Molds & Tooling
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LDPE Shrinkage 2-5%
Fenómeno del problema
Product dimensional deviation is large, shrinkage differs significantly between grades with different densities, and molds are not interchangeable
Análisis de la causa
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
Solución
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
Conclusión clave
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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