Injection Molding
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Out-of-Tolerance Coaxiality of Block Copolymer Polypropylene Injection Molded Products
Fenómeno do problema
The axes of the inner and outer circles or different shaft sections of the product do not coincide, and the coaxiality exceeds the tolerance requirement.
Out-of-tolerance coaxiality affects the dynamic balance and fitting accuracy of rotating parts, and is common in tubular products and stepped shaft products.
Análise das causas
（1）The mold core is eccentric or the core shifts during injection, resulting in uneven wall thickness
（2）The gate position is improper, and single-side feeding produces lateral force that pushes the core off
（3）The mold temperature is uneven, and the large temperature difference between the core and the cavity causes asymmetric shrinkage
（4）The holding pressure is uneven, and the shrinkage compensation on each side of the cavity is inconsistent
（5）The product structure is asymmetric, and the cooling shrinkage difference is large
Solução
（1）Check the core positioning accuracy, and control the coaxiality of the core and the cavity within 0.02mm
（2）Optimize the gate position and adopt symmetrical multi-point gates to reduce the eccentric force of single-side feeding
（3）Control the core and cavity temperatures to be uniform, with the temperature difference not exceeding 5°C (40-90°C range)
（4）Optimize the holding pressure scheme to ensure uniform shrinkage compensation in all directions
（5）Design the product as symmetric as possible to avoid eccentric structures
Conclusão principal
Out-of-tolerance coaxiality is caused by core shift or asymmetric shrinkage, and needs to be solved from mold precision, gate symmetry, and temperature uniformity.
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