Molds & Tooling
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PVC Shrinkage Rate Difference
Fenómeno del problema
Rigid PVC parts were dimensionally stable, but after switching to soft PVC the same mold produced seriously out-of-tolerance dimensions
Análisis de la causa
Rigid PVC shrinks only 0.2-0.6% with stable dimensions; soft PVC shrinks 1.0-2.5% due to plasticizer; molds for the two types cannot be shared, and material switching must be recalculated
Solución
①Design mold shrinkage allowance separately by rigid/soft category; ②allow 1.0-2.5% margin for soft PVC; ③verify first-piece dimensions when switching categories; after adjustment, continuously sample to verify the effect, and resume mass production after confirming stability
Conclusión clave
PVC shrinkage differs fivefold between rigid and soft; mold design must determine the category first, then set the allowance; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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