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The reduction in the dimensions of a plastic part compared with the mold dimensions.
Shrinkage occurs as the polymer cools and can vary in different directions.
Crystalline and semi-crystalline materials are particularly prone to thermal shrinkage; amorphous materials tend to shrink less. Excessive shrinkage can be caused by:
- Low injection pressure
- Short pack-hold time or cooling time
- High melt temperature
- High mold temperature
- Low holding pressure