Injection Molding
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Product Deformation Caused by Unbalanced Ejection of Low-Density Polyethylene Injection Molds
Problem Phenomenon
The product deforms or cracks during the ejection process, the ejector pin marks vary in depth, and white marks or cracks appear at some ejector pins.
Unbalanced ejection directly causes 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 the distribution is uneven, and the ejection force is concentrated on a few ejector pins
（2）The lengths of the ejector pins are inconsistent, and the ejection is not synchronized
（3）The demolding draft is insufficient, and the friction between the product and the cavity is large
（4）The mold temperature is uneven, and the shrinkage of various parts of the product is different, resulting in 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 the synchronization error not exceeding 0.02mm
（3）Increase the demolding draft, at least 1-2° for polyolefin materials, and polish the cavity side surfaces
（4）Control the mold temperature to be uniform, with the temperature difference between parts not exceeding 5°C (30-60°C range)
（5）Reduce the ejection speed and adopt a slow-fast-slow ejection speed curve
Key Takeaway
Unbalanced ejection is caused by ejector pin system design or large demolding resistance, and the ejector pin layout and demolding conditions need to be optimized.
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