Warpage
Warpage shows up as twist or bow after cooling. The warpage guide covers shrink, pack, and gate balance without duplicating the full fix list here.
Defect troubleshooting
Injection molding defects
Route to focused troubleshooting guides for warpage, flash, short shot, and other common defects. Each guide owns one topic so this hub stays a map, not a manual.
Defect troubleshooting
Injection molding defects: find the right guide
This hub routes you to focused guides. Each linked page owns one defect keyword so you do not have to search a single long article.
Injection molding defects span fill, pack, cooling, material, and tooling. Use the cards below to open the guide that matches what you see on the part or in the process window.
NetProto reviews CAD for manufacturability before a hardened steel tool is released, which often surfaces defect risks early. Upload a CAD file when you want DFM feedback tied to your geometry.
Defect guides
Browse injection molding defect guides
One short summary per defect. Full causes, fixes, and prevention live on the linked page.
Short shot
Short shots mean the cavity did not fill completely. See causes tied to fill, venting, and material behavior on the dedicated short shot page.
Short shotFlash
Flash is excess material at parting lines or shutoffs. The flash guide walks through clamp, wear, and process levers in one place.
Weld lines
Weld lines form where melt fronts meet. The weld lines page explains flow path, venting, and cosmetic risk for your geometry.
Knit lines
Knit lines are a related knit-front cosmetic issue. Compare knit line causes and fixes on the knit lines guide.
Flow lines
Flow lines read as surface streaks along the fill path. The flow lines page covers gate location, speed, and material appearance.
Jetting
Jetting looks like a snaking jet on the surface. See the jetting guide for gate design and injection profile starting points.
Burn marks
Burn marks signal overheated or trapped air. The burn marks page ties venting, speed, and trapped gas together.
Silver streaks
Silver streaks often trace to moisture or shear. Read the silver streaks guide for material prep and process checks.
Voids
Voids are internal empty pockets in thick sections. The voids page focuses on pack, cooling, and section design tradeoffs.
Bubbles
Bubbles can be cosmetic or structural depending on location. The bubbles guide separates venting, gas, and material causes.
Delamination
Delamination shows as layers peeling at the surface. See the delamination page for material, moisture, and shear interactions.
Black specks
Black specks usually point to degraded material or contamination. The black specks guide lists line-side checks in order.
Discoloration
Discoloration can follow overheating, residence time, or colorant issues. Open the discoloration guide for a structured checklist.
Brittleness
Brittleness shows up as cracking under load or handling. The brittleness page covers material, moisture, and stress concentrators.
Drag marks
Drag marks are scuffs from ejection or sticking. See the drag marks guide for draft, polish, and ejection balance.
Ejector pin marks
Ejector pin marks are cosmetic or stress risers at pin locations. The ejector pin marks page covers layout and force.
Gate blush
Gate blush is a dull or stressed region at the gate. Read the gate blush guide for gate style, size, and process pairing.
Cold slug
A cold slug is an unfused piece of material in the part. The cold slug guide covers nozzle, runner, and fill sequencing.
Air traps
Air traps leave incomplete fill or burn in corners. The air traps page focuses on venting and last-to-fill regions.
Unbalanced filling
Unbalanced filling drives warpage, weld lines, and size spread in multi-cavity tools. See the unbalanced filling guide.
Dimensional variation
Dimensional variation ties to shrink, pack, and tooling steel. Pair the dimensional variation guide with published commercial tolerance bands.
Surface haze
Surface haze dulls gloss or clarity on cosmetic parts. The surface haze guide covers material, venting, and cooling.
Parts sticking in the mold
Sticking parts slow cycles and risk damage at ejection. The sticking parts guide covers draft, polish, and release.
Sink marks
Thick sections and rib roots often show sink. NetProto already publishes a sink marks article with prevention angles for thick-wall parts.
Read the sink marks articleProgram approach
Catch defects in DFM, or chase them on every setup
Defect firefighting costs time when root cause moves between design, tooling, and process. A stable tooling decision keeps troubleshooting focused.
Design and one steel tool locked early
- DFM feedback before tooling release flags weld-line, vent, and cosmetic risks on your CAD.
- One hardened steel tool means one qualification cycle instead of relearning defect signatures on a throwaway tool.
- Commercial tolerance bands are published before you debate whether variation is a defect or an expected band.
- The same tool keeps running on reorders without a second tooling purchase.
Reactive troubleshooting on the floor
- Each new defect sends engineers through fill, pack, cooling, and material checks without a single owner page.
- Staged tooling paths can add a second qualification cycle where flash, short shot, and warpage show up differently than on the first tool.
- Softer tooling wears mid-program, so cosmetic defects appear after the process was already signed off.
- Teams fix symptoms shot by shot instead of locking geometry and gate strategy up front.
Defect hub questions
Common questions
What counts as an injection molding defect?
A defect is any feature that fails your cosmetic, fit, or function requirements. This hub lists named defects so you can open the guide that matches the symptom on the part or in the process window.
Should I change the process or the mold first?
It depends on whether the root cause is frozen in steel or adjustable in the current cycle. Each guide below separates design and tooling fixes from process levers for that defect.
Can design choices prevent common molding defects?
Yes. Gate location, uniform sections, and vent paths change how melt fills and packs. NetProto DFM review is meant to catch those risks before tooling is released.
Where do tolerances fit when a part looks out of spec?
Compare measured variation to the commercial tolerance bands on the Manufacturing Standards page. Dimensional variation has its own guide when shrink or pack drive spread.
Does NetProto help if I am already seeing defects on samples?
Upload CAD or contact engineering with photos and the defect name. DFM feedback and process review are part of quoting and production support, without publishing a single production lead time figure here.
Ready to quote
Want DFM feedback before defects show up on first shots?
Upload your CAD for instant quoting and manufacturability notes. NetProto builds one hardened steel tool and runs production from it.