Injection Molding
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PMMA Overpacking Cracking
Problem Phenomenon
Products crack near the direct gate, and cracking is relieved after reducing injection pressure
Cause Analysis
Overpacking causes excessive residual stress near the gate; direct gates have the least pressure loss but the most concentrated stress, and switching to pin gates or side gates can disperse stress; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
①For cracking near direct gates, switch to pin gates or side gates; ②raise material temperature to reduce viscosity and injection pressure; ③shorten injection and holding time or use two-stage holding; after adjustment, take samples continuously to verify the effect, and resume mass production only after confirming stability
Key Takeaway
PMMA gate area cracking is the signature of overpacking; changing gate type plus reducing pressure is a combination punch; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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