Injection Molding
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PMMA Sheet Vacuum Voids (Thick-Wall Shrinkage)
Problem Phenomenon
Vacuum voids appear in the center of thick-wall sheets, reduced after lowering injection speed and increasing pressure.
Cause Analysis
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.
Solution
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.
Key Takeaway
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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