Molds & Tooling
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Shrinkage and sink marks of PP thin-wall parts
Problem Phenomenon
Sink mark depressions appear on the back of rib positions and at locations with uneven wall thickness, resulting in poor appearance.
Cause Analysis
Uneven wall thickness makes the cooling shrinkage of thick areas uncompensated; insufficient holding pressure or time and early gate freeze-off all aggravate sink marks on thin-wall parts.; during on-site investigation, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solution
①Increase the holding pressure and time; ②control the rib thickness within 2/3 of the main wall thickness; ③core out thick areas to even out wall thickness; ④optimize the gate size.; after adjustment, continuously sample and verify the effect, and resume mass production after confirming stability
Key Takeaway
The radical cure of thin-wall part sink marks relies on structural uniformity; rib design following the 2/3 rule can balance strength and appearance.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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