Injection Molding
4 조회수
Roundness Out of Tolerance of High-Density Polyethylene Injection-Molded Products
문제 현상
The cross-section of a circular product is not round, and the ovality is out of tolerance, affecting sealing performance and fitting precision.
Roundness out of tolerance is common in circular products such as tubular products, bottle caps, and gears, and is closely related to uneven shrinkage and cooling differences.
원인 분석
(1) The mold cavity and core are cooled unevenly, and the shrinkage differences in different directions are large
(2) High-density polyethylene shrinks anisotropically, and the shrinkage in the flow direction is different from that in the perpendicular direction
(3) The gate position is improper, and single-side feeding causes asymmetric molecular orientation
(4) The holding pressure is unevenly distributed, and the shrinkage compensation in all directions of the cavity is inconsistent
(5) The wall thickness of the product is uneven, and the shrinkage difference between thick and thin parts is large
해결 방법
(1) Optimize the mold cooling system, with the cooling water channels of the cavity and core arranged symmetrically
(2) Control the mold temperature uniformity, with the temperature difference of each part not exceeding 5°C (range 30-80°C)
(3) Adopt multi-point gates or ring gates to make the melt fill the mold uniformly and reduce orientation differences
(4) Optimize the holding scheme to ensure uniform shrinkage compensation in all directions of the cavity
(5) Optimize the product design with as uniform wall thickness as possible, and the inner and outer circles concentric
핵심 요약
Roundness out of tolerance is caused by non-uniform shrinkage, and needs to be improved from three aspects: cooling symmetry, gate design, and wall thickness uniformity.
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