Injection Molding
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PP Holding Pressure and High Shrinkage
Problem Phenomenon
[Problem Phenomenon] Insufficient PP holding pressure causes severe sink marks, excessive holding pressure causes high internal stress
Cause Analysis
PP shrinkage 1.0-2.5% is relatively high, requiring sufficient holding pressure for feeding; holding pressure at 50-80% of injection with extended time; excessive holding pressure introduces internal stress warpage
Solution
Set holding pressure at 50-80%; extend time for thick-wall ribs; reduce holding pressure with annealing for internal stress parts; after adjustment, take continuous samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
PP's high shrinkage requires sufficient holding pressure, 50-80% with extended time; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence; include this case in the defect archive as a troubleshooting reference for similar future problems
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