Injection Molding
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Uneven Wall Thickness Caused by Core Shift in High-Density Polyethylene Injection Molds
Problem Phenomenon
The product wall thickness is thick on one side and thin on the other, and penetration occurs in severe cases.
Core shift leads to uneven wall thickness, affecting product strength and dimensional accuracy, and is common in long-core and slender products.
Cause Analysis
（1）The core is slender with insufficient rigidity, and bends and shifts under the melt pressure
（2）The gate position is improper, and single-side feeding produces lateral unbalanced pressure
（3）The core support is insufficient or the fixation is not firm
（4）The injection pressure is too high or the injection speed is too fast, and the impact force of the melt on the core is large
（5）The fitting gap between the core and the cavity is too large
Solution
（1）Optimize the core design, increase the cross-section of the core root or use high-strength mold steel
（2）Adjust the gate position, and adopt symmetrical multi-point gates to make the melt fill the mold uniformly
（3）Strengthen the core support structure to ensure the core is firmly fixed
（4）Appropriately reduce the injection pressure and injection speed to reduce the impact on the core
（5）Control the fitting gap between the core and the cavity within 0.02mm
Key Takeaway
Core shift is caused by insufficient rigidity or uneven force, and needs to be solved from core design, gate layout, and injection parameters.
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