Injection Molding
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Product deformation caused by unbalanced ejection of homopolymer polypropylene injection mold
Problem Phenomenon
The product deforms or cracks during ejection, with ejector pin marks of varying depth, and white marks or cracks at some ejector pins.
Ejection imbalance directly causes product deformation and scrap; in severe cases the product sticks in the mold.
Cause Analysis
(1) Insufficient ejector pin number or uneven distribution, ejection force concentrated on a few pins
(2) Inconsistent ejector pin lengths, unsynchronized ejection
(3) Insufficient draft angle, large friction between product and cavity
(4) Uneven mold temperature, different shrinkage of product parts causes large local clamping force
(5) Ejection speed too fast, impact force causes product deformation
Solution
(1) Increase ejector pin number, distribute reasonably, ensure uniform force on each pin
(2) Check and adjust each ejector pin length, synchronization error not exceeding 0.02mm
(3) Increase draft angle, at least 1-2° for polyolefin materials, polish cavity side walls
(4) Control mold temperature uniformity, temperature difference of each part not exceeding 5°C (40-90°C range)
(5) Reduce ejection speed, adopt slow-fast-slow ejection speed profile
Key Takeaway
Ejection imbalance is caused by ejector pin system design or large demolding resistance; ejector pin layout and demolding conditions need to be optimized.
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