guide covers adjacent topics.
Gate vestige control is a DFM decision, not a process fix. Once the mold is cut, relocating a gate or adding a valve gate requires welding and re-machining ($1,000–8,000). Specify the gate type, location and dimensions before steel is cut.
Frequently Asked Questions
Can gate vestige be removed after molding?
Yes — by trimming (manual or automated degating), sanding (flat surfaces) or laser trimming (precision parts). However, secondary operations add $0.02–0.10 per part and introduce variation. Manual trimming is inconsistent. The preferred approach is to control vestige at the mold: correct gate type, optimized dimensions, locked process parameters.
Secondary trimming should be the exception, not the rule. If every part requires vestige trimming, the mold or process needs adjustment — not a downstream fix.
How do you measure gate vestige?
Three methods. Height gauge or caliper: measures vestige height above the part surface (cosmetic spec: less than 0.1mm; non-cosmetic: less than 0.3mm). Visual comparison: the part is compared against a standard plaque with known vestige heights (0.05, 0.1, 0.2, 0.5mm) under standard lighting. Profilometer or optical scanner: measures the full vestige profile (height, width, volume) with micron-level accuracy — used for automotive and medical parts with strict cosmetic specs.
The acceptable range is defined by the customer’s cosmetic specification. Automotive interiors typically require less than 0.1mm; consumer electronics enclosures require less than 0.05mm (near-invisible).
Does the resin type affect gate vestige?
Yes. Amorphous resins (PC, ABS, PMMA) produce a smaller, cleaner vestige — they solidify gradually and do not crystallize at the gate. Semi-crystalline resins (PP, PE, PA, POM) produce a larger vestige because rapid crystallization creates a stress mark and color difference at the gate. Glass-filled resins (GF30+) produce the most visible vestige — glass fibers orient at the gate and create a rough, fibrous mark.
For glass-filled cosmetic parts: specify a valve gate and a textured surface at the gate location. The texture hides the fibrous vestige. Without both, the gate mark will be visible regardless of process adjustments.
Key Takeaways
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Gate vestige control starts at the DFM review — specify the vestige requirement, select the gate type that meets it, confirm the gate dimensions and location, and lock the process window at T1.
The cost of getting it wrong: $1,000–8,000 in mold rework, plus secondary trimming on every part for the life of the mold.
Sources
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Sources: Plastics Technology · Plastics Technology Online · Society of Plastics Engineers (SPE) · ThomasNet