Molds & Tooling
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POM dimensions continue to shrink after demolding
Problem Phenomenon
Products measure acceptable at demolding, but re-measurement after 24 hours shows dimensions are significantly smaller, and assembly reveals fits that are too tight or loose.
Cause Analysis
POM has high crystallinity, and crystallization continues after demolding, producing post-shrinkage that can last more than 24 hours; high demolding temperature and uneven mold temperature increase the post-shrinkage amount.
Solution
①Let products stabilize for 24 hours before measuring for inspection; ②design the mold with about 2.8% shrinkage compensation; ③extend in-mold cooling for shaping; ④stabilize mold temperature to reduce fluctuation.
Key Takeaway
POM post-shrinkage is an inherent material characteristic; dimensional judgment must be made after sufficient aging, and mold compensation and cooling shaping must reserve shrinkage allowance.; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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