Warpage Deformation of High-Density Polyethylene Injection-Molded Products

The product shows bending, twisting, or warpage deformation after demolding, with flatness out of tolerance and assembly difficulties. The deformation usually gradually intensifies within a few hours after demolding, and in severe cases the product is completely unusable; it is especially common in large flat and thin-walled products.

(1) High-density polyethylene has high crystallinity, and inconsistent shrinkage in all directions leads to non-uniform shrinkage, causing warpage (2) The wall thickness of the product is uneven; thick-wall sections shrink more and thin-wall sections shrink less, generating internal stress (3) The mold temperature is uneven, and differences in cooling rates across the cavity cause uneven shrinkage (4) The holding pressure is unevenly distributed; the pressure near the gate is high and the pressure at the far end is low, resulting in large shrinkage compensation differences (5) The cooling time is insufficient; the product is demolded before being fully cooled, and post-shrinkage causes deformation

(1) Optimize the product design with as uniform wall thickness as possible; the thickness of reinforcing ribs does not exceed 60% of the wall thickness, and fillets are enlarged at corners (2) Control the mold temperature uniformity, with a temperature difference not exceeding 5°C, reasonably set within the range of 30-80°C (3) Extend the cooling time to ensure the product is fully cooled and solidified before demolding; the demolding temperature is more than 10°C below the heat deflection temperature (4) Optimize the holding scheme and adopt multi-stage holding to ensure uniform shrinkage compensation in all parts of the cavity (5) Adjust the gate position and number to make the melt flow uniform and reduce molecular orientation differences

Warpage deformation is the core difficulty in the '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.