Molds & Tooling
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LDPE Shrinkage 2-5%
Problem Phenomenon
Product dimensional deviation is large, shrinkage differs significantly between grades with different densities, and molds are not interchangeable
Cause Analysis
LDPE has high branching and low crystallinity, with a shrinkage of 2-5%; at density 0.91-0.925g/cm³ the shrinkage is 2-5%, and at density 0.926-0.94 the shrinkage is 1.5-4%; actual shrinkage varies with molding conditions
Solution
① Allow mold allowance of 2-5% according to density grade; ② recalculation is mandatory when changing density grades; ③ correct shrinkage after trial molding for precision parts; after adjustment, take continuous samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
LDPE shrinkage varies in grades with density; mold design must first determine the density grade, so that the allowance has a basis; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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