Injection Molding
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Uneven wall thickness caused by core shift in random copolymer polypropylene injection mold
Problem Phenomenon
Product wall thickness is thick on one side and thin on the other, and in severe cases penetration occurs.
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, bending and shifting under melt pressure
(2) Improper gate position; single-side feeding produces lateral unbalanced pressure
(3) Core support is insufficient or fixation is not firm
(4) Injection pressure is too high or injection speed is too fast; the melt impacts the core greatly
(5) The fitting clearance between the core and the cavity is too large
Solution
(1) Optimize core design, increasing the core root cross-section or using high-strength mold steel
(2) Adjust gate position, using 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 injection pressure and injection speed to reduce 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 layout and injection parameters.
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