Sink marks (injection moulding defect)
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A sink mark is a localized shrinkage of the material during Injection Moulding process. Sink marks appear as depressions on the surface of an injection molded part which is not aesthetically acceptable in Plastics Manufacturing. [1]
Effect
- Visual defect
- Sink marks reflect light in different directions to the rest of the part
Causes
- Thick sections in product design
Areas of the part that are significantly thicker are prone to sink mark. [2]
- Improper design of the ribs, bosses, and gussets. These features are given for strengthening of the product.
Thickness of the ribs, bosses, and gussets in a product design should be 50 to 60 percent of the attached (base) wall thickness.
- Improper gate location
Gate should be placed near to the thicker sections
References
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