Engineering Insights
Injection Sink Marks: Check Structure Before Process
Sink marks are often related to local thick sections, ribs, bosses, packing transfer, and uneven cooling rather than one process setting.
Why they appear
Material in thick sections cools and shrinks more than the outer skin. Ribs, bosses, abrupt wall changes, early gate freeze, and uneven cooling can pull the surface inward.
How to diagnose
Match each mark with the structure behind it, then review wall transitions, gate distance, packing response, and cooling. A defect fixed in one location usually points to structure or tooling.
Improvement direction
Reduce material accumulation, use sensible rib and boss geometry, and improve gate, cooling, and packing conditions together instead of relying on excessive pressure.