Injection Molding
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PMMA Sheet Vacuum Voids (Thick-Wall Shrinkage)
Fenómeno del problema
Vacuum voids appear in the center of thick-wall sheets, reduced after lowering injection speed and increasing pressure.
Análisis de la causa
When wall thickness is large, the cooling shrinkage of the center is not compensated, forming vacuum shrinkage voids; fast injection speed and insufficient holding pressure aggravate central voids.; During on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based on experience alone.
Solución
①Reduce injection speed, increase injection and holding pressure; ②extend holding pressure time; ③raise mold temperature to delay freezing; ④optimize wall thickness design.; After adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability.
Conclusión clave
Thick-wall vacuum voids are a feeding compensation problem, not a moisture problem; the key identification point versus bubbles is a centered position with no accompanying silver streaks.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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