Molds & Tooling
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PMMA Sink Mark Depression
Problem Phenomenon
Sink marks appear at thick-wall areas and behind ribs; sink marks on transparent parts are also accompanied by abnormal light refraction.
Cause Analysis
Uneven wall thickness causes insufficient feeding compensation when thick areas shrink; insufficient holding pressure or time, or gate freezing too early, all prevent PMMA's relatively large shrinkage from being compensated.; During on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based on experience alone.
Solution
①Increase holding pressure and time; ②core out thick areas, uniformize wall thickness; ③enlarge gate and runner; ④adjust mold temperature to improve feeding compensation.; After adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability.
Key Takeaway
PMMA sink mark treatment follows the feeding compensation logic; sink marks on transparent parts also have optical effects, and structural uniformity is more reliable than process compensation.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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