Molds & Tooling
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PA6 Shrinkage and Post-Shrinkage
Fenómeno del problema
The part dimensions are qualified at demolding, but after several days of storage the dimensions go out of tolerance and assembly fit fails
Análisis de la causa
PA6 shrinkage is 1-1.5% and post-shrinkage continues after molding, while water absorption expansion partially offsets the shrinkage; the dual action of shrinkage and expansion causes dimensions to drift with time and ambient humidity
Solución
①Allow margin in the mold according to the 1-1.5% shrinkage and reserve space for mold trial and correction; ②Perform conditioning treatment on precision parts after molding to pre-stabilize dimensions; ③Perform dimensional inspection after conditioning reaches equilibrium
Conclusión clave
PA6 dimension management must account for both the shrinkage bill and the water absorption bill; conditioning pretreatment plus post-equilibrium inspection is the only way to lock dimensions in the service state; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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