Injection Molding
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Product deformation caused by unbalanced ejection of random copolymer 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.
Unbalanced ejection directly leads to product deformation and scrapping, and in severe cases the product gets stuck in the mold.
Cause Analysis
(1) The number of ejector pins is insufficient or unevenly distributed, concentrating ejection force on a few pins
(2) Ejector pin lengths are inconsistent, and ejection is not synchronized
(3) Draft angle is insufficient, and friction between the product and the cavity is large
(4) Mold temperature is uneven; different shrinkage across product areas causes large local clamping force
(5) Ejection speed is too fast, and the impact force causes product deformation
Solution
(1) Increase the number of ejector pins and distribute them reasonably to ensure uniform force on each pin
(2) Check and adjust each ejector pin length, with synchronization error not exceeding 0.02mm
(3) Increase draft angle, at least 1-2° for polyolefin materials, and polish the cavity side surfaces
(4) Control mold temperature uniformity, with temperature difference of each part not exceeding 5°C (40-80°C range)
(5) Reduce ejection speed, using a slow-fast-slow ejection speed curve
Key Takeaway
Unbalanced ejection 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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