Warpage deformation of polypropylene injection molded products

The product shows bending, twisting, or warpage deformation 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）Polypropylene has high crystallinity, and inconsistent shrinkage in all directions causes non-uniform shrinkage, resulting in warpage （2）The product wall thickness is uneven, the thick-walled parts shrink greatly and the thin-walled parts shrink little, producing internal stress （3）The mold temperature is uneven, and the difference in cooling rate of each part of the cavity causes uneven shrinkage （4）The holding pressure distribution is uneven, with high pressure near the gate and low pressure at the far end, and the shrinkage compensation difference is large （5）The cooling time is insufficient, 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 enlarge the fillets at the corners （2）Control the mold temperature uniformity, with the temperature difference not exceeding 5°C, reasonably set within the range of 40-90°C （3）Extend the cooling time to ensure the product is fully cooled and solidified before demolding, with the demolding temperature more than 10°C below the heat distortion temperature （4）Optimize the holding pressure scheme, using multi-stage holding pressure to ensure uniform shrinkage compensation in each part 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 difficulty of '2079851475616104452 of crystalline materials, and is essentially internal stress caused by non-uniform shrinkage, which needs to be systematically controlled from multiple dimensions of design, process, and mold.