Ordliste
Shrinkage — definition
The contraction of metal from casting temperature to room temperature, which the tool must be built to compensate for.
All metal contracts as it cools. The tool therefore has to be made larger than the finished part, with a shrinkage allowance specific to the alloy and the geometry.
Shrinkage happens in three phases: in the liquid, during solidification and after solidification. The middle phase is the one that produces shrinkage porosity if the section is not fed.
For the designer the important point is that shrinkage is not uniform. A part restrained by cores contracts differently in different directions, and that is one reason uneven wall thickness produces distorted parts.