Injection Molding
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Severe warpage deformation of homopolymer polypropylene PP products
Problem Phenomenon
PP injection products (especially thin-wall box-shaped parts and large flat parts) have severe warpage deformation, flatness out of tolerance.
Large PP crystallization shrinkage and uneven cooling cause warpage, a typical challenge in PP processing.
Cause Analysis
(1) High PP crystallinity, large crystallization shrinkage rate (1.5-2.5)
(2) Inconsistent shrinkage in each direction, large shrinkage differences between flow direction and perpendicular direction
(3) Uneven mold cooling, inconsistent shrinkage of each part
(4) Unreasonable product wall thickness design
(5) Insufficient or unevenly distributed holding pressure
Solution
(1) Use PP grades containing nucleating agents to reduce shrinkage rate and improve shrinkage uniformity
(2) Symmetric design of mold cooling system, ensure uniform cooling of each part
(3) Optimize product wall thickness design, uniform distribution
(4) Adopt multi-stage holding pressure, ensure uniform shrinkage compensation in each part
(5) Anneal the product after demolding (hold at 30-50°C below 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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