Casting

: This article is about the manufacturing process. For other uses, see casting (disambiguation).

Shrinkage

Like nearly all materials, metal is less dense as a liquid than a solid, and so a casting shrinks as it cools -- mostly as it solidifies, but also as the temperature of the solid material drops.

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The shrinkage caused by solidification can leave cavities in a casting, weakening it. Risers provide additional material to the casting as it solidifies. Risers add cost because some of their material must be machined off as waste, but they are often necessary to produce usable parts. Shrinkage after solidification can be dealt with by using an oversized pattern designed for the relevant alloy.

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