Molding Process
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Large Drop in Weld Line Strength of LCP
Problem Phenomenon
【Problem Phenomenon】LCP products crack very easily at weld lines; butt-type weld line strength can drop by about 90%, and under stress they fracture neatly along the weld line
Cause Analysis
LCP molecular chains are highly oriented along the flow direction; when two melt fronts butt together, the molecular chains align in parallel with very little transverse entanglement, so the weld line contributes almost no strength; the Celanese design guide records that butt weld strength drops by 90%, while flow-around-core weld can retain 50-60%
Solution
In structural design, avoid the stress direction being perpendicular to the weld line; lay out gates to move the weld line to a low-stress area; use flow around cores to form lapped weld lines; add overflow wells to lead cold material and weld lines away from the body
Key Takeaway
LCP weld lines are inherently weak; design avoidance and overflow well transfer are more effective than machine adjustment; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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