Injection Molding
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Severe Warpage Deformation of Polypropylene PP Products
Problem Phenomenon
PP injection-molded products (especially thin-walled box-shaped parts and large flat parts) show severe warpage deformation, with flatness out of tolerance.
Large crystallization shrinkage and uneven cooling of PP cause warpage, which is a typical difficulty in PP processing.
Cause Analysis
(1) PP has high crystallinity and large crystallization shrinkage (1.0-2.5)
(2) The shrinkage in all directions is inconsistent, and the shrinkage difference between the flow direction and the perpendicular direction is large
(3) The mold cooling is uneven, and the shrinkage of various parts is inconsistent
(4) The product wall thickness design is unreasonable
(5) The holding pressure is insufficient or unevenly distributed
Solution
(1) Use a PP grade containing a nucleating agent to reduce the shrinkage and improve shrinkage uniformity
(2) Design the mold cooling system symmetrically to ensure uniform cooling of all parts
(3) Optimize the product wall thickness design with uniform distribution
(4) Adopt multi-stage holding to ensure uniform shrinkage compensation of all parts
(5) Anneal the product after demolding (hold at 30-50°C below the melting point for 2h)
Key Takeaway
PP warpage needs to be comprehensively solved from three aspects: material selection (nucleating agent grade), mold cooling, and product design.
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