Shrinkage

Most materials shrink as they solidify. There are three types of shrinkage: shrinkage of the liquid, solidification shrinkage and patternmaker's shrinkage.

The shrinkage of the liquid is rarely a problem because more material is flowing into the mold behind it. Solidification shrinkage occurs because metals are less dense as a liquid than a solid, so during solidification the metal density dramatically increases. Patternmaker's shrinkage refers to the shrinkage that occurs when the material is cooled from the solidification temperature to room temperature, which occurs due to thermal contraction.