Pattern (casting) in the context of "Investment casting"

In casting, a pattern is a replica of the object to be cast, used to form the sand mould cavity into which molten metal is poured during the casting process. Once the pattern has been used to form the sand mould cavity, the pattern is then removed, molten metal is then poured into the sand mould cavity to produce the casting. The pattern is non consumable and can be reused to produce further sand moulds almost indefinitely.

Due to the fact that almost all metals contract or shrink as their temperature falls, casting patterns must be made larger in size than the actual casting they will produce. Aluminium casting contraction is ~1.3% for example, so patternwork for a cast aluminium part would be made 1.3% bigger than the cast part itself.