Injection Molding
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Warpage deformation of PP injection molded products
Problembeschreibung
After demolding, the product shows overall twisting, bowing, or local edge warping, which is especially obvious for flat and frame-type parts; during assembly the gaps are uneven and the parts cannot fit together, and in severe cases the entire batch is scrapped.
Ursachenanalyse
PP is a semi-crystalline material with a mold shrinkage rate as high as 1.5%~2.5%, and the shrinkage difference between the flow direction and the perpendicular direction is obvious; uneven cooling between core and cavity, large wall thickness differences, and differential shrinkage caused by molecular and filler orientation all accumulate residual stress inside the product, which is released after demolding and manifests as warpage.
Lösung
①Independent circuit temperature control for core/cavity, with the temperature difference between the two sides <5℃; ②appropriately increase the mold temperature to make crystallization more complete and uniform; ③reduce the holding pressure by 15%~25% under the premise of preventing flash and optimize the holding pressure curve; ④extend cooling by 20%~30%; ⑤make the wall thickness uniform, and adjust the gate position when necessary.
Wichtigste Erkenntnis
The essence of PP warpage is differential shrinkage; the treatment priority is: first balance the mold temperature field, then optimize holding pressure and cooling, and only finally consider structure and gate adjustments; never rely only on raising the mold temperature or only adding cooling—applying force on one side often makes it warp more the more you adjust.
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