Warpage Deformation of Low-Density Polyethylene Injection Molded Products

The product bends, twists, or warps after demolding, the flatness is out of tolerance, and assembly is difficult. The deformation usually gradually intensifies within a few hours after demolding, and in severe cases the product is completely unusable, especially common in large flat and thin-walled products.

（1）The crystallinity of low-density polyethylene is high, and the shrinkage in all directions is inconsistent, resulting in non-uniform shrinkage causing warpage （2）The product wall thickness is uneven, the thick-walled parts shrink more and the thin-walled parts shrink less, producing internal stress （3）The mold temperature is uneven, and the cooling rate differences between various parts of the cavity cause uneven shrinkage （4）The holding pressure distribution is uneven, with high pressure near the gate and low pressure at the far end, resulting in large differences in shrinkage compensation （5）The cooling time is insufficient, and the product is demolded before being fully cooled, and post-shrinkage causes deformation

（1）Optimize the product design, make the wall thickness as uniform as possible, the reinforcing rib thickness does not exceed 60% of the wall thickness, and increase the fillets at the corners （2）Control the mold temperature uniformity, with the temperature difference not exceeding 5°C, and set it reasonably within the 30-60°C range （3）Extend the cooling time to ensure the product is fully cooled and solidified before demolding, and the demolding temperature is more than 10°C lower than the heat deflection temperature （4）Optimize the holding pressure scheme, adopt multi-stage holding pressure, and ensure uniform shrinkage compensation in all parts of the cavity （5）Adjust the gate position and quantity to make the melt flow uniform and reduce molecular orientation differences

Warpage deformation is the core problem of '2079851475616104452 of crystalline materials; its essence is the internal stress caused by non-uniform shrinkage, and it needs to be systematically controlled from multiple dimensions of design, process, and mold.