Molds & Tooling
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POM Shrinkage Rate 1.8-3.5%
Fenómeno do problema
Large dimensional deviation of the part, shrinkage voids and sink marks in thick-walled areas, and inconsistent shrinkage at different wall thicknesses in the same mold
Análise das causas
POM has high crystallinity; when transitioning from melt to crystalline solid, the shrinkage rate is 1.8-3.5% and shrinkage is greater at thick walls; wall thickness differences cause density differences, and thick-wall melt flowing toward thin walls aggravates non-uniformity
Solução
①Allow margin in the mold according to shrinkage rate and correct through mold trials; ②make wall thickness as uniform as possible; ③strengthen holding pressure feeding for thick-walled parts to prevent shrinkage voids; after adjustment, take continuous samples to verify the effect, and resume mass production only after confirming stability
Conclusão principal
POM's shrinkage ranks among the highest in engineering plastics; uniform wall thickness, holding pressure compensation, and mold margin allowance are the three key elements of dimensional control; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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