Injection molding defects
Gate blush is a milky, whitish, or dull halo that radiates from the gate on filled or colored parts. It is usually tied to high shear at the gate, frozen-in orientation, or stress whitening where the melt enters the cavity at high velocity.
Defect troubleshooting
Gate blush appears as a cloudy ring or streak centered on the gate, most visible on dark, clear, or high-gloss surfaces. It is a cosmetic defect from molecular orientation and stress at gate entry, no
Gate blush appears as a cloudy ring or streak centered on the gate, most visible on dark, clear, or high-gloss surfaces. It is a cosmetic defect from molecular orientation and stress at gate entry, not a short fill or void.
Operators sometimes confuse blush with splay or jetting. Splay tends to look silvery and moisture-driven; jetting shows as a snaking jet mark. Blush stays anchored to the gate land even when fill balance is good on other faces.
Gate size, location, and angle should be reviewed in CAD while changes are cheap. NetProto DFM feedback with instant quotes helps teams discuss gate strategy before steel is cut on cosmetic programs.
Root causes
Use this table to decide whether the next change belongs in material prep, process, mold steel, or part design.
| Likely driver | What you see | First lever to try |
|---|---|---|
| Gate too small for shot size and material | Tight white halo at gate; worse on filled grades | Increase gate diameter or switch gate style per supplier shear guidance |
| High injection speed at gate entry | Blush grows when fill speed increases | Profile fill with slower gate entry segment |
| Gate on high-visibility cosmetic face | Blush on show surface even when function is good | Relocate gate to hidden edge or tab in next revision |
| Excessive pack immediately after fill | Halo intensifies with hold pressure | Reduce hold in small steps; verify gate seal time separately |
Diagnosis
Splitting ownership tells you whether material, process, or tooling is the honest fix path.
Troubleshooting
Document what you see, prove a fair process window, then escalate to steel or design when the limit is proven.
Cosmetic baseline
Use the same viewing angle and background for every trial. Mark gate center and measure halo radius if the customer spec requires it.
One variable
Reduce injection speed during the first percent of fill while monitoring short fill elsewhere.
Shear margin
Compare measured gate to supplier minimum for the grade and shot weight. Document any EDM or wear change.
Pack decoupled
Tune hold only after first-stage fill is stable. Blush often worsens when hold is used to compensate for a restrictive gate.
Design fix
When blush violates cosmetic spec on a show face, plan gate move or edge gate on a hidden flange in the next steel revision.
Prevention
Most recurring defects trace to setup discipline and design margin rather than a single out-of-spec shot.
Model gate location away from primary cosmetic faces when product design allows.
Size gates for shear-sensitive filled and clear grades using supplier guides, not copy-paste from another resin.
Document fill profile segments on the setup sheet, not only peak pressure.
Align texture and gloss spec with customer viewing conditions before T1 sign-off.
Run gate blush trials on colored and filled lots, not only natural resin.
Upload CAD for DFM gate recommendations during quoting.
Program context
Gate blush is often accepted or rejected based on viewing angle and color. Define cosmetic zones in the quality plan before production release.
FAQ
Flow lines follow melt path history across the part. Gate blush is localized to gate entry stress and orientation. They can coexist but the fix paths differ.
A larger gate reduces shear if size was the limiter, but it can worsen weld movement or flash if taken too far. Change one variable and measure blush under agreed lighting.
Blush is primarily cosmetic orientation and stress whitening. Structural concern depends on customer spec; document if blush zones overlap load-bearing features.
Yes if tip temperature or drop balance drives cold gate entry or excessive shear at the tip. Compare drops before blaming cavity steel alone.
Upload CAD for an instant quote and DFM feedback. Engineers can review gates, vents, wall transitions, and ejection risk while the hardened steel tool is still in planning, depending on part size and complexity. There is no minimum order quantity once the tool is running.
Ready to quote
Bring gate blush photos and CAD into an instant quote so gate placement and cosmetic zones are discussed with DFM before production hardening.
