Injection Molding
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Severe Warpage Deformation of Block Copolymer Polypropylene PP Products
Problem Phenomenon
PP injection molded products (especially thin-walled box-shaped parts and large flat parts) have severe warpage deformation, and the flatness is out of tolerance.
Large PP crystallization shrinkage and uneven cooling cause warpage, which is a typical problem in PP processing.
Cause Analysis
（1）The crystallinity of PP is high, and the crystallization shrinkage rate is large (1.2-2.0)
（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 PP grades containing nucleating agents to reduce the shrinkage rate 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 pressure 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 grades), mold cooling, and product design.
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