Injection Molding
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Severe warpage deformation of random copolymer polypropylene PP products
Problem Phenomenon
PP injection molded products (especially thin-walled box-shaped parts and large flat parts) warp severely, with flatness out of tolerance.
Large PP crystallization shrinkage and uneven cooling cause warpage, which is a typical challenge in PP processing.
Cause Analysis
(1) PP has high crystallinity and large crystallization shrinkage rate (1.0-2.0)
(2) Shrinkage is inconsistent in all directions, with large shrinkage differences between the flow direction and the perpendicular direction
(3) Mold cooling is uneven, and shrinkage is inconsistent across areas
(4) Product wall thickness design is unreasonable
(5) Holding pressure is insufficient or unevenly distributed
Solution
(1) Use PP grades containing nucleating agents to reduce shrinkage rate and improve shrinkage uniformity
(2) Design the mold cooling system symmetrically to ensure uniform cooling of all areas
(3) Optimize product wall thickness design for uniform distribution
(4) Use multi-stage holding pressure to ensure uniform shrinkage compensation in all areas
(5) Perform annealing after product demolding (holding 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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