Injection Molding
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PA6 Insert Root Cracking
Problem Phenomenon
After use of PA6 overmolded metal insert products, radial cracks appear at the insert root
Cause Analysis
The thermal expansion coefficient difference between metal and PA6 is large; during cooling the plastic shrinks and grips the insert, generating hoop tensile stress, and stress concentration at insert sharp corners causes cracking; during on-site troubleshooting, verify item by item according to this mechanism, avoiding blind machine adjustment based only on experience
Solution
Preheat inserts to 100-120°C to reduce the temperature difference; round the insert root and ensure sufficient plastic wall thickness (not less than 1/3 of the insert diameter); anneal or condition after molding to release stress
Key Takeaway
Insert cracking is controlled by the three of preheating, wall thickness and stress relief; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence; include this case in the defect archive as a troubleshooting reference for similar problems in the future
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