Molds & Tooling
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PA6 Internal Stress Cracking
Problem Phenomenon
After assembly, cracks appear at the root of screw bosses in PA6 products after a period of storage
Cause Analysis
Molecular orientation and uneven cooling during molding generate internal stress; stress concentrates at the wall-thickness sudden change at the screw boss root, and after assembly torque is superimposed, cracks propagate along the stress concentration zone
Solution
Raise mold temperature to reduce orientation stress and round the wall thickness transition; design root fillets and reinforcing ribs for screw bosses; control assembly torque; perform conditioning treatment to release stress if necessary
Key Takeaway
Internal stress cracking is a joint problem of design and process, and rounding plus conditioning are low-cost countermeasures; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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