Injection Molding
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Uneven Wall Thickness Caused by Core Shift of Polypropylene Injection Mold
Problem Phenomenon
The wall thickness of the product is thick on one side and thin on the other, and penetration occurs in severe cases.
Core shift causes uneven wall thickness, affecting product strength and dimensional accuracy, and is common in long cores and slender products.
Cause Analysis
(1) The core is slender with insufficient rigidity, and bends and shifts under the action of melt pressure
(2) The gate position is improper, and single-side feeding generates 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 clearance between the core and the cavity is too large
Solution
(1) Optimize the core design, increase the core root cross-section, or use high-strength mold steel
(2) Adjust the gate position and adopt symmetric 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 clearance 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 arrangement, and injection parameters.
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