Injection Molding
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General-purpose polyethylene injection molded products warpage deformation
Problem Phenomenon
After demolding, the product shows bending, twisting or warpage deformation, flatness is out of tolerance, and assembly is difficult.
The deformation usually gradually intensifies within several hours after demolding, and in severe cases the product is completely unusable, especially common in large flat and thin-wall products.
Cause Analysis
（1） General-purpose polyethylene has high crystallinity, inconsistent shrinkage in all directions causes warpage due to non-uniform shrinkage\
（2） Product wall thickness uneven, thick-wall parts shrink more and thin-wall parts shrink less, producing internal stress\
（3） Mold temperature uneven, differences in cooling rates at various cavity parts cause uneven shrinkage\
（4） Holding pressure distribution uneven, pressure high near the gate and low at the far end, large feeding differences\
（5） Cooling time insufficient, the product is demolded before fully cooled, post-shrinkage causes deformation
Solution
（1） Optimize product design, keep wall thickness as uniform as possible, rib thickness not exceeding 60% of wall thickness, enlarge fillets at corners\
（2） Control mold temperature uniformity, temperature difference not exceeding 5°C, set reasonably within the 30-80°C range\
（3） Extend cooling time, ensure the product is fully cooled and solidified before demolding, demolding temperature more than 10°C below the heat deflection temperature\
（4） Optimize the holding pressure scheme, adopt multi-stage holding pressure, ensure uniform feeding at all parts of the cavity\
（5） Adjust gate position and number to make the melt flow uniform and reduce molecular orientation differences
Key Takeaway
Warpage deformation is the core difficulty of crystalline materials in '2079851475616104452; its essence is internal stress caused by non-uniform shrinkage, requiring systematic control from multiple dimensions: design, process and mold.
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