Injection Molding
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COC Obvious Weld Lines
Problem Phenomenon
In COC transparent parts the weld line visibility is high, the strength at the confluence of multi-gate parts is low, cracking occurs along the weld line under stress, and optical uniformity is impaired.
Cause Analysis
When two melt fronts converge, the temperature drops, and the interfacial entanglement of amorphous COC depends on temperature; low mold temperature and insufficient injection speed cause the fronts to cool too much; poor venting aggravates interfacial weakening.
Solution
①Increase mold temperature and melt temperature, fill at medium-high speed to maintain front temperature; ②strengthen venting in the confluence area; ③optimize gate layout to move the weld line out of the optical zone and stressed zone; ④use a single-gate scheme if necessary.
Key Takeaway
COC weld lines have nowhere to hide on transparent parts; the gate scheme can cure the problem more radically than process adjustment; weld line planning for optical parts should be completed at the mold design stage.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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