Molds & Tooling
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PA6 Sink Marks
Problem Phenomenon
Depressions on the back of rib and boss positions, obvious on the appearance surface.
Cause Analysis
High shrinkage + insufficient holding pressure compensation; early gate freeze-off; excessively large rib thickness ratio is a structural inducement; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience.
Solution
①Increase holding pressure and extend holding time;②control rib thickness to 50%~60% of the main wall thickness;③appropriately enlarge the gate to reduce shear rate and pressure loss;④core-pull and reduce material at thick walls to reduce shrinkage from the source;⑤strengthen local cooling for that location (add inserts or conformal water channels).
Key Takeaway
PA6 sink marks = 'compensation management': holding pressure and freeze-off are the technique, rib thickness and thick walls are the root; crystalline materials shrink greatly, and compensation and structure must be emphasized equally; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence.
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