Injection Molding
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Bubbles and vacuum voids in PP injection molded parts
Problem Phenomenon
Vacuum voids appear inside thick-wall PP products, and holes are visible when sectioned.
Cause Analysis
The surface layer of the thick-wall area solidifies first, and the internal shrinkage is not compensated, forming vacuum voids; insufficient holding pressure or early gate freeze-off is the process cause.; during on-site investigation, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solution
①Core out thick areas to even out wall thickness; ②extend the holding pressure time; ③enlarge the gate to delay freeze-off; ④appropriately reduce the mold temperature gradient.; after adjustment, continuously sample and verify the effect, and resume mass production after confirming stability
Key Takeaway
PP thick-wall vacuum voids are a structural feeding problem; design thinning takes priority, with process compensation as a supplement.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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