Molds & Tooling
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PMMA Stress Whitening (Demolding)
Problem Phenomenon
Whitening appears around ejector pins, and stressed areas show white misty marks.
Cause Analysis
Small draft angle and rough mold cause excessive ejection force, and local stress exceeds the material whitening threshold; too-fast cooling also causes shrinkage stress whitening.; During on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based on experience alone.
Solution
①Reduce injection pressure, raise and uniformize mold temperature; ②anneal to eliminate stress; ③ensure draft angle and mold surface finish; ④optimize ejection design.; After adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability.
Key Takeaway
Stress whitening is a visible signal of local overload; starting from the ejection system and cooling uniformity, combined with annealing it can be completely eliminated.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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