Injection Molding
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Product Deformation Caused by Unbalanced Ejection of High-Density Polyethylene Injection Mold
Problem Phenomenon
The product deforms or cracks during ejection, the ejector pin marks vary in depth, and white marks or cracks appear at some ejector pins.
Unbalanced ejection directly leads to product deformation and scrapping, and in severe cases the product is stuck in the mold.
Cause Analysis
(1) The number of ejector pins is insufficient or they are unevenly distributed, and the ejection force is concentrated on a few ejector pins
(2) The lengths of the ejector pins are inconsistent, and they are not synchronized during ejection
(3) The draft angle is insufficient, and the friction between the product and the cavity is large
(4) The mold temperature is uneven, and the different shrinkage of various parts of the product leads to large local clamping force
(5) The 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 ejector pin
(2) Check and adjust the length of each ejector pin, with a synchronization error not exceeding 0.02mm
(3) Increase the draft angle, at least 1-2° for polyolefin materials, and polish the side of the cavity
(4) Control the mold temperature to be uniform, with the temperature difference of each part not exceeding 5°C (range 30-80°C)
(5) Reduce the ejection speed and adopt a slow-fast-slow ejection speed curve
Key Takeaway
Unbalanced ejection is caused by the ejector pin system design or large demolding resistance, and the ejector pin layout and demolding conditions need to be optimized.
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