Injection Molding
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Flatness out of tolerance of random copolymer polypropylene injection molded products (variant: strengthened measures)
Problem Phenomenon
The flatness of large flat products exceeds tolerance requirements, with undulations or bending on the surface.
Flatness out of tolerance affects product assembly and appearance, and is especially prominent in large-area thin-walled products.
Especially, additional attention is needed on top of the original basis; this problem is more prominent and requires focused attention.
Cause Analysis
(1) Random copolymer polypropylene crystalline material shrinks inconsistently in all directions, which is more evident in large flat surfaces
(2) Mold cooling is uneven, with cooling rate differences across large flat areas
(3) Product wall thickness is uneven and reinforcing rib distribution is asymmetric
(4) Improper gate position; a single melt flow direction causes anisotropic orientation shrinkage
(5) Cooling time is insufficient; the product continues to shrink and deform after demolding
(6) On top of the original basis, additional attention is needed as process parameter fluctuations or equipment condition changes aggravate this problem
Solution
(1) Optimize the mold cooling system, with cooling water channels evenly distributed in large flat areas, and temperature difference not exceeding 5°C
(2) Optimize product design, with reinforcing ribs symmetrically arranged and uniform wall thickness
(3) Use multi-point gates or fan gates to make the melt flow uniformly and reduce orientation differences
(4) Extend cooling time to ensure the product is fully cooled before demolding
(5) Appropriately increase mold temperature to the higher value within the 40-80°C range to reduce internal stress
(6) And strengthen process monitoring; on top of the original basis, additional attention is needed to pay special attention to parameter stability
Key Takeaway
Flatness out of tolerance is a manifestation of uneven shrinkage in large-area products and needs to be controlled by optimizing cooling, gates and product design for uniform shrinkage in all directions.
In different production scenarios, targeted preventive measures need to be taken.
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