Molds & Tooling
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PA66 sink marks
Problem Phenomenon
Depressions on the back of ribs and bosses, obvious on appearance surfaces.
Cause Analysis
High shrinkage + insufficient feeding; gate freezes early; rib thickness ratio too large; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based solely on experience; during troubleshooting, confirm item by item around key factors such as sink marks and holding pressure to avoid misjudgment.
Solution
①Increase holding pressure and extend holding time to ensure feeding at thick walls; ②control rib thickness to 50%~60% of the main wall thickness; ③appropriately enlarge the gate to reduce shear rate and pressure loss; ④core out and reduce material at thick walls to reduce shrinkage from the source; ⑤strengthen local cooling at this location (add inserts or conformal cooling channels).
Key Takeaway
PA66 sink mark='feeding': holding and freeze management is the technique, structural material reduction is the root; crystalline nylon shrinks greatly and both must be emphasized; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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