Molds & Tooling
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POM sink mark depressions
Problem Phenomenon
Surface depressions appear at thick walls and on the back of ribs; the depressions are reduced after increasing holding pressure but not completely eliminated.
Cause Analysis
Uneven wall thickness prevents thick areas from receiving melt replenishment during cooling shrinkage; insufficient holding pressure or time, and a too-small gate freezing early, all cause insufficient feeding.; 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; ②enlarge the gate to delay freezing; ③optimize wall thickness design and core out thick areas; ④increase mold temperature to improve feeding.; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
POM sink marks follow the general mechanism of insufficient feeding; thick-walled parts should start with structural coring-out, and process compensation can only alleviate, not cure.; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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