Injection Molding
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PSU Dents and Sink Marks
Problem Phenomenon
Dents and sink marks appear in thick-wall areas of PSU products; transparent parts show optical distortion; internal shrinkage porosity is visible on cross-section.
Cause Analysis
Mold temperature too high causing uneven cooling; injection and holding time too short causing insufficient compensation; injection pressure too low causing insufficient compaction; melt temperature too high aggravating shrinkage.; During on-site troubleshooting, verify item by item according to this mechanism, avoiding blindly adjusting the machine based solely on experience
Solution
①Appropriately lower mold temperature (but balance stress); ②Extend injection and holding time; ③Increase injection pressure; ④Appropriately lower barrel temperature.; After adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Treating PSU dents requires balancing the contradiction between temperature and stress; holding time is the main adjustment means; thinning thick-wall design is the root.; After confirming effectiveness, solidify the parameters and practices into the work instructions to prevent recurrence
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