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In-Depth Analysis of Sink Mark Defects in Injection Molded Products | Causes and Complete Solutions for Indentations at Ribs, Blind Holes and Grid Areas
I. Defect Overview: During injection molding production, the outer surfaces corresponding to reinforcing ribs, blind-hole screw bosses and grid rib positions of plastic products are highly prone to local sinking. The industry collectively calls this sink marks (shrinkage indentations). Mild sink marks affect the appearance of products and fail to meet the shipping standards for appearance parts; severe sink marks are accompanied by internal vacuum bubbles, reducing product structural strength and causing batch defects, raw material loss and delivery delays, making them a high-frequency pain point in the production of automotive parts, logistics baskets, daily necessities and home appliance housings...